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EFFECTS OF COMPETITION CONTROL ON ONE YEAR
SURVIVAL AND FIELD GROWTH OF SCOTCH PINE

(Pinus sylvestris)

 

BY

Celina Wisniewski Koehler

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Forestry

1979

ABSTRACT

EFFECTS OF COMPETITION CONTROL ON ONE YEAR
SURVIVAL AND FIELD GROWTH OF SCOTCH PINE
(Pinus sylvestris)

 

BY

Celina Wisniewski Koehler

Effect of competition control on first year survival
and field growth of Scotch pine was examined. Mechanically
planted seedlings were submitted to five treatments: 1) no
weed treatment; 2) elimination of shading (control);

3) weeding with simazine + glyphosate; 4) weeding with
glyphosate; 5) mechanical weeding.

Bud conditions and initial diameter were used as an
index of seedling quality and compared to survival and
growth. Depth of planting was also compared to survival.

Plant water stress was measured in three treatments
and compared to competition treatment.

All methods of competition control, except elimina-
tion of shading increased survival and growth. High qual—
ity seedlings had greater survival and growth. Depth of
planting had no effect on survival. Plant water stress
was lower where vegetation was removed mechanically.

Dissipation of simazine from soil followed a pseudo-
first order reaction. Only 1.5% of the concentration of

the parent compound applied remained after 120 days.

 

To my daughter Barbara

ii

 

VITA

Celina Wisniewski Koehler

Candidate for the Degree of

 

MASTER OF SCIENCE

Final examination: April 10, 1979

Guidance Committee: D. Penner, J. W. Wright, P.G. Murphy,
and J. B. Hart (Major Professor)

Biographical Items:
Born: June 20, 1953, Curitiba, Parana, Brazil
Married: Henrique Soares Koehler, July, 1976
Daughter, Barbara, September 12, 1978
Education:
Diploma from "Escola Tecnica Federal do Parana"
High School, Curitiba, Parana, Brazil
B.S. in Forestry from Federal University of Parana,
Brazil, 1975
M.S. in Forestry from Michigan State University, 1979
Professional Experience:

1974 Teaching assistant in Dendrology, while earning B.S.
degree

1975 Teaching assistant in Forest ecology while earning
B.S. degree

1976 Instructor of Ecology at the Federal University of
Parana, Brazil

Professional Organizations and Honoraries:

Forest Engineers Association of Parana State, Brazil
Xi Sigma Pi

iii

 

ACKNOWLEDGMENTS

I am grateful to the chairman of my Guidance Com-
mittee, Dr. J. B. Hart for his guidance and advice through-
out the course of this study. I am also grateful to the
other members of the Guidance Committee-—Drs. D. Penner,
J. W. Wright and P. G. Murphy--for their assistance and
suggestions.

Sincerest gratitude is also expressed to Dr. R.
Leavitt for permission to use the laboratory facilities
of the Pesticide Research Center and to A. B. Filonow for
his technical assistance. Appreciation is extended to
M. Fox for his invaluable help in the collection of data.

Special note of gratitude is expressed to my husband
Henrique for his assistance with the statistical aspects
of the project. His continuous encouragement and under-
standing made it possible for me to complete my studies

and prepare this work.

iv

 

LIST OF

LIST OF

CHAPTER

TABLE OF CONTENTS

TABLES O O O O O O 0 I O O O O O O O O O

FIGURES . . . . . . . . . . . . . . . .

I INTRODUCTION . . . . . . . . . . . . . . .

II LITERATURE REVIEW . . . . . . . . . . . .

Artificial Regeneration and Competition
Control . . . . . . . . . . . . . . .
Methods of Competition Control . . . . .

Mechanical Weed Control . . . . . .
The Use of Herbicides . . . . . . .
The Use of Simazine . . . . . . . .
The Use of Glyphosate . . . . . . .

Importance of Seedling Quality for Success-

ful Regeneration . . . . . . . .
Silvical Characteristics of Scotch Pine
Plant Moisture Stress as Related to

Competition . . . . . . . . . . . . .

III DESCRIPTION OF STUDY AREA . . .‘. . . . .

Climatic Description . . . . . . . . . .
Topoqraphic and Soil Description . . . .
History 0 O O O O O O O O O I O O O O 0

IV MATERIAL AND METHODS . . . . . . . . . .

Experimental Design . . . . . . . . . .
Study Establishment . . . . . . . . . .
Initial Tree Evaluation . . . . . . . .
Measurements . . . . . . . . . . . . . .
Statistical Analysis . . . . . . . . .

V RESULTS AND DISCUSSION . . . . . . . . . .

Survival and Height Growth . . . . . .

Page
vii

ix

19
21

21
21
22

24

24
25
28
30
32

34
34

Page

Survival . . . . . . . . . . . . . . . . . 34
Survival as Related to Initial Tree
Evaluation . . . . . . . . . . . . . . 35

Survival as Related to Bud Conditions
and Depth of Planting . . . . . . . . . 36
Height . . . . . . . . . . . . . . . . . . 38

Diameter . . . . . . . . . . . . . . . . . . . 40
Relationship Between Initial and Final

Seedling Characteristics . . . . . . . . . . 45
Plant Moisture Stress . . . . . . . . . . . . 48
Simazine Residues in Soil . . . . . . . . . . 51

VI CONCLUSIONS AND RECOMMENDATIONS . . . . . . . . 56

BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . 59

APPENDICES
A PROCEDURE FOR EXTRACTION OF SIMAZINE RESIDUES

FROM SOIL SAMPLES . . . . . . . . . . . . . . . 65

B ANALYSIS OF VARIANCE TABLES . . . . . . . . . . 67

C COMMON, TRADE AND CHEMICAL NAME OF HERBICIDES
AND RESPECTIVE MANUFACTURER . . . . . . . . . . 76

vi

 

10.

ll.

12.

LIST OF TABLES

Page

Bud Condition, Codes and Characteristics Used
to Evaluate Seedling Quality . . . . . . . . 29

Diameter Class Codes Used to Evaluate Seed-
ling Quality . . . . . . . . . . . . . . . . 29

Coding Used for Evaluation of Depth of
Planting . . . . . . . . . . . . . . . . . . 30

Codes and Characteristics Used to Evaluate
Growth Performance of Scotch Pine Seedlings
at the End of the First Growing Season . . . 31

First Year Field Survival of Scotch Pine
Seedlings with 5 Methods of Weed Control . . 35

Number of Trees and First Year Survival for
Small, Medium and Large Planted Scotch Pine
Seedlings . . . . . . . . . . . . . . . . . 36

First Year Field Survival of Medium and Small
Diameter Scotch Pine Seedlings with 5 Meth-
ods of Weed Control . . . . . . . . . . . . 37

Number of Trees and First Year Survival of
Scotch Pine Seedlings of Various Initial
Bud conditions I O O O O O O O O O O O O O O 37

Number of Trees and First Year Field Survival
of Scotch Pine Seedlings According to Depth
of Planting . . . . . . . . . . . . . . . . 38

First Year Total Height and Height Growth of
Scotch Pine Seedlings with 5 Methods of
Weed Control . . . . . . . . . . . . . . . . 39

First Year Total Height of Medium and Small
Diameter Scotch Pine Seedlings with 5 Meth-
ods of Weed Control . . . . . . . . . . . . 39

First Year Height Growth of Medium and Small

Diameter Scotch Pine Seedlings with 5
Methods of Weed Control . . . . . . . . . . 4O

vii

 

Table

13.

