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78-3479

DeHAYES , Donald Henry, 1951GENETIC VARIATION IN COLD
HARDINESS AND ITS EFFECTS ON THE
PERFORMANCE OF PONDEROSA PINE (PINUS
PONDEROSA) IN MICHIGAN.
----Michigan State University,
Ph.D., 1977
Agriculture, forestry and wildlife

University Microfilms International, AnnArbor.Michiganaskm

GENETIC VARIATION IN COLD HARDINESS
AND ITS EFFECTS ON THE PERFORMANCE
OF PONDEROSA PINE ( PINUS PONDEROSA) IN
MICHIGAN

By

Donald H. DeHayes

A DISSERTATION

Submitted to
Michigan S ta te U n iv e rs ity
in p a r t i a l f u l f i l l m e n t o f th e requirem ents
f o r th e degree o f

DOCTOR OF PHILOSOPHY

Department o f F o re s try

1977

ABSTRACT
GENETIC VARIATION IN COLD HARDINESS AND ITS
EFFECT ON THE PERFORMANCE OF PONDEROSA PINE
( PINUS PONDEROSA) IN MICHIGAN
By
Donald H. DeHayes

A rangewide provenance t e s t o f ponderosa p ine was e s ta b lis h e d in
1960 and In c lu d es two r e p lic a te d p la n ta tio n s 1n southern M ich ig an .

From

1975 to 1977 g e n e tic v a r ia t io n in s e ve ra l aspects o f co ld h ard iness and
o th e r eco n o m ically Im p o rtan t t r a i t s was s tu d ie d .
F o lia g e samples were c o lle c te d from 30 s e ed lo ts on 17 d i f f e r e n t
d ates from O cto b e r, 1975 to J a n u a ry , 1977.

F reezing te s ts were perform ed

on needles and tis s u e damage was assessed using e l e c t r i c a l c o n d u c tiv ity .
C r itic a l

te m p e ra tu re s , d e fin e d as th e h ig h e s t tem perature a t which cold

damage could be d e te c te d , were determ ined f o r each s e e d lo t.
f o r computing such tem peratures is d e s c rib e d .
p e rc e n t f o l i a r m o istu re co n te n t was d eterm in ed .
w in te r in ju r y were made d u rin g s e v e ra l y e a r s .

A procedure

On s ix a d d itio n a l dates
F ie ld o b s erva tio n s o f
O ther t r a i t s measured

were tim e o f le a fin g o u t, f o l i a r d ry in g r a t e from excised tw ig s , h e ig h t,
and s u s c e p t ib ilit y to two fungal d is e a r'*...
Trees grown from seed c o lle c te d In B r it is h Colum bia, W ashington,
Montana, and Nebraska ac c lim a te d to c o ld f a s t e s t , had th e lo w est
c r itic a l

tem peratures In m id w in ter ( - 4 0 to - 4 7 ° C ) , s u ffe re d l i t t l e

or

no cold o r d isease damage, le a fe d out e a r l i e s t , had r e l a t i v e l y low f o l i a r

Donald H. DeHayes
m oisture and slow d ryin g ra te s and were among th e t a l l e s t tre e s a t age 16
(averaged 2 0 .5 f t t a l l ) .

Trees from northern Colorado and Utah were

s im ila r in several respects but were o n ly 14-15 f t t a l l a t age 16.

Trees

grown from seed c o lle c te d 1n C a lif o r n ia acclim ated to cold s lo w e s t, had
th e h ig h e st c r i t i c a l tem peratures 1n m id w in ter (-2 2 to -2 4 ° C ), s u ffe re d
severe cold and disease damage, le a fe d out l a t e s t , had high f o l i a r
m o is tu re , and f a s t d ryin g r a te s , and were among th e s h o rte s t tre e s a t
age 16 (averaged 14 f t t a l l ) .

Trees grown from seed c o lle c te d in

A rizona and New Mexico had c r i t i c a l

tem peratures o f -3 2 °C , were 1 6 .5 f t

t a l l a t age 16, s u ffe re d severe disease damage, had r e l a t i v e l y slow
f o l i a r d ryin g r a te s , and were in te rm e d ia te 1n co ld damage, tim e o f
le a fin g out and f o l i a r m oisture c o n te n t.
C a lif o r n ia tre e s s u ffe re d severe cold damage most years because they
d id not achieve a s u f f ic ie n t depth o f hardiness to w ith stand Michigan
w in te r s .

In c o n tr a s t, A rizo n a , New Mexico, and co a stal Oregon tre e s

were s u f f i c i e n t ly hardy in m idw inter to avoid cold damage.

However,

they s u ffe re d needle In ju r y 1n years when low tem peratures occurred in
e a r ly w in te r , b efo re they a tta in e d maximum h ard in ess.

Trees from northern

o rig in s avoided damage because they acclim ated to cold q u ic k ly and became
ve ry hardy In m id w in ter.
W in ter d e s ic c a tio n was considered as a p o s s ib le source o f w in te r
In ju r y In ponderosa p in e .

However, the r e la tio n s h ip between f o l i a r

d ryin g ra te s and w in te r In ju r y was not stron g .

Trees from Washington and

B r it is h Columbia lo s t w ater more r a p id ly 1n w in te r than tre e s from Arizona
and New Mexico but s u ffe re d no cold damage.

Coastal Oregon tre e s d rie d

o u t th e f a s t e s t , but s u ffe re d less cold damage than C a lifo r n ia o r
A rizona tr e e s .

Thus, 1 t appeared th a t d e s ic c a tio n was less Im portant

than cold tem perature 1n causing damage to ponderosa p in e .

Donald H. DeHayes
Time o f le a fin g out appeared to be re la te d to cold hardening and
dehardening.

Trees from W ashington, B r it is h Colum bia, Montana, and

Colorado hardened to cold f a s te s t 1n f a l l , dehardened most r a p id ly In
l a t e w in te r , and le a fe d o u t 10-14 days e a r l i e r than tre e s from southern
o r ig in s .

D esp ite d iffe re n c e s in le a fin g out phenology, sp rin g f r o s t

damage was not a problem In ponderosa p in e .
F o lia r m oisture co n ten t v a rie d seas o n a lly as w e ll as among s e e d lo ts ,
decreasing by 15-16% from summer to w in te r .

In g e n e ra l, tre e s w ith high

m oisture co n ten t were most s u s c e p tib le to cold damage.

This r e la tio n s h ip

seemed to hold from sumner to w in te r and als o from n o rth to south w ith in
the sp ecies.

A p p a re n tly , tre e s w ith high f o l i a r m o istu re co n ten t had

more I n t r a c e l l u l a r w ater and thus more w ater to fre e z e and cause damage.
W in ter In ju r y had an e f f e c t on growth r a te and age-age h eig h t
r e la tio n s h ip s 1n ponderosa p in e .

Trees grown from seed c o lle c te d In

C a lif o r n ia , A riz o n a , and New Mexico were t a l l e s t a t e a r ly ages, but lo s t
t h e i r growth s u p e r io r ity because o f repeated w in te r I n ju r y .

By age 1 6 ,

hardy tre e s from B r it is h Columbia, Washington, Montana, and Nebraska were
t a l l e s t , A rizona and New Mexico tre e s were averag e, and C a lif o r n ia tre e s
were s h o rte s t.

Repeated w in te r In ju r y to southern tr e e s , a ls o re s u lte d

in an In crease In the magnitude o f h e ig h t d iffe re n c e s among ecotypes
from age fo u r to e ig h t.

E rro r variances decreased g ra d u a lly w ith age

as average growth r a te In c re a s e d , but were a p p a re n tly u n a ffe c te d by
w in te r In ju r y .
S u s c e p tib ilit y to damage from two fungal diseases appeared secondary
to w in te r In ju r y .

Trees which were p h y s io lo g ic a lly weakened by repeated

co ld damage s u ffe re d th e most tw ig dleback from d is ea se .
s u ffe re d l i t t l e

Trees which

or no cold damage were le a s t a ffe c te d by d is e a s e .

Donald H. DeHayes
O ther t r a i t s stu d ied Included m o r ta lit y le a f le n g th , cone p ro d u c tio n ,
stem ta p e r , diam eter grow th, and incidence o f stem fo rk s .

Trees grown

from seed c o lle c te d 1n the N orthern P lateau (Oregon, W ashington, and
B r it is h Columbia) were most d e s ir a b le 1n a l l

re sp ec ts.

In a d d itio n to

being th e t a l l e s t and among th e most cold hardy, they had th e la r g e s t
diam eters (8 .5 1n a t age 1 6 ), th e le a s t m o r t a lit y , th e lo n g e st needles
( 7 .5 to 8 .0 in lo n g ), the most c y lin d r ic a l boles and s u ffe re d o n ly a
moderate amount o f fo r k in g .

Trees grown from seed c o lle c te d 1n th e

Northern P lateau a re recommended f o r fo r e s t and ornamental p la n tin g s In
southern M ichigan.

ACKNOWLEDGEMENTS

I wish to extend njy s in c e re g r a t itu d e to my m ajor p ro fe s s o r,
D r. Jonathan W. W rig h t, whose guidance and a s s is ta n c e were e s s e n tia l
to th e su ccessfu l com pletion o f my g rad u ate program.

I would a ls o

l i k e to thank D r. G. S. Howell f o r h is v a lu a b le d iscu ssio n s and f o r
p ro v id in g equipment which was e s s e n tia l to t h is stu d y .

In a d d it io n ,

I wish to express my a p p re c ia tio n to th e o th e r members o f my guidance
co n m lttee — D rs . J . W. Hanover, J . R. Hannan, and E. H, Everson —
f o r t h e i r e s s e n tia l c o n tr ib u tio n s .
I owe a s p e c ia l d eb t o f a p p re c ia tio n to my c lo s e f r ie n d and
c o lle a g u e Bruce B ongarten, whose a s s is ta n c e , d is c u s s io n s , and f r ie n d sh ip were In v a lu a b le .
I a ls o wish to thank my p are n ts f o r t h e i r unending support and
encouragement throughout my academic c a r e e r .

F in a l l y , I am In d eb ted

to my w if e , Annm arle, f o r her p a tie n c e , encouragement, and s a c r if ic e s
which were In s tru m e n ta l 1n e n a b lin g me to pursue my personal g o a ls .

i1

TABLE OF CONTENTS

Page
LIST OF TABLES

v

LIST OF FIGURES

v ii

CHAPTER
1.

INTRODUCTION

1

2.

PHYSIOLOGY AND GENETICS OF COLD HARDINESS IN PLANTS:
LITERATURE REVIEW

3

3.

In tr o d u c tio n

3

F ree zin g and death in p la n t tis s u e s

4

The r o le o f l i g h t

6

A c c lim a tio n

8

P h y s io lo g ic a l and m e ta b o lic changes d u rin g hardening

14

G e n e tic re g u la tio n o f c o ld a c c lim a tio n

20

G en etic v a r ia t io n

25

In h e r ita n c e o f c o ld re s is ta n c e In p la n ts

27

CRITICAL TEMPERATURE DETERMINATIONS IN COLD HARDINESS
STUDIES USING ELECTRICAL CONDUCTIVITY MEASUREMENTS

34

In tr o d u c tio n

34

E le c t r ic a l c o n d u c tiv ity as a v i a b i l i t y t e s t

35

C r i t i c a l tem p eratu re d e te rm in a tio n

36

H i

CHAPTER
4.

5.

6.

7.

Page

GENETIC VARIATION IN SEVERAL ASPECTS OF COLD HARDINESS
IN PONDEROSA PINE

42

In tro d u c tio n

42

O b je c tiv e s

44

M a te ria ls and methods

45

R esu lts

55

THE EFFECTS OF WINTER INJURY ON AGE-AGE HEIGHT
RELATIONSHIPS IN PONDEROSA PINE

92

In tro d u c tio n

92

M a te ria ls and methods

95

Results

97

IMPROVED PONDEROSA PINE FOR MICHIGAN

106

In tro d u c tio n

106

M a te ria ls and methods

108

The v a r ie t ie s and ecotypes

110

R esults

111

P ra c tic a l recommendations

125

SUFtlARY

129

iv

LIST OF TABLES

TABLE
1.

2.

3.

4.
5.

6.

7.

8.

9.

Page
R e la tio n s h ip between c r i t i c a l tem peratures ( ° C ) , as
determ ined from la b o r a to ry fre e z in g te s ts on December
3 , 1976* and v i s ib l e co ld In ju r y to needles o f tre e s
from s ix ponderosa p in e provenances fo llo w in g exposure
o f tre e s to -2 6 C tem peratures on December 3 , 1976, 1n
a r e p lic a te d southern M ichigan p la n ta tio n .

40

C r i t i c a l tem peratures (1n °C ) f o r needles o f tre e s from
e ig h t ponderosa p in e ecotypes on 14 d a te s .
C r itic a l
tem perature Is d e fin e d as th e h ig h e s t tem p eratu re a t
which c o ld In ju r y could be d e te c te d .
Data f o r J u ly .
1976 Is based on s ix s e e d lo ts .

56

C onsistency and magnitude o f co ld hardiness d iffe re n c e s
among s e e d lo ts w ith in two g e n e t ic a lly v a r ia b le ponderosa
p in e eco typ es.

63

D iffe re n c e s 1n cold hardiness between tw ig s and needles
o f ponderosa p in e s e e d lo ts on fo u r d ates 1n 1976.

64

Comparison between damage caused by unseasonably co ld
w eather (te m p e ra tu re o f -26°C on December 3 , 1976) 1n
e a r ly w in te r and c o ld hardiness as measured by c r i t i c a l
tem peratures on th e same d a te . The c r i t i c a l tem peratures
a re an average o f c r i t i c a l tem peratures on November 1 1 , 1976
and December 1 7 , 1976.

71

R e la tiv e tim e o f bud break o f 16 y e a r o ld ponderosa
p in e tre e s from e ig h t ecotypes growing a t K ellogg
F o res t In southwestern M ich ig an .

82

Ecotype and seasonal d iffe r e n c e s 1n f o l i a r m o istu re
co n te n t o f ponderosa p in e growing a t K ellogg F o res t
In southwestern M ich ig an .

84

Simple c o r r e la tio n s between f o l i a r m o istu re c o n te n t and
needle c r i t i c a l tem peratures f o r 30 ponderosa p in e
s e e d lo ts on s e ve ra l dates 1n 1975 and 1976.

87

Summary o f phenotypic c o r r e la tio n s f o r h e ig h t a t d i f f e r e n t
ages 1n g e n e tic v a r ia tio n s tu d ie s o f ponderosa p in e .

94

v

Page

TABLE
10.

Age-Age c o r r e la tio n s f o r h e ig h t among 55 provenances
o f ponderosa p in e a t two t e s t p la n ta tio n s In southern
M ichigan

100

V a r ia tio n w ith age 1n range o f ecotype means and
p ro p o rtio n o f t o ta l g e n e tic v a ria n c e due to ecotype
and s e e d lo t w ith in eco typ e.

103

Changes 1n th e c o e f f i c ie n t o f v a r ia tio n ( C . V . ) , F
v a lu e among s e e d lo ts , and p la n ta tio n mean h e ig h t
w ith age 1n th e n u rsery and two permanent t e s t
p la n ta tio n s .

104

M o r t a lit y and m o r t a lit y Increm ents o f 16 y e a r -o ld
ponderosa p in e ecotypes growing a t K ellogg and
Russ F orests 1n southw estern M ich ig an .

112

14.

Growth r a t e and bole form o f ponderosa p in e eco typ es.

113

15.

Seasonal d iffe re n c e s 1n cold h ard iness o f needles
among ponderosa p in e eco typ es.

116

G en etic d iffe r e n c e s among ecotypes 1n s u s c e p t ib ilit y
to stem fo rk in g a t K ello gg and Russ F o re s t p la n ta tio n s .

120

L o cation o f th e two b est stands o f ponderosa p in e In
th e N orthern P la te a u and N orthern I n t e r i o r regio ns
based on perform ance in two southern M ichigan
p la n ta tio n s .

126

11.

12.

13.

16.
17.

v1

LIST OF FIGURES

Page

FIGURE
1.
2.

3.

4.

5.

6.

7.

A h y p o th e tic a l model o f g e n e tic re g u la tio n o f
cold a c c lim a tio n 1n p la n ts .

23

D is t r ib u t io n o f ponderosa p ine In th e U n ited S ta te s
and B r it i s h Colum bia, showing th e lo c a tio n o f stand
c o lle c tio n s used 1n t h is study (map r e p r in te d from
W e lls , 1 9 6 2 ).

47

Ecotype d iv is io n s o f ponderosa p in e progeny in c lu d ed
1n t h is stu d y .
Ecotypes a re d esig n ated by l e t t e r s as
fo llo w s :
A. NORthern C A H fo rn ia and Southern C A llf o r n la
B. NORthern PLATEAU
C. Arizona-New Mexico
D. southern U Tah-northern New Mexico
E. NORthern INTERIOR
F.
NORthern COlorado-UTah
G. COASTal ORegon
(Map and ecotype boundaries a f t e r W e lls , 1 9 6 2 ).

53

Seasonal p a tte r n o f co ld hardening and dehardening
f o r fo u r I n t e r i o r v a r ie t y ( v a r . scopulorum) ecotypes
o f ponderosa p in e growing a t K ellogg f o r e s t in
southern M ich ig an .

58

Seasonal p a tte r n o f co ld hardening and dehardening
f o r fo u r c o a s ta l v a r ie t y ( v a r . ponderosa) ecotypes
o f ponderosa p in e growing a t K ellogg F o res t 1n
southern M ich ig an .

60

R e la tiv e e x te n t o f needle w in te r in ju r y on tre e s from
e ig h t ponderosa p in e ecotypes a t d i f f e r e n t p la n ta tio n s
and ages. Age 17 d ata was c o lle c te d fo llo w in g th e
severe w in te r o f 1976-77.

67

M o ttlin g on ponderosa p in e needles damaged by tem per­
a tu re o f -2 6 C on December 3 , 1976.
From l e f t to r i g h t
th e s e e d lo ts a r e :
No. 2234 from A riz o n a , moderate
damage; No. 2197 from Montana, no damage; and No. 2036
from C a li f o r n ia , severe damage.

70

v11

Page

FIGURE
8.

Seasonal changes 1n c o ld h ard iness f o r fo u r s e e d lo ts o f
ponderosa p in e .
Numbered arrows d e s ig n a te dates o f
Im p o rta n t c lim a t ic changes as fo llo w s :
Arrow
Arrow
Arrow
Arrow
Arrow
Arrow

9.

10.

11.

12.

No.
No.
No.
No.
No.
No.

1
2
3
4
5
6

January 18 , 1976 - f i r s t day below -27°C
February 15 , 1976 - f i r s t day above 16°C
October 18 , 1976 - f i r s t day below -5 C
December 3 , 1976 - f i r s t day below -2 6 C
December 3 1 , 1976 - f i r s t day below -2 8 C
February 7 , 1977 - f i r s t day above 5°C

74

G en etic d iffe r e n c e s 1n w in te r d ryin g ra te s and f o l i a r
m o istu re c o n te n t o f ex cis ed tw ig s from f i v e ponderosa
p in e s e e d lo ts c o lle c te d on November 2 8 , 1976. S eed lo ts
2034, 2014, and 2091 a re from th e c o a s ta l v a r ie t y ;
s e e d lo ts 2164 and 2248 a re from th e i n t e r i o r v a r ie t y .

80

Seasonal changes 1n f o l i a r m o istu re c o n te n t and co ld
hardiness f o r tre e s from two ponderosa p in e ecotypes
growing a t K ello gg F o re s t 1n southw estern M ich ig an .

89

Change in r e l a t i v e h e ig h t (expressed as a percentage o f
p la n ta tio n o r n u rsery means) w ith age f o r tre e s from fo u r
ponderosa p in e eco typ es.

99

Severe stem crook causing permanent damage to a t r e e o f
New Mexico o r ig in growing a t th e K ellogg Forest
p la n t a tio n .

v i 11

122

CHAPTER 1

INTRODUCTION

Ponderosa pine ( Plnus ponderosa) 1s n a tiv e to th e w estern U nited
S ta te s and Is th e la r g e s t ranging species o f pine 1n North Am erica.
I t s t a l l , s tr a ig h t tru n k and l i g h t , e a s ily worked wood make 1 t one o f
th e most Im p o rtan t tim b e r species 1n th e w o rld .
h ig h ly regarded f o r I t s beauty.

Ponderosa p in e 1s als o

I t s long cle an b o le s , orange p la te d

bark and l i g h t green fo lia g e a re admired by most w estern t r a v e le r s .
Because o f I t s ra p id growth r a te and a d a p t a b ilit y , ponderosa pine
1s w id e ly used as an e x o tic .

In th e G reat P la in s and e a s te rn U nited

S ta te s , 1 t Is convnonly used In s h e lt e r b e lt and ornamental p la n tin g s and
1s o fte n considered as a p o t e n t ia lly v a lu a b le tim b er o r pulp sp e c ie s .
Cold tem perature is one o f th e most Im p o rtan t fa c to rs l im it i n g th e
d is t r ib u t io n o f ponderosa p in e .
In ju r y o fte n occurs.

When 1 t 1s p la n te d as an e x o tic , w in te r

Such In ju r y 1s a problem o f m ajor economic Im p o rt­

ance, o fte n causing severe red u ctio n s 1n growth r a te and u n s ig h tly damage.
Ponderosa p in e Is an e x tre m e ly v a r ia b le species g e n e t ic a lly .

As a

r e s u l t , one would expect to d is c o v e r la r g e d iffe re n c e s 1n c o ld hardiness
among I t s geographic ra c e s .

However, In s p ite o f I t s im p ortan ce, l i t t l e

d ir e c t evidence has been compiled which ev a lu a te s In t r a s p e c if ic v a r ia tio n
In ponderosa p in e f o r fa c to r s which are r e la te d to co ld h ard in e ss .

Such

In fo rm a tio n 1s e s s e n tia l f o r th e s e le c tio n and breeding o f new adapted
ra c e s , and f o r o b ta in in g the maximum p o te n tia l o f t h is species as an e x o tic .

The s tu d ie s re p o rte d 1n t h is th e s is were undertaken to determ in e
g e n e tic v a r ia t io n 1n s e ve ra l aspects o f cold hardiness 1n ponderosa p in e
and to d eterm in e which aspects a re most Im p o rta n t 1n l im it i n g th e growth
and development o f th e species 1n M ich ig an .

O th er goals were to study

g e n e tic v a r ia tio n In s e ve ra l o th e r eco n o m ically Im p o rta n t t r a i t s and
to d eterm ine th e b est seed sources f o r p la n tin g 1n M ich ig an .

CHAPTER 2
PHYSIOLOGY AND GENETICS OF COLD HARDINESS IN PLANTS:
LITERATURE REVIEW
INTRODUCTION

The a b i l i t y o f p la n ts to s u rv iv e s u b fre e z in g tem peratures 1s
one o f th e most Im p o rtan t fe a tu re s a f f e c t in g the d i s t r i b u t i o n ,
m ig ra tio n and u t i l i t y o f a s p e c ie s .

Upon th e onset o f changing

environm ental c o n d itio n s 1n th e f a l l , many p h y s io lo g ic a l and b io ­
chemical processes a re I n i t i a t e d which Im p art a s ta tu s o f co ld
re s is ta n c e to p la n ts .

However, th e Im pact o f c o ld re s is ta n c e goes

f a r beyond th e p h y s io lo g ic a l and biochem ical Im p lic a tio n s .

F ree zin g

damage to o u r n a tiv e v e g e ta tio n and crop p la n ts 1s an im p o rta n t
problem , w ith m ajor economic Im p acts.

In o rd e r to enhance y i e l d s ,

research ers have worked toward a c h ie v in g a b e t t e r understanding o f
the p h y s io lo g ic a l and g e n e tic processes In v o lv e d 1n co ld h a rd in e s s .
To d a te , th e p h y s io lo g ic a l aspects a re much b e t t e r understood
b u t th e re has a ls o been some b reeding w ork.

The u ltim a te advance 1n

co ld hardiness Improvement w i l l p ro b ab ly n o t be ach ieved u n t i l
p h y s io lo g is ts and g e n e tic is ts combine t h e i r s k i l l s

1n an e f f o r t to

determ in e th e g e n e tic b asis f o r th e p h y s io lo g ic a l and m e ta b o lic events
which r e s u lt 1n c o ld re s is ta n c e among many h ig h e r p la n ts .
In th e ensuing d is c u s s io n , I d e s c rib e th e p h y s io lo g ic a l p ro ­
cesses which a re b e lie v e d to be In v o lv e d In th e In d u c tio n o f cold

hardiness 1n p la n ts .

I a ls o s p e c u la te on th e r o le o f g e n e tic re g u la ­

t io n and th e p o s s ib le modes o f In h e r ita n c e o f such p h y s io lo g ic a l
processes.
FREEZING AND DEATH IN PLANT TISSUES
F re e zin g 1n p la n t tis s u e s 1s th e conversion o f liq u id s 1n c e lls
and tis s u e to a s o lid s t a t e w ith an accompanying loss o f h e a t.
types o f fr e e z in g a re recognized 1n p la n ts :

Two

s o lid ific a tio n o f c e llu la r

co n ten ts In to a non c r y s t a l l i n e s t a t e w ith o u t an o r d e r ly m o le c u la r
arrangem ent, and s o l i d i f i c a t i o n

t h a t in v o lv e s c r y s t a l l i z a t i o n o r an

arrangem ent o f liq u id m olecules In to o rd e rly s tr u c tu r e s (A lden and
Hermann, 1 9 7 1 ).
The f i r s t typ e o f fr e e z in g 1s c a lle d v i t r i f i c a t i o n

and occurs

as a r e s u lt o f e x tre m e ly ra p id fr e e z in g o f p la n t tis s u e s .

This type

o f fr e e z in g r a r e ly occurs 1n n a tu re and 1s m a in ly o f academic In t e r e s t
because c e lls can s u rv iv e v i t r i f i c a t i o n

to ve ry low te m p e ra tu re s .

If

fr e e z in g 1s ra p id enough to produce subm lcroscoplc ic e c r y s t a l s , no
In ju r y occurs in th e p la n t c e l ls ( L e v i t t , 1 9 5 6 ).
Most fr e e z in g damage t h a t occurs in p la n ts Is due to th e second
typ e o f f r e e z in g .

In n a tu re the a i r tem perature r a r e ly decreases

more than a few degrees p e r hour.

A t such low ra te s o f f r e e z in g ,

1ce forms f i r s t o u ts id e c e lls where w a te r 1s p u re s t.

Hardy woody

p la n ts can s u rv iv e e x t r a - c e l l u l a r fr e e z in g o f t h is ty p e .

However,

i f 1ce c r y s ta ls form w it h in th e p ro to p lasm , such I n t r a c e l l u l a r
fr e e z in g u s u a lly r e s u lts 1n c e ll d ea th .
The method by which fr e e z in g In ju r y occurs has been debated
1n th e l i t e r a t u r e .

W elser (1 9 7 0 ) suggested t h a t d u rin g fr e e z in g a

p o in t 1s reached when a l l

r e a d ily a v a ila b le w a te r has been fro z e n

e x t r a c e l l u l a r l y and o n ly " v i t a l " w a te r remains 1n th e pro top lasm .
With continued lo w erin g o f tem perature v i t a l w a te r 1s p u lle d away
from p ro to p la sm ic c o n s titu e n ts to th e e x t r a c e l l u l a r Ic e .

This s e ts

o f f a ch ain re a c tio n o f d e n a tu ra tlo n , a d d itio n a l v i t a l w a te r r e le a s e ,
and u lt im a t e ly d e a th .

This proposal allo w s f o r an e x p la n a tio n o f

death based on e i t h e r mechanical damage, p ro te in d e n a tu r a tlo n , o r
d eh yd ratio n o f th e c e l l .
Mechanical damage may occur when I n t e r c e l l u l a r spaces a re too
sm all to accommodate 1ce fo rm a tio n and c e l ls a re ru p tu re d by s p l i t ­
t in g o f t h e i r w a lls along th e m id dle la m e lla .

In ju r y from I n t r a ­

c e l l u l a r 1ce fo rm a tio n r e s u lts from m echanical d is o r g a n iz a tio n o f
th e protoplasm by 1ce c r y s ta ls ( L e v i t t , 1 9 5 6 ).

P ro te in d e n a tu ra tlo n

occurs when c e l l u l a r w a te r 1s removed and s a lt s become co n c e n tra te d
1n the c e l ls to such an e x te n t t h a t p ro te in s a re I r r e v e r s ib l y damaged.
Severe d eh yd ra tio n sh rin ks the e n t i r e c e l l , In c lu d in g th e c e ll w a l l ,
and causes loose tis s u e .

O ften th e dehydrated cytoplasm c o n tra c ts

around th e nucleus and p la sm atic stran d s b re a k .

S u rv iv a l o f c e lls

pro bably depends on the te n a c ity o f w a te r b in d in g to p ro to p la sm ic
c o n s titu e n ts , o r th e e x te n t to which bound w a te r 1s re p la c e d by
p r o te c tiv e m olecules (H e b e r, 1 9 6 8 ).
L e v i t t (1 9 6 2 ) proposed a th e o ry which e x p la in s c o ld damage on
th e b asis o f p ro te in d e n a tu ra tlo n r e s u lt in g from th e fo rm a tio n o f d i ­
s u lf id e bonds between a d ja c e n t s u lfh y d r y l groups o f p r o te in s .

Since

th e suggestion o f t h is th e o ry In 1962, c o n s id e ra b le evid en ce has
been presented 1n support o f L e v i t t 's

Id e a .