14.

15.

16.

17.

B1.

B2.

B3.
B4.

B5.

B6.

B7.

BB.

B9.

B10.

First Year Diameter of Scotch Pine Seedlings
with 5 Methods of Weed Control . . . . . .

First Year Diameter of Medium and Small
Initial Diameter Scotch Pine Seedlings with
5 Methods of Weed Control . . . . . . . . .

Number of Scotch Pine Seedlings of Various
Initial Bud Conditions and Percentage with
Various Final Tree Condition . . . . . . . .

Number of Scotch Pine Seedlings with Initial
Diameter Size and Percentage with Various
Final Tree Condition . . . . . . . . . . . .

Water Stress of Scotch Pine Seedlings with
3 Methods of Weed Control . . . . . . . . .
Analysis of Variance for Survival . . . . . .
Analysis of Variance by Initial Diameter
for Survival . . . . . . . . . . . . . . . .
for Initial Height .

Analysis of Variance

Analysis of Variance for Total Height . . .
Variance by Initial Diameter

Height . . . . . . . . . . . . . .

Analysis of
for Total
Analysis of Variance for Height Growth . . . .
Analysis of Variance by Initial Diameter
for Height Growth . . . . . . . . . . . . .

Analysis of Variance for Diameter at the
of the Growing Season . . . . . . . . . . .

Analysis of Variance by Initial Diameter Size
for Diameter at the End of the First Grow—
ing Season

0 O C O O O O O O O O O O I O O 0

Analysis of Variance for Plant Moisture Stress
Measurements . . . . . . . . . . . . . . . .

viii

Page

41

41

46

47

49

67

68
69

69

70

71

72

73

74

75

 

LIST OF FIGURES

Figure Page

1. Curves showing the disappearance of simazine
from two depths of a sandy loam soil follow-
ing application of 2.2 kg/ha (2 lb/a).
Points are average of seven replications . . 52

2. Average concentration of simazine in two

depths of a sandy loam soil following appli-
cation of 2.2 kg/ha (2 1b/a) . . . . . . . 53

ix

CHAPTER I

INTRODUCTION

Forest planting has become a major forest activity
in Brazil since 1966. The principal objectives of the
plantations are to produce raw material for pulp, paper
and fiberboard industries, although lumber production may

in some cases be an important goal. Pinus elliottii,

 

P. EEEQE and tropical pines such as P. caribaea and P.
oocarpa are the most widely used coniferous species in
reforestation programs. The seedlings are planted syste-
matically either by hand or by machine. Direct seeding

is not a widespread regeneration method and natural regen-
eration is yet impractical for these species are not
native to Brazil.

To insure the success of any reforestation program
it is necessary to know the causes of failure and their
relative importance for any given locality under specific
conditions. Failures have frequently been associated with
the competitive influence of herbaceous vegetation. The
forester, therefore, has to decide whether or not compet-
ing vegetation should be removed before tree seedlings are

planted. This decision has to be based on knowledge of

 

how the vegetation affects the seedlings for any partic—
ular site. The source of this knowledge is either very
careful scientific field observation or research such as
reported in this study.

Once competition control has been decided upon,
several methods are available to accomplish it. The choice
between various alternative practices should take into
consideration the cost per unit of long-term gain, bearing
in mind the management objectives, as well as responsabil-
ities to society.

Herbicides are becoming one of the most important
and effective means of vegetation control. Use of herbi-
cides has several advantages over alternative methods such
as prescribed burning, scarifcation or cultivation. They
are more selective, do not disturb the soil and can provide
a long lasting effect.

The fact that herbicides cause no physical distur-
bance in the soil becomes very important when reforestation
is to be done in soils subjected to erosion as is the case
in some areas of southern Brazil. In such areas agricul-
ture is impractical and a forest stand would represent the
best alternative land use. To assure success in the early
years, herbicides can be used to control competing vegeta-
tion while the mulch of dead herbs and grasses protect the
fragile soil. However, the environmental consequences of
herbicides must be very well understood so that they can

be used with minimum impact on the environment.

 

The primary objective of this study was to investi-
gate the effects of competition control on survival and

field growth of planted Scotch pine (Pinus sylvestris L)

 

in the first growing season. The possible effects of
seedling quality as defined by diameter size, and bud
conditions as well as depth of planting were also to be
examined.

A secondary objective was to determine the persis-
tence of the herbicide simazine in the soil and its pos-
sible effects on survival and growth.

This study combines forest ecology and weed science
in a field experiment relating to planting of conifer for-
ests. This is relevant to my home country, Brazil, as
well as relevant to the regeneration of conifers in the
North Central United States.

The study is to be continued in the future years pro-
viding more detailed information about the effects of com—

petition control.

 

CHAPTER II

LITERATURE REVIEW

The primary concern of this review is the response
of pines to competition control in the first year after
planting and the methods used to achieve this control.
Only artificial regeneration will be considered.

Artificial Regeneration and
Competition Control

 

 

The establishment of a new timber stand requires
favorable conditions. These conditions have to be created
and maintained and this includes the elimination of exist-
ing vegetation that would compete with the seedlings for
moisture, space, nutrients and light.

Manipulation of existing vegetation can have sub-
stantial influence on the severity of the habitat and can
improve survival and growth of the seedlings and the over-
all quality of the stand (Lane and McComb, 1948; Wilhite,
1961; Newton, 1964a and 1964b; White, 1967 and 1975; An.
1968; Wilde, 1968).

The degree and <iuration.<3f competition control re-
quired will depend on the species to be established and

on the environment. Critical aspects to seedling survival

 

and development include such things as soil moisture reten-
tion capacity, composition and habits of competing vegeta-
tion and length and severity of the growing season (Newton,
1973).

Two growing seasons without serious moisture stress
according to White (1975) and An. (1968) seems to be ade—
quate for the establishment of conifers under relatively
severe conditions. Shading and mechanical action of
woody vegetation can be important on some sites and release
must be sufficient to bring about conifer dominance. This
usually happens in the first five years.

Therefore one concludes that a successful conifer
regeneration program requires control of herbaceous vege-
tation and grasses in the first two years. After the seed-
lings are established they normally outcompete the existing

vegetation.

Methods of Competition Control

 

The suitability of a method to achieve these two
years of competition control has to take into consideration
the silvical requirements of the pine species and the char-
acteristics of particular sites. Improvement of the envir-
onment has to be maximized in relation to detrimental
effects. It is also an economics problem. The cost of
achieving the desired control by the various methods
available has to be considered and also how much can be

spent to obtain maximum results based on the productive

capacity of the new stand.

Competition control should not result in erosion or
compaction of the soil. If a chemical is used it should
not cause injury to the desired trees or animals on or

off site.

Mechanical Weed Control

 

As used in this review mechanical weed control is
the same as mechanical site preparation.

Mechanical methods of site preparation may range in
intensity from simple buldozing of the vegetation to a
combination of treatments such as shearing, raking, piling
and burning the residues, followed by disking or bedding.
The machinery utilized ranges from standard farm and con-
struction implements to specific equipment for the clear-
ing of difficult sites. Some of the methods not only re-
move unwanted vegetation but also may prepare the soil for
reforestation. This soil disturbance, however, may be
aesthetically undesirable, may increase erosion, adversely
affect streams and may also be detrimental for wild life
habitat (An., 1968; Carter et 31., 1975).

Cultivation tends to shift the location of weed
seeds, bringing them closer to the surface where conditions
are more favorable to germination (Anderson, 1977).