He thought t h a t high

w a te r s tre s s has an e f f e c t upon th e s u lfh y d r y l groups o f p r o te in .
As th e la y e r o f w a te r around th e p ro te in m olecule becomes t h in n e r ,

th e s u lfh y d ry l groups begin to c o n ta c t each o th e r 1n a d ja c e n t pro­
te in s .

Upon o x id a tio n the hydrogen 1s removed and d is u lf id e lin k a g e s

a re formed.

A f t e r re h y d ra tio n , th e d is u lf id e lin k a g e s hold p ro te in s

to g e th e r 1n such a May th a t th e developing w a te r la y e r re s u lts 1n
d is to r tio n s o f the p ro te in m olecules.

Assuming h is hypothesis 1s

v a l id , re s is ta n c e to co ld damage 1s re la te d to an In h ib it io n o f th e
In te rm o le c u la r d is u lf id e bonds which form between p ro te in s and u l t i ­
m ately d is t o r t them.

Heber (19 68 ) found th a t in co ld r e s is ta n t

herbaceous p la n ts sugar replaces w a te r 1n form ing a p r o te c tiv e s h e ll
around th e p ro te in m o lecu les, and thus in h ib it s fo rm a tio n o f d is u lf id e
lin k a g e s .
THE ROLE OF LIGHT
L ig h t 1s g e n e ra lly b e lie v e d to a f f e c t the development o f cold
hardiness through a p ho to p erfo d lc response.

E a rly th e o rie s suggested

th a t photoperiod a ffe c te d cold re s is ta n c e o f woody p la n ts by Inducing
dormancy.

Tumanov e t a l

(19 64 ) found th a t b lack lo c u s t ( Rob1n1a

p su ed oacada) and w h ite b irc h ( B etula v e rru c o s a ), which d id not e n te r
dormancy because o f continuous Illu m in a t io n , f a i l e d to develop complete
to le ra n c e to cold a t hardening tem p eratu res.

They th e re fo r e concluded

th a t co ld hardiness could be Induced o n ly a f t e r th e dormant s ta te had
been reached.
More re c e n t s tu d ie s have shown th a t dormancy m erely accompanies
th e onset o f cold a c c lim a tio n and th a t both processes a re Ind ep en d en tly
trig g e re d by a p h o to p erlo d ic mechanism.

Zehnder and Lanphear (19 66 )

showed t h a t f o lia g e o f Taxus cu spldata developed more hardiness under
an 8-h o u r than under a 16-hour photoperiod.

Removal o r co verin g o f

the leaves In te r f e r e d w ith th e development o f h a rd in e s s , thus suggest­
ing th a t th e leaves a re the re c e p to r o f th e l i g h t stim ulus which
I n i t i a t e s h ardening.

W illia m s e t a l (19 72 ) suggested th a t reduced

photoperiods Induce r e s t and a sim ultaneous In c re as e In hardiness
through a phytochrome mediated response.

They demonstrated th a t

dark p erio d In te rru p tio n s w ith red r a d ia tio n suppressed cold a c c lim a ­
tio n 1n Comus and Weigel a . When red l i g h t was fo llo w e d by f a r red
l i g h t , suppression was r e lie v e d .

Thus they hypothesized th a t s h o rt

days (lo n g n ig h ts ) a llo w an accum ulation o f th e Pr form which 1s
subsequently In v o lv ed 1n Implementing cold h ard in ess.

Ir v in g and

Lanphear (1 9 6 7 a , 1967b) found th a t Acer negundo. Viburnum pUcatum
tomentosum. and Weigel a f l o r l d a , which remain 1n a non-growing
c o n d itio n w ith o u t bud dormancy under a 6 hour p h o to p e rio d , developed
the same degree o f hardiness as dormant p la n ts under an 8 hour photo­
p erio d a f t e r hardening f o r th e same p erio d o f tim e .

In a d d it io n ,

re s is ta n c e to f r o s t by Viburnum p la n ts placed under supplemental
l i g h t to p reven t dormancy, equaled th e re s is ta n c e o f p la n ts under
n a tu ra l d aylen g th s.

These authors th e re fo r e concluded t h a t dormancy

Is not re q u ire d f o r hardening and th a t hardiness was Induced by a
p h o to p erlo d ic response s im ila r to dormancy and flo w e r In d u c tio n .
In c re as in g weeks o f s h o rt days, fo llo w e d by a low tem perature harden­
ing p e rio d , brought about a p ro g ressive In crease 1n h a rd in e s s . Addi­
tio n a l evidence was provided by Young (19 61 ) on g r a p e fr u it .

Photo­

p erio d was shown to have no e f f e c t on bud dormancy 1n th is p la n t , but
p la n ts under s h o rt days developed a g r e a te r re s is ta n c e to co ld than
p la n ts under long days.

A com bination p h o to p e rlo d ic and p h o to s y n th e tic r o le 1n co ld
hardiness was suggested by Steponkus and Lanphear (1 9 6 8 ) 1n t h e i r
work on th e l i g h t req u irem ent o f Hedera h e lix d u rin g c o ld a c c lim a tio n .
They found th e fo llo w in g e f f e c t s :

1.

S h ort day l i g h t increased

development o f c o ld to le ra n c e d u rin g th e f i r s t 6 weeks o f hardening*
2.

A f t e r t h is tim e , va rio u s photoperiods from 8 to 24 hours had no

e f f e c t on to le r a n c e * 3.
4.

Low I n t e n s it ie s o f l i g h t fa v o re d h ard e n in g ,

Reduced C02 and darkness d u rin g hardening caused a loss o f t o l e r ­

ance^ 5.

In creased p h o to s y n th e tic area exposed to l i g h t In creased stem

h a rd in e s s ; and 6 .

A high c o n c e n tra tio n o f a p h o tosyn thesis I n h i b i t o r

(slm eto n e) decreased h ard iness o f leaves and had no e f f e c t on the
stems.

They b e lie v e d t h a t e f f e c t s 1 , 4

l i g h t In a c c lim a tio n 1s p h o to s y n th e tic .

and 5 show t h a t th e r o le o f
They could e x p la in th e d is ­

crep an cies noted 1n 2 and 3 o n ly I f a sm all p o rtio n o f th e photosynth a te produced was re q u ire d f o r cold a c c lim a tio n .

A p h o to p e rlo d ic

response s im ila r to phytochrome Induced flo w e rin g and dormancy was
in d ic a te d In e f f e c t s 2 , 3 and 5 .

The authors concluded t h a t

the phytochrome system 1s a t work and I t

In flu e n c e s carb o h yd rate

m etabolism , p ro te in s y n th e s is , and o x id a tiv e p h o sp h o ry latio n 1n
prom oting th e development o f co ld h a rd in e s s .
ACCLIMATION
Woody p la n ts c h a r a c t e r is t ic a l l y undergo a s e rie s o f changes 1n
the f a l l which en ab le them to cope w ith th e oncoming fr e e z in g s tre s s e s
o f w in te r .

The process by which p la n ts c a rry o u t th ese changes 1s

c a lle d a c c lim a tio n .

The a c c lim a tio n process In p la n ts 1s g e n e r a lly

b e lie v e d to be c a r r ie d o u t In 2 o r sometimes 3 phases.

The f i r s t stage o f a c c lim a tio n 1n p la n ts 1s Induced by the onset
o f sh o rt days and 1s p erceived by th e leaves (Howell and W else r, 1970a;
Fuch1gam1 e t a l . 1971; Ir v in g and Lanphear, 1967a, 1967b ).

Short days

1n the autumn are d etected by a phytochrome clock 1n th e leaves and
the Pr form accum ulates.

Decreasing photoperiods cause th e cessatio n

o f growth and thereby a llo w f o r sto rag e o f photosynthates which are
the energy producing s u b s tra te s necessary f o r a c c lim a tio n (Fuchlgarni
e t a l , 1 9 7 1 ).

Temperature also plays a r o l e , low tem peratures o fte n i n h i b i t

1ng the f i r s t s ta g e .

Once th is phase has been Induced, very l i t t l e

hardiness Is a c t u a lly a tta in e d 1n the p la n t .

A p p a re n tly , th e prim ary

r o le o f th e f i r s t stage 1s to cease growth and to I n i t i a t e

th e meta­

b o lic changes which f a c i l i t a t e the p la n ts response to low tem perature
during the second stage o f a c c lim a tio n .
The means by which the f i r s t stage m etab olic changes begin 1s
not f u l l y known.

However, 1 t has been shown (Fuch1gam1 e t a l , 1971;

Howell and W elser, 1970a) th a t upon re c e p tio n o f th e s h o rt day s tim u lu s ,
the sh o rt day l e a f produces a tra n s lo c a ta b le substance which promotes
a c c lim a tio n .

Through a s e rie s o f m o d ified p la n t s tu d ie s , I t has been

shown th a t th e hardiness promoting fa c t o r 1s o n ly syn th esized 1n s h o rt
day le a v e s .

Long day leaves produce a su b stance(s) which In h ib it s the

In d u c tio n o f a c c lim a tio n .

T h e re fo re , under long days and n a tu ra l f a l l

tem p eratu res, hardiness can be a tta in e d o n ly a f t e r removal o f the long
day leaves ( Ir v in g and Lanphear, 1967b ).

Through th e use o f g r a ftin g

s tu d ie s , I t has been shown t h a t both In h ib it o r s and promoters o f
hardiness e x is t .
The second stage o f a c c lim a tio n 1s Induced by low tem peratures.
In f a c t , f r o s t o fte n appears to be the tr ig g e r in g stim u lus (Howell

10
and W elser, 1970a).

I t has been f u r t h e r noted th a t th e f r o s t Induced

phase o f a c c lim a tio n does not In v o lv e tra n s lo c a ta b le fa c to r s .

Because

o f t h i s , many authors have suggested th a t th e second stage o f a c c lim a ­
tio n 1s a p hysical r a th e r than a m etab o lic process.

However, t h is 1s

not l i k e l y because a number o f enzyme mediated re a c tio n s a re known to
be Induced by low tem peratures (W e ls e r, 19 7 0 ).
W elser (1970) has suggested th a t the second stage o f a c c lim a tio n
may In v o lv e a r e o r ie n ta tio n o f macromolecules In to s ta b le forms which
can w ith stand severe d e h yd ra tio n .

P ro tein s and hydrophobic residues

are known to be tem perature s e n s itiv e .

In the polym erized s t a t e ,

many p ro te in s a re b io lo g ic a lly a c tiv e b u t s tre s s s e n s itiv e w h ile
depolym erized molecules a re In a c tiv e but s tre s s r e s is t a n t .

W elser

proposed th a t th e re may be a tem perature r e v e r s ib le re g u la tio n o f
h yd ratio n which re s u lts In the conversion o f p ro te in s from a polym erized
to a depolym erized c o n fig u ra tio n a t low tem p eratu re.

The u ltim a te

r e s u lt o f such a re a c tio n 1s the high degree o f cold hardiness which
1s a tta in e d during th e second stage o f a c c lim a tio n .

During the l a t t e r

stages o f t h is phase hardy p la n ts become very cold r e s is t a n t , tis s u e
h y d ra tio n decreases and m etab olic a c t i v i t y 1s s l i g h t .

I t Is p o s sib le

th a t many o f the macromolecular and c e l l u l a r s tru c tu re s asso ciated
w ith a c tiv e growth and metabolism are disassembled and 1n a re s tin g
s ta te f o r th e w in te r .
Tumanov and Krasavtsev (19 59 ) observed t h a t th e re o fte n 1s a
t h ir d stage o f a c c lim a tio n 1n hardy woody p la n ts which Is Induced by
u ltr a lo w tem peratures In the range o f -5 0 ° C.

Prolonged exposure o f

prehardened tis s u e to tem peratures In t h is range can d r iv e th e h a r d i­
ness to le v e ls which a re not o r d in a r ily experienced 1n n a tu re .
kind o f hardiness is q u ic k ly l o s t .

This

They noted th a t 1 f hardy stems

11

were thawed f o r as l i t t l e

as 6 hours t h e i r hardiness le v e ls would

decrease from -1 9 5 ° to -4 5 °C .
Tumanov and Krasavtsev als o suggested th a t th e t h ir d phase o f
a c c lim a tio n 1s a physical process asso ciated w ith reduced In te rm o le c u la r d istances and thermal motion o f molecules in fro zen c e l ls .
Welser (1 9 7 0 )* however, thought th is phase o f a c c lim a ^ o n 1s r e la te d
to the amount and degree o f o r ie n ta tio n o f q u a s i-c r y s ta l11ne w ater
1n the c e l l .

He p o s tu la te d th a t prolonged low tem peratures c re a te

a high degree o f o rd e r among w ate r m olecules.

T h is , 1n t u r n . Increases

the te n a c ity o f binding which Increases the p ro p o rtio n o f bound w ater
and thus Increases d ehydration re s is ta n c e o r reduces th e q u a n tity o f
a v a ila b le w ate r f o r d e s tr u c tiv e c r y s t a l l i z a t i o n .

Upon warming, therm al

a c t i v i t y Increases and thawed e x t r a c e llu la r w ate r q u ic k ly relnvades the
c e ll causing ra p id decreases in hardiness le v e ls .

Burke e t a l

(1974)

stu d ied the n u c le a r magnetic resonance o f w a te r 1n a c c lim a tin g Cornus
s t o lo n lfe r a and provided evidence which supports W e ls e r1s th e o ry .

They

found th a t the a b i l i t y o f dogwood to s u rv iv e low tem perature depends
p r im a r ily on I t s a b i l i t y to t o le r a t e dim inished q u a n titie s o f w a te r
and high protoplasm ic c o n c e n tra tio n s .

They a ls o showed th a t the

te n a c ity o f hydrophobic w a te r b in d in g Increased a t low tem peratures
which re s u lte d 1n Increased re s is ta n c e to deh yd ratio n In c e l ls .
The hardiness promoter
The n atu re o f th e hardiness promoter which plays a r o le 1n th e
f i r s t stage o f a c c lim a tio n 1s s t i l l

a m ystery.

I t 1s known th a t the

hardiness promoting fa c to r 1s synthesized 1n leaves exposed to s h o rt
days.

I t 1s als o known th a t th e fa c to r 1s not species s p e c i f ic , I . e .

12
the hardiness promoting f a c t o r from leaves o f a hardy species (o r
genotype) can enhance a c c lim a tio n o f a le s s hardy species (o r geno­
ty p e ) when th e two a re g r a fte d .

A f te r re vie w in g a m a jo r ity o f th e

work r e la t in g to th is a re a , W elser (19 70 ) has concluded th a t the
promoting substance Is e i t h e r a I n h i b i t o r , a sugar o r a re g u la to ry
substance.
Growth I n h i b i t o r .

I t 1s p o s s ib le th a t the hardiness promoter

may p la y an In d ir e c t r o le 1n a c c lim a tio n by m erely stopping grow th,
an event which 1s necessary f o r th e onset o f a c c lim a tio n In woody
p la n ts .

Ir v in g (19 69 ) showed th a t an I n h i b i t o r e x tra c te d from s h o rt

day leaves o f Acer negundo was s im ila r to a b s c ls lc a c id 1n chromotograph1c p r o p e rtie s .

Subsequent tre a tm e n t o f Acer negundo w ith the

e x tra c te d I n h i b i t o r o r a b s c ls lc a d d Increased h a rd in e s s .

He, th e re ­

fo r e , concluded t h a t th e hardening process appears to be c lo s e ly
c o rre la te d to a b u ild up o f a b s c ls lc a c id le v e ls which a re s tim u la te d
by sh o rt days.

I t Is p o s s ib le t h a t a b s c ls lc a d d p lays a r o le In

a c c lim a tio n by causing growth c e s s a tio n , however, t h a t does not
account f o r th e wide spectrum o f m e tab o lic changes which occur d u rin g
a c c lim a tio n .

I t 1s more l i k e l y th a t th e hardiness prom oter plays an

a c tiv e re g u la to ry r o le which does n o t begin u n t i l growth ceases.
Sugar.

A co n s id e ra b le amount o f evidence p o in ts to the p o s s i­

b i l i t y th a t sugar may be th e tra n s lo c a ta b le f a c t o r .

Fuch1gam1 e t a l

(19 71 ) has shown th a t p la n ts cannot a c c lim a te when they a re d ep leted
o f p h o to s yn th e tic s u b s tra te .

Heber (19 68 ) has shown th a t sugar p ro ­

te c ts the enzyme system a s s o c ia te d w ith o x id a tiv e phosp ho rylation 1n
spinach c h lo ro p la s ts th a t a re su b jected to fr e e z in g .

He b e lie v e s

t h a t the p ro te c tiv e In flu e n c e o f sugars may be due to t h e i r a b i l i t y

13
to r e ta in o r s u b s titu te w a te r o f h y d ra tio n o f p ro te in s v ia hydrogen
b in d in g .

Steponkus (19 71 ) showed th a t Hedera h e lix p ro te in from cold

acclim ated tis s u e e x h ib ite d a h ig h e r sugar bin din g c a p a c ity than
p ro te in from nonacclim ated tis s u e .

Furtherm ore, he a ls o noted a

dram atic In c re as e 1n la b e lle d sucrose 1n p ro te in from acclim ated
tis s u e s .
a r tific ia l

A d d itio n a l evidence was o ffe re d by L e v it t (19 59 ) th a t an
In c re as e In sugar co n ten t increased the c o ld hardiness

1n cabbage le a v e s .

He noted th a t 1n leaves I n f i l t r a t e d w ith fru c to s e

osmotic p o te n tia l was h ig h e r and th e f r o s t k i l l i n g p o in t was s i g n i f i ­
c a n tly low er than 1n c o n tro l le a v e s .

He concluded, however, t h a t an

In crease 1n sugars could account f o r only p a rt o f the n a tu ra l In c re as e
1n hardiness and t h a t th e re must be a d d itio n a l fa c to rs In v o lv e d .

Many

authors have found seasonal increases In sugar co n te n t which were
h ig h ly c o rr e la te d w ith Increases in cold re s is ta n c e .

P arker (1959)

found s lig h t Increases 1n su cro se, glucose and fru c to s e In 6 co n ife ro u s
species during w in te r .

He a ls o found d r a s tic in creases in r a ffln o s e

and stachyose 1n th e 6 s p e c ie s , which were d ir e c t l y c o rr e la te d w ith
w in te r h ard in e ss .
In s p ite o f th e c o lle c t iv e w eigh t o f e v id e n c e , no exp erim en tal
data has been a b le to show increased hardiness 1n woody p la n ts as a
r e s u lt o f a r t i f i c i a l

Increases In sugar.

There Is l i t t l e

doubt th a t

some basic le v e l o f sugar 1s necessary f o r a c c lim a tio n , but w hether
o r not sugar 1s th e tra n s lo c a ta b le hardiness promoter has s t i l l

not

been c le a r ly e s ta b lis h e d .
R egulatory hormone.

Although th e re 1s no exp erim en tal e v id e n c e ,

Welser b e lie v e s th a t the hardiness promoter may be a hormone o r complex
o f hormones which p lay a s p e c ific r o le 1n re g u la tin g a c c lim a tio n .

If

14
th is 1s th e case, then 1 t 1s probable th a t u ltim a te re s is ta n c e 1s
th e product o f seve ra l d is t in c t processes.
PHYSIOLOGICAL AND METABOLIC CHANGES DURING HARDENING
Water r e la tio n s
Hypotheses to e x p la in p la n t s u rv iv a l a t low tem peratures assume
th a t i n t r a c e l l u l a r 1ce fo rm atio n Is avoided in hardy tis s u e s .

In

ten d er tis s u e s , an In c re as e 1n the p r o b a b ility o f I n t r a c e l l u l a r 1ce
occurs during f r o s t due to a la rg e amount o f w ate r w ith in c e lls .
McKen2 i e e t a l (1974a) have shown th a t w a te r co n ten t o f stems de­
creases co n s id e ra b ly d u rin g th e I n i t i a l stage o f a c c lim a tio n .

This

re s u lts as a fu n c tio n o f decreased stom atal re s is ta n c e and Increased
ro o t re s is ta n c e to th e uptake o f w a te r.

The I n i t i a l high r a te o f l e a f

tr a n s p ir a tio n r e f le c t s th e In c re as e 1n metabolism asso ciated w ith th e
i n i t i a l s h o rt day Induced stage o f a c c lim a tio n .

McKenzie e t a l (1974b)

a ls o showed t h a t during th e f i r s t stage o f a c c lim a tio n w ate r permea­
b i l i t y o f th e phloem and c o r t ic a l parenchyma c e lls Increased s i g n i f i ­
c a n tly , and re s u lte d In an Increase 1n hardiness In Comus s t o lo n lf e r a .
R e la tio n s h ip s between re s is ta n c e to w a te r flo w 1n p la n ts and
hormones a re w e ll known.

McKenzie e t a l

(1974b) Im ply th a t th e r a t io

o f c y to k ln ln s and ABA may d ir e c t th is a d a p tiv e response o f th e p la n t
In v o lv in g w a te r flo w .

They als o suggest th a t th e tra n s lo c a ta b le

hardiness promoter may fu n c tio n p r im a r ily by c o n tr o llin g the hydra­
tio n o f o v e rw in te rin g tis s u e .
Chi oropl as ts
During hardening two opposing types o f changes have been observed
1n the c h lo ro p la s ts :

in some cases the c h lo ro p la s ts r e ta in t h e i r

15
I n t e g r i t y , but m ig ra te from a summer p o s itio n near the c e ll w a ll to
a crowded p o s itio n In th e c e ll I n t e r i o r , w ith some loss 1n c h lo ro p h y ll
c o n te n t; 1n o th e r cases, th e c h lo ro p la s ts have been shown to a g g lu t i­
n a te , lo s e t h e i r I n t e g r i t y and merge w ith each o th e r to become a
continuous mass from which c h lo ro p la s ts reform again as sp rin g
approaches (P a r k e r, 1 9 6 3 ).
N u cle ic acids
LI and W elser (1968) have shown th a t n u c le ic acids 1n apple
tw igs begin to show an In c re as e 1n co n c e n tra tio n one week p r io r to a
ra p id In crease In cold h ard in e ss .

S o lu b le RNA Increased 382 in one

week, l i g h t and heavy rlbosomal RNA Increased 412 in two weeks ju s t
p r io r to and d urin g th e stage o f ra p id cold a c c lim a tio n .

Follow ing

t h is p erio d th e re was a s lig h t decrease In these th re e n u c le ic ac id
f r a c t io n s .

DNA co n ce n tratio n s fo llo w e d the same p a tte rn although

the t o ta l c o n c e n tra tio n was much lo w er.

These re s u lts suggested

th a t sh o rt days a n d /o r low tem peratures 1n the autumn tr ig g e r s the
production o f an endogenous growth re g u la to r which Induces ra p id
synthesis o f s o lu b le RNA.

The s o lu b le RNA p a r tic ip a te s d ir e c t ly

1n p ro te in syn th esis and a ls o probably fu n c tio n s 1n th e re g u la tio n
o f a l l RNA and p ro te in syn th esis through a re p re s s o r-in d u c e r type
o f system.

Such a system may 1n f a c t be working because the tim ing

o f RNA Increases suggest th a t i t may be one o f th e i n i t i a l steps In
the hardening process.
F u rth e r In fo rm a tio n on the r o le o f n u c le ic acids In cold
hardiness was ex p la in ed by K essler and F ra n k -T ls h e l (19 62 )

They

discovered th a t d eh yd ratio n increased th e r a t io o f guanine and

16
c y to s in e to adenine and u r a c il 1n th e RNA o f o li v e le a v e s .

Guanine

and c y to s in e p a ire d to form an a d d itio n a l hydrogen bond between the
double h e lix o f th e n u c le ic a c id s , which was hyp oth esized to
g re a te r s t a b i l i t y to RNA m o lecu les.

Im p a rt

They concluded t h a t a high

guanine and c y to s in e c o n te n t In RNA 1s r e la te d to c o ld re s is ta n c e
1n p la n ts and the a b i l i t y to s y n th e s ize RNA th a t 1s ric h 1n guanine
and c y to s in e 1s a b as ic p a rt o f th e co ld hardening process In p la n ts .
P ro te in s
S1m1nov1tch and Briggs (19 53 ) re p o rte d th a t th e c o n c e n tra tio n s
o f w a te r s o lu b le p ro te in Increased In th e bark o f b la c k lo c u s t In
th e f a l l

along w ith th e development o f co ld h a rd in e s s .

In th e

s p rin g , t h is c o n c e n tra tio n d e c lin e d a b ru p tly w ith th e disappearance
o f h a rd in e s s .

Pomeroy e t a l

(1 9 7 0 ) found a s i m ila r tre n d 1n the bark

and needles o f red p in e ( Plnus r e s ln o s a ).
re p o rte d a f a l l

F u rth erm o re, P a rk e r (1 9 6 3 )

In c re a s e 1n w a te r s o lu b le p ro te in 1n some s p e c ie s .

These works u lt im a t e ly le d to the co n clusion t h a t th e In c re a s e 1n
s o lu b le p ro te in may p la y an Im p o rta n t r o le 1n th e development o f
f r o s t h a rd in e s s .
There a re two schools o f thought which a tte m p t to e x p la in th e
p a r a lle lin g In c re a s e 1n w a te r s o lu b le p ro te in s and development o f
h a rd in e s s .

Many s tu d ie s In d ic a te t h a t th e In c re a s e 1n p ro te in r e s u lts

from a breakdown o f p a r t o f th e more complex p ro te in s and n o t from
s yn th esis o f new amino acid s and p r o te in s .

This view 1s supported

by Heber (1 9 6 8 ) who suggested t h a t p ro te in In c re as es a s s o c ia te d w ith
the development o f to le ra n c e to co ld may r e s u lt from changes 1n
e x tra c ta b 1 1 1 ty o f p ro te in s In flu e n c e d by seasonal changes 1n pH.
Others b e lie v e t h a t th e In c re a s e 1n w a te r s o lu b le p ro te in s

17
r e s u lt s from p r o te in s y n th e s is .

L1 e t a l

(1 9 6 5 ) found an In c re a s e

In t o t a l p r o te in and a decrease In amino a c id s upon h ard e n in g o f
Comus s t o l o n l f e r a .

The d e c lin e In amino a c id s p ro b a b ly in d ic a te s

th e y w ere used 1n s y n th e s iz in g w a te r s o lu b le p r o te in s .
S1m1nov1tch (1 9 6 3 ) showed t h a t an In c re a s e 1n RNA w ith o u t an
in c re a s e 1n DNA o cc u rred p rec ed in g th e In c o r p o r a tio n o f la b e lle d
g ly c in e In t o p r o t e in , n e t p r o te in s y n th e s is and c o ld r e s is ta n c e
1n th e parenchyma c e l l s o f b la c k lo c u s t b a rk . The In c o r p o ra tio n o f
la b e lle d g ly c in e In t o w a te r s o lu b le p r o te in v e r i f i e s
t e i n s y n th e s is 1s In v o lv e d .

t h a t t r u e p ro ­

The In c re a s e 1n amino a c id s and n u c le o ­

t id e s n ecessary f o r p r o te in s y n th e s is p ro b a b ly occurs as a r e s u l t o f
d e g ra d a tio n , h y d r o ly s is , and movement o f p ro te in s and n itr o g e n from
th e le a v e s in t o th e tru n k d u rin g autumn.

The In c re a s e d RNA Is b e lie v e d

to s y n th e s iz e s p e c i f ic w a te r s o lu b le p ro te in s t h a t promote f r o s t
r e s is ta n c e o r tra n s fo rm th e p r o te in s y n th e tic c a p a b i l i t i e s
th e photoplasm lc substances 1n th e bark c e l l s .

to In c re a s e

The changed p h y s ic a l

p r o p e r tie s o f th e p ro to p lasm e n a b le 1 t to r e s i s t s tr e s s from d eh yd ra­
t io n caused by I n t r a c e l l u l a r f r e e z in g .
Amino a c id s
S e v e ra l w orkers have a n a ly ze d th e amino a d d c o n te n t o f w a te r
s o lu b le p ro te in s d u rin g h ard en in g and d e h a rd e n in g .

P a u li and Zech

(1 9 6 4 ) found t h a t a la n in e , a r g in in e , a s p a ra g in e , g lu ta m ic a c id and
h l s t l d l n c o n te n ts o f w a te r s o lu b le p ro te in s from w in t e r w heat In c re a s e d
to a maximum d u rin g h ard e n in g and d e c lin e d d u rin g d e h a rd e n in g .

These

amino a d d s p ro b a b ly p ro v id e p ro te in s w ith r e a c t iv e s id e c h a in s t h a t
can d is r u p t an 1ce l a t t i c e o f w a te r m o lecules formed around n o n p o la r
s id e ch ain s 1n th e p r o t e in .

P ro te in s w ith p o la r amino a d d

s id e ch ain s

In c re a s e d 1n hardened tw ig s e c tio n s o f Cornus s t o lo n lf e r a d u rin g h ard e n in g

18

and a re b e lie v e d to preserve w a te r and p reven t d e n a tu ra tlo n o f pro­
t e in when th e protoplasm 1s dehydrated by e x t r a c e ll u la r fo rm atio n
o f Ic e (Van Huystee e t a l . 1 9 6 5 ).
L i e t a l , (19 65 ) sumnarlzed th e co ld a c c lim a tio n changes 1n 15
amino acids o f Comus s t o lo n ife r a tw igs by grouping them in to th re e
general c a te g o rie s .

Group 1 decreased d urin g cold a c c lim a tio n and

included the 3 prim ary amino a c id s , a s p a r ta te , g lu ta m a te , and
a la n in e .

Group 2 amino acids increased 1n c o n c e n tra tio n during

cold a c c lim a tio n and Included g lu ta m in e ,
la n in e , le u c in e and 1soleuc1ne.

-a m in o b u ty ra te , phenyla­

Group 3 flu c tu a te d 1n c o n c e n tra tio n

during a c c lim a tio n and Included s e r in e , th re o n in e , a s p ara g in e, 8 a la n ln e and c y s tin e .
Enzyme a c t i v i t y
The changes In amino a c id s , p ro te in s and o th e r o rg an ic compounds
as p la n ts a c c lim a te to cold must be brought about by changes 1n enzymes
and enzyme a c t i v i t y .

Thus, most research in th is area has focused on

the e f f e c t o f low tem perature on enzyme syn th esis and a c t i v i t y .
The r o le o f enzymes in Inducing cold hardiness and the enzymes
Involved a re not as y e t known.

Van Huystee e t a l (1 9 6 5 ) have suggested

th a t hormonal a c tio n could In flu e n c e the enzyme systems re sp o n s ib le
f o r the m etab olic changes 1n cold a c c lim a tio n .

They b e lie v e d th is

because changes 1n hardiness a re c lo s e ly asso ciated w ith the horm onally
reg u lated ce ss atio n o f growth 1n autumn.

Roberts (1 9 6 9 ), on the o th e r

hand, has proposed th a t th e d e le te rio u s e ffe c ts o f low tem perature may
be o f f s e t by th e s u b s titu tio n o f one 1sozym1c form o f a p ro te in f o r a
d if f e r e n t form o r by changing the r e l a t i v e p ro p o rtio n s o f th e Isozymes
p res en t.

19
Two enzymes which have y ie ld e d re s u lts c o n s is te n t w ith R o b erts'
hypothesis a re In v e rta s e and p ero xid ase.

I t has been c o n c lu s iv e ly

demonstrated th a t In v e rta s e 1s not I r r e v e r s ib ly In a c tiv a te d by
k illin g fro s ts .

This enzyme* which hydrolyzes sucrose to glucose

and fr u c to s e , has been shown to In crease a t low tem peratures u n t il
1 t exceeds th e c o n c e n tra tio n o f some c o m p e titiv e I n h i b i t o r and
then re s u lts In an Increased h y d ro ly s is o f sucrose and accum ulation
o f reducing sugars.

Roberts (19 69 ) found a low er tem perature

c o e f f ic ie n t f o r In v e rta s e e x tra c te d from leaves o f cold hardened
than from leaves o f unhardened w heat. He suggested t h a t s t r u c t u r a lly
d if f e r e n t forms o f th e enzyme a re syn th esized a t low er tem p e ra tu res .
He concluded th a t In v e rta s e c o n sists o f a number o f Isozymes w ith
d if f e r e n t tem perature c o e ffic ie n ts and th a t growth a t low tempera­
tu res Increases the p ro p o rtio n o f In v e rta s e Isozymes w ith low tem per­
a tu re c o e f f ic ie n t s .
Evidence f o r changes In 1sozym1c components have a ls o been
re p o rte d f o r p ero x id as e.

W in ter clones o f Planthus showed a gradual

synthesis o f 2 to 4 new peroxidase Isozymes d u rin g the co ld hardening
p eriod (McGown

e t a l . 1 9 6 9 ).

Roberts a ls o re p o rte d th a t more

peroxidase Isozymes were found In leaves o f wheat p la n ts grown a t 6°C
than 1n leaves grown a t 20°C.

McGown

e t a l (1969) concluded th a t changes

1n peroxidase Isozymes during hardening may re g u la te p e rm e a b ility and
p reven t In ju r y a t s u b fre e zin g tem peratures.
Carbohydrates
The f a c t th e re d u c tio n o f carbohydrate reserves reduces co ld
hardiness 1n w in te rin g p la n ts 1s w e ll known.

Starch decreases to a

minimum and sugar Increases to a maximum as p la n ts become a c clim a ted

20

to c o ld .

Many authors have re p o rte d s ta rc h to sugar changes 1n

bark tis s u e and evergreen leaves o f vario u s tre e s t h a t have developed
cold hardiness (evidence c ite d 1n P a rk e r, 1 9 6 3 ).

Although s ta rc h to

sugar changes a re f a i r l y w e ll understood, th e conversion o f sugars
to o th e r sugar complexes and th e r o le o f sugars 1n f r o s t hardiness
has not been f u l l y worked o u t.
Although no attem p t w i l l be made here to review the myriad o f
hypotheses on sugar Involvem ent 1n c o ld h a rd in e s s , one p a r t ic u la r
study is worth m entio nin g.

O Uen (19 67 ) s tu d ie d the In te rfe r e n c e

o f fre e z in g caused by la rg e w a te r s o lu b le p olysacch arid e polymers
e x tra c te d from the c e ll w a lls o f hardened wheat p la n ts .

These sub­

sta n c es , which co n tain ed la r g e amounts o f sugars (x y lo s e and a ra b ln o s e ),
In t e r f e r e d w ith fre e z in g by competing w ith w a te r molecules f o r s ite s
1n th e 1ce l a t t i c e a t th e l iq u id In t e r f a c e .

The r e s u lt was th a t they

tended to stop c r y s ta l grow th, causing an Im p e rfe c t Ic e mass to form.
Only polymers from co ld hardy p la n ts re s u lte d 1n Im p e rfe c t c ry s ta l
fo rm atio n 1n th e p la n t.
GENETIC REGULATION OF COLO ACCLIMATION
A f t e r re v ie w in g th e p h y s io lo g ic a l changes as so c ia ted w ith the
achievement o f cold re s is ta n c e 1n p la n ts , one must

wonder how p la n ts

a re a b le to re g u la te t h e i r metabolism to a t t a in such a s t a t e .

Because

o f the la rg e a rra y o f m etab o lic changes In v o lv e d , I t seems l i k e l y th a t
th e re g u la to ry processes fu n c tio n a t th e le v e l o f n u c le ic ac id tra n s ­
c r ip t io n .

W elser (19 68 ) has proposed a hypothesis and asso ciated model

(19 70 ) which attem pts to e x p la in the g e n e tic re g u la tio n and asso ciated
m etab o lic changes which occur during co ld hardening 1n p la n ts .

He has

proposed th a t s h o rt days 1n autumn a re d e te c te d by a phytochrome clo ck

21

in the leaves and th e Pr form accum ulates.

The Pr phytochrome p ro ­

motes synth esis o f a tra n s lo c a ta b le hardiness promoter which a c t i ­
vates DNA th a t Is n orm ally n o n -fu n c tio n a l during the a c tiv e growing
season.

New kinds o f mRNA and subsequently s tr u c tu r a l o r enzym atic

p ro te in s a re produced which b rin g about th e f i r s t stage o f co ld
a c c lim a tio n .

The f i r s t stage p h y s io lo g ic a lly and m e ta b o lle a lly

prepares the p la n t so i t

1s a b le to respond to low tem perature

s tim u li which t r ig g e r the second, tem perature a c tiv a te d stage o f
hardening.

During th is s ta g e , low tem perature induces n o n trans-

1o c a ta b le but r e a d ily re v e r s ib le a lt e r a t io n s 1n the c e lls which
In clu d es the b in d in g o f w a te r to p ro te in s and th e re s is ta n c e o f
the protoplasm to d e h y d ra tio n .
The model by W elser o ffe r s an e x c e lle n t summary o f the meta­
b o lic changes which occur during a c c lim a tio n .

However, h is tre atm en t

o f the g e n e tic re g u la tio n in volved 1n co ld a c c lim a tio n seems Incom­
p le te 1n l i g h t o f th e model proposed by B r itte n and Davidson (1 9 6 9 ).
They have proposed th a t fo u r types o f genes and a c t iv a to r RNA mole­
cules a c t 1n sequence to tr a n s fe r the message o f an environm ental
s tim u li to the r e s u ltin g m etab olic changes known to occur 1n p la n ts .
I have attem pted to employ the B r itte n and Davidson model o f gene
re g u la tio n to e x p la in th e sequence o f events which occurs from the
onset o f s h o rt days 1n the autumn to the a c t iv a tio n o f m etab olic
changes which r e s u lt 1n cold h ard in e ss .
1n F ig ure 1.

These events are o u tlin e d

The hypotheses proposed to e x p la in cold hardiness f i t

th e B r itte n and Davidson model o f gene re g u la tio n 1n alm ost every
as p e c t.

However, in stage G a s lig h t discrepancy 1s noted.

B r it t e n

and Davidson have proposed th a t th e a c tiv a to r RNA molecules a c t

d ir e c t ly on th e re c e p to r genes; I have suggested th a t these mole­
cules must code f o r an enzyme o r p ro te in which 1s In vo lved 1n the
production o f a hardiness promoter which 1n tu rn fu n c tio n s by
a c tiv a tin g th e re c e p to r genes.

B r itt e n and Davidson m ention,

however, th a t the r o le proposed f o r a c t iv a to r RNA could w e ll be
c a rr ie d out In d ir e c t ly by p ro te in molecules coded f o r by these
RNA m olecules.
remained I n t a c t .

Thus, I fe e l th e b asic s tr u c tu r e o f the model has

23

FIGURE 1.

A h y p o th e tic a l model o f g e n e tic r e g u la tio n o f c o ld
a c c lim a tio n in p la n ts .

24
GENETIC REGULATION IN COLD ACCLIMATION
A) S h ort days a c t as th e e x t e r ­
nal s tim u li (a ls o s p e c tra l
changes 1n s u n lig h t ) .

H) The h ard iness prom oter is
tra n s lo c a te d throughout th e
p la n t .

W

*
B) The sensor gene cannot
d i r e c t l y d e te c t an e n v iro n ­
mental s t i m u l i.
The s tim u li
must be tr a n s la te d through
a chem ical form (phytochrom e)

I)

The prom oter a c tiv a te s the
re c e p to r g e n e (s ).

*

#

J) The re c e p to r g en e(s) causes
the t r a n s c r ip t io n o f the
producer g en e(s) to o cc u r.

C) S h o rt days a re d e te c te d by
a phytochrome c lo c k 1n th e
leaves and th e PR form
accum ulates.

K) The producer g en e(s) y ie ld s
new kinds o f messenger RNA.

W

D) The phytochrome tu rn s on a
sensor gene, which re c e iv e s
th e s ig n a l from th e e n v iro n ­
ment.

*
E) The sensor gene a c tiv a te s
the s e t o f In t e g r a t o r genes.

#
F) The In t e g r a t o r genes fu n c tio n
1n th e sy n th e s is o f a c t iv a t o r
RNA.
G) The a c t iv a t o r RNA must code
f o r an enzyme o r p ro te in which
1s th e h ard iness prom oter o r
1s In v o lv e d In producing the
h ard iness prom oter.
The
B ritte n -D a v id s o n model allo w s
f o r such a r e a c tio n .

*

+

L) The new mRNA codes f o r
s tr u c tu r a l a n d /o r enzym atic
p ro te in s which b rin g about
th e f i r s t stag e o f a c c lim a ­
t io n .

+
M) The f i r s t s ta g e o f a c c lim a ­
tio n predisposes th e p la n t
to respond to low tem perature
s tim u li which tr ig g e r s th e
second stage o f h ard en in g .

25
GENETIC VARIATION
In species w ith wide geographic ranges the e x is te n c e o f w e ll
d e fin e d groups o f p la n ts w ith co n sid e ra b le g e n e tic v a r i a b i l i t y among
the groups Is q u ite l i k e l y .

Such v a r ia tio n due to seed source u s u a lly

p a r a lle ls geographic and c lim a tic d iffe re n c e s o f the physical h a b ita t
and Is o fte n c h a ra c te riz e d by extreme forms
range w ith a c l I n a l

a t the p e rip h e ry o f the

In te rg ra d in g o f forms between th e extrem es.

The

coiranon method o f studying such species v a r i a b i l i t y 1s the uniform
environm ent p lo t .

This technique has been s u c c e s s fu lly employed to

d escrib e geographic v a r ia tio n in fo u r types o f fre e z in g In ju r y th a t
can occur 1n woody p la n ts .

E vert (19 67 ) has c la s s if ie d these types

o f fre e z in g damage as In ju r y th a t can occur:
onset o f a c c lim a tio n ; 2.

1.

in f a l l b efo re the

a t w in te r tem peratures too low f o r the

maintenance o f c e l l u l a r s tru c tu re and fu n c tio n ; 3.
o r p h y s io lo g ic a l drought; and 4 .

from w in te r bum

from sp rin g f r o s t s .

For th e purposes o f t h is discussion o n ly the f i r s t two types o f
in ju r y a re Im p o rta n t.

The o th ers a re re la te d to p h y s io lo g ic a l pro­

cesses which are only I n d i r e c t l y

as so c ia ted w ith the a b i l i t y o r

I n a b i l i t y o f th e p la n t to become

acclim ated to cold tem peratures.

In th e case o f th e damage from w in te r b u m , th e Im p o rtan t determ in in g
fa c to rs a re tem perature and m oisture c o n d itio n s In th e environm ent,
as w e ll as m oisture co n ten t and tr a n s p ir a tio n ra te s 1n th e p la n ts .
Even p la n ts acclim ated to cold can s u f f e r th is type o f damage given
s p e c ific environm ental c o n d itio n s .

Damage from sp rin g fr o s ts Is

as so c ia ted p r im a r ily w ith e a r ly bud break 1n th e sp rin g b efo re the
danger o f f r o s t has passed.

I t 1s c lo s e ly asso ciated w ith th e response

o f s p e c if ic genotypes to lo c a l environm ental c o n d itio n s .

26
Probably th e most conation type o f co ld In ju r y in woody p la n ts
occurs as a r e s u lt o f g e n e tic d iffe re n c e s 1n tim in g o f a c c lim a tio n
among c lim a tic races o f a sp e cies .

Such v a r ia tio n has been demon*

s tr a te d In many woody p e re n n ia ls ( F l i n t , 1 9 7 2 ), e s p e c ia lly Comus
s t o lo n lf e r a .

Smlthberg and W elser (19 68 ) c o lle c te d c u ttin g s o f 25

races o f t h is species from widespread lo c a tio n s 1n North America and
grew them in a uniform environment p lo t 1n S t. P a u l, M innesota.

The

re s u lts o f cold hardening te s ts showed th a t a l l clones became e q u a lly
hardy (-1 9 6 °C ) by m id w in te r; however, d iffe re n c e s 1n tim in g o f a c c l i ­
m ation were profound.

N orthern clones a c clim a ted e a r l i e r than those

o f southern o r co a stal o rig in s and thus escaped w in te r I n ju r y .

Clones

from S e a ttle were th e l a s t to harden and as a r e s u lt su stain ed ex ten ­
s iv e w in te r I n ju r y .

As would be exp ected , th e dates a t which clones

acclim ated to s p e c ific tem peratures were c lo s e ly c o rre la te d to w in te r
minimum tem perature and len g th o f growing season a t p lace o f o r ig in .
Thus, i t was concluded th a t w in te r In ju r y occurred because some clones
f a i l e d to a c c lim a te on tim e even though a l l clones u lt im a te ly a c c l i ­
mated to le v e ls o f cold f a r beyond any th ey would encounter 1n n a tu re .
The second type o f cold In ju r y mentioned re s u lts from g e n e tic
d iffe re n c e s 1n a b i l i t y o f p la n ts to w ith s ta n d low w in te r tem peratures.
W in ter damage o f t h is type has been demonstrated f o r many herbaceous
(K ln b a ch er, 1962; M a rs h a ll, 1969; Suneson and M a r s h a ll, 1 9 6 7 ), as w ell
as woody p e re n n ia ls .

A study o f g e n e tic v a r ia tio n In th is type o f

w in te r in ju r y was performed on e a s te rn w h ite pin e ( P1nus s tro b u s ) by
Maronek and F l i n t (1 9 7 4 ).

They compared tim in g o f a c c lim a tio n and

m id w in ter k i l l i n g tem peratures o f 15 seed sources o f e a s te rn w h ite
pin e growing In western M ichigan.

They found th a t n orthern sources

27
hardened much e a r l i e r than southern sources and a ls o achieved g r e a te r
m id w in te r h ard in ess le v e ls .

N orthern sources could w ith s ta n d January

tem peratures o f -90 °C w h ile southern sources were damaged a t tem per­
a tu re s below -3 0 °C .

V a r ia tio n In k i l l i n g tem p e ra tu re was c l i n a l and

c o n s is te n tly s i g n i f i c a n t between th e n o rth e rn and southern extremes
o f th e sampled rang e.

Although a l l

seed sources achieved s u f f i c i e n t

h ard iness to w ith s ta n d normal M ichigan w in te r te m p e ra tu re s , g e n e tic
v a r ia t io n d id e x i s t in th e a b i l i t y o f d i f f e r e n t genotypes to w it h ­
stand low te m p e ra tu re s .
Numerous s tu d ie s have been perform ed on woody p la n ts which
i l l u s t r a t e p a tte rn s o f g e n e tic v a r ia tio n in v i s i b l e w in te r I n j u r y .
No a tte m p t has been made here to review th ese s tu d ie s .
INHERITANCE OF COLD RESISTANCE IN PLANTS
Upon e s ta b lis h in g t h a t g e n e tic v a r ia tio n e x is ts 1n c o ld h a rd in e s s ,
th e n ext ste p 1s to examine th e In h e r ita n c e o f th e t r a i t .

I t seems,

however, t h a t most rese arch ers have not taken t h is f i n a l step, p ro bably
because o f e a r ly In d ic a tio n s o f co m p licated In h e r ita n c e o f t h is
c h a ra c te r .
Dantuma (1 9 5 8 ), in b reed in g wheat and b a rle y f o r w in te r h a rd in e s s ,
d isco vered t h a t th e crosses made between w in te r X s p rin g v a r ie t ie s and
w in t e r X w in te r v a r i e t i e s re s u lte d 1n progeny which d id not ach ieve
th e w in te r h ard in ess o f th e most r e s is t a n t p a re n t.

In a d d it io n ,

a n a ly s is o f 139 F2 progeny from w in te r wheat crosses showed In te rm e d ­
i a t e In h e r ita n c e w ith p o s s ib le p a r t i a l dominance.

They a ls o noted

t h a t the d iv e r s i t y o f forms w ith regard to w in t e r h ard iness and th e
complex o f e x te r n a l fa c to r s which in flu e n c e w in te r h a rd in e s s , suggest

28

th a t i t

1s a com plexly In h e r it e d t r a i t .

Eunus e t a l

th e d ata on th e In h e r ita n c e o f w in te r b a r le y .

(19 62 ) an alyzed

They observed t h a t no

two v a r i e t i e s behaved s i m i l a r l y In th e crosses and concluded t h a t
w in te r hardiness was c o n tr o lle d in each v a r ie t y by a d i f f e r e n t
com bination o f genes, both a d d itiv e and n o n -a d d 1 tlv e .

F urth erm o re,

they found t h a t w in te r h ard iness In b a rle y 1s c o n tr o lle d by genes
ranging from com plete dominance to com plete re c e s s iv e n e s s .

Thus,

re s u lts from th e d ia l l e i experim ent in d ic a te t h a t many genes are
In v o lv e d 1n w in te r h ard iness in h e r ita n c e and t h a t I t 1s a complex
c h a ra c te r .

E v id e n tly , genotype X environm ent In t e r a c t io n Is a ls o

c o n s id e ra b le In such experim ents and a c ts to confuse th e Issue
fu rth e r.
Reid (1 9 6 5 ) an a ly zed 13 w in te r X s p rin g b a rle y h yb rid s f o r
w in te r s u rv iv a l 1n th e Fg, F^, and F^ g e n e ra tio n s .

None o f th e

t h ir t e e n crosses were as h a rd y , on the a v e ra g e , as th e h a rd ie s t p are n t
but many In d iv id u a l

F4 lin e s were w ith in th e p a re n ta l s u rv iv a l range.

Thus, as one would e x p e c t, s e g re g a tio n among F^ progeny had occurred
and re s u lte d 1n a range o f In te rm e d ia te types between th e p a re n ts .
T h is study a ls o showed t h a t d i f f e r e n t w in te r and s p rin g v a r ie t ie s
v a rie d 1n t h e i r a b i l i t y to produce hardy progeny.
v a r ie t ie s

Two w in te r

(Kearney and D lc k to o ) and 2 s p rin g v a r ie t ie s

(M ln s tu rd l

and C15890) c o n trib u te d more h ard in ess to t h e i r progeny than o th e r
v a r ie tie s .

Such v a r ia tio n suggests t h a t th e genes c o n t r o llin g

w in te r hardiness 1n b a rle y d i f f e r f o r d i f f e r e n t v a r i e t i e s .

The

o v e r a ll co n clusion drawn from th e aforem entioned s tu d ie s Is t h a t
cold h ard iness 1s q u a n t it a t iv e ly in h e r it e d , t h a t 1 s , 1 t Is con­
t r o l l e d by many genes w ith sm all e f f e c t s .

29
Evidence f o r an a d d itiv e mode o f In h e rita n c e
Daday and Greenham (I9 6 0 and 1964) s tu d ie d the In h e rita n c e o f
cold re s is ta n c e among 4 v a r ie t ie s o f a l f a l f a

( Medlcago s a t l v a ) .

T h e ir In v e s tig a tio n s demonstrated c le a r d iffe re n c e s w ith in and be­
tween v a r ie tie s 1n hardiness to c o ld .

From a study o f d i a l l e i

crosses among the 4 v a r i e t i e s , I t was found th a t th e average p e r­
formance (g en eral combining a b i l i t y ) o f th e parents In crosses were
s ig n if ic a n t ly d if f e r e n t and th a t th e F^'s were g e n e ra lly In te rm e d ia te
1n hardiness between the p a re n ts .

S tudies o f s p e c ific combining

a b i l i t y y ie ld e d n o n -s 1 g n 1 fle a n t r e s u lt s .

The s ig n if ic a n t d iffe re n c e s

1n general combining a b i l i t y suggest th a t th is c h a ra c te r is c o n tro lle d
by genes w ith a d d itiv e e f f e c t s . I . e . one would expect values o f th e
Fj g en eratio n to be ap p ro xim ately equal to the mean o f t h e i r p a re n ts .
This la c k o f s ig n if ic a n t d iffe re n c e s 1n s p e c ific combining a b i l i t y
In d ic a te s th a t dominance o r n o n -a d d itiv e g e n e tic e ffe c ts are less
im p o rta n t.
A d d itio n a l evidence suggesting a d d itiv e gene e ffe c ts 1n the
In h e rita n c e o f co ld hardiness was provided by Omran e t a l
f la x ( Linum ).

(1968) in

Two-hundred F2 fa m ilie s from each o f 2 crosses were

stu d ie d In th e F^ and F^ g en eration s f o r re a c tio n s to co ld tempera­
tu re s .

A co ld hardiness Index was c a lc u la te d from th e degree o f

In ju r y and the percentage o f p la n ts in ju r e d .

Dominance d e v ia tio n s

could not be d etec ted 1n th e F^ o r F4 g e n e ra tio n s .

Narrow sense

h er1 tab 11 1ty es tim ate s o f cold hardiness In d ic e s were g e n e ra lly
h ig h .

Narrow sense her1tab 111t1es a re an e s tim a te o f the c o n trib u ­

tio n o f a d d itiv e g e n e tic varia n c e to the t o ta l v a r ia t io n .

Thus,

th e high h e r1 ta b 1 l1 t1 e s combined w ith th e f a c t th a t dominance
d e v ia tio n s could not be d e te c te d . In d ic a te s th a t In h e rita n c e o f

30
co ld h ard iness 1n f l a x Is p r im a r ily under th e c o n tro l o f many genes
w ith a d d it iv e e f f e c t s .
G en etics o f c o ld re s is ta n c e 1n wheat
P robably th e most comprehensive g e n e tic study o f cold re s is ta n c e
was perform ed by Law and Jenkins (1 9 7 0 ) on h ex ap lo ld wheat (T r itlc u m
a e s tlv u m ).

Through th e use o f backcross procedures and c y to lo g lc a l

m arkers, s in g le homologous p a irs o f chromosomes from a hardy wheat
v a r ie t y (C a p p e lle -D e s p re z) were s u b s titu te d f o r t h e i r homologues 1n
a co ld s e n s itiv e wheat v a r ie t y (Chinese S p r in g ).

As a r e s u l t , 1 t

was p o s s ib le to produce s u b s titu tio n lin e s f o r each o f th e 21 p a irs
o f wheat chromosomes.

M oreover, each o f these s u b s titu tio n lin e s

d if f e r e d from th e r e c ip ie n t v a r ie ty (C hinese s p rin g ) by a s in g le
p a ir o f homologous chromosomes.

S u bseq uen tly, chromosome assay e x p e r­

iments were c a r r ie d out to determ ine which chromosomes c a r r ie d genes
In v o lv e d 1n th e d e te rm in a tio n o f co ld re s is ta n c e .
The r e s u lts o f th e experim ent In d ic a te d t h a t s i g n i f i c a n t d i f f e r ­
ences occurred between Chinese s p rin g and th e s u b s titu tio n lin e s
c a rry in g chromosomes 4D, 5D and 7A o f C a p p e lle -D e s p re z.

These th re e

lin e s were a ls o s i g n i f i c a n t l y d if f e r e n t from C a p p elle-D es p rez which
suggests t h a t th e le v e ls o f re s is ta n c e expressed by these s u b s titu tio n
lin e s was in te rm e d ia te .

In a d u p lic a te exp erim en t e s ta b lis h e d a t a

l a t e r d ate th e same r e s u lts were d is c o v e re d .

This s u b s ta n tia te d t h a t

th e d iffe r e n c e s noted 1n the f i r s t experim ent were a t t r ib u t a b le to
th e s u b s titu te d chromosomes and n o t to s e g re g a tio n o f genes f o r c o ld
re s is ta n c e In th e background.
The d ata acq u ired from the f i r s t two experim ents was subsequently

31
used to determ ine w hether genes on chromosomes 4D , 5D and 7A behave
in an a d d itiv e fa s h io n o r a re Independent 1n t h e i r a c tio n .

This

was determ ined by summing th e d iffe r e n c e s between th e Chinese sp rin g
mean (which In c lu d es th e mean o f th e 18 s u b s tit u t io n lin e s and
Chinese s p rin g ) and the 3 s u b s titu tio n lin e s c a rry in g chromosomes
f o r co ld re s is ta n c e and comparing t h is w ith th e d iffe r e n c e between
C ap p elle-D esp rez and Chinese S p rin g .

In th e absence o f between

chromosome In te r a c tio n s th ese d iffe re n c e s should be th e same.
In both experim ents th e two d iffe r e n c e s were s im ila r and when
te s te d a g a in s t t h e i r stan d ard e r r o r were n o t s i g n i f i c a n t l y d if f e r e n t
from each o th e r .

This evidence 1s c o n s is te n t w ith an a d d it iv e b e h a v io r

o f th e genes on th e th re e s u b s titu te d chromosomes.
These experim ents using i n t e r v a r i e t a l chromosome s u b s titu tio n s
su g gest, on f i r s t appearance, th a t th e g e n e tic c o n tro l o f co ld h a r d i­
ness 1n wheat 1s n o t o v e rly complex.

However, when one co n siders t h a t

1n h exap lo ld wheats t r i p l i c a t e d lo c i a re p ro bably in v o lv e d , the s i t u ­
a tio n becomes more complex.

On th e s im p le s t hyp oth esis o f one lo c i f o r

each o f th e th re e Is o la te d chromosomes, s ix o th e r homologous lo c i
could o cc u r.

I t 1s th e r e fo r e l i k e l y t h a t 1n more c o ld r e s is ta n t

v a r ie t ie s some a l l e l i c v a r ia t io n a t th ese lo c i may o cc u r.
P o ss ib le m aternal In h e r ita n c e o f c o ld re s is ta n c e
The c o n d u c tiv ity o f e le c t r o ly t e s d iffu s in g o u t o f fro ze n and
thawed tis s u e o f 3 ap p le v a r ie t ie s hardened under Id e n t ic a l co n d i­
tio n s In d ic a te d t h a t th ey d if f e r e d s i g n i f i c a n t l y 1n s u s c e p t ib ilit y
to co ld I n j u r y .

N orthern Spy (NS) was a te n d e r v a r i e t y , McIntosh

was In te rm e d ia te In h ard iness and Antonovka (A ) was the h a rd ie s t

32

o f the th re e v a r ie t ie s .

In an e f f o r t to study th e In h e rita n c e o f

cold hardiness among apple v a r i e t i e s , M iln e r (19 65 ) made a l l p o s sib le
crosses among the th re e v a r ie t ie s In c lu d in g th e r e c ip ro c a ls .

The F1

progeny were su b jected to a range o f fre e z in g tem peratures and t h e i r
r e l a t i v e cold hardiness was a s c e rta in e d by use o f th e e l e c t r o l y t i c con­
d u c t iv it y method.

The progenies o f the crosses In v o lv in g th e h a rd ie r

v a r ie t ie s A and Me g e n e ra lly were more hardy.
F u rth e r study o f the data showed th a t progeny o f crosses In ­
v o lv in g hardy fem ale v a r ie t ie s were c o n s is te n tly h a r d ie r than the
re c ip ro c a l crosses.

This was v e r if ie d by 19 o f th e 21 comparisons

made.
D iffe re n c e s 1n re c ip ro c a l crosses have been observed In a number
o f tr a its

1n s e ve ra l p la n t s p e c ie s , and they u s u a lly In d ic a te the

occurrence o f an e x tra n u c le a r o r cytoplasm ic type o f In h e r ita n c e .
Several Im p o rtan t b io lo g ic a l p ro p e rtie s have been shown to be
In h e r ite d through the cytoplasm .