Another point to consider is that sometimes large
areas of forest land consist of steep rocky sites where

mechanical equipment cannot be used efficiently.

 

7

After the trees are planted, weed control may be
carried out by power driven rotary tillers that operate
through the cutting action of revolving knifes. Where labor
is available hand tools such as hoes, grub hoes and
matocks may be used. Hand pulling is best adapted to the
removal of weeds growing near or between trees where it
is difficult to reach with a hoe or cultivator.

Various methods all have the objective of removing
vegetation or preparing the soil. Specific effects may
be obtained by various methods and equipment. The point
of interest for this study are the specific effects ob—
tained with mechanical weed control and not the technique

used to achieve this control.

The Use of Herbicides

 

The chemical terminology as set forth by the Weed
Science Society of America is listed in Appendix C for
the herbicides mentioned in this review.

The utilization of herbicides in forest management
has been reviewed by McQuilkin (1960) and Hovind (1967).

The use of chemicals to control unwanted vegetation
in forestry made little progress until after World War II.
Sodium arsenite and sodium chlorate, some oils and carbon
disulfide were used, but the availability of effective and
easy to handle chemicals apparently was the limiting factor.

The discovery of the herbicidal properties of the

phenoxy_ compounds and the develOpment of aerial spraying

 

techniques greatly increased use of herbicides in forestry
practice. Since then a great number of new chemicals for
use on both herbaceous and woody plants have developed,
making herbicides a standard tool for forest management.

McQuilkin (1960) reported the use of 2,4-D with poor
results, and then 2,4,5-T by the early 1950's as the most
effective against woody plants. According to Hovind (1967)
the practicability of establishing conifer plantations
without mechanical site preparation was demonstrated in
the late 1950's and early 1960's by the use of simazine,
dalapon and amino-triazole.

Carvell (1960) tested radapon, trichloroacetic acid
(TCA) and Varsol for grass control for conifers planted
in old fields. Their effects on herbaceous vegetation and
injury to pine were compared. A concentration of 30 g per
liter of water (0.25 lb/gal) of radapon was used to treat
spots 60 cm in diameter prior to planting. Half were
sprayed in late fall, half in early spring. Excellent
control of grasses was obtained in both cases during three
growing seasons. Additional experiments showed that the
same concentration of radapon applied after planting dur-
ing the growing season caused severe injury to white pine,
while fall application did not result in damage to the
seedlings. TCA applied at the same concentration (30 g/l
of water) controlled only grasses and injured the new
foliage of white pine, Scotch and red pine and also Norway

spruce. Undiluted Varsol gave good control of grasses

and herbs but since it is a contact poison the roots were
not killed and control lasted only one year. Only minor
damage to the foliage of pines and spruce was observed.

Furtick (1961) listed the herbicides simazine, atra—
zine and diuron as the most promising for silvicultural
purposes because of the marked insensitivity towards conif-
erous trees while killing a broad spectrum of annual and
some perennial weeds. According to the author these
herbicides will control unwanted vegetation for 6 to 12
months depending on species, soil type and rainfall. He
also mentions Umrtherbicides dalapon and amitrole can be
used successfully only where direct application to the
conifers is avoided.

Swingle (1961) reports the use of ammonium sulfam-
ate and amino-triazole (amitrole) as foliage spray herbi-
cides and fenuron pellets for brush control. Also in 1961,
Kuntz described the use of herbicides such as simazine,
atrazine and other triazines, dalapon, monuron, diuron and
amitrole, alone or in combination to treat new tree plant-
ings, with the results varying with dosage, rainfall, soil
type and weed species. White (1967) lists as effective
herbicides to control most types of weeds in the eastern
and north central states, simazine, atrazine, amitrole-T,
2,4,5—T, 2,4,5-T mixed with 2,4-D, casoron, cacodylic
acid and paraquat. The same author in 1975 includes asulam,
glyphosate and 2,4,5-TP to the ones mentioned above regard—

ing them as "the most commonly mentioned by researchers,

 

 

10

extention workers and forest managers for weed control."

Newton (1973) also points out that the s-triazine
herbicides, the phenoxy_ compounds, picloram, amitrole,
dalapon and organic arsenicals may be used safely in refor-
estation. Dichlorprop (An_., 1968) and dicamba (U.S.D.A.,
1975) have also been included as Chemicals used for site
preparation techniques.

The selection of an herbicide will depend on each
particular situation. Availability of application equip-
ment, weed species to be controlled, species to be planted
and its sensitivity to chemicals, potential hazards to en-
vironment, costs and management objectives are variables
to be carefully considered if the best possible results
are to be obtained.

If the proper herbicide and application technique
are selected, weed control in tree plantations will be more
economical and effective than mechanical methods (White,
1967). The soil will not be disturbed, reducing the danger
of stream siltation and erosion (Newton, 1973). The mois-
ture will be better retained under a mulch of dead weeds
than where the vegetation is removed by scalping (Heidmann,
1967). As the dead plant material is decomposed organic
matter content of soil will be increased. The increase in
organic matter improves physical properties of the soil,
increases cation adsorption capacity and supply and availa-
bility of nutrients (Brady, 1974).

Persistence of herbicide residues in soil do not

 

11

usually constitute a problem in forest management. Com-
bination of herbicides, one giving quick kill and the
other giving lasting effect will be desirable so as to
obtain control for more than one growing season.

The herbicides simazine and glyphosate (Roundup)
were chosen to be used in this study because they had been
successfully used in similar experiments (White, 1975).

No endorsement of named products is intended.

The Use of Simazine

 

Simazine, [2°chloro-4, 6-bis(ethy1amino)-§7triazine]
or Princep is a member of the diamino-grtriazine herbicide
family which has been successfully used for site prepara—
tion. Princep is a registered trademark of CIBA-Geigy.

The §ftriazine herbicides are used for selective
pre-emergence and post-emergence control of grasses and
broadleaved weeds, being in general more effective against
the latter. Most of them are applied to the soil where
they are readily absorbed by the roots and translocated
upwards to the leaves via the transpiration stream. They
are classified as inhibitors of photosynthesislurinterfer-
ence with the Hill reaction: the evolution of oxygen from
water in the presence of chloroplasts and one electron
acceptor. Inhibition of other metabolic processes are
also considered to occur (Moreland et 31., 1959; Ashton
and Crafts, 1973; Kearney and Kaufman, 1975). The plant

hormone metabolism may be influenced since at subtoxic

 

12

levels stimulation of growth was shown to occur. The ni-
trogen metabolism is also thought to be affected.

The usual phytotoxic symptoms are foliar chlorosis
followed by necrosis. Depending on the concentration used,
increased greening of the leaves or even no change can
occur (Ashton and Crafts, 1973). Selective weed control
with triazines is achieved by either physiological toler-
ance or herbicide placement.

Anderson (1977) recommends simazine for nonselective
vegetation control in non-crOp areas at rates of 5.6 kg
to 44.8 kg per hectare (5 to 40 1b/a), depending on the
weeds to be controlled. Hovind (1959) using 2.0 kg/ha
(1% 1b/a) of simazine obtained only 35% grass control
while 3.4 kg/ha (3 lb/a) gave 55% control and a mixture
of simazine at 2.0 kg/ha (1% 1b/a) and dalapon at 8.7
kg/ha (7% 1b/a) controlled 99% of the grasses. Heidemann
(1967) applying simazine at 11.2, 22.4 and 44.8 kg/ha
(10, 20 and 40 lb/a) killed 80% of perennial grasses.
White (1967) testing the efficiency of various chemicals
for pre-planting weed control in heavy quack-grass used
simazine alone and in combination with other herbicides.
With simazine alone better control was obtained at 9.0
kg/ha (8 1b/a) than at 4.5 kg/ha (4 1b/a). Of the combin-
ations amitrol-T at 18.7 l/ha (2 gal/a) plus simazine at
4.5 kg/ha (4 lb/a) gave the best results. The same author
(1975) reports effective control of vigorously growing

grasses when simazine at 3.4 kg/ha (3 1b/a) was used

 

f4
(,0

in combination with glyphosate at 1.7 kg/ha (1.5 1b/a).