The re s u lts o f M iln e r ’ s work o ffe r s

evidence which suggests th a t cold hardiness 1n apples may be c y to ­
plasm ic 1n In h e rita n c e and tra n s m itte d m ainly when brought from the
m aternal s id e .

The more l i k e l y e x p la n a tio n 1s probably th a t both

n u c le a r and e x tra n u c le a r In h e rita n c e systems a re re q u ire d f o r complete
g e n e tic expression o f an In d iv id u a l.
Genetics o f hardiness 1n f r u i t tre e s
Studies e lu c id a tin g the g e n e tic c o n tro l o f cold hardiness 1n woody
p la n ts a re not numerous.

However, re p o rts c h a ra c te r iz in g hardiness

d iffe re n c e s among c u lt lv a r s a re a v a ila b le and a re discussed by S tu sh n o ff
(1 9 7 2 ).

Dorsey and Bushnell (19 25 ) stu d ied th e In h e rita n c e o f cold

hardiness in several in t e r s p e c if ic h yb rid progenies o f plums.

They

33
found th a t the h a rd ie s t progenies re s u lte d from crosses in which one
o r both parents were s e le c te d from areas o f extreme cold 1n t h e i r
n a tu ra l h a b ita t .
Watkins and Spangelo (19 70 ) determ ined th e g e n e tic v a ria n c e components
f o r w in te r s u rv iv a l and In ju r y in apple tre e s using two d l a l l e l s .

T ip

In ju r y and stem damage were estim ated to e x h ib it 90 to 100% a d d itiv e
va ria n c e and ro o t damage was estim ated a t 59 and 82% in the two s tu d ie s .
They concluded th a t w ith th e p o s s ib le exception o f ro o t damage th e re
was no evidence to show e it h e r e p is ta s is o r dominance as a m ajor component
o f g e n e tic v a ria n c e f o r co ld h ard in e ss .

T h e ir evidence 1s in agreement

w ith an a d d itiv e mode o f In h e rita n c e f o r cold hardiness as shown In
crop p la n ts .

CHAPTER 3

CRITICAL TEMPERATURE DETERMINATIONS IN COLD
HARDINESS STUDIES USING ELECTRICAL
CONDUCTIVITY MEASUREMENTS

INTRODUCTION

I d e n t i f i c a t i o n o f a procedure to d i f f e r e n t i a t e between c o ld hardy
and te n d e r p la n t m a te r ia l
c o ld h ard in ess 1n p la n ts .

1s a p r e r e q u is ite to conducting re search on
S u rv iv a l o r s u b je c tiv e r a t in g o f v i s ib l e

w in te r I n j u r y 1n th e f i e l d has commonly been used f o r t h is purpose.
However, th e u t i l i t y o f such procedures Is lim it e d because o f th e
In c o n s is te n c y o f t e s t w in te rs and confounding e f f e c t s o f f i e l d
r e la t e d to o th e r causes.

in ju r y

Over th e p ast few decades. In c re as ed In t e r e s t

1n s tre s s p h ysio lo g y o f p la n ts has s tim u la te d th e use o f a r t i f i c i a l
fr e e z in g te s ts f o r th e purpose o f e v a lu a tin g r e l a t i v e p la n t co ld
h a rd in e s s .

One d i f f i c u l t y a s s o c ia te d w ith such la b o r a to r y te s ts Is

d e te rm in in g th e amount o f In ju r y to p la n t tis s u e a f t e r fr e e z in g .

Many

tis s u e v i a b i l i t y procedures have been devised f o r use 1n c o ld hardiness
s tu d ie s .

T h e ir e ffe c tiv e n e s s and r e l i a b i l i t y

has been discussed by

s e v e ra l In v e s tig a to r s (P a r k e r, 1953; van den D rle s s c h e , 1969a and 1976;
S te rg lo s and H o w e ll, 1973; B la z lc h
34

e t a l . 1 9 7 4 ).

35
S e le c tio n o f v i a b i l i t y te s ts f o r co ld h ard iness depends on many
fa c t o r s , In c lu d in g s p e c ie s , p la n t t is s u e , tim e and th e o v e r a ll
o b je c tiv e s o f th e hardiness re s e a rc h .

There 1s p ro bably no one "b est"

method f o r a l l

No m a tte r which procedure 1s

species o r c o n d itio n s .

adopted, 1 t Is d e s ir a b le to r e l a t e la b o r a to ry r e s u lts to a c tu a l f i e l d
e v a lu a tio n s o f co ld In ju r y w herever p o s s ib le .

G e n e r a lly , a v i a b i l i t y

t e s t which Is o b je c t iv e , r e l a t i v e l y q u ic k , and cap ab le o f u t i l i z i n g
sm all q u a n t itie s o f p la n t tis s u e is p r e fe r r e d .

A ls o , i t

is d e s ir a b le

th a t a s in g le m eaningful exp ressio n o f r e l a t i v e co ld h ard iness can
be d e riv e d from th e v i a b i l i t y r e s u lt s , such as a k i l l i n g

te m p e ra tu re ,

T50 o r some o th e r d e fin a b le Index o f h a rd in e s s .
ELECTRICAL CONDUCTIVITY AS A VIABILITY TEST
A procedure which has been e f f e c t i v e 1n e v a lu a tin g tis s u e v i a b i l i t y
a f t e r fr e e z in g te s ts 1s e l e c t r i c a l c o n d u c tiv ity .
d escrib ed by D e x te r e t a l

T his method, as f i r s t

(1 9 3 2 ), is based on th e p r in c ip le t h a t l i v e

c e lls q u ic k ly lo s e t h e i r a b i l i t y to re g u la te t h e i r co n ten ts when t h e i r
c e l l membranes a re damaged.

As a r e s u l t , e le c t r o ly t e s d if f u s e In to

s o lu tio n th e re b y causing an in c re a s e In s p e c ific c o n d u c tiv ity o f the
s o lu t io n .

Thus, th e g r e a te r th e In ju r y to p la n t tis s u e from low

te m p e ra tu re , th e h ig h e r th e c o n d u c tiv ity o f th e e x t r a c t .
In e a r ly s tu d ie s , s p e c if ic c o n d u c tiv itie s o f le a c h a te s from fro z e n
and u nfrozen samples were compared.

These comparisons were u s e fu l, but

not e x a c t, because t o t a l e le c t r o ly t e s v a rie d f o r d i f f e r e n t samples.
S tu a r t (1 9 3 9 ) and M iln e r (1 9 5 9 , 1960) improved on th e procedure by
exp ressin g th e amount o f c e l l e le c t r o ly t e s re le a s e d a f t e r fr e e z in g as
a percentage o f th e t o t a l e le c t r o ly t e s re le a s e d a f t e r h e a t - k i l l i n g .
This measure o f In ju r y has been u s e fu l f o r comparing r e l a t i v e co ld

36
hardiness o f tis s u e exposed to va rio u s te m p e ra tu re s , but does not
p ro vid e a s in g le d e fin a b le exp ressio n o f cold h a rd in e s s .

F lin t

e t a l (1 9 6 7 ) converted th e percentage re le a s e o f e le c t r o ly t e s to an
Index o f In ju r y (1 ^ ) s c a le where th e unfrozen c o n tro l sample 1s given
a value o f zero and th e heat k i l l e d

sample a v a lu e o f 100.

A fte r

d eterm in in g 1^ f o r samples exposed to a s e rie s o f t e s t te m p e ra tu re s ,
a tem perature corresponding to any s e le c te d I t co u ld be found and used
as an exp ressio n

o f hardiness 1n which to compare samples.

In making co ld
o f p la n t t is s u e .

h ard iness comparisons between p la n ts o r samples

I t is d e s ir a b le to fin d a s in g le

which to comparea l l

d e fin a b le p o in t a t

samples. K i l l i n g tem p eratu re would be

a u s e fu l

c r i t e r i a , but 1 t 1s o fte n d i f f i c u l t to d eterm in e when a p a r t i c u l a r
sample o f p la n t tis s u e 1s dead.

An e q u a lly d e fin a b le c r i t e r i a

1s

th e tem perature corresponding to th e p o in t o f e a r l i e s t d e te c ta b le
fr e e z in g In j u r y .

T h is c r i t i c a l

tem p eratu re can be e a s ily c a lc u la te d

using th e percentage re le a s e o f e le c t r o ly t e s from u nfrozen c o n tro l
samples and samples fro z e n a t v a rio u s t e s t te m p e ra tu re s .
The o b je c tiv e o f th e fo llo w in g d iscu ssio n 1s to d e s c rib e a
procedure f o r c a lc u la tio n o f c r i t i c a l te m p e ra tu re , where c r i t i c a l
tem perature 1s d e fin e d as th e h ig h e s t tem perature a t which fr e e z in g
In ju r y to p la n t tis s u e s can be d e te c te d .
CRITICAL TEMPERATURE DETERMINATION
The procedure I w i l l d e s c rib e f o r c a lc u la tin g c r i t i c a l tem peratures
presupposes th a t co ld hardiness comparisons a re being made among s e v e ra l
s e e d lo ts and t h a t e l e c t r i c a l c o n d u c tiv ity Is used as a measure o f tis s u e
v ia b ility .

The steps a re as fo llo w s :

Prepare several tis s u e samples per s e e d lo t.
R etain some samples o f each s e e d lo t as unfrozen c o n tro ls .
Subject th e rem aining samples to fre e z in g a t a s e rie s o f low
tem peratures, r e p lic a t in g each se ed lo t a t each t e s t tem p e ra tu re.
Choose t e s t tem peratures so th a t a l l

seed lo ts w i l l not be

damaged a t th e h ig h est t e s t tem p e ra tu re, but w i l l be damaged
a t th e low est t e s t tem p eratu re.
At each o f th e p re s e le c te d t e s t tem p eratu res, remove samples
from th e fre e z in g apparatus and a llo w them to thaw s lo w ly .
A f t e r fre e z in g and th aw in g , determ ine tis s u e v i a b i l i t y by
th e e l e c t r i c a l c o n d u c tiv ity method.

To do t h i s , soak each

sample In a measured q u a n tity o f d eio n ized w ater to a llo w
lea ch in g o f e le c t r o ly t e s .

A f t e r 24 to 30 hours, measure

c o n d u c tiv ity o f th e le a c h a te .
Autoclave the samples (In c lu d in g le a c h a te ) and measure
c o n d u c tiv ity a g a in .
C a lc u la te r e l a t i v e c o n d u c tiv ity according to the form ula
100 x (C^/C^.), where C^ * c o n d u c tiv ity o f the le a c h a te
b efo re a u to c la v ln g , and C^ = t o t a l c o n d u c tiv ity a f t e r
a u to c la v ln g .
Perform an a n a ly s is o f v a ria n c e on r e l a t i v e c o n d u c tiv itie s .
In c lu d in g data f o r th e th re e h ig h e st t e s t tem peratures o f
each s e e d lo t.

Choosing data from only th e th re e h ig h e s t

tem peratures m inim izes problems o f unequal variances In
th e a n a ly s is .
From th e ANOVA, compute a standard e r r o r o f the mean
c o n d u c tiv ity a f t e r exposure to any one tem p eratu re.

M u ltip ly the standard e r r o r by an a p p ro p ria te m u l t ip l ie r
to o b ta in a "Least S ig n ific a n t D iffe re n c e " (LSD).
11.

Add t h is LSDto th e r e l a t i v e c o n d u c tiv ity

o f th e c o n tro l

samples f o r each s e e d lo t to determ ine th e low est r e l a t i v e
c o n d u c tiv ity s ig n if ic a n t ly d if f e r e n t from the c o n tr o l.
12.

The c r i t i c a l

tem perature corresponding to t h is r e l a t i v e

c o n d u c tiv ity

Is found by in te r p o la tin g between th e two

t e s t tem peratures f o r each s e e d lo t w ith in whose range the
c a lc u la te d c o n d u c tiv ity value l i e s .

In te r p o la tio n assumes

th a t a lin e a r r e la tio n s h ip e x is ts between r e l a t i v e conduc­
t i v i t y and t e s t tem perature a f t e r damage has been I n i t i a t e d .
This c r i t i c a l

tem perature Is th e h ig h e st tem perature a t

which cold in ju r y to each s e e d lo t can be d e te c te d .
13.

Determine c r i t i c a l

tem peratures fo r each r e p lic a t e o f every

s e e d lo t and e v a lu a te d iffe re n c e s In c r i t i c a l tem peratures
among seedlots by conventional s t a t i s t i c a l methods.
C r i t i c a l tem peratures re p res en t the tem peratures correspondlng
to the e a r l i e s t s t a t i s t i c a l l y s ig n if ic a n t In c re as e in r e l a t i v e conduc­
t i v i t y due to cold In ju r y .

The e x te n t o f cold in ju r y a t th a t te m p e ra tu re ,

from a b io lo g ic a l s ta n d p o in t, can o n ly be found by e v a lu a tin g the
r e la tio n s h ip between c r i t i c a l tem peratures and v i s ib l e cold In ju r y 1n
f i e l d p la n ta tio n s o r c o n tro lle d environment s tu d ie s .
Correspondence between c r i t i c a l tem peratures and f i e l d
I have used e l e c t r i c a l c o n d u c tiv ity and c r i t i c a l

In ju r y

tem peratures

In comparing th e cold hardiness o f needles from 30 se ed lo ts o f ponderosa
p ine on 17 d if f e r e n t d a te s .

The m a te ria l was d e riv e d from a range wide

provenance t e s t 1n southern Michigan (W righ t e t a l . 1 9 6 9 ).

The re s u lts

39
revealed la rg e hardiness d iffe re n c e s among provenances which were
s tro n g ly asso ciated w ith c lim a tic c o n d itio n s In th e regio n o f
provenance o r ig in .

F ie ld o b servatio n s o f w in te r I n j u r y , made a t the

end o f th e 1976-77 w in te r , were h ig h ly c o rre la te d ( r = 0 .8 8 ) w ith
c r itic a l

tem peratures computed th a t w in te r .

Thus, a t le a s t In a

r e l a t i v e sense, c r i t i c a l tem peratures seemed to p ro vid e a good e s tim a te
o f cold hardiness d iffe re n c e s among s e e d lo ts .
I a ls o had the o p p o rtu n ity to e v a lu a te th e r e l i a b i l i t y o f c r i t i c a l
tem peratures when th e tem perature dropped to -26°C on December 3 , 1976
In the t e s t p la n ta tio n .

On th a t d a te , I c o lle c te d needles from s ix

seed lo ts f o r th e purpose o f d eterm in in g t h e i r c r i t i c a l tem peratures
In la b o ra to ry fre e z in g t e s t s .

A few days l a t e r , I c o lle c te d f o lia g e

samples from th e same tre e s and re tu rn e d them to th e la b o ra to ry f o r
clo se v is u a l In s p e c tio n o f needle cold In ju r y .

The r e s u lts conformed

very c lo s e ly to what was expected based on th e la b o ra to ry t e s t s .
P ercent v i s ib l e needle In ju r y and c r i t i c a l
seed lo ts a re summarized 1n T able 1.

tem peratures f o r th e s ix

Needles from s e ed lo ts w ith c r i t i c a l

tem peratures below -26°C on December 3 , 1976, s u ffe re d no v is ib le w in te r
I n ju r y , w h ile needles from o th e r s e ed lo ts were damaged.

Thus, a c tu a l

damaging tem peratures 1n th e f i e l d seemed to be w ith in a few degrees
o f the c r i t i c a l tem peratures as determ ined 1n la b o ra to ry s tu d ie s .
The c lo s e r e la tio n s h ip between la b o ra to ry and f i e l d data 1n th e
case o f the ponderosa p ine study suggests t h a t c r i t i c a l tem peratures
p ro vide meaningful In fo rm a tio n on th e co ld hardiness o f d if f e r e n t
s e e d lo ts .

However, th e f a c t th a t th e procedure has worked e f f e c t i v e l y

on ponderosa pine 1n Michigan does not guarantee th a t 1 t w i l l perform
In a s im ila r fash io n on a d if f e r e n t species or under a d if f e r e n t s e t

40
TABLE 1.

R e la tio n s h ip between c r i t i c a l

tem peratures ( ° C ) , as d e te r ­

mined from la b o ra to ry fre e z in g te s ts on December 3 , 1976,
and v is ib le cold In ju r y to needles o f tre e s from s ix
ponderosa p in e provenances fo llo w in g exposure o f tre e s to
-26°C tem peratures on December 3 , 1976, In a r e p lic a te d
southern Michigan p la n ta tio n .

S e ed lo t
S ta te o f
C r itic a l
Amount o f
Mo.____________O rig in __________Temperature________Needle D is c o lo ra tio n
°C

%

2012

AZ

-2 4 .9

25

2040

CA

-1 8 .3

63

2053

CA

-1 7 .2

40

2116

UT

-2 6 .1

0

2124

BC

-2 7 .6

0

2197

MT

-4 1 .4

0

41

o f c o n d itio n s .
c r itic a l

N e v e rth e le s s , p r e lim in a ry r e s u lts suggest t h a t th e

tem p eratu re procedure may be a v a lu a b le means o f d e te rm in in g

a s in g le d e fin a b le exp ressio n o f p la n t c o ld h a rd in e s s .

CHAPTER 4

GENETIC VARIATION IN SEVERAL ASPECTS OF
COLD HARDINESS IN PONDEROSA PINE

INTRODUCTION

Ponderosa p in e 1s one o f th e most im p o rta n t f o r e s t t r e e species 1n
th e w o rld .

In th e w estern U n ited S ta te s , where 1 t Is n a t iv e , 1 t f u r n i ­

shes more tim b e r than any o th e r species o f pin e and 1s th e m ainstay o f
th e econooty in many a re a s .

I t 1s a ls o h ig h ly regarded f o r i t s

b eau ty.

I t towers to g re a t h e ig h ts and produces lo n g , s t r a i g h t , c le a n ly pruned
boles which a re admired by t o u r is t s as w e ll as lumbermen.
Cold tem p eratu re appears to be one o f th e most Im p o rtan t fa c to r s
l im it i n g th e d is t r ib u t io n o f ponderosa p in e .
taken from I t s

n a tu ra l

When

ponderosa p in e 1s

range and moved to n o rth e rn o r

fr e e z in g in ju r y o fte n occurs.

In la n d lo c a tio n s

Such In ju r y causes u n s ig h tly damage and

reduced grow th.
Ponderosa p in e , as do o th e r species w ith la rg e ran g es, e x h ib its
c o n s id e ra b le g e n e tic v a r ia tio n as a r e s u lt o f long term n a tu ra l s e le c tio n
o ve r a range o f h a b ita ts and c lim a te s .

When s e v e ra l geographic races

o f th e species a re grown 1n a common lo c a t io n , la r g e d iffe r e n c e s 1n
many m orphological and growth t r a i t s a re observed.

Among such g e n e t ic a lly

v a r ia b le t r a i t s a re growth r a t e , needle le n g th , f o lia g e c o lo r and
42

43
s u s c e p t ib ilit y to w in te r I n j u r y .

Accounts o f such v a r ia t io n were

re p o rte d by Kempff (1 9 2 8 ), Weidman (T 9 3 9 ), W ells (1 9 6 4 ) , and W rig h t
e t al

(1 9 6 9 ).
S tu d ies In v e s tig a tin g g e n e tic v a r ia t io n 1n th e development o f c o ld

hardiness 1n woody p la n t sp ecies have re v e a le d th a t co ld re s is ta n c e may
be r e la t e d to th e r a t e o f c o ld hardening o r th e depth o f h ard iness p la n ts
can ac h ie ve 1n m id w in te r.

Sm ithberg and W elser (1 9 6 8 ) found th a t

n o rth e rn clones o f re d o s le r dogwood ( Cornus s t o l o n l f e r a ) a c c lim a te d to
cold e r a l l e r and f a s t e r than clones from warm re g io n s , when a l l were
grown under Minnesota c o n d itio n s .

A S e a t t le , Washington clo n e was

th e l a s t to harden and as a r e s u lt su s ta in e d e x te n s iv e co ld In ju r y to
tw ig s d u rin g f a l l o r e a r ly w in t e r .

However, a l l clones became hardy

enough to w ith s ta n d tem peratures o f -90°C 1n m id w in te r.
Maronek and F l i n t (1 9 7 4 ) c o lle c te d needles o f 15 provenances o f
e a s te rn w h ite p in e ( P1nus s tro b u s ) grown In M ich ig an .

They c o lle c te d

them m onthly and made la b o ra to ry te s ts to determ ine seasonal d iffe r e n c e s
1n h a rd in e s s .

They found d iffe r e n c e s among provenances In r a te o f c o ld

hardening as w e ll as 1n a b i l i t y to w ith s ta n d extrem e tem peratures 1n
m id w in te r.

Needles o f n o rth e rn tre e s hardened most r a p id ly and could

w ith s ta n d th e lo w est tem peratures In m id w in te r.

In December and Jan u ary,

tre e s from th e southern A ppalachians were damaged a t tem p eratu res o f -30°C
whereas tre e s from Canada could w ith s ta n d tem peratures o f -6 0 °C .

44

OBJECTIVES

The o b je c tiv e s o f t h is study were to d e te c t th e presence o f g e n e tic
v a r ia tio n In ponderosa p in e 1n th e fo llo w in g aspects o f co ld h a rd in e s s :
depth o f h a rd in e s s , r a te o f c o ld hardening and dehardening and w in te r
d e s ic c a tio n .

I a ls o In v e s tig a te d g e n e tic v a r ia tio n 1n le a f in g o u t

phenology and I t s

r e la t io n to sp rin g

f r o s t damage.

In a d d itio n ,

I hoped to a s c e r ta in th e c o n tr ib u tio n o f each o f these aspects to th e
v i s ib le w in te r In ju r y which has occurred to ponderosa p in e 1n M ich ig an .
A f i n a l o b je c tiv e was to determ in e th e amount o f g e n e tic and seasonal
v a r ia t io n 1n f o l i a r m o istu re c o n te n t and to r e l a t e t h a t v a r ia tio n to
g e n e tic d iffe re n c e s among s e e d lo ts In co ld h a rd in e s s .

45
MATERIALS AND METHODS
Establishm ent o f p la n ta tio n s

The tre e s used in my study are p a rt o f a range wide provenance
study s ta rte d 1n 1960 by Dr. 0 . 0 . W e lls , now g e n e tic is t w ith the
U. S. F orest S e rvic e a t G u lfp o r t, M is s is s ip p i, w ith seed su p p lied by
Dr. R. Z. Callaham , now D ir e c to r o f the P a c ific Southwest F orest and
Range Experiment S ta tio n .

The seeds were c o lle c te d from 60 n a tu ra l

stands lo c ate d In a l l p a rts o f th e w estern U n ited S ta te s (F ig u re 2 ) .
The seeds were sown 1n Michigan S ta te U n iv e r s ity 's experim ental
nursery a t East Lansing and grown th e re f o r two y e a rs .

In 1962

th ey were p lan ted 1n two permanent t e s t lo c a tio n s a t W. K. Kellogg
F orest (Augusta, M ichigan) and Fred Russ Forest (Dowaglac, M ic h ig a n ).
The p la n ta tio n s fo llo w a randomized complete block design w ith s ix
tr e e p lo t s , a 2 .5 * 2.5m spacing, and f i v e r e p lic a te s per p la n ta tio n .
These p la n ta tio n s , which averaged 5 .0 and 5 .5 m t a l l

re s p e c tiv e ly 1n

1976, were the source o f m a te ria l fo r my s tu d ie s .
C o lle c tio n and p re p a ra tio n o f samples
On 13 d if f e r e n t dates between O cto ber, 1975 and F eb ru ary, 1977
I c o lle c te d tw igs from two vigorous tre e s (th e same tre e s each tim e )
per p lo t f o r each o f 30 s e le c te d seed lo ts a t the Kellogg p la n ta tio n .
A t o t a l o f ten tre e s from f i v e r e p lic a te s were sampled f o r each s e e d lo t
on every d a te .

Each tw ig was c o lle c te d from th e m iddle o f the crown

on th e west sid e o f the t r e e .

I Im m ediately placed th e tw igs 1n p la s t ic

bags, sealed th e bags, and sto re d them In th e shade a t n ear-am bient
tem perature c o n d itio n s .

46

FIGURE 2 .

D i s t r i b u t i o n o f ponderosa p in e 1n th e U n ite d S ta te s and
B r i t i s h C o lu m b ia, showing th e lo c a t io n o f s ta n d c o l l e c ­
tio n s used 1n t h i s s tu d y (map r e p r in t e d from W e lls , 1962

K

f

.

t

iO *

W»9»*

r

$

t

48
W ith in 24 hours th ese samples were re tu rn e d to th e la b o r a to r y
and prepared f o r th e fr e e z in g t e s t s .

This p re p a ra tio n s ta r te d w ith

the removal o f 18 needle fa s c ic le s p e r tw ig (1 2 -1 5 g o f n e e d le s ).
Needles were c u t In h a l f and p la c e d , c u t end down, in la b e le d t e s t
tu b es.

The needles were ap p o rtio n ed 1n such a manner as to r e s u lt 1n

12 t e s t tubes p e r s e e d lo t.

Those com prising la b o r a to ry r e p lic a t io n

No. 1 were from th e tre e s 1n p la n ta tio n blocks Nos. 1 , 2 , and 3;
those com prising la b o r a to ry r e p lic a t io n No. 2 were from p la n ta tio n
block Nos. 4 and 5 .

For each la b o ra to ry r e p lic a t io n th e re were s ix

t e s t tubes p er s e e d lo t, each to be fro z e n a t a d if f e r e n t te m p e ra tu re .
This p a r t i c u l a r method o f r e p lic a t io n In su red th a t th e e r r o r terms
In c lu d e d b io lo g ic a l as w e ll as in s tru m e n ta l e r r o r .
On fo u r a d d itio n a l d a te s , tw ig s as w e ll as needles were prepared
f o r f r e e z in g .

A f t e r removing 1 cm from each end, th e rem ainder o f

th e tw ig s were c u t In to 3 cm segments and placed 1n t e s t tubes In
the same way as th e n e e d le s .

Twigs were sampled f o r o n ly s ix o f th e

30 s e e d lo ts f o r which needle samples were ta k e n .
F ree zin g methods
A f t e r th e needles o r tw ig s were placed 1n th e t e s t tu b e s , th e
t e s t tubes were sto p p ered .
In a c o ld room held a t 4°C .

Then two from each s e e d lo t were placed
These were th e unfrozen c o n tr o ls .

The

o th e r ten from each s e e d lo t were placed In a co ld room a t 0°C and
were l e f t to e q u il i b r a t e f o r 12 hours.

A f t e r e q u il i b r a t i o n , th e t e s t

tubes were placed 1n In s u la te d c o n ta in e rs and p u t In a fr e e z e r s e t
I n i t i a l l y a t -2 0 °C .

Temperatures w ith in th e In s u la te d c o n ta in e rs were

m onitored w ith a s e rie s o f therm ocouples.
a tu re c o n tro l was lowered 4 to 6°C .

Every two hours th e tem per­

The e x a c t amount o f lo w erin g was

49
ju s t enough to m a in ta in a 20°C d i f f e r e n t i a l between th e f r e e z e r
and th e in s id e o f th e c o n ta in e rs .
2 to 3°C p er hour.

F ree zin g ra te s v a rie d from

A t each o f f i v e p re s e le c te d tem peratures two t e s t

tubes per s e e d lo t were removed from the fr e e z e r and thawed s lo w ly In
th e In s u la te d c o n ta in e rs .

Thawing took p la c e a t th e r a te o f about

5°C p er hour.
The range o f fr e e z in g tem peratures chosen f o r each sampling d ate
was such as to r e s u lt In no damage a t th e h ig h e s t tem p eratu re but
some damage to th e h a rd ie s t s e e d lo ts a t th e low est te m p e ra tu re .
V i a b i l i t y e v a lu a tio n s
T issue v i a b i l i t y was d eterm ined using a m o d ific a tio n o f th e e le c ­
t r o l y t i c d if f u s io n method as d escrib ed by D e x te r e t a l , (1 9 3 2 ).

This

method 1s based on th e p r in c ip le t h a t l i v e c e lls q u ic k ly lo s e th e a b i l i t y
to r e g u la te t h e i r co n ten ts when t h e i r c e l l membranes a re damaged.

As

a r e s u l t , e le c t r o ly t e s d if f u s e In to s o lu tio n th e re b y causing an In c re a s e
In s p e c if ic c o n d u c tiv ity o f th e s o lu tio n .

Thus, th e g r e a te r th e in ju r y

to p la n t tis s u e s from low te m p e ra tu re s , th e h ig h e r th e c o n d u c tiv ity
o f th e e x t r a c t .
A f t e r th aw in g , 25 ml o f d e io n iz e d w a te r was added to each t e s t
tu b e .

Samples were soaked f o r 28 hours a t 4°C .

W hile s t i l l

a t 4 °C ,

c o n d u c tiv ity o f th e le a c h a te was measured using a c o n d u c tiv ity b rid g e
and a p ip e t t e -ty p e c o n d u c tiv ity c e l l .

The sam ples, In c lu d in g th e

le a c h a te , were then a u to clav ed a t 121°C f o r 20 m inutes to k i l l a l l
rem aining l i v e tis s u e s .

Samples were a g a in placed In a co ld room a t

4°C f o r s ix hours a f t e r which t h e i r c o n d u c tiv itie s were remeasured.
The c o n d u c tiv itie s determ ined In th e above manner were termed
s p e c if ic c o n d u c tiv itie s .

They could v a ry w ith sample s iz e as w e ll as

50
amount o f damage.

For f u r t h e r c a lc u la tio n s th ey were co n verted to

r e l a t i v e c o n d u c t iv it ie s , by exp ressin g each as a p e rc e n t o f th e
c o n d u c tiv ity o f th e a u to c la v e d sample.
D e te rm in a tio n o f c r i t i c a l

tem p eratu re

C r i t i c a l tem p eratu re was d e fin e d as th e h ig h e s t tem p eratu re a t
which damage could be d e te c te d s t a t i s t i c a l l y .

To determ ine i t ,

I

f i r s t su b jected th e r e l a t i v e c o n d u c tiv itie s to an a n a ly s is o f v a ria n c e .
The e r r o r term from th e a n a ly s is o f v a ria n c e was used to compute a
" le a s t s i g n i f i c a n t d iffe re n c e " (L S D ) v a lu e ( a t th e \% l e v e l ) .

The

LSD v a lu e , when added to th e r e l a t i v e c o n d u c tiv ity o f c o n tro l samples
f o r each s e e d lo t, provided th e p e rc e n t c o n d u c tiv ity corresponding to
th e p o in t a t which s i g n i f i c a n t co ld In ju r y could f i r s t be d e te c te d .
The tem perature corresponding to t h is p o in t was then found by I n t e r ­
p o la tio n and re p resen ted th e c r i t i c a l

te m p e ra tu re .

C r i t i c a l tem per­

a tu re s were determ ined f o r each r e p lic a t e o f ev ery s e e d lo t.
F o lia r m o istu re c o n te n t and w in te r d ry in g ra te s
In September, 1975 and on f i v e d i f f e r e n t dates between J u ly , 1976
and Jan u ary, 1977 I c o lle c te d 15-20 cm tw ig s from ten tre e s

(fiv e

r e p lic a t io n s ) o f each o f 30 s e le c te d s e e d lo ts 1n th e K ellogg F o res t
p la n t a t io n .

The same tre e s were used as in th e c o ld h ard iness s tu d ie s .

The samples were im m ed iately placed 1n p la s t ic bags and taken to th e
la b o ra to ry where t h e i r fre s h w eights were d eterm in ed .
placed In a d ry in g oven f o r 48 hours and rew eighed.

They were then
F o lia r m o istu re

c o n ten t was c a lc u la te d as a percentage o f fre s h w e ig h t.
Rate o f d ry in g o f cu t branches under la b o r a to ry c o n d itio n s was
determ ined f o r 15 s e ed lo ts sampled on November 2 3 , 1976.

The tw ig

samples were c o lle c te d from blocks 1 to 3; each sample o f tw igs from

51
two tre e s 1n a p lo t was kept s e p a ra te .

The c u t ends were waxed, th e

tw igs were placed in p la s t ic bags, and th e fre s h w eigh ts o f th e tw igs
were determ ined w ith in two hours.

Then th e tw ig s were spread o u t on

la b o ra to ry benches In a room ke p t a t 20°C but w ith u n c o n tro lle d r e l a ­
t i v e h u m id ity .

The tw ig s were weighed d a lly f o r th e f i r s t fo u r days

and then ev ery two days.

A f t e r ten days th e tw ig s were oven d rie d and

reweighed to d eterm in e r e l a t i v e f o l i a r m o istu re c o n te n t.
L e a f phenology
On May 2 0 , 1976, I scored tn e e x te n t o f shoot development f o r a l l
60 s e e d lo ts p la n te d a t K ellogg F o re s t.

I

used a sco ring system o f

1 (= buds In w in te r c o n d itio n ) to 10 (=1eaves 2 1n lo n g ).

These grades

corresponded to a tim e d iffe r e n c e o f a p p ro x im a te ly two weeks In th e
s t a r t o f grow th.
F ie ld sco rin g o f w in te r In ju r y
E stim ates o f w in te r In ju r y were made 1n th e n ursery and a t va rio u s
ages 1n both t e s t p la n t a tio n s .

Damage was recorded as th e percentage

o f needles t h a t tu rn ed brown as a r e s u lt o f w in te r c o ld .

F ie ld scorings

were made 1n e a r ly s p rin g fo llo w in g damaging w in te r s .
S t a t i s t i c a l a n a ly s is
For each t r a i t measured, the d ata were summarized by s e e d lo t and
r e p lic a t io n .

In th ese sunvnarles, th e s e e d lo ts were grouped by th e

ecotypes and v a r i e t i e s recognized in th e p u b lic a tio n s by W ells (1 9 6 4 )
and W rig h t e t a l

(1 9 6 9 ).

The ecotypes and t h e i r boundaries a re

I l l u s t r a t e d in F ig u re 3.
A f t e r such sum m arization, an a n a ly s is o f v a ria n c e was perform ed f o r
each s e t o f d a ta .

There was, f o r exam ple, a sep arate a n a ly s is , f o r th e

c r i t i c a l tem peratures o b ta in ed a t each d a te .

In these a n a ly s e s , mean

52

FIGURE 3 .

Ecotype d iv is io n s o f ponderosa p in e progeny In c lu d e d 1n
t h i s s tu d y .

Ecotypes a r e d e s ig n a te d by l e t t e r s as f o l i o

A.

NORthern C A H fo r n la and S o uth ern C A H fo r n la

B.

NORthern PLATEAU

C.

A rizo n a -N e w M exico

D.

S outhern U T a h -n o rth e rn New M exico

E.

NORthern INTERIOR

F.

NORthern CO lorado-UTah

G.

COASTal ORegon

(map and e c o ty p e b o u n d aries a f t e r W e lls , 1 9 6 2 ).

53

2»»7

to f 4

*o *^ 0 ^fooo
\

*0 8 *

1164

*04 f 0

54
squares were c a lc u la te d f o r e c o ty p e, s e e d lo t w ith in eco typ e, r e p lic a t io n ,
and e r r o r (s e e d lo t x r e p l i c a t io n ) .
As a lre a d y m entioned, a "Least S ig n ific a n t D iffe re n c e " (LSD)
was c a lc u la te d f o r th e fre e z in g d ata f o r each d a te .

This was c a lc u ­

la te d from th e form ula
LSD = 2 374

E rro r Mean Square)

This LSD was then used to determ ine th e c r i t i c a l tem perature a t which
cold In ju r y could f i r s t be d e te c te d .
An a n g u la r tra n s fo rm a tio n was used b efo re a n a ly s is on a l l data
recorded in p ercen tag e.

55
RESULTS
G enetic d iffe re n c e s in cold hardiness

Depth o f hardiness and r a te o f hard ening .

S ig n ific a n t d iffe re n c e s

in needle c r i t i c a l tem peratures were found among th e e ig h t ponderosa
pine ecotypes on n e a rly a l l sampling dates (T a b le 2 ) .

Only In J u ly * 1976*

were a l l tre e s a t appro xim ately th e same le v e l o f cold h ard in e ss .

In

g e n e ra l, tre e s from n orthern regions could w ith sta n d low er tem peratures
w ith o u t damage than could southern tr e e s .
In the I n t e r i o r v a r ie ty (F ig u re 4 ) , tre e s grown from seed c o lle c te d
1n the N orthern I n t e r i o r (c e n tr a l Montana, South Dakota, Nebraska)
hardened to co ld f a s t e r than those from southern re g io n s , and achieved
a g re a te r depth o f hardiness by m id w in te r.

Northern tre e s reached

maximum hardiness In January when th ey could w ith sta n d tem peratures
below -45°C w ith o u t needle damage.

At the o th e r extrem e, A rizona and

New Mexico tre e s hardened more slo w ly and, a t maximum h a rd in e s s ,
s u ffe re d damage a t -3 1 °C .

A ls o , A rizona and New Mexico tre e s d id not

In crease in hardiness from December to January as d id n o rth e rn tr e e s .
In the co a stal v a r i e t y , a s im ila r p a tte rn was e v id e n t (F ig u re 5 ) .
Trees grown from seed c o lle c te d 1n the Northern P lateau regio n (Oregon,
Washington, n o rth e as te rn C a lif o r n ia and B r it is h Columbia) harden to co ld
r a p id ly 1n the f a l l and achieved a maximum depth o f hardiness a t -39°C
In January.

Trees from th e two C a lif o r n ia ecotypes, on th e o th e r hand,

were slow to harden and were damaged by tem peratures o f -22°C In e a r ly
December.

As w ith th e Arizona-New Mexico t r e e s , th e C a lif o r n ia tre e s

d id not become more hardy In January than 1n December.

TABLE 2.

Critical temperatures (In °C) for needles of trees from eight ponderosa pine ecotypes on 14 dates.
Critical temperature is defined as the highest temperature at which cold Injury could be detected.
Data for July, 1976 Is based on six seedlots.

Critical temperature (°C) on
Variety &
Ecotype

Oct. Dec. Jan. Feb. Mar. Apr. Jul. Aug. Sep. Oct. Nov. Dec. Jan. Feb.
22
26
27
30
31
17
30
7
17
10
2
28
11
10
1975 1975 1976 1976 1976 1976 1976 1976 1976 1976 1976 1976 1977 1977

Nor. Plateau

-16

-27

-39

-23

-17

-10

- 6

- 7

- 8

-19

-22

-31

-39

-33

Coast. OR

-13

-22

-32

-15

-17

- 9

—

- 7

- 7

-15

-24

-27

-31

-31

Nor. CA

-10

-23

-22

-19

-15

- 6

- 5

- 6

- 7

-13

-17

-21

-24

-22

Sou. CA

- 8

-20

-22

-19

-13

- 6

- 5

- 7

- 7

-12

-15

-20

-22

-23

Nor. Interior

-19

-38

-45

-28

-19

-15

- 6

- 7

-11

-22^

-28

-39

-47

-41

Nor. CO-UT

-14

-32

-41

ro

var. ponderosa

-19

-13

- 5

- 7

- 9

-21

-26

-35

-42

-36

Sou. NT-NK

-13

-29

-35

-27

-18

- 9

—

- 6

- 8

-20

-24

-31

-35

-32

AZ-NK

-11

-29

-31

-25

-17

- 7

- 5

- 5

- 7

-17

-22

-30

-32

-31

Least Significant
Difference (5* level)

3.5

3.1

5.9

3.4

3.3

2.2

.56

.85

2.7

2.4

2.9

4.0

3.9

1

var. Scopulorum

^Needles not damaged at lowest test temperature

57

FIGURE 4 .

Seasonal p a tte r n o f c o ld h ard ening and dehardening
f o r fo u r I n t e r i o r v a r ie t y

( v a r . Scopulorum) ecotypes

o f ponderosa p in e growing a t K ello g g F o re s t in so u thern
M ic h ig a n .

INTERIOR VARIETY

O r

CRITICAL

TEMPERATURE

CC)

-10

-20
AZ-NM

cn
00

-30

SOU UT-NM
NOR CO-UT

-40

NOR INTERIOR

-50
J-4. I . . I . . I . . I i a

-60
OCT NOV DEC JAN
1975

FEB MAR APR MAY JUN JUL

I

AUG SEP OCT NOV DEC JAN

1976
DATE OF OBSERVATION

FEB

1977

59

FIGURE 5 .

Seasonal p a t t e r n o f c o ld h a rd e n in g and d eh ard e n in g
f o r fo u r c o a s ta l

v a r ie ty

(v a r.

Ponderosa) eco ty p es

o f ponderosa p in e grow ing a t K e llo g g F o re s t 1n s o u th e rn
M ic h ig a n .

COASTAL VARIETY
0

CRITICAL

TEMPERATURE

PC)

-10

■20
SOU CA

-30

NOR. CA
COAST OR

-40

NOR. PLATEAU

-50
-60

I

. i I i . Ii . 1i iI

1.

. 1 i i 1 * i I . . I . ■I . . I . . I . . 1 , , I . . I . . I

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL
1975
1976

AUG SEP OCT NO/ DEC JAN FEB
1977

DATE OF OBSERVATION

61

Comparison o f hardiness le v e ls on October 3 0 , 1975 and October
2 8 , 1976, In d ic a te s t h a t cold a c c lim a tio n began e a r l i e r In 1976 than
1n 1975.

In O ctober, 1976, c r i t i c a l tem perature f o r th e 30 se ed lo ts

averaged alm ost 5°C low er than In the previous y e a r .

By December, 1976,

tre e s were o n ly 2°C h a rd ie r than 1n 1975 and by January y e a r ly d i f f e r ­
ences were n e g lig ib le .

These d iffe re n c e s may be ex p la in ed by comparing

c lim a tic data from Kellogg F o res t f o r the two y e a rs .

Monthly mean

minimum tem peratures were 3°C c o ld e r and ab s o lu te mlnlmums were 6°C
c o ld e r In O ctober, 1976 than in th e previous y e a r .

Also tem peratures

dropped below 0°C on ten days d urin g September and O ctober, 1976 as
compared to two days during th e same months In 1975.
The geographic d iffe re n c e s fo r ponderosa p in e a re s im ila r to
those re p o rte d f o r e a s te rn w h ite pine by Maronek and F l i n t (1 9 7 4 ).
They a ls o found n orthern seed sources to harden to cold more r a p id ly
and to achieve a maximum depth o f hardiness In January.

In c o n tr a s t,

southern w h ite pines hardened slow er In the f a l l , hardened less In w in te r ,
and reached maximum hardiness in l a t e November.
Rate o f dehardening.

A ll tre e s had dehardened somewhat by m iddle

o r l a t e February o f both years (F ig u re s 4 and 5 ) .

C r i t i c a l tem peratures

f o r n orthern tre e s decreased by about 16°C from January to F eb ru ary, 1976.
For southern tr e e s , c r i t i c a l tem peratures decreased by about 4°C during
t h a t p e rio d .

D esp ite d if f e r e n t dehardening r a te s , n o rth e rn tre e s

remained h a rd ie r than southern tr e e s .
Dehardening occurred a f t e r th e advent o f r e l a t i v e l y warm w eather
1n both years and proceeded more r a p id ly from January to F eb ru ary, 1976
than the fo llo w in g y e a r.
1n 1976 than 1n 1977.

This was a p p a re n tly due to th e wanner w eather

Maximum d a lly tem peratures a t Kellogg Forest

averaged n e a rly 10°C h ig h e r 1n February, 1976 than 1n Feb ru ary, 1977.

62
D iffe re n c e s w ith in eco typ es.
among ecotypes.

So f a r I have discussed o n ly d iffe re n c e s

There were a ls o la rg e and c o n s is te n t d iffe re n c e s among

seed lots from the same re g io n .
Data f o r In d iv id u a l se ed lo ts w ith in the two most v a ria b le ecotypes
are given In Table 3.

Among th e seed lo ts from the Northern P la te a u ,

No. 2124 from B r it is h Columbia was among th e h a rd ie s t on a l l d a te s ,
having a c r i t i c a l

tem perature as much as 18°C low er than s e e d lo t No.

2045 from n o rth e a s te rn C a lif o r n ia .

There were also la rg e d iffe re n c e s

among seed lo ts from the n orthern I n t e r i o r re g io n .

S eed lo t No. 2197 from

c e n tra l Montana was h a rd ie s t on alm ost a l l d a te s , w h ile s e e d lo t No. 2095
from southern Montana was among the le a s t hardy.
Hardiness o f tw igs vs n ee d les.

The re s u lts o f cold hardiness

comparisons between needles and tw igs f o r s ix ponderosa pine seed lots
on fo u r dates are summarized 1n Table 4 .

On most d a te s , tw igs had

s l i g h t l y low er c r i t i c a l tem peratures than n eedles.

In December, the

c r i t i c a l tem perature was several degrees low er f o r tw igs than f o r n eed les.
This e x p la in s why v is ib le w in te r In ju r y in th e f i e l d was u s u a lly confined
to n eedles.
G e n e ra lly , on any one d a te , those seed lo ts w ith the low est c r i t i c a l
tem perature f o r needles als o had th e low est c r i t i c a l tem perature f o r
tw1 g s .
My data on needle and tw ig hardiness o f ponderosa p ine a re c o n s is te n t
w ith those o f Parker (19 57 ) who could not d e te c t hardiness d iffe re n c e
between a c c lim a tin g tw igs and needles o f th is species 1n n orthern Idaho.
By m id w in ter 1n P a rk e r's stu d y, hardiness o f tw igs and needles exceeded
the tem perature lim it s o f h is fre e z in g apparatus so th a t comparisons
could not be made,

However, Sakai and Okada (19 71 ) found ponderosa

63
TABLE 3.

Consistency and magnitude o f cold hardiness d iffe re n c e s
among seed lo ts w ith in two g e n e tic a lly v a ria b le ponderosa
p ine ecotypes.

Ecotype,
S eedlot No.
& S ta te
o f O rig in

Ranking tot c r i t i c a l 1tem perature on
Apr.
Sep.
Nov.
dan.
rla r.
17
31
11
26
30
1976
1976
1976
1976
1976

O ct.
30
1975
-

- 1 = most hardy , 5 = le a s t hardy - -

-

■

Jan.
10
1977
-

-

Nor. P lateau
2124 BC

1

1

1

2

1

1

1

2032 MA

2

2

4

3

2

2

2

2102 WA

3

3

3

4

4

4

3

2034 OR

4

4

5

5

3

3

4

2045 CA

5

5

2

1

5

5

5

C r it i c a l Temperature Range
from:

-1 0

-2 8

-1 6

- 6

- 7

-1 8

-31

to :

-23

-46

-1 9

-12

- 8

-25

-4 7

2197 MT

1

1

1

3

1

1

1

2190 NB

2

4

2

1

2

2

3

2029 SD

3

2

3

2

3

3

2

2095 MT

4

3

4

4

4

4

4

Nor. I n t e r i o r

C r i t i c a l Temperature Range
from:

-17

-41

-1 8

-1 4

-10

-25

-4 3

to :

-21

-5 2

-2 0

-16

-11

-29

-5 0

64
TABLE 4 .

D iffe re n c e s 1n co ld hardiness between tw ig s and needles
o f ponderosa p in e s e e d lo ts on fo u r dates In 1976.

C r itic a l

S eedlot No.
J u l. L

and S ta te
o f O rig in

l

76

Needles Twigs

tem peratures ( °C ) on

Aug. 26 , 76
Needles Twigs

O ct. 7 , 76
Needles Twigs

Dec. 3 , 76
Needles Twigs

2012 AZ

-5 .4

-5 .4

-7 .8

- 8 .6

-9 .5

-8 .1

2040 CA

-5 .4

-5 .5

-6 .9

-7 .1

-7 .4

-7 .7

- 1 8 .3

-1 7 .8

2053 CA

-5 .4

-5 .4

-7 .1

- 7 .7

-7 .2

-7 .3

-1 7 .2

- 2 8 .4

2116 UT

-5 .4

-5 .0

-8 .4

-9 .8

-1 0 .1

-9 .1

-2 6 .1

-3 5 .2

2124 BC

-5 .6

-5 .7

-9 .4

-1 0 .3

-8 .5

-1 0 .7

-2 7 .6

- 4 0 .2

2197 MT

-5 .5

-5 .8

- 1 0 .4

-1 0 .9

-1 2 .7

- 1 3 .2

-4 1 .4

- 4 1 .4

Mean

-5 .4

-5 .5

-8 .3

- 9 .2

-9 .2

-9 .4

- 2 5 .9

-3 2 .5

-2 4 .9

-31 .7

Were d iffe re n c e s s ig n if ic a n t a t 1 * le v e l?
Between tis s u e s
Among s e e d lo ts

Vac

No
No

No

Yes

No
Yes

Yes

Yes
Yes

Yes

Yes

65

pine tw ig s to be about 10°C h a r d ie r than needles in m id w in te r in a
study conducted 1n Hokkaido, Japan.
V is ib le w in te r I n j u r y .
n u rsery (W e lls , 1 9 6 4 ).

W in te r in ju r y was f i r s t observed in th e

I t has been observed s e v e ra l tim es s in c e ,

p a r t i c u l a r l y a t K ellogg F o re s t.

Most o f the In ju r y has been to

needles r a th e r than to buds o r cambium.
The In ju r y was most severe on y e a r -o ld s e e d lin g s and a t age 17
fo llo w in g the c o ld e s t M ichigan w in te r on re c o rd .

D e s p ite d iffe r e n c e s

in s e v e r it y from y e a r to y e a r , a s im ila r geographic p a tte r n 1n
s u s c e p t i b i l it y to w in te r In ju r y was e v id e n t a t a l l

s ite s and in a l l

ye ars (F 1g . 5 ) .
W in te r In ju r y was n i l on I n t e r i o r tre e s from Colorado n o rth w a rd ,
w h ile C a lif o r n ia tre e s s u ffe re d severe damage to t h e i r needles 1n
a l l ye a rs t h a t w in te r In ju r y was a problem .

Some C a lif o r n ia tre e s

a ls o had cambium damage a f t e r th e c o ld w in te r o f 1 9 7 6 -7 7 .

Coastal

Oregon and Arizona-New Mexico tre e s s u ffe re d moderate damage 1n most
y e a rs .

Trees grown from seed c o lle c te d 1n th e N o rth ern P la te a u (O regon,

W ashington, and B r it i s h Columbia) were m o d erately damaged In th e n u rse ry
but recovered s u f f i c i e n t l y to be among th e le a s t damaged tre e s a t
l a t e r ages.
A n o rth to south geographic p a tte r n In w in te r In ju r y has been shown
f o r many f o r e s t t r e e s p e c ie s .

In a D o u g la s -fir ( Psuedotsuqa m e n z le s l1 )

provenance t e s t In P e n n s y lv a n ia , Gerhold (1 9 6 5 ) observed heavy In ju r y
to c o a s ta l t r e e s , moderate In ju r y to A rizo n a and New Mexico t r e e s , and
little

o r no damage on tre e s from th e n o rth e rn Rocky M ountains.

E1che

(1 9 6 6 ) a ls o found a n o rth to south p a tte r n 1n w in te r In ju r y In a n o rth
Swedish provenance t e s t o f Scotch p in e ( P1nus s y l v e s t r l s ) .

In e a s te rn

66

FIGURE 6 .

R e la t iv e e x te n t o f n e e d le w in t e r I n j u r y on t r e e s from
e ig h t ponderosa p in e e c o ty p es a t d i f f e r e n t p la n t a t io n s
and ag es.

Age 17 d a ta was c o lle c t e d f o llo w in g th e

s e v e re w in t e r o f 1 9 7 6 -7 7 .

ECOTYPES

NURS

KELLOGG FOREST

WE I

NOR PLATEAU
COAST OR
NOR CA
SOU. CA
NOR INTERIOR
NOR CO-UT
SOU UT-NM
AZ-NM

AGE 4

AGE 6

LM LM

O

100

0

100 0

RUSS FOREST

AGE 17

AGE 4

AGE 17

LM k LM

100 0

100

% OF MAXIMUM DAMAGE

0

100 0

100

68
hemlock ( Tsuga can ad en sis) , N le n s ta e d t (1 9 5 8 ) noted a high c o r r e la t io n
between f a l l

f r o s t damage and provenance growing season le n g th f o r 17

seed sources te s te d In W isconsin.

Southern tre e s were a p p a re n tly

adapted to r e l a t i v e l y long growing seasons and were damaged most s e v e re ly
by f r o s t o c c u rrin g in autumn.
In C a l i f o r n i a , Conkle e t a l

(1 9 6 7 ) d es crib ed a unique geographic

p a tte r n o f w in te r In ju r y among 43 sources o f w h ite f i r

( Abies c o n c o lo r) .

S eed lin gs from n o rth e rn C a lif o r n ia su stain ed more w in te r in ju r y than
did southern t r e e s .
fir

( Abies q ra n d ls ) .

This is p ro b ab ly due to 1ntrogress1on w ith grand
Grand f i r ,

alth ou gh a more n o rth e rn s p e c ie s ,

grows a t much low er e le v a tio n s than w h ite f i r and 1s co n sequ en tly le s s
w in te r h ard y .

W hite f i r from n o rth e rn C a lif o r n ia has more grand f i r

germplasm and th e r e fo r e le s s h ard in ess than w h ite f i r from f a r t h e r so u th.
R e la tio n s h ip between c r i t i c a l tem p eratu re and f i e l d
r e la t io n s h ip between c r i t i c a l

in ju r y .

tem peratures and a c tu a l f i e l d

The

In ju r y were

In v e s tig a te d d u rin g the w in te rs o f 1975-76 and 19 7 6 -7 7 .
During th e w in te r o f 1 9 7 5 -7 6 , th e low est tem perature recorded In
th e K ello gg F o re s t p la n ta tio n was -2 7 °C .
mid Jan u ary.

T his low was recorded 1n

That w in te r tre e s o f th e C a lif o r n ia ecotypes s u ffe re d

a sm all amount o f c o ld In ju r y to th e n ee d les .

Trees from o th e r ecotypes

had s u f f i c i e n t l y hardened by m iddle Jan u ary, having c r i t i c a l

tem peratures

o f - 3 1 °C o r below to w ith s ta n d th e -27°C te m p e ra tu re .
The fo llo w in g w in te r was o n ly s l i g h t l y c o ld e r w ith a low tem p e ra tu re
o f -2 8 °C .

However, e x tre m e ly c o ld w eather o ccurred e a r ly 1n th e season.

A t K ellogg F o r e s t, th e tem p e ra tu re dropped to -26 °C on December 3 , 1976.
F o lia g e samples were c o lle c te d a few days l a t e r and brought In to th e
la b o r a to ry f o r c lo s e e x am in a tio n .

W in te r In ju r y was measured as th e

69

FIGURE 7 .

M o t t lin g on ponderosa p in e n ee d les damaged by te m p e ra tu re
o f -2 6 °C on December 3 , 1 9 7 6 .
s e e d lo ts a r e :

From l e f t to r i g h t th e

No. 2234 from A r iz o n a , m oderate damage;

No. 2197 from M ontana, no damage; and No. 2036 from
C a l i f o r n i a , s e v e re damage.

70

71
TABLE 5 .

Comparison between damage caused by unseasonably cold w eather
(tem p eratu re o f -26°C on December 3 , 1976) in e a r ly w in te r
and co ld hardiness as measured by c r i t i c a l tem peratures on
the same d a te .

The c r i t i c a l

tem peratures a re an average o f

c r i t i c a l tem peratures on November 11, 1976 and December 17,
1976.

V a rie ty

P ro p o rtio n o f f o lia g e

C r i t i c a l tem peratures

and

in ju re d on

(average o f values fo r

Ecotype______________December 3 , 1976__________ Nov. 11 and Dec. 17)
%

°C

0

- 2 6 .5

Coast. OR

15

-2 5 .5

Nor. CA

45

-1 9 .0

Sou. CA

65

-1 7 .5

Nor. I n t e r i o r

0

-3 3 .5

Nor. CO-UT

0

- 3 0 .5

Sou. UT-NM

5

-2 7 .5

20

-2 6 .0

v a r. ponderosa
Nor. P lateau

v a r. Scopulorum

AZ-NM

72
amount o f m o ttlin g p resen t on needles (F ig u re 7 ) .
summarized in T ab le 5 .

The r e s u lts a re

Also In c lu d ed 1n th a t t a b le a re th e probable

c r i t i c a l tem peratures reached by December 3 (averag es o f th e c r i t i c a l
tem peratures measured on November 11 and December 1 7 ).
As shown 1n T ab le 5 , those ecotypes which had hardened s u f f i c i e n t l y
to a t t a i n c r i t i c a l tem peratures o f - 2 7 ° C by December 3 were not o r
o n ly s l i g h t l y In ju re d by th e -26°C tem peratures on t h a t d a te .

Trees

from C a lif o r n ia ecotypes s u ffe re d very severe m o ttlin g as a r e s u lt o f
th e co ld w e a th e r.

Trees from c o a s ta l Oregon and A rizona-N ew Mexico

s u ffe re d a moderate amount o f damage.

N orthern P la te a u and A riz o n a -

New Mexico tre e s d if f e r e d In th e amount o f ap parent w in te r In j u r y even
though both were alm ost e q u a lly hardy acco rd ing to th e la b o r a to ry t e s t s .
The r e s u lts summarized 1n T ab le 5 In d ic a te a stron g but not
p e r fe c t r e la tio n s h ip between co ld hardiness as measured In th e la b o r a to ry
and a c tu a l damage from co ld under f i e l d c o n d itio n s .
" c r itic a l

A p p a re n tly , th e

tem perature" as I measured 1 t In the la b o r a to ry 1s w ith in

two o r th re e degrees c e n tig ra d e o f th e a c tu a l c r i t i c a l tem p eratu re o f
f i e l d grown p la n ts .
Seasonal changes in cold hardiness
The seasonal p a tte r n o f c o ld a c c lim a tio n f o r needles o f fo u r
ponderosa p in e s e e d lo ts 1s I l l u s t r a t e d

1n F ig u re 8 .

That graph 1s

based on co ld hardiness d ata f o r fo u r s e e d lo ts which were s tu d ie d 1n
more d e t a il d u rin g f a l l ,

1976.

The curves f o r th e C a lif o r n ia and A rizo n a s e e d lo ts were h ig h e r
than f o r th e o th e r two s e e d lo ts a t a l l

tim e s .

They were much h ig h e r

d u rin g w in t e r , b u t o n ly s l i g h t l y h ig h e r d u rin g summer.
F o llo w in g o th e rs , th e seasonal changes 1n co ld h ard iness can be
d iv id e d In to stages as fo llo w s .

The f i r s t occurred from J u ly to e a r ly

73

FIGURE 8 .

Seasonal changes In c o ld h a rd in e s s f o r fo u r s e e d lo ts o f
ponderosa p in e .