Residual activity is essential for weed control and
soil sterilization. In forest management persistence in
soil is a desireable characteristic, for control of unwanted
vegetation can be maintained for a longer period of time.

A complete review of the persistence of triazine herbicides
in soil is provided by Sheets (1970). Among the triazine
herbicides, persistence is related to chemical structure.
Those with a chloro substituent, as is the case for sima-
zine, are less persistent than those with a methoxy
substituent. Differences in persistence have also been ob-
served among the chloro substituted triazines with simazine
being usually the more persistent.

Persistence is affected by soil, weather and climate,
the rate of application, the interval between applications
and the formulation of herbicide applied. Effects of soil
type are difficult to assess due to complicating influences
of Climate. While it is a fact that persistence varies
among soils,it is difficult to determine the exact causes
for the differences (Sheets, 1970). Weather and climate
influence the rate of disappearance through their effects
on volatilization, surface runoff, erosion and leaching.
These processes do not alter persistence since the herbi-
cide molecules continue to exist in other parts of the en-
vironment. Persistence is altered through the effects of
weather and climate on photochemical, chemical and bio-

logical degradation. Herbicides can also disappear due

14

to uptake by plants. Longer persistence may also result

from subsurface than surface application.

The Use of Glyphosate

 

Glyphosate (N-(phosphomomethyl)glycine) or Roundup
is a water soluble herbicide which may be used for control
of herbaceous and deciduous vegetation prior to the plant-
ing of tree seedlings and also for the control of annual
and perennial weeds, woody brush and deciduous trees as
a conifer release treatment. Roundup is a registered
trademark of Monsanto Company. When applied to the foliage
of actively growing plants, glyphosate is readily trans-
located throughout the plant.

Jaworski (1972) investigated the possible sites of
action of glyphosate. Results suggested that it inter-
feres with the biosynthesis of phenylalanine, more specif-
ically with the metabolism of chorismic acid in the aroma-
tic aminoacid biosynthetic pathway. Sprankle 35 £1. (1975)
studying absorption, action and translocation of glyphosate
concluded that respiration and photosynthesis are either
slowly inhibited or are only affected after some other
plant process has been inhibited.

Contact of glyphosate with foliage or green stems
of desirable trees must be avoided since severe injury
or death may result. Lund-Hoie (1976) found that the

tolerance of Picea abies to Roundup depends on the stage

 

of growth with a high degree of tolerance during mature

 

15

growth stage and less during shoot elongation.

Supplemental labeling for the experimental use of
Roundup in silvicultural site preparation and conifer re-
lease recommends application of 1.2 to 11.7 l/ha (% to
5 quarts/a), depending on the weeds to be controlled. For
conifer release 1.2 to 7 1/ha (% to 3 quarts/a) may be
applied with the lower rates for more susceptible conifers.

Lund-Hoie (1975) reports glyphosate as being an
alternative to pre-and post-emergence herbicide for the
control of unwanted vegetation in forest plantations in
Norway. A rate of 500 g/ha was optimum to control broad-
leaved weeds and brushes while 1 kg/ha was the optimum rate
for control of undiSturbed perennial grasses. White
(1975) reports the use of Roundup as a preplant and directed
spray in established conifers at a rate of 1.7 kg/ha
(1.5 lb/a) with increased effectiveness when used in com-
bination with 3.4 kg/ha (3 lb/a) of simazine.

In experiments to control herbaceous weeds in western
Oregon, excellent selective control has been obtained with
Roundup at rates of 2.3 l/ha (l quart/a) or less (Newton,
1977). In field plantations control of mixed perennial
weeds resulted when 3.4 Kg/ha (3 lb/a) of atrazine mixed
with 1.2 and 2.3 l/ha (1 and 2 pints/a) of Roundup were
sprayed. Roundup alone did not provide satisfactory resid-
ual control. For site preparation 2.3 1/ha (2 quarts/a)
of glyphosate was effective against most species of de-

ciduous brushes.

 

 

l6

Combinations of glyphosate with other pre-emergence
herbicides will slow down or reduce its effect according
to Monsanto (1974). However increased effectiveness has
been reported when glyphosate was used in combination with
simazine (White, 1975; Newton, 1977), atrazine (Newton,
1977) and alsoxmiflnterbuthylazin (Lund-Hoie, 1975).

Glyphosate undergoes complete and rapid degradation in
soils. Rueppel gtgi. (1977) studying soil degradation of the
herbicide concluded that biodegradation by soil microflora

rather than chemical breakdown is the major degradation pathway.

The rate of dissipation in three representative soil types
(Ray silk loam, Norfolk sandy loam and Drummer silty clay
loam) was measured.' Complete biodegradation was observed
in 112 days for Drummer and Ray soils. In the Norfolk

soil degradation was slower. The results agree with actual
field studies by Sharp (as mentioned by Rueppel gt gt.,
1977) on different soil types where one average half life
of two months was observed.

Importance of Seedling Quality for
Successful Regeneration

 

Newton (1973) advises that the proper choice of
species and size of the planting stock in combination
with the use of herbicides are the key factors for a
successful regeneration. Large seedlings usually tolerate
more abuse from animals. Drought hardy stock is less
likely to need weed control in the following years.

Chapmann and Wray (1957) indicate the advantages

17

of transplants over seedlings for Christmas tree planta-
tions. Transplants are larger and sturdier than seedlings
of the same age and usually develOp more woodiness. They
also tend to have larger and better root systems. These
Characteristics make them hardy and more able to survive.
Bell and White (1966) however, warn that a large planting
stock will not always give the best results. The larger
the seedling at planting time the greater will be the
planting shock. While it is also true that they may bet-
ter withstand weed competition.

Koslowski (1971) points out the importance of hand-
ling with bareroot transplants. Exposure of the roots may
affect survival and growth.

Lavender (1964), investigating the effect of date of
lifting and cold storage of Douglas fir seedlings con-
cluded that seedlings lifted after buds began to swell in
the spring and submitted to any period of cold storage
were adversely affected as evidenced by reduced growth and
poor field survival.

More detailed discussion about seedling quality is

presented in the Results and Discussion section.