Numbered arrow s d e s ig n a te d ates o f

im p o rta n t c lim a t ic changes as fo llo w s :
Arrow No. 1:

January 1 8 , 1976 - f i r s t day below -2 7 °C

Arrow No. 2:

F ebruary 15 , 1976 - f i r s t day above 16°C

Arrow No. 3:

O ctober 1 8 , 1976 - f i r s t day below - 5°C

Arrow No. 4:

December 3, 1976 - f i r s t day below -2 6 °C

Arrow No. 5:

December 31 , 1976 - f i r s t day below -2 8 °C

Arrow No. 6:

Feb ru ary 7 , 1977 - f i r s t day above

5°C

O r

CRITICAL

TEMPERATURE

(°C)

-10

-20
2040-CA

•MIMUIH

-30

2012-AZ
2II6-UT

-4 0

2197-MT

-50

-6 0

ja

11

.

i

. «

i

J5 i IS 1 1 .

i

. .

i

..

i

..

i

..

OCT NOV DEC JAN FEB MAR APR MAY JUN JUL
1975
1976

i

. 1

11

1

1 .^11

1 .

.

iS .

AUG SEP OCT NOV DEC JAN FEB
1977

DATE OF OBSERVATION

i

75
O cto b e r, 1976 and was one o f gradual h ard en in g .

The second o ccurred

from O ctober to mid December and was c h a ra c te riz e d by an a c c e le ra te d
r a te o f h ard en in g .

The t h ir d stage In v o lv e d d i f f e r e n t changes 1n

d i f f e r e n t s e e d lo ts and extended from mid December to mid January 1n both
w in te r s .

During th e t h ir d s ta g e , th e re was no change 1n c r i t i c a l

tem perature f o r s e e d lo ts from warm c lim a te s .
f u r t h e r lo w e rin g o f c r i t i c a l

However, th e re was a

tem peratures f o r s e e d lo ts from cool

c lIm a te s .
The r e s t o f th e seasonal co ld hardiness c y c le In v o lv e d d ehardening.
The fo u r th stage occurred in January and F eb ru ary.

I t was c h a ra c te riz e d

by a loss o f th e a d d itio n a l hardiness gained 1n th e t h ir d s ta g e s , le a v ­
ing th e tre e s w ith n e a rly th e same hardiness as th e y had In e a r ly
December.

The f i f t h

end o f A p r i l .
fifth

stage o ccurred from th e end o f February through th e

I t was a p erio d o f ra p id d ehardening.

The fo u r th and

stages seemed to run to g e th e r f o r cool c lim a te s e e d lo ts , but were

more d i s t i n c t f o r th e warm c lim a te s e e d lo ts .

Presumably th e re 1s a

s ix th stage from la t e sp rin g to e a r ly summer, b u t th e re a re no d ata f o r
t h a t p e rio d .
The stages o f co ld hardiness enumerated above a re s im ila r to
those re p o rte d f o r hardwoods (Tumanov and K ra s a v te v , 1959; Ir v in g and
Lanphear, 1967b) and o th e r c o n ife rs (G lerum , 1 9 7 3 ).
W elser (1 9 7 0 ) has done much work 1n co ld h ard iness on a v a r ie t y
o f s p e c ie s .

Many s tu d ie s conducted by him and h is stu d en ts were c a r r ie d

o u t under c o n tr o lle d c o n d itio n s and enabled them to study th e e n v iro n ­
mental fa c to r s re s p o n s ib le f o r th e seasonal changes.

In a summary

p a p e r, W elser (1 9 7 0 ) p o s tu la te d th a t th e f i r s t stage o f c o ld a c c lim a tio n
1s Induced by sh o rten in g photoperiods from summer to f a l l and 1s

76

c h a ra c te riz e d by r e l a t i v e l y minor Increases in cold h ard in ess.

His

conclusions a re supported by stu d ie s on Japanese yew ( Taxus c u s p id a ta )
(Zehnder and Lanphear, 1966) and D o u g la s -f1 r (van den D rle ss ch e, 1970)
and seem to be a reasonable ex p la n a tio n f o r th e f i r s t stage observed
in ponderosa p in e .
The second stage o f a c c lim a tio n 1s a p p a re n tly induced by fre e z in g
tem peratures (W e lse r, 1970; Howell and W elser, 19 7 0 a ).

In my exp erim en t,

s lig h t fro s ts ( - 2 ° to -3 °C ) In September and e a r ly October had l i t t l e
e f f e c t on th e cold hardiness o f ponderosa p in e .

However, th e re was a

ra p id Increase 1n cold hardiness o f a l l ponderosa pine se ed lo ts fo llo w in g
tem peratures o f -6 ° to -8°C during la t e O ctober, 1976 (arrow No. 3 1n
F ig ure 8 ) .

In c o n tro lle d environment s tu d ie s , van den D rlessche (1969b)

found no In crease 1n hardiness o f seed lin g D o u g la s -f1 r exposed to
tem peratures o f -1 °C , whereas Hmmls and W o rra ll (19 75 ) found th a t
evening fro s ts o f -7°C caused ra p id hardiness Increases 1n D o u g la s -f1 r.
In c o n tra s t, Zehnder and Lanphear (1966) found th a t su b free zin g
tem peratures were no more e f f e c t iv e than 2°C tem peratures f o r Inducing
hardiness Increases 1n Japanese yew.
W elser (1970) speculated th a t a d is t in c t t h ir d stage o f cold
a c c lim a tio n occurrs in hardy woody p la n ts subjected to very low
tem peratures ( -3 0 ° to -5 0 ° C ).

This stage 1s c h a ra c te riz e d by a ra p id

In crease 1n hardiness th a t 1s q u ic k ly lo s t upon re tu rn to m ild temper­
a tu re s .

Such a t h ir d stage appeared to be present In the n o rth ern

seed lo ts o f ponderosa p in e , which became much h a rd ie r In January than
1n December.

Whether o r not 1 t was trig g e re d by extreme co ld weather

Is d e b a ta b le .

In both seasons the c o ld e s t day o f th e w in te r (arrow

Nos. 2 and 4 1n F igure 8 ) seemed to c o in c id e w ith r a th e r than precede
the p erio d o f maximum h ard iness.

77
What tr ig g e r s th e fo u rth s ta g e , the loss o f hardiness which s ta rte d
In January?

Several authors (van den D rlessch e, 1969; Zehnder and

Lanphear, 1966) thought th a t warm w eather 1n m id w in ter was th e e n v iro n ­
mental fa c to r causing the dehardening.

Howell and W elser (1 9 7 0 b ), who

worked w ith tre e s in c o n tro lle d environm ents, found th a t exposure to
warm tem peratures was fo llo w ed by a g re a t decrease in hardiness w ith in
a day.
During th e 1975-76 w in te r , the c o ld e s t day (-2 8 °C ) was January 18,
1976 (arrow N o ..l on F ig ure 8 ) , and the s t a r t o f w eather warmer than
16°C was February 15 , 1976 (arrow No. 2 ) .

During th e next w in t e r , th e

c o ld e s t day (-2 8 °C ) was December 31, 1976 (arrow No. 5 ) .

That was p a rt

o f a very cold s p e ll o f 54 consecutive days in which tem peratures were
below fr e e z in g .

The end o f th a t p erio d o f below fre e z in g w eather

occurred on February 7 , 1977 (arrow No. 6 ) when th e thermometer reached
+6°C.
As a lre a d y n oted, 1 t has been hypothesized t h a t the development o f
maximum hardiness is trig g e re d by very cold w ea th e r, and th a t dehardening
is trig g e re d by a p erio d o f warm w eather 1n m id w in ter.

I f th e f i r s t

hypothesis 1s c o rre c t fo r ponderosa p in e , hardiness remained a t a near
constant le v e l fo llo w in g th e December sam plings, o n ly to in crease
d ra m a tic a lly a f t e r th e very cold days (arrow Nos. 1 and 5 on F ig ure 8 ) .
I f the second hypothesis Is c o r r e c t, the p erio d o f maximum hardiness
la s te d f o r 20 days o r more (from arrow No. 1 to arrow No. 2 and from
arrow No. 5 to arrow No. 6 ) , and then hardiness decreased a f t e r th e
beginning o f warm w eather.
W in te r d ryin g ra te s
W in ter d e s ic c a tio n can occur in evergreen p la n ts when the s o il 1s
fro ze n and p la n ts begin tra n s p ir in g in response to warm tem peratures o r

78
d ry w in d s.

Such damage 1s o fte n thought to be more Im p o rta n t than

In ju r y from low tem peratures and has been a problem on ve ry c o ld
r e s is ta n t species In some areas (S a k a i, 1 9 7 0 ).

To d eterm in e th e

r e l a t i v e Im portance o f d e s ic c a tio n and low tem p eratu re I n j u r y , I
performed th e d e s ic c a tio n experim ent d es crib ed under "M ethods."
There were s i g n i f i c a n t d iffe re n c e s 1n d ry in g ra te s among th e 15
s e ed lo ts sampled on November 2 3 , 1976.

Cut branches o f a l l

s e e d lo ts

o f th e c o a s ta l v a r ie t y lo s t m o istu re more r a p id ly than d id c u t branches
o f any s e e d lo t o f th e i n t e r i o r v a r i e t y .

T h is is shown 1n F ig u re 9 ,

which Inclu d es d ata f o r f i v e s e e d lo ts re p re s e n tin g th e extrem es f o r
each v a r ie t y .

These d iffe re n c e s 1n d ry in g r a t e may be r e la t e d to

d iffe re n c e s between v a r ie t ie s in f o lia g e c o lo r .

Trees from th e c o a s ta l

v a r ie t y (v a r . ponderosa) a re b r ig h t green whereas tre e s from th e I n t e r i o r
v a r ie t y ( v a r . scopulorum) a re g ra y -g re e n .

The c o lo r d iffe r e n c e s a re due

to d iffe re n c e s 1n s tr u c tu r e o f th e e p id e rm is , th e I n t e r i o r tre e s having
a rough ep iderm is which probably a c ts to r e ta r d t r a n s p ir a t io n .
There were a ls o d iffe r e n c e s w ith in th e v a r i e t i e s .

Four s e e d lo ts

from th e n o rth e rn h a l f o f th e i n t e r i o r v a r ie t y (re p re s e n te d by 2164 in
F ig u re 9 ) had slo w er d ry in g ra te s than d id th e fo u r (re p re s e n te d by
2248) from f a r t h e r so u th .

In th e c o a s ta l v a r i e t y , tre e s from C a l i f o r ­

n ia and c o a s ta l Oregon had th e f a s t e s t d ry in g r a te s .
I c a lc u la te d th e c o r r e la tio n between m o istu re co n te n t o f th e fre s h
needles (based on th e d iffe r e n c e between fre s h w e ig h t and o ve n -d ry
w e ig h t) and d ry in g r a t e as measured by th e slo pe o f th e curves In F ig u re
9.

For th e 15 s e e d lo ts , th e c o r r e la tio n was high ( r = 0 . 9 1 ) .

In o th e r

words, tre e s w ith th e h ig h e s t m o istu re co n te n t d rie d out the f a s t e s t .
T h is 1s o p p o s ite to th e r e la tio n s h ip found In D o u g la s -f1 r (DeHayes and

79

FIGURE 9 .

G e n e tic d iffe r e n c e s in w in t e r d ry in g ra te s and f o l i a r
m o is tu re c o n te n t o f ex c is e d tw ig s from f i v e ponderosa
p in e s e e d lo ts c o lle c te d on November 2 8 , 1976.

S e e d lo ts

2 0 3 4 , 2 0 14 , and 2091 a re from th e c o a s ta l v a r i e t y ;
s e e d lo ts 2164 and 2248 a re from th e I n t e r i o r v a r i e t y .

80

IO O

2248

95

SOU. UT
2164 NOR CO

90

X

OF FRESH WEIGHT

574
65

80

75

5813
5R I
2034

OR

70
2014

623

NOR CA

65
2091 COAST OR

626

60

55

50
O

40

80

120
TIME

160
(hours)

200

240

moisture
content

81
W rig h t, 1976) and Norway spruce ( Picea a b le s ) ( S a lte r s d a l, 1 9 6 3 ).
W lln e r (1 9 5 2 ), working w ith tw igs o f d if f e r e n t hardwood s p e c ie s , found
the same r e la tio n s h ip as 1n ponderosa p in e .
Trees from co a stal Oregon had much f a s t e r d ry in g ra te s than tre e s
from n o rth e rn C a lifo r n ia but s u ffe re d much les s w in te r I n ju r y .

Trees

from A rizona and New Mexico had s l i g h t l y slow er d ryin g ra te s than tre e s
from B r it is h Columbia and e a s te rn Oregon, but s u ffe re d more w in te r
in ju r y .

Such comparisons in d ic a te th a t cold w eather has been more

Im portant than d e s ic c a tio n 1n causing w in te r in ju r y to ponderosa p in e .
L ea f phenology
The changes In cold hardiness in the w in te r a re c y c lic phenomena.
Leaf development In the sp rin g is p a rt o f another c y c lic phenomenon.
In o rd er to determ ine whether the two are r e la t e d , I measured e x te n t
o f l e a f development on May 2 0 , 1976, using grades o f 1 (buds s t i l l
w in te r c o n d itio n ) to 10 (le a v e s 2 in lo n g ).

In

These grades correspond

to an approxim ate 14 day d iffe r e n c e 1n the s t a r t o f growth.
The r e s u lt s , summarized 1n Table 6 , show a n o rth to south tre n d .
Trees from the n o rth e rn , c o ld e r regions began growing the e a r l i e s t ,
about 12 to 14 days b efo re tre e s from A riz o n a , New M exico, and
C a lif o r n ia .

In o th e r words, the same n orthern seed lo ts were f i r s t

to become hardened 1n th e f a l l

in p re p a ra tio n fo r w in te r c o ld , f a s t e s t

to deharden in l a t e w in te r , and f i r s t to s t a r t growth In the s p rin g .
Hanover (1 9 6 3 ), re p o rtin g on a ponderosa pin e provenance t e s t 1n
northern Idaho als o re p o rte d th a t southern seed lo ts s ta r te d growth
la te s t.

So d id S te in e r (19 75 ) who re p o rte d on several species In c lu d in g

ponderosa p in e .

However, D o u g la s -flr and black w alnut were e x c e p tio n a l,

southern seed lo ts s t a r t in g growth l a t e s t 1n both sp e cies .

82
TABLE 6 .

R e la tiv e tim e o f bud break o f 16 y e a r o ld ponderosa pine
tre e s from e ig h t ecotypes growing a t Kellogg F o rest 1n
southwestern M ichigan.

V a rie ty
and
Ecotype

Time o f bud
1 - l a t e , 10

v a r. ponderosa
Nor. P lateau

1 0 .0

Coast. OR

5 .2

Nor. CA

2 .9

Sou. CA

1 .0

v a r. scopulorum
Nor. I n t e r i o r

8 .7

Nor. CO-UT

8 .9

Sou. UT-NM

4 .4

AZ-NM

1 .6

83
In o th e r s p e c ie s , such as w h ite spruce ( Picea g la u c a , N ie n s ta e d t
and King, 1 9 7 0 ), balsam f i r
flr

( Abies balsamea, L e s te r, 1970) and Douglas-

(S te in e r and W rig h t, 1 9 7 4 ), d iffe re n c e s In date o f growth I n i t i a t i o n

a re r e la te d to amount o f damage from la t e sp rin g f r o s t s .

G e n e ra lly ,

those seed lo ts which s t a r t growth e a r l i e s t s u ffe r th e most damage.
This r e la tio n s h ip 1s not tru e f o r ponderosa p in e .

Newly expanded

leaves o f th a t s p e c ie s , and most o th e r pines as w e l l , are not damaged
by th e tem peratures o f - 2 ° to -4°C which occur so fre q u e n tly a f t e r the
s t a r t o f th e growing season 1n M ichigan.

Evidence to th is has been

re p o rte d by Sorenson and M ile s (1974) on ponderosa pine and lodgepole
pin e ( P1nus c o n to rta ) 1n c e n tra l Oregon.

Frosts o f -3°C In e a r ly

June damaged f l o r a l s tru c tu re s but not leaves In both sp ecies.

Appar­

e n t ly , ponderosa p ine needles a re a b le to w ith sta n d a few degrees o f
f r o s t a t any stage o f development.
F o lia r m oisture co n ten t
The m o istu re co n ten t o f a l l

30 seed lo ts was measured in September,

1975 and on s ix dates from J u ly , 1976 to January, 1977.

The re s u lts

a re shown in Table 7 .
On each date th e re was a one to fo u r percent d iffe r e n c e between
th e two v a r ie t ie s .

N e a rly a l l seed lo ts o f th e west coast v a r. ponderosa

had a h ig h e r m oisture co n ten t than any seed lo ts o f I n t e r i o r v a r.
scopulorum.
There were als o d iffe re n c e s w ith in th e v a r i e t i e s , the southern
ecotypes o f each being more su ccu lent than th e n o rth ern ones.

On

most dates th e re were two to th re e percent d iffe re n c e s among ecotypes
from the same v a r ie t y .

84
TABLE 7.

Ecotype and seasonal d iffe re n c e s 1n f o l i a r m o istu re c o n ten t
o f ponderosa p in e growing a t K ellogg F o re s t 1n southw estern
M ich ig an .

F o lia r m o istu re c o n ten t on
V a r ie ty

Sep.

J u l.

Aug.

and

20

Nov.

Jan.

28

25

Ecotype

1975

1976

1976

1976

1976

1977

%

%

%

%

%

%

Nor. P la te a u

6 5 .4

7 1 .0

6 2 .5

61 .6

5 7 .9

5 6 .9

Coast. OR

6 8 .6

73.1

6 6 .2

6 4 .8

61 .6

5 7 .2

Nor. CA

6 7 .7

7 3 .0

6 5 .7

6 3 .4

6 0 .8

5 6 .9

Sou. CA

6 8 .2

7 3 .7

6 6 .3

6 4 .3

61.1

5 7 .7

Nor. I n t e r i o r

6 2 .5

6 9 .5

6 1 .2

59.1

5 6 .0

5 5 .8

Nor. CO-UT

6 4 .0

7 0 .4

6 1 .3

5 9 .6

5 6 .9

5 6 .4

Sou. UT-NM

6 5 .8

71 .0

6 2 .3

6 0 .0

5 7 .4

5 6 .6

AZ-NM

6 5 .8

7 2 .4

64.1

6 1 .9

5 8 .5

5 6 .7

.9

.9

.6

7

26

O ct.
7

v a r. ponderosa

v a r. scopulorum

Least S ig n if ic a n t D iffe r e n c e (5% l e v e l )
1 .4

.9

1 .2

85
P h a rls and F e r r e ll

(1 9 6 6 ) found d iffe r e n c e s In f o l i a r m o istu re

c o n te n t o f D o u g la s -flr v a r ie t ie s even g r e a te r than those I found f o r
ponderosa p in e .

In t h e i r w ork, th e west co ast v a r ie t y averaged s ix

p e rc e n t g r e a te r m o istu re c o n te n t than th e I n t e r i o r v a r i e t y .
S everal au th ors have found n o rth to south d iffe re n c e s in l e a f
succulence 1n o th e r c o n ife r s .

Among th e species which have been s tu d ie d

a re Scotch p in e (L a n g le t, 1 9 3 6 ), Norway spruce ( S a lt e r s d a l, 1 9 6 3 ), ja c k
pine ( P1nus banks1a n a, T e lc h , 1968) and D o u g1as-f1r (DeHayes and W rig h t,
1 9 7 6 ).

In c o n tr a s t, McLemore e t a l

(19 61 ) found no geographic p a tte r n

to th e d iffe r e n c e s 1n m o istu re co n te n t o f l o b l o l l y p in e ( Pinus ta e d a ) .
There were a ls o seasonal d iffe r e n c e s 1n f o l i a r m o istu re c o n te n t
(T a b le 7 ) .

In g e n e r a l, m o istu re c o n te n t d e c lin e d from summer to w in t e r .

The most ra p id decrease o ccurred between J u ly and August when r e l a t i v e
m o istu re co n ten ts f o r tre e s o f a l l ecotypes decreased by seven to e ig h t
p e rc e n t.

T h e r e a fte r , r e l a t i v e m o istu re c o n te n t decreased a t a steady

r a te through November.

By November, tre e s from n o rth e rn ecotypes reached

a n ea r co n s ta n t f o l i a r m o istu re c o n te n t, but tre e s o f southern o r ig in
continued to d e c lin e .

In Jan u ary, 1977, th e d iffe re n c e s among ecotypes

were s m a lle r than a t any p reviou s d a te .
S im ila r d e c lin e s 1n r e l a t i v e f o l i a r m o istu re c o n te n t from summer
to w in te r have been shown f o r s e v e ra l hardwood and c o n ife ro u s species
(L a n g le t, 1936; A c k le y , 1954; Kozlowskl and C lausen, 1965; P h a r ls , 1967;
Jameson, 1 9 6 6 ).

In c o n tr a s t, Gary (1 9 7 1 ) could f in d o n ly s lig h t changes

In m o istu re co n te n t o f one y e a r o ld Engelmann spruce ( P1cea en q elm a n n H )
needles from summer to w in t e r .
R e la tio n s h ip between f o l i a r m o istu re co n te n t and h a rd in e s s .

S ig n i­

f i c a n t n e g a tiv e c o r r e la tio n s were found between f o l i a r m o istu re c o n te n t

86
and c r i t i c a l

tem peratures on a l l

sampling dates (T a b le 8 ) .

seedlots w ith th e h ig h e st m o istu re were le a s t hardy to c o ld .
re la tio n s h ip has been re p o rte d by o th e rs .

In g e n e ra l,
A s im ila r

Telch (1 9 6 8 ), working w ith

ja c k p in e , found a strong r e la tio n s h ip between f o l i a r m o istu re co n ten t
and cold In j u r y , th e most succulent seed sources s u ffe re d th e most cold
damage.

M e tc a lf e t a l

(1 9 7 0 ) demonstrated a s im ila r p a tte rn f o r th re e

c u lt lv a r s o f b a rle y ( Hordeum v u lg a re ) and wheat ( T rltic u m aestlvu m ) .
The seasonal r e la tio n s h ip between m oisture co n ten t and cold
hardiness Is I l l u s t r a t e d in F ig u re 10.

As m o istu re co n ten t decreased,

from summer to w in te r , hardiness In c re a s e d .

However, the seasonal

changes 1n m o istu re were not p ro p o rtio n a l to th e seasonal changes 1n
h ard iness.

For exam ple, th e decrease 1n succulence was g re a te s t In

midsummer whereas th e changes 1n hardiness were g re a te s t In th e f a l l .
The p a tte rn o f h ard ln e ss -m o is tu re co n ten t changes 1n ponderosa
pine agrees w ith th a t found by McKenzie e t a l
o s ie r dogwood.

(1974) 1n stems o f re d -

T h e ir s tu d ie s in d ic a te d th a t m o istu re c o n ten t changes

during summer were caused by decreased stom atal re s is ta n c e to tr a n s ­
p ir a tio n and sim ultaneous increased ro o t re s is ta n c e to w a te r u ptake.
They suggested th a t th e s h o rt day Induced stage o f cold a c c lim a tio n
may o p e ra te v ia re g u la tio n o f processes In v o lv ed In p la n t w a te r r e la t io n s .
Furtherm ore, th e I n i t i a l

la rg e d e c lin e 1n tis s u e m oisture co n ten t may

be a p r e r e q u is ite f o r th e subsequent la rg e In creases 1n cold hardiness
th a t occur durin g f a l l and w in te r .
The le v e l o f tis s u e m o istu re c o n ten t has o fte n been Im p lic a te d as a
fa c to r which Is re sp o n s ib le f o r d iffe re n c e s 1n p la n t co ld h a rd in e s s .
In s ta n c e , McKenzie e t a l

(19 74 ) thought th a t a t high m o istu re contents

th e re Is an Increased lik e lih o o d o f I n t r a c e l l u l a r 1ce fo rm atio n and

For

87
TABLE 8 .

Simple c o r r e la tio n s between f o l i a r m oisture co n ten t and
needle c r i t i c a l tem peratures fo r 30 ponderosa p ine seed lo ts
on several dates In 1975 and 1976.

C o rr e la tio n between
M oisture c o n ten t on:

_______

and C r i t i c a l tem perature on:

C o rr e la tio n
c o e f f ic ie n t

Sep. 2 0 , 1975

O ct. 3 0 , 1975

-.6 6 * *

J u l. 7, 1976

Aug. 2 , 1976

-.3 7 *

Aug. 26 , 1976

Sep. 17, 1976

-.7 6 * *

Oct. 7 , 1976

Sep. 17, 1976

-.8 4 * *

O ct. 7 , 1976

Nov. 11, 1976

-.7 9 * *

Nov. 2 8 , 1976

Nov. 11, 1976

-.7 7 * *

Nov. 28 , 1976

Dec. 17, 1976

-.8 9 * *

Jan. 2 5 , 1977

Jan. 1 0 , 1977

-.5 3 * *

*

S ig n if ic a n t a t 5 * le v e l

**

S ig n if ic a n t a t 1 * le v e l

88

FIGURE 10 .

Seasonal changes in f o l i a r m o is tu re c o n te n t and c o ld
h a rd in e s s f o r tr e e s from two ponderosa p in e e c o ty p es
g row ing a t K e llo g g F o re s t in s o u th w e s te rn M ic h ig a n .

MOISTURE CONTENT

WEIGHT)
OF FRESH
(%

MOISTURE

SOU. CA

-20
NOR. INTERIOR

DATE OF OBSERWION

TEMPERATURE

CO

FOLIAR

CRITICAL

CONTENT

COLO HARDINESS

90
c o ld I n j u r y d u rin g a f r o s t because o f th e la r g e amount o f w a te r w it h in
c e lls .

In a summary p a p e r, Burke e t a l

(1 9 7 6 ) su p p o rte d t h is

v ie w p o in t.

They suggested t h a t , a t h ig h m o is tu re c o n te n ts , la r g e q u a n t i t ie s o f
w a te r f r e e z e r a p i d ly and th e r e s u l t in g
tio n .

ic e c r y s t a ls cause t is s u e d is r u p ­

O th ers have s u p p lie d e v id e n c e in s u p p o rt o f a h a rd in e s s -m o 1 s tu re

c o n te n t r e l a t i o n s h i p .
a r tific ia l

B ltte n b e n d e r and How ell

(1 9 7 5 ) d em o n strated t h a t

In c re a s e s in t is s u e h y d ra tio n w ere accompanied by a d ec rea se

In c o ld h a rd in e s s o f flo w e r buds o f hlghbush b lu e b e r r y ( V accln iu m
a u s t r a l e ) . w h ile a d e c re a s e in m o is tu re c o n te n t was r e la t e d to an In c re a s e
1n h a rd in e s s .

In a d d i t i o n , L i and W elser (1 9 6 9 ) and Chen e t a l

(1 9 7 5 )

found t h a t p a r t i a l d e h y d ra tio n and w a te r s tr e s s caused a d e c re a s e in
t is s u e m o is tu re c o n te n t and an In c re a s e in c o ld h a rd in e s s 1n stems o f
re d -o s 1 e r dogwood.
Based on th e e v id e n c e d is c u s s e d , 1 t i s

te m p tin g to co n clu d e t h a t

f o l i a r m o is tu re c o n te n t 1s a key f a c t o r c a u s in g d if f e r e n c e s
h a rd in e s s 1n ponderosa p in e .

1n c o ld

How ever, th e problem is to e x p la in why

tr e e s w it h h ig h m o is tu re c o n te n t a r e th e most s u s c e p tib le to c o ld damage.
T h is 1s a r e l a t i o n s h i p w hich seems t o h o ld fro m summer t o w i n t e r , and
a ls o from n o rth to so u th w it h in th e s p e c ie s .
D iffe r e n c e s 1n o sm o tic c o n c e n tr a tio n due t o th e p resen ce o f sugars
In c e l l

sap can o f f e r p r o t e c t io n a g a in s t f r e e z in g to te m p e ra tu re s a few

degrees below f r e e z i n g .

How ever, th e c o n c e n tr a tio n o f s o lu te s I n a

p la n t s ' sap 1s n e v e r enough to p re v e n t w a te r from f r e e z in g a t th e low
te m p e ra tu re s a c h ie v e d d u rin g a M ic h ig a n w in t e r .
W else r (1 9 7 0 ) s ta t e d t h a t th e fo rm a tio n o f Ic e c r y s t a ls w it h in c e l l s
is th e p rim a ry mechanism o f c o ld damage.

A p p a re n tly I n t e r c e l l u l a r w a te r

can f r e e z e In most h ard y tis s u e s w ith o u t c a u s in g to o much damage.

91

I f W elser 1s c o r r e c t , then 1 t is p o s s ib le th a t th e h ig h e r th e m o istu re
co n ten t 1n g e n e r a l, th e h ig h e r th e m o istu re c o n te n t w it h in c e l l s , and th e
g re a te r th e amount o f w a te r to be fro ze n and cause damage.

CHAPTER 5

THE EFFECTS OF WINTER INJURY ON AGE-AGE
HEIGHT RELATIONSHIPS IN PONDEROSA PINE

INTRODUCTION

Growth r a t e 1s one o f th e most Im p o rtan t c h a r a c te r is t ic s considered
In a f o r e s t tr e e improvement program.

The expression o f growth r a te

o b ta in ed f o r tre e s o f d i f f e r e n t seed sources In fo r e s t g e n e tic s ex p er­
iments 1s a com bination o f In h e re n t growth p o te n tia l and response o f tre e s
to environm ental s tre s s e s such as w in te r c o ld .

T h is ch a p te r e v a lu a te s

th e e f f e c t s o f w in te r In ju r y on age-age h e ig h t re la tio n s h ip s In th e
ponderosa p in e provenance t e s t .
The r e la tio n s h ip between ju v e n ile and l a t e r growth r a te In proven­
ance te s ts o f many species has been good when w in te r In ju r y and diseases
have n o t been problem s.

Nanson (1 9 6 8 ) re p o rte d strong c o r r e la tio n s

between h e ig h t a t ages fo u r to ten and ages 40 to 60 years 1n provenance
te s ts o f Scotch p in e and D o u g la s -flr .

Others have a ls o demonstrated

strong age-age c o r r e la tio n s 1n provenance te s ts o f th e same species
(W rig h t e t a l . 1957; Namkoong e t a l , 1 9 7 2 ).
In ponderosa p in e , age-age c o r r e la tio n s have been re p o rte d by
several In v e s tig a to rs from many d if f e r e n t types o f g e n e tic s tu d ie s .
T h e ir r e s u lts a re summarized 1n T able 9.

In g e n e ra l, c o r r e la tio n s from

provenance te s ts and e le v a tlo n a l zone comparisons were stro n g when w in te r
92

93
In ju r y was not a problem.

For m iddle and low e le v a tio n p la n ta tio n s In

C a lif o r n ia , Conkle (19 73 ) found very strong c o r r e la tio n s between h eig h ts
a t ages 3 and 25.

However, in a high e le v a tio n p la n ta tio n th e age 3 to

25 h e ig h t c o r r e la tio n was low , presumably because o f w in te r In ju r y which
occurred a t age 10.

Kempff (1 9 2 8 ) a t t r ib u t e d changes in h e ig h t ranking

among 21 provenances o f ponderosa p ine to w in te r in ju r y In a n o rth e rn
Idaho provenance t e s t .

94
Stannary o f phenotypic c o r r e la tio n s f o r h e ig h t a t d if f e r e n t
ages In g e n e tic v a r ia tio n stu d ie s o f ponderosa p in e .

Last

C o rre la tio n s between h e ig h t a t la s t measurement

Author^

Measi
1

{Age

2 or 3

5

6 or 7

8

11 o r 12

20

25

Comparisons o f tre e s from seven e le v a tio n zones
25

—

.92

.9 8

.98

—

—

.96

—

Co

25

—

.87

.91

.91

—

.96

.98

—

Co

25

—

.14

.04

.02

—

.45

.98

—

Co

---------

W& P

Comparisons o f 10 to 35 provenances
8

.5 7

.66

.81

---------

—

---------

CQ

42

C
ft. c
J
Q
5

.O T

30

—

.81

.51

.67

—

.56

.7 3

—

s & s

30

—

.4 0

.85

.83

—

.91

.88

—

s & s

30

—

.53

.75

.7 9

—

.90

.91

—

s & s

30

—

.51

.54

.61

—

.75

.89

—

s &s

30

—

.92

.61

.75

—

.90

.87

—

s & s

25

.81

_ —

.84

—

---------

---------

---------

Mo

.85

1 .0 0

N & Co

—

—

W ft P

Comparisons o f 71 to 271 h a l f - s1b fa m ilie s
29

—

.0 5

.19

-.4 7

8

.23

.37

.7 3

---------

15

---------

.30

~ ——

-.6 0
—

—— -

.64
—

C & H

95
Table 9 continued

Comparisons o f 112 to 448 in d iv id u a l tre e s
25

------------

.12

.19

.37

------------

.62

.93

—

Co

25

-----------

.25

.60

.70

------

.84

.94

—

Co

25

------

.41

.60

.68

------

------

.93

—

Co

20

-----

.08

.02

------------

------------

.75

------------

------------

C & D

20

_ _ _

.02

.18

___

_

__

.67

— — —

— •» —

C & D

^ C o = C onkle, 1973

N & Co ■ Namkoong and C onkle, 1976

W & P = Wang and P a te e, 1973

C & H * Callaham and H a s e l, 1961

S & S = S q u ill ace and S i l e r , 1962

C & D 3 Callaham and D u f f le ld , 1962

Mo = Moore, 1944

96

MATERIAL AND METHODS

The ponderosa pine study is p a r t o f a range wide provenance t e s t
I n i t i a t e d in 1960.

Seed from 60 provenances was sown 1n an East Lansing,

Michigan nursery using a fo u r r e p lic a te d randomized complete block
design.

Two years l a t e r , seed lin g s were tra n s fe rre d to two permanent

te s t p la n ta tio n s a t W. K. Kellogg F orest (Augusta, M ichigan) and Fred
Russ Forest (Dowagiac, M ichigan) 1n southern M ichigan.

The p la n ta tio n s

fo llo w a randomized complete block design w ith s ix tr e e p lo ts and a 2 .5
x 2 .5 m spacing.

F u rth e r d e t a ils o f p la n ta tio n design and estab lish m en t

are provided by W right e t a l

(1 9 6 9 ).

H eight measurements were made in the nursery a t ages one and two
and a t va rio u s ages 1n both t e s t p la n ta tio n s up through age 16.

Estim ates

o f w in te r In ju r y to needles were made fo llo w in g th e f i r s t y e a r In the
nursery and a t ages 4 , 6 , and 17 In th e p la n ta tio n s .
Analyses o f varia n c e were performed on a l l nursery and p la n ta tio n
data using p lo t means as Item s .

From th e analyses o f v a ria n c e and

expected means squares from h e ig h t d a ta , varian ce components due to
ecotype and s e e d lo t w ith in ecotype e f f e c ts were c a lc u la te d .

These

components were expressed as a percentage o f th e t o t a l g e n e tic varia n c e
(sum o f ecotype and s e e d lo t w ith in ecotype components).

C o e ffic ie n ts o f

v a r ia tio n were computed f o r each age from the e r r o r mean squares.
Product moment c o rr e la tio n s were c a lc u la te d between s e e d lo t mean h eights
a t age 16 and a l l previous h e ig h t measurements.

97
RESULTS
Changes in r e l a t i v e growth r a te

The g e n e tic v a r ia tio n p a tte rn f o r h e ig h t 1n ponderosa p in e changed
d ra m a tic a lly w ith age (F ig u re 1 1 ).

A fte r the f i r s t growing season, the

la r g e s t tre e s were those grown from seed c o lle c te d 1n C a lif o r n ia and
Arizona-New Mexico.

The s m a lle s t tre e s were those grown from seed

c o lle c te d In the n o rth e rn I n t e r i o r (Montana, South Dakota, Nebraska) and
northern Colorado and U tah.

By age 16, tre e s grown from seed c o lle c te d

In the northern P late au regio n (Oregon, Washington, B r it is h Columbia)
and northern I n t e r i o r were fa s te s t grow ing, Arizona-New Mexico tre e s
were below average, and C a lif o r n ia tre e s were s m a lle s t.
The g re a te s t changes in r e l a t i v e h e ig h t growth occurred during
the f i r s t f iv e years o f growth (T ab le 1 0 ).

C o rre la tio n s between h e ig h t

a t age 16 and a t ages 1 and 2 were n e g ative o r near zero f o r both p la n ta ­
tio n s .

A f t e r p la n ta tio n e s ta b lis h m e n t, c o rr e la tio n s Increased somewhat

but were s t i l l

g e n e ra lly le s s than ju v e n ile -m a tu re c o r r e la tio n s rep o rted

1n o th e r ponderosa p ine provenance te s ts (T ab le 9 ) .
The poor c o r r e la tio n s were brought about by a sharp d e c lin e 1n
growth f o r th e C a lifo r n ia tre e s which was accompanied by a steady In crease
In r e l a t i v e growth o f n orthern P late au and n orthern i n t e r i o r tr e e s .

By

age s ix , the rankings among seed lots had s t a b iliz e d and remained constant
through age 16.
The changing p a tte rn o f growth w ith age was caused by w in te r In ju r y
which occurred 1n th e n ursery and a t vario u s ages 1n both p la n ta tio n s
(F ig u re 6 ) .

During the f i r s t w in te r 1n the n u rs e ry , tre e s from C a lif o r n ia

and co astal Oregon o rig in s s u ffe re d s e v e re ly .

Arizona-New Mexico and

98

FIGURE 1 1 .

Change in r e l a t i v e

h e ig h t (e x p re s s e d as a p e rc e n ta g e o f

p la n t a t io n o r n u rs e ry means) w ith age f o r tr e e s from fo u
ponderosa p in e e c o ty p e s .

I50r
140
130

120s
110-

A Z -N M

100

s,

SOU CA

13
(YEARS)

15

17

100
TABLE 10.

Age-Age c o r r e la tio n s f o r h e ig h t among 55 provenances o f
ponderosa pine a t two t e s t p la n ta tio n s 1n southern M ichigan.

P la n ta tio n
S ite

C o rre la tio n between h e ig h t a t age 16 and a t age
1

2

4

5

6

7

8

9

10

Kellogg

-.3 1

.0 8

.56

.57

.73

.78

.85

.91

Russ

- .0 7

.07

.49

---

—

.65

---

—

13

.93
—

.97

101
northern P la te a u tre e s s u ffe r e d moderate damage.
o rig in s s u ffe re d l i t t l e

o r none.

Trees from a l l o th e r

The e f f e c t s o f c o ld on C a lif o r n ia

tre e s were so severe t h a t th ey could no lo n g e r m a in ta in t h e i r ra p id
growth r a te a f t e r age one.

Arizona-New Mexico tre e s recovered s u f f i c ­

i e n t l y to c o n tin u e t h e i r ra p id growth r a t e through age fo u r .

However,

repeated in ju r y 1n subsequent y e a rs in th e t e s t p la n ta tio n s re s u lte d 1n
a gradual d e c lin e 1n growth r a t e .

N orthern P la te a u tre e s s u ffe re d l i t t l e

1n th e f i e l d and became th e f a s t e s t growing tre e s in both p la n ta t io n s .
Northern i n t e r i o r tr e e s emerged as r e l a t i v e l y ra p id growers a f t e r f i e l d
p la n tin g p r im a r ily because o f t h e i r high degree o f c o ld r e s is ta n c e .
Among the I n j u r y - f r e e n o rth e rn s e e d lo ts , h e ig h t ranking s were
c o n s is te n t from y e a r to y e a r .
one were t a l l e s t t h e r e a f t e r .

The s e e d lo ts which were t a l l e s t a t age
However, among th e h e a v ily damaged C a l i f o r ­

n ia and A rizona-N ew Mexico s e e d lo ts , ran kin g v a rie d g r e a t ly w ith age.
W ith in th e southern C a lif o r n ia e c o ty p e , th e th re e t a l l e s t s e e d lo ts a t
age one, were n ear average a t age tw o , and among th e s h o rte s t a t age 16.
Thus 1n th e absence o f w in te r I n j u r y , age-age c o r r e la tio n s 1n
ponderosa p in e a re expected to be h ig h .
Changes 1n v a ria n c e components due to ecotype
and s e e d lo t w ith in ecotype
W ells (1 9 6 4 ) d es crib ed e ig h t geographic ecotypes o f ponderosa p in e ,
basing h is d e s c rip tio n s on n u rse ry measurements.

W rig h t e t a l

and Kung and W rig h t (1 9 7 2 ) fo llo w e d th e same c l a s s i f i c a t i o n .

(1 9 6 9 )
I d id ,

to o , because W e lls ' o r ig in a l grouping o f s e e d lo ts In t o ecotypes was as
v a lid a t age 16 as a t age 3 .
N orthern ecotypes m a in ta in ed th e same growth r a te s as 1n e a r ly years
whereas southern ecotypes s u ffe re d rep eated w in te r In ju r y and severe

102
reductions 1n growth r a t e .

They were s h o rte s t a t age 16.

range 1n ecotype means has Increased (T a b le 1 1 ).

Thus, the

This in c re as e caused

an Increase 1n the p ro p o rtio n o f the t o t a l g e n e tic v a ria n c e due to
between-ecotype d iffe re n c e s

(T ab le 1 1 ).

At age f o u r , those d iffe re n c e s

accounted f o r 67% o f th e t o t a l g e n e tic v a ria n c e .

That r a t io Increased

to 76% by age e ig h t and remained n e a rly co n stant t h e r e a f t e r .
Changes 1n e r r o r varia n c e w ith age
One might expect th a t repeated w in te r in ju r y would cause an
Increase In e r r o r v a ria n c e and, th u s , a l t e r experim ental p re c is io n .

To

in v e s tig a te t h is r e la t io n s h ip , I computed c o e ff ic ie n t s o f v a r ia tio n f o r
height measurements made a t a l l ages.

These are given 1n T able 12.

The c o e ff ic ie n ts decreased from age one to two in the n ursery d e s p ite
severe In ju r y th e f i r s t w in te r .

A p p a re n tly , th e w in te r In ju r y s u ffe re d

on th e nursery was so uniform w ith in seed lo ts as to c o u n te ra ct any
Increased v a r i a b i l i t y 1n growth ra te from age one to age two.
C o e ffic ie n ts o f v a r ia tio n 1n th e t e s t p la n ta tio n s seemed to change
1n r e la t io n to average growth r a te r a th e r than w in te r in ju r y .

A fte r

f i e l d p la n tin g , tre e s grew r e l a t i v e l y slo w ly f o r th e next two years
(Table 12) and c o e ffic ie n ts o f v a r ia tio n Increased s h a rp ly .

Trans­

p la n tin g shock undoubtedly c o n trib u te d to slow and e r r a t i c growth.
These e f f e c t s lessened by age f i v e a t Kellogg F orest but not u n t il
a f t e r age seven a t Russ F o re s t.

T h e r e a fte r , the v a r ia tio n c o e ff ic ie n t s

d eclin ed g ra d u a lly as average growth r a te In c re a s e d , s im ila r to th e
fin d in g o f Namkoong and Conkle (1 9 7 6 ).

W in ter In ju r y d id not seem to

e f f e c t e r r o r variances In th e t e s t p la n ta tio n s .
H eight d iffe re n c e s among seed lo ts were la r g e r a t Kellogg F orest
than a t Russ F orest as In d ic a te d by th e h ig h e r F values (T a b le 1 2 ).

103
TABLE 11.

V a ria tio n w ith age in range o f ecotype means and p ro p o rtio n
o f t o t a l g e n e tic va ria n c e due to ecotype and s e e d lo t w ith in
ecotype.

Age

Range In
Ecotype
Means

P ro p o rtio n o f t o t a l
g e n e tic varian ce due to
_________________________
Ecotype

S eedlot
w ith in
____________________________________________________________ ecotype
years

%

*

%

4

35

67

33

5

40

70

30

7

—

73

27

8

50

76

24

9

49

76

24

16

52

75

25

TABLE 12.

Changes 1n the c o e ffic ie n t o f variation (C .V .), F value among seedlots, and plantation mean height
with age 1n the nursery and two permanent tes t plantations.

Pertinent
Site

Statistics

Nursery

C .V . (X)

7

8

9

10

13

16

—

—

—

— -

---

—

1

2

15.9

12.3

—

16

—

—

19.3

17.1

16.5

17.7

15.3

13.7

—

14.5

9 .6

11.4

8 .9

9,0

10.5

10.7

—

9 .5

4

5

C
r uv aa il Uita
c

Russ

5

C .V.

—

{ %)

Aw

—

F value

—

Mean Ht. (cm)

—

—

28

C.V.

—

—

18.2

—

19.6

—

—

4.4

—

4.3

( %)

F value
Mean Ht. (cm)

. . .

38

50

107

88

131

r

—

177

222

—

—

490

—

—

—

14.9

14.4

-- -

—

—

5.8

5.5

------

. . .

. . .

397

520

104

Kellogg

Mean Ht. (cm)

105
This was t r u e even though e r r o r v a ria n c e s were th e same.

The la r g e r

d iffe re n c e s a t K ellogg F o re s t a re p ro b ab ly r e la te d to th e more severe w in te r
In ju r y a t th a t s i t e which tended to maximize g e n e tic d iffe r e n c e s 1n
h e ig h t.

W in te r In ju r y was e v id e n t a f t e r many w in te rs a t K ellogg F o re s t,

but o n ly a f t e r th e fo u r th and seven teen th growing seasons a t Russ F o re s t.

CHAPTER 6

IMPROVED PONDEROSA PINE FOR MICHIGAN

INTRODUCTION

Those f a m i l i a r w ith th e w e s te rn

U n ite d S t a t e s , q u ic k ly d e v e lo p

a p p r e c ia t io n f o r th e s iz e and b e a u ty o f ponderosa p in e .
n a tu r a lly

in e v e ry s t a t e

and M e x ic o .

T h is i s th e

1n A r iz o n a .

I t grows

w est o f th e p la in s and a ls o 1n p a rts o f Canada
mostw id e ly d is t r i b u t e d s p e c ie s o f p in e 1n

N o rth A m e ric a , found fro m n e a r sea le v e l
1 0 ,0 0 0 f t

an

Its

ta ll

1n th e P a c i f i c N o rth w est to

s t r a i g h t b o le s , orange p la t y back and

r ic h y e llo w -g r e e n f o l i a g e fram e many o f th e g ra n d e s t view s a s s o c ia te d
w ith th e rugged w e s te rn t e r r a i n .
In a d d it io n to i t s
tim b e r t r e e .

W ith in i t s

a e s t h e t ic v a lu e , ponderosa p in e 1s a v a lu a b le
n a tu r a l ra n g e ,

p o n d e ro s a

p in e fu rn is h e s more

tim b e r th an any o t h e r p in e and 1s th e m a in s ta y o f th e economy f o r many
a re a s .
Ponderosa p in e grows r a p i d l y , a c h ie v e s la r g e s iz e
a d a p ta b le .

T ree s o v e r 200 f t t a l l

Nevada M o un tains a r e n o t uncommon.
a ttra c te d
S ta te s .

and 8 f t

and 1s v e ry

In d ia m e te r in th e S ie r r a

F o r th e s e re a s o n s , th e s p e c ie s has

i n t e r e s t from f o r e s t e r s 1n th e c e n tr a l and e a s te r n U n ite d
I t has been used comnonly as a s h e l t e r b e l t t r e e 1n th e G re a t

P la in s , as an o rn am en tal f a r t h e r e a s t , and Is b e in g te s te d f o r use 1n
106

107
s t r ip mine reclam atio n In Pennsylvania (D avidson, 1 9 7 7 ).

Ponderosa

pine als o appears to have p o te n tia l as a tim b er tr e e In th e E a st.

For

example, a 29 y e a r -o ld stand 1n East Lansing, Michigan has outgrown
n a tiv e hard pines p la n te d near 1 t and averaged 45 f t t a l l and 8 .5 In
In d ia m e ter.
Ponderosa pine Is an ex tre m e ly v a r ia b le species g e n e t ic a lly .
grown from seed c o lle c te d 1n some areas grow
seed c o lle c te d o th e r p la c e s .

Trees

th re e tim es as f a s t as

Some seed sources s u f fe r severe damage

from w in te r c o ld , o th e rs are hardy to even th e most extreme c o ld .

A ls o ,

tre e s from some areas have long n eed les, w h ile o th ers have r e l a t i v e l y
sh o rt needles s im ila r to those found on A u s tria n p ine ( Pinus n ig r a ) .
Thus, th e success and value o f ponderosa p ine p la n ta tio n s In th e e a s te rn
United S ta te s depends as much on choosing th e proper seed source as on
s it e s e le c tio n and c u ltu r a l p r a c tic e s .

Work rep o rted 1n t h is ch a p te r

was undertaken to p ro vide M ichigan nurserymen w ith p r a c tic a l In fo rm a tio n
on th e best seed sources to use f o r tim b e r and ornamental p la n tin g s .

108
MATERIAL AND METHODS

In 1959, D r. 0 . 0 . W ells (p re s e n tly w ith the USFS, Southern Exper­
iment S ta tio n ) re ce ived seed c o lle c te d from 60 n a tu ra l stands o f ponder­
osa pine lo c ate d throughout I t s

n a tu ra l range.

Each stand was represented

by a bulked seed c o lle c tio n from several average tre e s which w i l l h ere­
a f t e r be re fe r re d to as a s e e d lo t.

In fo rm a tio n concerning l o c a l i t y o f

o r ig in as w e ll as c lim a tic data from p a re n ta l stands accompanied each
s e e d lo t.

C o lle c tio n

was accomplished through th e cou rtesy o f R. Z.

Callaham o f the U. S. F orest S e rv ic e .
In May, 1960, the seed was sown 1n Michigan S ta te U n iv e r s ity 's
experim ental nursery 1n East Lansing.

The tre e s were tra n s fe r re d as

2 -0 stock to two r e p lic a te d p la n ta tio n s 1n 1962.
The two p la n ta tio n s a re lo c a te d 60 m iles a p a rt 1n southwestern
M ichigan.

The W. K. K ellogg F o res t p la n ta tio n Is lo c a te d 1n Kalamazoo

county and contains 57 seed lo ts and 7 r e p lic a t io n s .

The Fred Russ

Forest p la n ta tio n 1s lo c a te d In Cass County and co n tain s 55 seed lo ts
and 5 r e p lic a t io n s .
s ix tr e e p lo ts .

The tre e s were p la n te d in a 8 * 8 f t spacing 1n

Weed c o n tro l consisted o f a p p lic a tio n s o f slmazene and

a m ln o trla z o le f o r th re e years a t the Kellogg p la n ta tio n and one y e a r
a t the Russ p la n ta tio n .
Measurements were made a t age one In the nursery and have continued
through age 17.

H eight has been measured a t fre q u e n t i n t e r v a ls , as

has m o r t a lity and In ju r y from w in te r c o ld .

O ther t r a i t s measured one o r

more tim es In c lu d e bole fo rm ,d is e a s e damage, tim e o f bud b u r s t, f o l i a r
n u tr ie n t c o n te n t, d ia m e te r, amount o f f o r k in g , f o l i a r m oisture c o n te n t,
and s u s c e p t ib ilit y to damage from a r t i f i c i a l

fr e e z in g .

Many o f the

109
measurements made through age two and age e ig h t have been re p o rte d on
p re v io u s ly by W ells (19 64 ) and W right e t a l

(1 9 6 9 ).

Each s e t o f measurement data was sub jected to a n a ly s is o f v a ria n c e ,
using p lo t means as Item s.

A ls o , sim ple c o rr e la tio n s were c a lc u la te d

f o r some t r a i t s , using s e e d lo t means as Item s.

110
THE VARIETIES AND ECOTYPES

For convenience, I used th e s u b d iv is io n o f ponderosa p in e In t o
v a r ie t ie s and ecotypes as d e lin e a te d by W ells (1 9 6 4 ).
W ells recognized two v a r i e t i e s , as d escrib ed p re v io u s ly by taxo n o m ists.
They a re west co ast v a r. ponderosa and I n t e r i o r var. scopulorum .

The west

coast v a r ie ty In c lu d es th e ponderosa p ine from w estern Montana, Id a h o ,
Washington, Oregon, and C a li f o r n ia .

The i n t e r i o r v a r ie ty In c lu d e s

ponderosa p in e from th e Rocky Mountain a re a .
The s e p a ra tio n o f ponderosa p in e in to two v a r ie t ie s has a b io lo ­
g ic a l fo u n d a tio n .

The two d i f f e r 1n s e v e ra l resp ects and In some t r a i t s

th e re 1s no o v e rla p p in g .

The c h ie f ways In which th e y d i f f e r a re summar­

ized 1n th e fo llo w in g 1 1 s t.
As compared w ith th e I n t e r i o r v a r i e t y ,

th e West co a st v a r ie t y has:

G reener and lo n g e r needles
E re c t cone p r ic k le s
Browner and more lo o s e ly appressed bud s c ale s
H igher f o l i a r c o n c e n tra tio n s o f N, K, P , Ca, and B
A more c y lin d r ic a l stem form
H ig h er f o l i a r m o istu re co n te n t
G re a te r p a l a t a b m t y to Jack r a b b its 1n Nebraska.
W ells subdivided th e v a r ie t ie s In to ecotypes o r ra c e s , based m a in ly
on growth t r a i t s

such as growth r a t e and w in te r h a rd in e s s .

h is ecotypes in such a manner t h a t d iffe r e n c e s among
compared to those w ith in ec o ty p es , a t le a s t

1n

He d e lin e a te d

ecotypes were la rg e

most t r a i t s .

I use h is

c la s s if ic a t io n p a r t ly as a m a tte r o f convenience, because 1 t 1s much
e a s ie r to understand ta b le s g iv in g the means f o r e ig h t ecotypes than f o r
a l l 60 s e e d lo ts Inclu d ed 1n th e exp erim en t.

Ill
RESULTS
M o r t a lit y

M o r t a lit y by th e end o f th e 1975 growing season was 43% and 40%
f o r K ello gg and Russ F orests r e s p e c t iv e ly .

M o r t a lit y ra te s were low

(13%) f o r the N orthern P la te a u ecotype and moderate o r high f o r th e
o th e rs (T a b le 1 3 ).

Although th e cu m u lative m o r t a lit y in th e two

p la n ta tio n s was s im ila r a t age 16 , th e r a t e a t which m o r t a lit y o ccurred
was d i f f e r e n t .

At Russ F o res t n e a rly a l l deaths o ccurred d u rin g th e

f i r s t two growing seasons.

At K ellogg F o r e s t, where i n i t i a l m o r t a lit y

was r e l a t i v e l y lo w , death o f tr e e s has co ntinued every y e a r s in c e age
f o u r , e s p e c ia lly f o r tre e s o f C a lif o r n ia and Arizona-New Mexico o r ig in s .
This continued m o r t a lit y a t K ellogg F o res t 1s p ro bably due to repeated
w in te r In ju r y a t th a t p la n t a t io n .
Growth r a t e
H e ig h t.

H eight d ata f o r th e K ello gg and Russ F o re s t p la n ta tio n s

were averaged and a re presented 1n T ab le 14.

At age 1 6 , average h e ig h ts

were 16 and 17 f t a t th e K ellogg and Russ F o res t p la n t a t io n s , r e s p e c t iv e ly .
In both p la n ta t io n s , tre e s grown from seed c o lle c te d 1n th e N o rth ern
P la te a u (O regon, W ashington, B r it i s h Colum bia) grew f a s t e s t (T a b le 1 4 ).
They averaged 22 f t t a l l a t both p la n ta tio n s a t age 16 .

Trees grown

from seed c o lle c te d 1n th e N orthern I n t e r i o r (c e n tr a l M ontana, South
D akota, Nebraska) and c o a s ta l Oregon were a ls o above average a t both
p la n ta tio n s .

N orthern I n t e r i o r tre e s averaged 19 f t and 18 f t , whereas

c o a stal Oregon tre e s averaged 17 f t and 21 f t a t K ellogg and Russ F orests
r e s p e c tiv e ly .

Slow est growing tre e s were grown from seed c o lle c te d 1n

southern C a li f o r n ia , th ey averaged 13 f t and 15 f t

In th e two p la n ta tio n s .

112
TABLE 13.

M o r t a lit y and m o r ta lity Increm ents o f 16 y e a r -o ld ponderosa
p ine ecotypes growing a t Kellogg and Russ F orests 1n
southwestern M ichigan.

V a rie ty

Kellogg Forest

and

M o r t a lIt y

Ecotype

(1975)
%

Russ F orest

M o r t a lit y
Increm ent—^
%

M o r t a lit y
(1 9 7 5 )
%

M o r t a lit y
In c re m e n t^
i

v a r. ponderosa
Nor. P lateau

14

6

12

0

Coast. OR

58

9

67

0

Nor. CA

49

28

42

0

Sou. CA

68

37

44

8

Nor. I n t e r i o r

40

11

45

0

Nor. CO-UT

32

10

34

2

Sou. UT-NM

39

17

36

3

AZ-NM

45

19

43

5

Mean

43

17

40

2

v a r. scopulorum

^ M o r t a l i t y Increm ent Is expressed as % m o r ta lity 1n 1975 minus %
m o r t a lit y 1n 1964.

113
TABLE 14.

Growth r a te and bole form o f ponderosa p ine ecotypes.

V a rie ty

R e la tiv e h e ig h t a t

R e la tiv e

R a t lo ^

and

age

diam eter

M ld-dlam .

age 16

basal d1am.

Ecotype

4

2
-

16

- % o f experim ent mean - - -

v a r. ponderosa
Nor. P lateau

96

113

130

128

.62

Coast. OR

67

86

113

124

.64

Nor. CA

104

88

98

98

.65

Sou. CA

90

85

83

86

.65

Nor. I n t e r i o r

96

111

110

99

.54

Nor. CO-UT

81

83

91

86

.59

Sou. UT-NM

106

104

100

103

.5 5

AZ-NM

148

114

99

101

.56

16

34

505

v a r. scopulorum

Average (cm)

^ D a t a from LaFarge, 1971

1 6 .2

114
R e la tiv e growth ra te s have changed w ith tim e (T a b le 1 4 ).

The

re sp o n sib le fa c to r has probably been d i f f e r e n t i a l w in te r In j u r y .
Southern C a lif o r n ia tre e s were t a l l e s t a t th e end o f th e f i r s t growing
season but s u ffe re d so much from cold th e f i r s t w in te r as to become
among th e s h o rte s t by age two.
ra te w ith age.

They continued to d e c lin e in growth

Trees from A rizona and New Mexico s u ffe re d s lig h t

w in te r in ju r y 1n the nursery and more severe w in te r In ju r y 1n l a t e r
y e a rs .

Thus, although recommended f o r p la n tin g 1n M ichigan a t age

tw o, they were no lo n g e r among th e lea d e rs a t age 16.