Silvical Characteristics of Scotch Pine

 

Scotch pine (Pinus sylvestrisL.) is the most widely

 

distributed conifer in the world, growing naturally from
the Atlantic in the west, across Europe and Asia to the

Pacific Ocean in the east and from Scandinavia to the

18

Mediterranean. It is one of the most adaptable tree
species, growing in the most diverse climates (Steven and
Carlisle, 1959). Introduced into the United States and
Canada as a timber tree it fell into disfavor, but rapidly
won popularity as a Christmas tree, especially in the Lake
States. It is the most common Christmas tree species in
Michigan. It prefers well drained sandy loam soils.
Scotch pine grows rapidly, the normal Christmas tree rota-
tion being 5 to 7 years. Site preparation is required to
assure survival and good shape of the trees. Fertilizing
at time of planting is not recommended since good quality
planting stock, competition control and careful planting
techniques will result in satisfactory development and 85
to 90% survival (Bell and White, 1966). Controlling weeds
after planting is important to maintain the growth and
foliage color (Chapman and Wray, 1957). 4

Brown (1969) studying variations in survival and
growth of different provenances of Scotch pine found that
during the period of most active height growth root growth
was relatively slight. It was not until after terminal
shoot growth had slowed down or ceased that root growth
took place. Growth of the seedlings was dependent ini-
tially on food materials stored in the seed, then on cur-
rently produced photosynthate used primarily for top
growth. Survival was closely correlated with the length
of the root system at the time of transplanting and the

growth of new roots after transplanting. During the early

19

part of the growing season neither the amount of root
present at transplanting nor new growth after tranSplant-
ing was sufficient to supply moisture to the actively
growing trees and survival was very low.

Plant Moisture Stress as Related
_’to Competition

 

 

The basic idea of competition control is to improve
the seedling environment. This vegetation manipulation
causes many changes, and one of the most important is
increased moisture availability.

A seedling's moisture status is dependent on soil
moisture supply, duration of dry period, vegetational
cover and transpirational forces acting in the seedling.
The transpirational losses by competing vegetation are
considered to be more important than evaporation for most
soils (Newton, 1973). The same author (1964a) demonstrated
that the rate of moisture depletion of the tOp 3 feet of
soil was a linear function of vegetative cover. Decreasing
the amount of vegetation by the use of chemicals conserved
considerable moisture, resulting in better survival and
vigor of several coniferous species tested.

The use of a portable pressure bomb to measure
plant moisture stress was demonstrated by Waring and
Cleary (1967). The theory behind it is described by Ritchie
and Hinckley (1975). Sampling errors may vary from less
than i 1 atm to i 10 atm depending on the degree of stress.

Measurements of plant moisture status in conifer needles

20

is reviewed by Ritchie and Hinckley (1975). They concluded
that needles may be preferable for they are a better indica-
tor of the water potential in the photosynthetizing and
transpiring tissues. They also point out the advantages of
smaller samples as less gas usage and easier recognition

of the point of external and internal pressure balance.

CHAPTER III

DESCRIPTION OF STUDY AREA

The study was conducted at the Tree Research Center

facilities of Michigan State University. The experimental

area is located along the western boundary.

Climatic Description

 

The summer is mild and the winter fairly cold. Pre-
cipitation is evenly distributed during most of the year,
showing a midsummer decline. The normal annual precipita-
tion is about 31 inches. The average frost free period is
approximately 160 days, generally from May 3 to October
10. The mean annual temperature is 8°C (47°F) with a
winter (January) mean of ~4OC (24°F) and a summer (July)
mean of 20°C (69oF). The average:annualwind velocity is
4 Km per hour (7 miles/hour) with an average maximum of 9

Km per hour (14 miles/hour).

TopographiC and Soil Description

 

The study was installed in a level to gently sloping
field on glacial ground moraine. The experimental plots
were placed on level areas on a hill tOp (Kalamazoo sandy

loam soil) and in a lower area (Metea sandy loam soil).

21

22

The Kalamazoo series is a member of the fine-loamy,
mixed, mesic family of Typic Hapludalfs. They are well
drained soils with a sandy loam to loam plow layer. A
typical profile as described by the Soil Conservation Ser—
vice for Kalamazoo County, Michigan, has a dark grayish
brown Ap horizon, dark reddish brown sandy clay loam and
gravelly sandy loam Bt horizon containing considerable
gravel, and dominantly brown B3 horizon of loamy sands,
sands and gravels. The runoff is slow on level areas.
Permeability of the upper part of the profile is moderate
and of the lower part is rapid.

The Metea series is a member of the loamy, mixed,
mesic family of Arenic Hapludalfs. A typical profile as
described by the Soil Conservation Service for Fulton
County, Indiana, has a dark grayish brown loamy sand A
horizon, and a B2 horizon that is yellowish brown loamy sand
in the upper part and dark yellowish brown clay loam in the
lower part. The soil is well drained and runoff is slow.
Permeability is very rapid in the sand upper layers and
moderate in the lower layers. Moisture supplying capacity

varies with the depth of the loam material.

History

The Tree Research Center is an 8 ha area of former
agricultural land. The natural vegetation of the experi-

mental area consisted mainly of quackgrass (Agropyron

 

repens), yellow foxtail (Setaria lutescens), broad leaf

 

23

plantain (Plantagp major), wood sorrel (Oxalis europea),

cinquefoil (Potentilla sp.) and wild vetch (Vicia angusti-

 

folia). The area had not been used for the previous three
years. No chemicals were applied during this period. The

weeds were mowed periodically during the growing season.

CHAPTER IV

MATERIALS AND METHODS

Experimental Design

 

The size of the available area and differences in
soil and slope, required the use of a Randomized Complete
Block design with seven replications for each of the five
treatments listed below.

Treatment 1 ~ no weed treatment, with the weeds
shading the seedlings.

Treatment 2 - Weeds clipped around each seedling to
prevent shading. This treatment was chosen as the control
treatment.

Treatment 3 - Weed treatment with simazine and gly-
phosate.

Treatment 4 - Weed treatment with glyphosate.

Treatment 5 - Mechanical weed control.

Weed control treatments were applied in such a way
so as to keep the plots free of competing vegetation for
the entire length of the first growing season.

The following comparisons of treatments were of
special interest in the study:

1) Treatments 1 and 2 with treatments 3, 4, and 5.

24

25

This comparison evaluates competition control as a method
to increase survival and growth in the first year.

2) Treatments 3, 4 and 5.

Through these comparisons three methods of competition
control are evaluated.

3) Treatment 3 with treatment 4.

Differences between them would be due to residual
effects of simazine.

4) Treatment 1 with treatment 2.

Evaluates the effects of competition for light.

Study Establishment

 

Sixty—four trees were planted in a 1 x 0.9 m (3% ft.
x 3 ft) spacing in each treatment plot. The measurement
plot consisted of at least 36 trees, marked with flags at
the beginning and end of each row. The buffer consisted
of one row of trees on all sides.

A composite soil sample of five 6—inch cores
were taken from each plot and analysed for percent organic
matter and estimated nitrogen release (ENR); available P,
exchangeable K, Mg and Ca, soil pH, cation exchange capac-
ity and percent base saturation of cation elements. Per-
cent organic matter, available P and Mg, soil pH and cation
exchange capacity were chosen to be the most appropriate
soil characteristics for a cluster analysis and subsequent
blocking of the plots.

The cluster analysis procedure used was that

26

described by Ward Jr. (1963). According to the results
obtained a set of seven homogeneous blocks were selected
and the treatments randomly assigned within each block.
The total number of treatment plots was therefore, thirty-
five. Initially, 46 plots were layed out, each with an

2 (439 ftz).

area of 41 m

Three thousand 9—12" (%23-3OCm)"Vans 35 Scotch pine"
seedlings were bought from Vans Pines Inc., West Olive,
Michigan. The seedlings were graded for size and apparent
bud conditions. Very small seedlings and seedlings without
viable buds were discarded. The remaining trees were
stored in a cold room until the time of planting on May
15. The "forester tree planter" planting machine from
Utility Tool and Body Company Inc., Clintonville, Wisconsin,
was used. This machine consists of a continuous slit
planter utilizing a coulter blade and rubber packing wheels
attached to a four—wheel tractor. It was difficult to
maintain the same spacing within rows, therefore, not all
plots had exactly the same number of trees.