N orthern P lateau

and Northern I n t e r i o r se ed lo ts emerged as r e l a t i v e l y ra p id growers 1n
the p la n ta tio n s p r im a r ily because o f t h e i r high degree o f co ld h ard in e ss .
D iam ete r.

The d ata on d iam eter (measured 1 f t above ground) a t age

16 a re summarized 1n Table 14.

In g e n e ra l, d ia m e ter d if f e r e d among

ecotypes 1n much th e same way as h e ig h t.

Fast growing N orthern P lateau

tre e s had th e la r g e s t diam eters (8 .6 1n and 8 .0 In th e two p la n t a t io n s ) ,
and slow growing southern C a lif o r n ia and n orthern C olorado-U tah tre e s
had th e s m a lle s t d ia m e te rs .

Trees from th e Northern I n t e r i o r ecotype

were an excep tio n to t h is g e n e r a lit y .

Although among the t a l l e s t tre e s

1n both p la n ta tio n s , th ey were below average 1n d ia m e te r.

Thus, N orthern

I n t e r i o r tre e s produce a le s s e r volume o f wood than N orthern P lateau
and Coastal Oregon tre e s o f th e same h e ig h t.
Stem ta p e r
LaFarge (19 71 ) measured stem form In th e Kellogg F o rest p la n ta tio n
as th e r a t io o f m id -d iam ete r to basal d ia m e te r.

He found la rg e d iffe re n c e s

between v a r ie t ie s 1n stem ta p e r , but no d iffe re n c e s w ith in v a r ie t ie s
(T ab le 1 4 ).

Trees from the w estern v a r ie ty were most n e a rly c y l i n d r i c a l .

This strong v a r ie t y d iffe r e n c e was e v id e n t d e s p ite c o n s id e ra b le v a r ia tio n

115
In h e ig h t and d iam eter growth w ith in each v a r ie t y .

Thus, f a s t growing

seed lots from th e Northern P lateau had th e same ta p e r as slow growing
tre e s from southern C a lif o r n ia .
Fast growing tre e s w ith a high ta p e r r a t io a re l i k e l y to produce
more wood than e q u a lly f a s t growing tre e s w ith low ta p e r r a t io s .

Trees

producing the g re a te s t volume o f wood 1n th is study a re those grown from
seed c o lle c te d 1n th e Northern P la te a u .
W in ter in ju r y
W in ter In ju r y was f i r s t noted a t age one in the nursery and has
continued to be e v id e n t 1n many years sin ce p la n ta tio n e s ta b lis h m e n t.
In ju r y appears as needle d is c o lo r a tio n d urin g w in te r and u lt im a t e ly ,
as needle browning by s p rin g .

L i t t l e damage has occurred to buds o r

cambium and few tre e s have been k i l l e d Im m e d ia tely, but many succumbed
a f t e r repeated needle damage.
W in ter In ju r y es tim ates 1n th e nursery and p la n ta tio n s are summarized
1n F igure 6.

In the w estern v a r ie t y , Northern P lateau tre e s have been

damaged s l i g h t l y , co astal Oregon tre e s have s u ffe re d moderate damage and
C a lif o r n ia tre e s have s u ffe re d s e v e re ly .

In th e I n t e r i o r v a r i e t y , tre e s

from C olorado, Utah and northward have s u ffe re d no damage, whereas tre e s
from A rizona and New Mexico s u ffe re d moderate damage.
In o rd e r to le a rn more about th e cause o f w in te r In ju r y 1n ponderosa
p in e , c o n tro lle d la b o ra to ry fre e z in g stu d ie s were perform ed.

Needles

were su b jected to fre e z in g tem peratures a t va rio u s tim es o f y e a r and
damage was measured by e l e c t r i c a l c o n d u c tiv ity t e s t s .
summarized 1n T ab le 15.

The r e s u lts a re

In J u ly , a l l tre e s were e q u a lly h ard y, t h e i r

needles s u ffe r in g damage a t -5 .5 ° C .

Subsequently, however, tre e s from

northern regions acclim ated to cold f a s t e r than those from southern

116

TABLE 15.

Seasonal d iffe re n c e s In cold hardiness o f needles among
ponderosa p ine ecotypes.

V a rie ty
and
Ecotype

Temperature (°C ) a t which needle damage occurred on
9 /1 7 /7 6

1 0 /2 8 /7 6

1 2 /1 7 /7 6

1 /1 0 /7 7 _______

v a r. ponderosa
Nor. P lateau

-7 .9

-1 9 .2

-3 1 .1

- 3 8 .9

Coast. OR

- 6 .7

-1 4 .7

-2 7 .1

-3 0 .9

Nor. CA

- 6 .7

-

12.6

-2 0 .9

-2 4 .1

Sou. CA

-6 .7

-

1 2 .0

-1 9 .8

-

■10.7

■

2 2 .0

-3 9 .0

-4 6 .6

Nor. CO-UT

-9 .1

■

2 1 .2

-3 4 .9

-4 1 .6

Sou. UT-NM

-

-

20.0

-3 1 .4

-3 5 .0

AZ-NM

- 7 .2

■17.0

-3 0 .2

-31 .7

22.2

v a r. scopulorum
Nor. I n t e r i o r

8.0

117
regions and achieved a g re a te r degree o f hardiness by m id w in te r.

Trees

from a l l eco typ es, except n orthern and southern C a lif o r n ia , seemed to
achieve s u f f ic ie n t m id w in ter hardiness to t o le r a t e th e minimum tem per­
atu res recorded a t Kellogg and Russ F o re s ts .

However, due to a slow

ra te o f cold a c c lim a tio n , tre e s from A rizona and New Mexico are s u s c e p tib le
to cold In ju r y 1n years when low tem peratures occur in l a t e November o r
e a r ly December.

That happened on December 3 , 1976, when the tem peratures

dropped to -26°C a t Kellogg F o re s t.

F ie ld observations made on December

17, 1976, revealed severe damage on C a lif o r n ia tre e s and moderate damage
on co astal Oregon and Arizona-New Mexico tr e e s .
escaped w in te r In ju r y .

Trees from o th e r regions

During th e w in te r o f 1975-76 th e low est tem perature

recorded was -27°C in mid January.

By t h is tim e , c o a stal Oregon and

Arizona-New Mexico tre e s had achieved s u f f ic ie n t hardiness to t o le r a t e
such tem peratures and o n ly C a lifo r n ia tre e s s u ffe re d damage.

Thus,

tim in g o f co ld appears to be an Im p ortan t fa c to r c o n tr o llin g p la n t
s u s c e p t ib ilit y to low tem perature In ju r y .
Disease damage
Twig d le b a ck , caused by a com bination o f two fungal d is e a s e s , was
no ticed a t th e Kellogg Forest p la n ta tio n durin g sunmer, 1975.

D r. John

H art ( f o r e s t p a th o lo g is t o f Michigan S ta te U n iv e r s ity ) thought th a t the
resp o n sib le fungi were D lp lo d ia pinea and Cenanglum ferruginosum .
causes dieback o f the c u rre n t season's growth o f hard p in e s .
fre q u e n tly serio u s on A u s tria n p in e , but caused l i t t l e
ponderosa p in e .

D ip lo d ia

I t is

damage to the

Cenanglum. also c a lle d "pruning d is e a s e ", c h a r a c te r is ­

t i c a l l y s ta r ts on low er branches and g ra d u a lly progresses upward.

I t is

o fte n considered to be a secondary pathogen which causes most damage to
tre e s which have been p h y s io lo g ic a lly weakened by adverse w eather

118
c o n d itio n s .

The fungus has been asso ciated w ith e x te n s iv e fla g g in g

In ju r y on ponderosa pine In the southwest (McKenzie e t a l , 1948) and
w ith crown dleback on A u s tria n pine a t Kellogg Forest (W heeler e t a l .
19 76 ).

I t has not been a problem on e it h e r A u s tria n o r ponderosa pine

a t Russ F o re s t.
I t proved d i f f i c u l t to sep arate w in te r in ju r y from disease damage,
and even

more d i f f i c u l t to recognize damage from th e two fu n g i.

Thus,

damage estim ates made 1n 1977 were f o r both diseases combined.
In g e n e ra l, disease damage was p ro p o rtio n a l to the amount o f w in te r
in ju r y .

Northern tre e s s u ffe re d much les s (8 to 12% o f tw igs damaged)

than the

nonhardy types from C a lif o r n ia , A rizona and New Mexico (28 to

30% o f tw igs damaged).
Although th e diseases seemed to cause o n ly secondary damage 1n
the provenance t e s t p la n ta tio n , th e re was als o minor disease damage
e v id e n t 1n o ld e r p la n ta tio n s o f ponderosa pine a t Kellogg F o re s t.

These

p la n ta tio n s are 39 years o ld and co n tain tre e s th a t are b e lie v e d to be
o f n o rth ern o r ig in .

There has been no v is ib le w in te r In ju r y 1n these

p la n ta tio n s , y e t a few tre e s have s u ffe re d serio us damage and were k i l l e d
from what appears to be Cenanglum.
Stem s tra ig h tn e s s
Ponderosa pine has th e In h e re n t c a p a c ity to grow s t r a ig h t .

Crooks

and fo rks w i l l d evelop , however, 1 f the te rm in a l bud o r le a d e r 1s damaged
o r suppressed.

I f such damage o ccu rs, the le a d in g shoot Is re p la ce d by

la t e r a l branches and crooks o r fo rk s develop p a rt way up the stem.
Depending on the s e v e r ity o f th e damage, crooks may e it h e r be overgrown
w ith in a few years o r may p e r s is t r e s u ltin g 1n a perm anently malformed
tr e e which Is useless from th e tim b er s ta n d p o in t.

119
Stem fo rk in g Mas Induced by some unknown agent between th e e le v e n th
and fo u rte e n th growing season a t both ponderosa p in e p la n t a t io n s .
counted th e number o f tre e s w ith fo rk s a t age 17 .

I

A t t h a t t im e , 36% and

14% o f th e tr e e s were fo rk e d a t K ello gg and Russ F o re s ts , r e s p e c t iv e ly .
The geographic p a tte r n in s u s c e p t i b i l it y to fo r k in g was s i m il a r
f o r both p la n ta tio n s (T a b le 1 6 ).

Trees w ith th e h ig h e s t p ro p e n s ity

to fo rk in g were grown from seed c o lle c te d 1n A rizo n a and New M exico ,
N o rth ern I n t e r i o r and c o a s ta l Oregon.

In th e K ello gg and Russ F o re s t

p la n t a t io n s , 69% and 30% o f th e A rizo n a and New Mexico tr e e s had f o r k s .
A rizo n a and New Mexico tr e e s n o t o n ly had th e h ig h e s t p erc en tag e o f
f o r k s , b u t a ls o th e most severe fo rk s (F ig u re 1 2 ) .
w i l l be perm anently m alform ed.

Most o f th ese tr e e s

F ast growing N o rth ern P la te a u tr e e s and

tr e e s from southern Utah p aren tag e were In te rm e d ia te 1n f o r k in g .

The

s h o rte s t t r e e s , from C a l i f o r n i a , n o rth e rn Colorado and U ta h , had th e
few e st number o f fo r k s .
G e n e r a lly , tre e s above average In h e ig h t a t th e tim e o f le a d e r damage
were most prone to f o r k in g , w h ile th e s h o rte s t tre e s were most r e s i s t a n t .
Such a p a tte r n suggests t h a t an In s e c t which s e le c ts th e t a l l
be th e causal a g e n t.

However, s in c e th e t a l l e s t tr e e s from th e N o rth ern

P la te a u ecotype s u ffe r e d o n ly In te rm e d ia te f o r k in g , i t
d iffe r e n tia l

tre e s may

1s l i k e l y t h a t

re s is ta n c e among ecotypes a ls o e x is t s .

From th e s ta n d p o in t o f tim b e r p ro d u c tio n , tr e e s grown from seed
c o lle c te d In th e N o rth ern P la te a u gave th e most s a t is f a c t o r y growth
r a t e , co ld h ard in ess and stem s tr a ig h tn e s s a t both p la n t a t io n s .

Most

crooked tr e e s from th e ecotype would be removed 1n an e a r ly th in n in g ,
le a v in g more th an enough s t r a i g h t tr e e s to y i e l d a f i n a l
q u a lit y saw logs.

stand o f h ig h

N o rth ern I n t e r i o r t r e e s , w hich a re a ls o f a s t growing

120
TABLE 16 .

G en etic d iffe r e n c e s among ecotypes 1n s u s c e p t i b i l it y to
stem fo rk in g a t K ellogg and Russ F o re s t p la n ta tio n s .

V a r ie ty
and
Ecotype

P ro p o rtio n o f fo rk e d tre e s a t :
K ellogg F o re s t

Russ F o re s t
■% - -

v a r. ponderosa
Nor. P la te a u

34

13

C oast. OR

40

20

Nor. CA

16

8

Sou. CA

22

5

Nor. I n t e r i o r

48

22

N or. CO-UT

19

11

Sou. UT-NM

35

15

AZ-NM

69

30

Mean %

36

14

v a r . scopulorum

121

FIGURE 12

S evere stem croo k ca u sin g perm anent damage to a t r e e c
New M exico o r i g i n gro w in g a t th e K e llo g g F o re s t p la n ts

123
and c o ld h a rd y , s u ffe r e d to o much fo r k in g a t K e llo g g F o re s t to produce a
f u l l y stocked stand o f q u a l i t y tim b e r t r e e s .
Stem s tr a ig h tn e s s 1s n o t as Im p o rta n t in ornam ental p la n tin g s as
1n tim b e r p la n t in g s .

Most growers p r e f e r tr e e s t h a t a re r e l a t i v e l y f a s t

growing and p ic tu re s q u e f o r o rn a m e n ta ls .

Thus, s e v e r it y o f crooks o r

fo rk s Is a more im p o rta n t c o n s id e ra tio n than th e number o f cro o k s.
Stem crooks in most N o rth ern P la te a u and N o rth ern I n t e r i o r tr e e s were
m inor and u n im p o rtan t from th e a e s th e tic s ta n d p o in t; th e y co u ld n o t be
seen a t d is ta n c e s g r e a t e r than 1 0 -1 5 f t from t r e e s .

On th e o th e r hand,

tr e e s from A riz o n a and New Mexico had such severe crooks t h a t th e y would
be u se le ss as o rn am en tals as w e ll as tim b e r t r e e s .
L e a f le n g th
There a re la r g e d iff e r e n c e s 1n n ee d le le n g th in ponderosa p in e .
Trees from th e c o a s ta l v a r i e t y were u n ifo rm 1n having th e lo n g e s t n eedles
re g a rd le s s o f e c o ty p e .
1n le n g th .

They had n ee d les ra n g in g from 7 .0 to 8 .0 1n

In th e I n t e r i o r v a r i e t y , n o rth e rn seed sources had th e

s h o rte s t n e e d le s , ra n g in g from 4 .5 to 5 .5 1n lo n g .

Trees from A r iz o n a ,

New M exico , and so u th ern Utah were in te rm e d ia te In l e a f le n g th having
n ee d les from 6 . 0 to 7 .0 1n lo n g .
N eedle le n g th s were so u n ifo rm w it h in th e c o a s ta l v a r i e t y and th e
i n t e r i o r v a r i e t y e c o ty p e s , t h a t 1 t re p re s e n ts a good c r i t e r i a
tify in g
ta tio n s .

f o r Id e n ­

ponderosa p in e v a r i e t i e s and ecotypes 1n provenance t e s t p la n ­
For In s ta n c e , long n eedled tre e s which a re f a s t growing 1n

M ichigan c l e a r l y belong to th e n o rth e rn P la te a u e c o ty p e , whereas s h o rt
needled tr e e s w hich a r e f a s t growing can be u n m ls tak ea b ly I d e n t i f i e d as
b elo n g in g to th e N o rth e rn I n t e r i o r .
L e a f le n g th may be an Im p o rta n t c o n s id e ra tio n f o r th o se w is h in g to
grow ponderosa p in e as an o rn a m e n ta l.

G e n e r a lly , long n eed led tr e e s a re

124

more p ictu resq u e and are considered more d e s ira b le f o r ornamental o r
roadside p la n tin g s .

I f th e lo n g est p o s sib le needles a re d e s ire d ,o n e

can combine f a s t growth w ith long needles by growing tre e s from seed
c o lle c te d In th e Northern P la te a u .
Cone production
Cone pro du ction was f i r s t n o tice d a t age 13 a t Kellogg and Russ
Forests and has been con fin ed alm ost e x c lu s iv e ly to tre e s grown from
seed c o lle c te d In th e n o rth ern Rocky M ountains.

Of 121 tre e s which

produced cones a t age 13 o r 16 , 110 o f them were grown from seed c o lle c te d
1n th e Northern I n t e r i o r o r northern Colorado and U tah.

At age 16 a t

Kellogg F o re s t, each f r u i t i n g tr e e had an average o f 24 cones.
production has been very l i g h t on f a s t growing seed lo ts from the
Northern P la te a u .

Cone

125
PRACTICAL RECOMMENDATIONS

Choosing th e proper seed source 1s th e most Im p ortan t c o n s id e ra tio n
f o r those w ishing to grow ponderosa p in e 1n M ichigan.

W in te r In ju r y has

been so severe on tre e s from some areas th a t seed d e a le rs and nurserymen
must s p e c ify ex ac t lo c a tio n s when requ esting seed.
In g e n e ra l, the best regions o f seed c o lle c tio n f o r tim b e r o r
ornamental p la n tin g s In southern M ichigan a re th e Northern P late au
(Oregon, W ashington, B r it is h Colum bia, and western Montana) and Northern
I n t e r i o r (c e n tr a l Montana, South D akota, and Nebraska) re g io n s .

Trees

grown from seed c o lle c te d 1n th e N orthern P lateau have grown fa s t e s t
under M ichigan c o n d itio n s and have not been damaged by w in te r c o ld .
They a ls o have th e lo n g e st n ee d les , the le a s t m o r ta lit y and a re
r e s is ta n t to d is ea se s.

most

Trees grown from seed c o lle c te d 1n th e Northern

I n t e r i o r a re a ls o f a s t grow ing, have sh o rt n eed les, and a re th e most
co ld hardy o f a l l tre e s te s te d .

However, they seem somewhat prone to

fo rk in g and have r e l a t i v e l y slow d iam eter growth.
Although the Northern P lateau and Northern I n t e r i o r g e n e ra lly produced
the best tre e s f o r M ichigan, th e re were la rg e enough d iffe re n c e s 1n growth
r a te among tre e s w ith in these regions to w arran t s e le c tio n o f p a r t ic u la r
d e s ira b le stand s.

P e rtin e n t In fo rm a tio n on th e lo c a tio n o f th e best

stands 1s provided 1n Table 17.

S eed lo t Nos. 2102 (W ashington) and 2034

(Oregon) were 17% t a l l e r a t age 16 than some o th e r seed lo ts from the
Northern P la te a u .

W ith in th e Northern I n t e r i o r , s e e d lo t Nos. 2095

(Montana) and 2180 (Nebraska) were t a l l e s t by 24% a t age 16 1n both
Michigan p la n ta tio n s .

126
TABLE 17.

Location o f th e two best stands o f ponderosa p ine 1n th e
N orthern P lateau and Northern I n t e r i o r regions based on
performance in two southern Michigan p la n ta tio n s .

S eedlot No.

S ta te

Ecotype

L a titu d e

Longitude

County

E le v a tio n

2102

UA

Nor. P lateau

48°46*

118 ° 0 7 ’

Stevens

1400 f t

2034

OR

Nor. P lateau

44°16*

120°26

Crook

5000 f t

2095

MT

Nor. I n t e r i o r

45°15*

108°28'

Horn

4500 f t

2180

NE

Nor. I n t e r i o r

4 2 °4 5 '

9 9 °3 2 '

Rock

2100 f t

127

By using seed c o lle c te d from these s e le c te d a re a s , growers can
expect growth ra te s a t le a s t as good as th a t o f o th e r hard pines
recommended f o r p la n tin g 1n M ichigan.

D r. Donald Dlckmann (Departm ent

o f F o re s try , Michigan S ta te U n iv e r s ity ) made growth measurements 1n
fo u r 39 y e a r o ld hard p ine p la n ta tio n s o f unknown seed o r ig in a t Kellogg
F o re s t.

The re s u lts a re ta b u la te d below.

Ponderosa pin e was comparable

In growth r a te to th e o th e r th re e pines th a t a re commonly p la n te d as
ornam entals 1n southern M ichigan.
c h a r a c te r is tic s as w e ll.

Ponderosa pine has o th e r d e s ira b le

For in s ta n c e , 1 t has lo n g e r needles than

Scotch p in e , outgrows red p ine on many southern Michigan s i t e s , and
appears to be les s plagued by disease problems than A u s tria n p in e .
Ponderosa p ine represents th e best choice o f th e long needled pines f o r
ornamental p la n tin g s 1n southern M ichigan.

Growth o f dominant tre e s
Species

H eloht

Diam eter

ft

1n

Ponderosa pine

58

12 .9

Red pine

57

1 0 .8

A u s tria n pine

62

1 2 .3

Scotch pine

67

1 2 .3

Seed source s e le c tio n Is th e most Im p o rtan t but not th e o n ly fa c t o r
to co n sider when growing ponderosa pine 1n M ich ig an .

To o b ta in best

re s u lts good seed q u a li t y , s i t e s e le c tio n t and ca re a f t e r p la n tin g a re
necessary.

I f p la n te d on good s ite s and given good I n i t i a l weed c o n tr o l,

128
tre e s grown from seed c o lle c te d in th e N orthern P la te a u w i l l

become

e x c e lle n t ornam ental o r f o r e s t p la n tin g s in southern M ich ig an .

CHAPTER 7

SUMMARY

A rangewlde provenance t e s t o f ponderosa p in e was e s ta b lis h e d 1n
1960 and In c lu d e s two r e p lic a t e d p la n ta tio n s 1n southern M ich ig an .

From

1975 to 1977 g e n e tic v a r ia t io n in s e v e ra l aspects o f co ld h ard iness and
o th e r eco n o m ically Im p o rta n t t r a i t s was s tu d ie d .
F o lia g e samples were c o lle c te d from 30 s e e d lo ts on 17 d i f f e r e n t
d ates from O cto b e r, 1975 to Jan u ary, 1977.

F re e zin g te s ts were perform ed

on needles and tis s u e damage was assessed using e l e c t r i c a l c o n d u c tiv ity .
C r i t i c a l te m p e ra tu re s , d e fin e d as th e h ig h e s t tem p eratu re a t which c o ld
damage could be d e te c te d , were determ ined f o r each s e e d lo t.
f o r computing such tem peratures 1s d e s c rib e d .
p e rc e n t f o l i a r m o istu re c o n te n t was d eterm in ed .
w in te r In j u r y were made d u rin g s e v e ra l y e a rs .

A procedure

On s ix a d d itio n a l dates
F ie ld o b s e rv a tio n s o f
O ther t r a i t s measured

were tim e o f le a f in g o u t, f o l i a r d ry in g r a t e from e x c is e d tw ig s , h e ig h t,
and s u s c e p t i b i l it y to two fu ng al d is e a s e s .
Trees grown from seed c o lle c te d 1n B r it i s h Colum bia, W ashington,
Montana, and Nebraska a c c lim a te d to c o ld f a s t e s t , had th e lo w est
c r itic a l

tem peratures In m id w in te r ( - 4 0 to - 4 7 ° C ) , s u ffe re d l i t t l e

or

no co ld o r d is ea se damage, le a fe d o u t e a r l i e s t , had r e l a t i v e l y low f o l i a r
m o istu re and slow d ry in g ra te s and were among th e t a l l e s t tre e s a t age 16
(averaged 2 0 .5 f t t a l l ) .

Trees from n o rth e rn Colorado and Utah were
129

130
s im ila r 1n s e v e ra l re sp ec ts b u t were o n ly 14-15 f t t a l l

a t age 16.

Trees

grown from seed c o lle c te d 1n C a lif o r n ia a c c lim a te d to c o ld s lo w e s t, had
the h ig h e s t c r i t i c a l

tem peratures 1n m id w in te r (- 2 2 to - 2 4 ° C ), s u ffe re d

severe c o ld and d isease damage, le a fe d out l a t e s t , had high f o l i a r
m o is tu re , and f a s t d ry in g r a t e s , and were among th e s h o rte s t tre e s a t
age 16 (averaged 14 f t t a l l ) .

Trees grown from seed c o lle c te d In

A rizo n a and New Mexico had c r i t i c a l tem peratures o f - 3 2 °C , were 1 6 .5 f t
t a l l a t age 1 6 , s u ffe re d severe d isease damage, had r e l a t i v e l y slow
f o l i a r d ry in g r a t e s , and were In te rm e d ia te 1n c o ld damage, tim e o f
le a f in g o u t and f o l i a r m o istu re c o n te n t.
C a lif o r n ia tre e s s u ffe re d severe c o ld damage most years because th ey
d id n o t ach ieve a s u f f i c i e n t depth o f h ard iness to w ith s ta n d M ichigan
w in te r s .

In c o n tr a s t, A riz o n a , New M exico, and c o a s ta l Oregon tre e s

were s u f f i c i e n t l y hardy 1n m id w in te r to avo id co ld damage.

However,

they s u ffe re d needle In ju r y in ye ars when low tem peratures o ccurred 1n
e a r ly w in t e r , b e fo re th ey a tta in e d maximum h a rd in e s s .

Trees from n o rth e rn

o r ig in s avoided damage because th e y a c c lim a te d to co ld q u ic k ly and became
very hardy 1n m id w in te r.
W in te r d e s ic c a tio n was considered as a p o s s ib le source o f w in te r
In ju r y 1n ponderosa p in e .

However, th e r e la t io n s h ip between f o l i a r

d ry in g ra te s and w in te r In ju r y was not s tro n g .

Trees from Washington and

B r it is h Columbia lo s t w a te r more r a p id ly In w in te r than tre e s from A rizo n a
and New Mexico b u t s u ffe re d no c o ld damage.

C oastal Oregon tre e s d rie d

o u t th e f a s t e s t , but s u ffe re d le s s c o ld damage than C a lif o r n ia o r
A rizo n a t r e e s .

Thus, I t appeared th a t d e s ic c a tio n was le s s Im p o rta n t

than c o ld tem p eratu re In causing damage to ponderosa p in e .

131
Time o f le a fin g out appeared to be re la te d to cold hardening and
dehardening.

Trees from Washington, B r it is h Columbia, Montana, and

Colorado hardened to cold fa s te s t 1n f a l l , dehardened most r a p id ly 1n
l a t e w in te r , and le a fe d out 10-14 days e a r l i e r than tre e s from southern
o r ig in s .

D esp ite d iffe re n c e s In le a f in g out phenology, sp rin g f r o s t

damage was not a problem in ponderosa p in e .
F o lia r m oisture co n ten t v a rie d seaso n ally as w e ll as among s e e d lo ts ,
decreasing by 15-16% from summer to w in te r .

In g e n e ra l, tre e s w ith high

m o istu re co n ten t were most s u s c e p tib le to cold damage.

This re la tio n s h ip

seemed to hold from summer to w in te r and als o from n o rth to south w ith in
the sp e c ie s .

A p p a re n tly , tre e s w ith high f o l i a r m oisture co n ten t had

more I n t r a c e l l u l a r w ate r and thus more w ate r to fre e z e and cause damage.
W in ter In ju r y had an e f f e c t on growth r a te and age-age h e ig h t
re la tio n s h ip s 1n ponderosa p in e .

Trees grown from seed c o lle c te d In

C a lif o r n ia , A riz o n a , and New Mexico were t a l l e s t a t e a r ly ages, but lo s t
t h e i r growth s u p e r io r ity because o f repeated w in te r In ju r y .

By age 16,

hardy tre e s from B r it is h Columbia, Washington, Montana, and Nebraska were
t a l l e s t , A rizona and New Mexico tre e s were averag e, and C a lifo r n ia tre e s
were s h o rte s t.

Repeated w in te r In ju r y to southern tr e e s , a ls o re s u lte d

In an in crease 1n the magnitude o f h e ig h t d iffe re n c e s among ecotypes
from age fo u r to e ig h t .

E rro r variances decreased g ra d u a lly w ith age

as average growth r a te In c re a s e d , but were a p p a re n tly u n a ffe c te d by
w in te r In ju r y .
S u s c e p t ib ilit y to damage from two fungal diseases appeared secondary
to w in te r In ju r y .

Trees which were p h y s io lo g ic a lly weakened by repeated

cold damage s u ffe re d the most tw ig dleback from d is e a s e .
s u ffe re d l i t t l e

Trees which

o r no cold damage were le a s t a ffe c te d by d is ea se .

132

O th er t r a i t s

s tu d ie d In c lu d ed m o r t a lit y l e a f le n g th , cone p ro d u c tio n ,

stem t a p e r , d ia m e te r g ro w th , and In c id e n c e o f stem fo r k s .

Trees grown

from seed c o lle c te d 1n th e N orthern P la te a u (O regon, W ashington, and
B r it is h Colum bia) were most d e s ir a b le In a l l

re s p e c ts .

In a d d itio n to

being th e t a l l e s t and among th e most co ld h a rd y , they had th e la r g e s t
diam eters ( 8 .5 1n a t age 1 6 ) , th e le a s t m o r t a li t y , th e lo n g e s t needles
( 7 .5 to 8 .0 In lo n g ), th e most c y lin d r ic a l boles and s u ffe re d o n ly a
moderate amount o f fo r k in g .

Trees grown from seed c o lle c te d in th e

N orthern P la te a u a re recommended f o r f o r e s t and ornamental p la n tin g s in
southern M ich ig an .

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