All treatments except mechanical weed control were
applied after the trees had been planted. For treatment
1 the plots were left undisturbed, the idea being that the
seedlings would be shaded by the surrounding vegetation.
For treatment 2 the weeds around the trees were clipped
with a rotary type mower at about the bud height to prevent
shading. Treatments 3 and 4 were designed to test chemical

weed control. Treatment 3 consisted of one application of

27

Roundup (41% water soluble) on May 27 at a rate of 1.7
kg/ha (1.5 lb/a), followed by one application of simazine
80% wettable powder (Princep) on June 2nd at a rate of
2.2 kg/ha (2 1b/a). Treatment 4 consisted of one appli—
cation of Roundup,(4l% water soluble),also on May 27 at

a rate of 1.7 kg/ha (1.5 lb/a). A three gallon capacity

hand sprayer utilizing CO cartridges at 30 1b pressure,

2
delivering 187.1 1/ha (20 gal/a), with a nozzle number
8002 was used.

All herbicides were applied as directed spray and
care was taken not to spray over the trees to avoid injury.
At the time of spraying the weather was sunny with little
or no wind.

To meet treatment specifications reapplications of
Roundup were made in June and July for both treatments 3
and 4. At these times a th1 can was used to protect the
trees because the buds were growing actively and severe
injury could occur.

The plots for treatment 5 were cultivated prior to
planting, using a tractor mounted cultivator to work the
soil to a depth of 6 inches. To keep the area free of
weeds during the growing season a 5 HP "Trojan II" roto-
tiller was used. Weeds around the seedlings were pulled
by hand.

Treatment 3, where the herbicide Simazine was sprayed
was subject to an additional study of the persistence of

this chemical in the soil. Composite soil samples at two

28

depths, 0 to 3 inches and 3 to 6 inches were taken 30,
60 and 120 days after spraying. The samples were ex-
tracted by partition chromatography technique using a
hexane-acetone solvent system, as described in Appendix
A. The recovery of the extraction procedure determined
by fortification of a soil sample with 4 ml of a stand—
ard simazine solution (20 ppm in benzene) was 78%.

The extract was cleaned up using the method de-
scribed by Mills gt gt. (1972).

The residues were quantitatively evaluated by gas
Chromatography using a Coulson electrolytic conductivity

detector model Tracor 560.

Initial Tree Evaluation

 

In early July all seedlings in the measurement
plots were classified for bud condition, diameter and
depth of planting. Conditions of the buds and diameter
class were used as an index of seedling quality. The pur-
pose of this classification was to assess the effects of
seedling quality and depth of planting on survival and
growth at the end of the first growing season. Buds were
examined for physical conditions, dormancy and stage of
development; each tree receiving a code name and number
according to its characteristics as described in Table 1.

In the same way, three diameter classes were charac—
terized as shown in Table 2.

Regarding depth of planting, seedlings were

29

Table 1. Bud Condition, Codes and Characteristics Used
to Evaluate Seedling Quality -

 

 

Code Code D . t'
Number Name escrip ion

1 Dormant Buds did not develop

2 Broken Damaged physically

3 Elongating l to 2.5 cm in size

4 Candles More than 2.5 cm in size, without
needles

5 Leaders More than 2.5 cm in size, with
needles

6 Secondary Only secondary buds were developing

 

Table 2. Diameter Class Codes Used to Evaluate Seedling

 

 

Quality
Code Diameter Class (cm)
Small 0.1 - 0.4
Medium 0.41 - 0.59

Large

0.60 or larger

 

30

classified as described in Table 3. The criteria used

in this classification were based on the relative height
of the tree above ground. A seedling was considered
shallow planted when the uppermost part of the root sys-
tem was visible. A seedling was considered deeply planted
when the length of the stem without needles was less than
1/3 of the total height of the tree above ground. All
other trees were considered normally planted. This proce-

dure was used to evaluate planting technique.

Table 3. Coding Used for the Evaluation of Depth of

 

 

Planting
Code Depth of Planting
0 Shallow
1 Normal
2 Deep

 

Measurements

 

At the end of the first growing season growth mea-
surements and seedling characteristics were recorded.
Characteristic were measured that would represent the total
growth of the trees. For each tree, the initial height,
from the soil surface up to the first branches, the final
height, from soil surface to the tip of the tree and the
new growth, the difference between final and initial

height were recorded. A caliper was used for measuring

31

diameter. The number of lateral branches for each tree was
recorded, as well as the number of dead trees in each plot.
A final evaluation was made for each individual tree based
on growth performance as described in Table 4.

Table 4. Codes and Characteristics Used to Evaluate

Growth Performance of Scotch Pine Seedlings
at the End of the First Growing Season

 

Code Code

 

N ler Name Description

0 Dead Dead

1 No Growth Buds did not Elongate

2 Primary Only primary bud developed

3 Laterals Only lateral branches developed

4 Primary + Primary bud and 1-3 lateral branches
1-3 developed

5 Primary + Primary bud and 4-6 lateral branches
4—6 developed

6 Primary + Primary bud and 7 or more lateral
> 6 branches develOped

 

A comparison between initial and final evaluation
was used to assess the effect of seedling quality on
growth performance.

To measure the degree of moisture stress imposed to
trees subject to different competition control methods,
predawn pressure bomb measurements were taken on August
22. Plant moisture stress readings were taken on three

treatments: 1) Control, 2) Chemical weed control with

32

Roundup and 3) Mechanical weed control. The readings were
taken from 4:10 to 6:35 AM, when plant moisture is in
equilibrium with soil moisture. Two representative trees
on each plot were selected and the plant water potential
in bars was read using a fascicle removed from the new

growth, approximately 5 cm below the tip.

Statistical Analysis

 

Data were analyzed on the CDC 6500 computer at
Michigan State University. The SPSS: Statistical Package
for the Social Sciences (Nie gt gt., 1970) was used. An—
alyses of variance (Snedecor and Cochran, 1967) were per-
formed to analyse the differences among treatment means
for survival, initial height, final height, height growth,
diameter and plant moisture stress measurements. Analyses
of variance were also performed for trees separated accord—
ing to initial diameter class. The equality of the means
were tested by F test at .05 probability level. Tukey's
multiple comparisons procedure at .05 probability was used
to compare treatment means.

Frequency tables were prepared to relate initial and
final tree characteristics, survival and initial tree
evaluation. The independence of the variables was tested
by a Chi-square test.

Pearson correlations were used to evaluate the rela-
tionships of plant moisture stress to height growth, plant

moisture stress to survival and plant moisture stress to

33

diameter at the end of the growing season.
A disappearance curve, showing the relationship be—
tween concentration of Simazine residues and time was

constructed.

CHAPTER V

RESULTS AND DISCUSSION

Results obtained in the experiment present evidence
that control of competing vegetation during the first grow-
ing seasOn increases survival, height growth and diameter
of Scotch pine seedlings. No significant differences were
observed among the different methods of competition control
or between shading and not shading.

Results for survival and growth, as well as those
related to the importance of seedling quality, plant moisture
stress and simazine residues in the soil are presented and
discussed in detail.

Analyses of variance tables are enclosed as Appendix

Survival and Growth

 

Survival

Highly significant differences among treatments were
found for survival. The results of the Tukey's multicom-
parison test for survival are presented in Table 5.
Higher percent survival resulted on treatments where com-

peting vegetation had been removed. No significant

34

35

Table 5. First Year Field Survival of Scotch Pine
Seedlings with 5 Methods of Weed Control

 

 

Treatments Survival* %
Mechanical 87 a
Glyphosate 84 a
Glyphosate + simazine 81 a
Unshaded control 65 b
Shaded 61 b

 

*Means with the same letter are not significantly
different at a = .05 level.

differences were observed between the methods of competition

control employed.

Survival as Related to Initial
Diameter Classes

 

 

Seedlings with large diameters had the best survival,
followed by the medium size diameter. Seedlings with
smallest diameters had the poorer survival. Percent sur-
vival for seedlings separated by initial diameter class
can be seen in Table 6. Results are for the entire exper-
iment, regardless of treatment.

The analysis of variance showed that the treatments
did not influence survival of the large diameter seedlings.
They had the highest percent survival in all treatments.

For trees with medium and small diameter there was a signif-

icant difference among treatments. Resultsiknrfirst year

36

Table 6. Number of Trees and First Year Survival for
Small,Medium and Large Planted Scotch Pine
Seedlings

 

Initial Diameter

 

Number of Survival*
Class Code Seedlings %
Small 0 370 72
Medium 1 732 87
Large 2 70 97

 

*Chi-Square significant at 1% probability level.

survival of medium and small diameter seedlings are shown in
Table 7. Percent survival was higher on treatments were
competing vegetation was removed. For small seedlings how—
ever, the mean survival for treatment 3 where the compet-
ing vegetation was removed with Roundup and simazine was
not significantly different from treatments 1 and 2 where
competing vegetation was not removed.

Survival as Related to Bud Conditions
and Depth of Planting

 

 

Results of Chi-square test showed that survival was
dependent on bud conditions as described in the initial
tree evaluation and also on initial diameter size but not
on depth of planting. First year survival according to
bud conditions and depth of planting is shown in Tables 8
and 9 respectively.

Trees whose primary or secondary buds had already

 

37

Table 7. First Year Field Survival of Medium and Small
Diameter Scotch Pine Seedlings with 5 Methods
of Weed Control

 

Initial Seedling Diameter Class
Treatment Medium Small

Survival* %

 

Mechanical 94 a 81 a
Glyphosate 92 a 80 a
Glyphosate + simazine 91 a 76 a b
Unshaded control 78 b 68 b
Shaded 73 b 57 b

 

*Means for a given seedling size with the same
letter are not significantly different at O = .05 level.

Table 8. Number of Trees and First Year Survival of
Scotch Pine Seedlings of Various Initial Bud

 

 

Conditions
Bud Conditions Number of Survival*
Code Name Code Number Seedlings %
Dormant l 64 34
Broken 2 14 70
Elongating 3 153 77
Candles 4 234 96
Leaders 5 459 98
Secondary 6 47 90

 

*Chi—square significant at 1% probability level.

38

Table 9. Number of Trees and First Year Field Survival
of Scotch Pine Seedlings According to Depth
of Planting

 

 

Depth of Planting Number of Survival*
Code Name Code Number Seedlings %
Shallow 0 20 83
Normal 1 557 83
Deep 2 393 82

 

*Chi-square non significant.

started developing by early July had better survival than

those still dormant or with any physical damage.

Height

The total height as well as height growth was signif-
icantly higher in treatments where competing vegetation had
been removed. No significant differencesvnnxadetected be-
tween the methods of control used. There were also no
differences between control and treatment 1. The first
year height and height growth are shown in Table 10.

The analyses of variance performed for seedlings
separated according to initial diameter size for both
total height and height growth showed that trees with
medium and small diameter sizes performed better in treat-
ments where weeds had been removed. Again the method of
weed control used had no influence on the results. Total

height and height growth of medium and small diameter

39

Table 10. First Year Total Height and Height Growth of
Scotch Pine Seedlings with 5 Methods of Weed

 

 

Control
Treatment Total Height* Height Growth*
(cm) (cm)
Mechanical 29 a 12 a
Glyphosate 29 a 13 a
Glyphosate + simazine 27 a 12 a
Unshaded control 23 b 6 b
Shaded 21 b 6 b

 

*Means with the same letter are not significantly
different at a = .05 level.
seedlings are shown in Tables 11 and 12 respectively. For
seedlings with large initial diameter there was no sig—
nificant difference between treatments at 5% probability.
Table 11. First Year Total Height of Medium and Small

Diameter Scotch Pine Seedlings with 5 Methods
of Weed Control

 

Initial Seedling Diameter Class
Treatment Medium Small

Total Height* (cm)

 

Mechanical 30 a 26 a
Glyphosate 30 a 25 a
Glyphosate + simazine 29 a 22 ab
Unshaded control 24 b 20 b
Shaded 23 b 18 b

 

*Means for a given seedling size with the same let-
ter are not significantly different at O = .05 level.

40

Table 12. First Year Height Growth of Medium and Small
Diameter Scotch Pine Seedlings with 5 Methods
of Weed Control

 

Initial Seedling Diameter Class
Treatment Medium Small

Height Growth* (cm)

 

Mechanical 12 a 8 a
Glyphosate 12 a 8 a
Glyphosate + simazine 11 a 7 a
Shaded 5 b 3 b
Unshaded control 5 b 3 b

 

*Means for a given seedling size with the same letter

are not significantly different at d = .05 level.
Diameter

The same general trend was observed for diameter at
the end of the first growing season. Trees with the larg-
est diameter were found to be in plots without competing
vegetation, and they were significantly different from
those where vegetation had not been removed. This is
Shown in Table 13.

Analysis of variance performed for trees separated
according to initial diameter size showed that for seed-
lings with large initial diameter, weed control had no
effect in the final diameter. Seedlings with medium and
small initial diameter had comparatively higher final di-

ameter when competition from weeds was absent, as Shown

41

Table 13. First Year Diameter of Scotch Pine Seedlings
with 5 Methods of Weed Control

 

 

Treatment Diameter* (cm)
Mechanical 7 a
Glyphosate 7 a
Glyphosate + simazine 7 a
Unshaded control 5 b
Shaded 5 b

 

*Means with the same letter are not significantly
different at d = .05 level.

Table 14. First Year Diameter of Medium and Small
Initial Diameter Scotch Pine Seedlings with
5 Methods of Weed Control

 

Initial Seedling Diameter Class
Treatment Medium Small

Diameter* (cm)

 

Mechanical 9 a 7 a
Glyphosate 9 a 6 a
Glyphosate + simazine 8 a 6 a b
Unshaded control 7 a b 4 b
Shaded 8 b 4 b

 

*Means for a given seedling size with the same
letter are not significantly different at d = .05 level.

 

in Table 14.

There are many factors involved in the competitive
process and one of the most important is certainly moisture
consumption. Moisture deficiencies illustrate interaction of
environmental factors that play a vital role in the survival of
planted seedlings. Koslowski (1971), views survival and
growth of trees as being dependent more on availability
of water than anything else.

As water is readily absorbed from the soil, nutri-
ents are also being absorbed and circulated and therefore
growth is vigorous as long as there are no other limiting
environmental factors. As the soil dries, nutrient absorp-
tion is reduced and leaf water deficits develop because trans-
piration is higher than absorption. Photosynthesis and
other physiological processes are affected and growth of
meristems is reduced. If rain does not recharge the
soil, internal water stress becomes so intense that
growth may cease prematurely (Zahner, 1968).

Newton (1964a), studying the influence of herbaceous
vegetation on coniferous seedling habitat showed that the
rate of moisture depletion was a direct function of the
amount of vegetation. Lane and McComb (1948) investigat-
ing soil moisture consumption by tree seedlings and grass
came to the conclusion that grasses can rapidly reduce the
available soil moisture and in consequence retard the de—
velOpment of roots resulting in a decrease in top growth

and increase in mortality. Similar results of better

43

survival and growth following competition control for
other coniferous species have been obtained; Holt gt gt.
(1973) and Voeller gt gt. (1974) for loblolly pine, Larson
and Schubert (1969) for ponderosa pine, Lambert gt gt.
(1972) and Wittenkamp and Wilde (1964) for red pine. The
latter authors concluded that a 300 percent increase in
yield was due to elimination of competing vegetation and a
consequent increased supply of moisture.

Although the soil moisture consumption has not been
followed in this first growing season, it is not improper
to regard it as the most important factor involved in the
outcome of this study since the effects of other soil
characteristics were controlled by the layout of the ex-
periment. Results of plant moisture stress will be dis-
cussed in another section.

The method used to control unwanted vegetation did
not have any influence on the responses obtained. Al-
though trees subjected to mechanical weed control (T5)
generally had the best responses, they were not signifi-
cantly different from the responses obtained with chem-
ical weed control. Cost factors and soil disturbance
caused by cultivation Should be considered in the event of
selecting a practice.

Treatments 1 and 2 (control) were not significantly
different from each other. This suggests, for the par-
ticular site studied, competition for light is not strong

enough to affect growth and survival of seedlings.

44

The results also present evidence of the importance
of seedling quality in artifical regeneration. Trees with
larger diameter at the time of planting had better survi-
val and growth, regardless of the treatment applied. Seed-
lings whose buds started developing earlier and with no
physical damage had better survival. Wakeley (1954) work-
ing with southern pines noted that high physiological
quality appears to result in formation of new roots and
consequent favorable water balance in seedlings shortly
after planting. He also points out that although it is
difficult to evaluate accurately the physiological condi-
tions of the seedlings, various techniques in the nursery
may affect their phySiology.

Stone (1955) used the absence of root development as
a criterion to indicate an unsatisfactory physiological
condition of seedlings. He reasoned that if the root sys-
tem did not increase in size at a fairly rapid rate, the
seedling would die of drought when the moisture content
of the soil surrounding the roots approached the wilting
point. Lack of top development, would probably not become
critical during the first year after planting. He concluded
that the ability of seedlings to produce roots could not be
associated with external morphological differences.

As mentioned earlier, Lavender (1964) reported del-
eterious effects of cold storage and early lifting on
physiology of Douglas fir seedlings. For this experiment

seedlings were submitted to cold storage for 10 days.

45

Further studies would be needed to assess the effects of
such factors on seedling physiology and consequent perform—
ance in the field.

The conditions of the buds as described in the ini-
tial tree evaluation were determined by their external
appearance with no additional physiological basis.

The depth of planting did not influence survival,
suggesting that this is not an adequate measure of the
adequacy of the planting technique.

Relationship Between Initial and
Final Seedling Characteristics

 

 

The results of Chi-square test indicate a signifi-
cant relationship between the final classification with
bud conditions and initial diameter class but not with
depth of planting.

This final tree evaluation summarized the growth
performance of each tree. Table 15 shows the number of
trees in each bud condition class and percent of each
class with final tree classification. Table 16 shows the
same for initial diameter size and final tree classifica-
tion.

Again it can be seen that seedlings with buds that
had already started development by early July, the ones
designated as elongating,"cand1es" and "leaders," had
the best growth performance, developing a main bud and
3 to 6 lateral branches by the end of the first growing

season. Sixty-six percent of the seedlings with dormant

46

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wumEHHm kaEHHm mumEHHm z mmcHHpomm H
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coHpHpcou TOMB Hmch mSOHHm> EDHS mmmucmoumm

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48

buds died. As would be expected, 30% of the trees with
broken buds develOped only lateral branches, but another
30% managed to develop a main bud and 3 to 6 lateral
branches and 30% died. Sixty-four percent of the trees
that had only secondary buds developing by early July,
ended up with only lateral branches.

The results for diameter show the same trend as
discussed earlier. Seedlings with large initial diameter
had better growth performance, developing a main bud and
many branches. Forty-six percent of the seedlings
with medium initial diameters developed a main
bud with 3 to 6 lateral branches while only 37% of the
ones with small diameter did So; another 29% of them died.

These results emphasize the importance of seedling
quality, expressed in terms of diameter and bud conditions,
on the growth performance during the first growing sea-

SOD.

Plant Moisture Stress

 

Plant moisture stress was measured in treatments 2
(control without shading), 4 (weed control with roundup)
and 5 (mechanical weed control). The highest readings were
in the control plots, with a mean of 4.8 bars. This
result however was not significantly different from that
obtained for treatment 4—-weed control with roundup with
an average of 3.2 bars. The lowest stress was found to

take place where weeds were removed mechanically with an

49

average of 2.9 bars, and it was significantly different
from the control plots but not from the chemical weed con—
trol plots. These results can be seen in Table 17.

Table 17. Water Stress of Scotch Pine Seedlings with 3
Methods of Weed Control

 

 

Treatment Plant Moisture Stress* (bars)
Unshaded Control 4.8 a

Glyphosate 3.2 a b
Mechanical 2.9 b

 

*Means with the same letter are not significantly
different at d = .05 level.

A negative correlation was obtained between plant
moisture stress and height growth {-0.7268), plant moisture
stress and final diameter (-0.4087), and plant moisture
stress and survival (-0.3102).

The use of the pressure chamber technique has become
a standard method for assessing plant water status in the
field. Pressure chamber determinations are estimates of
the total water potential of the xylem sap. Measurements
just before dawn are a function of soil moisture if it is
assumed that during the night there is no transpiration be-
cause the atmospheric demand for water is low and the
stomata are closed and therefore equilibrium exists between
water potential in the plant and the soil (Ritchie and

Hinckley, 1975). The plant moisture stress measured

50

therefore is the same as soil moisture tension. As would
be expected plant moisture stress was higher in the control
plots where competitive vegetation had not been removed
and consequently the transpirational losses were higher.

The method of competition control did not signifi—
cantly influence moisture stress. One could postulate
that mechanical weed control, where the soil is exposed,
would result in higher plant moisture stress due to in—
creased evaporation. More intensive investigation using
more accurate techniques is needed to provide a better un—
derstanding of competition and moisture relations.

Growth is dependent on cell division and elongation
and ultimately on the supply of carbohydrates from photo-
synthetic tissue; both processes are intimately linked to
the water balance in a plant (Hsiao, 1973). This would
explain the negative correlation found between plant moisture
stress and height growth and diameter.

Sands and Rutter (1959) studied the growth of Ptggg

sylvestrisixxrelation to soil moisture tension. Compared

 

with plants growing in soil at 0.1 atm (0.1013 bars),
growth in the first year was significantly reduced when the
soil tension was 0.3 atm (0.3039 bars). The effects of
soil moisture tension on growth were due mainly to varia-
tions in net assimilation rate. Jarvis and Jarvis (1963)
also investigated the growth response of several species

of forest trees, including Pinus sylvestris,to water

 

regime. The results obtained for Scotch pine were similar

 

 

51

to those obtained by Sands and Rutter (1959).

Simazine Residues in Soil

 

The disappearance curve for Simazine is shown in
Figure l. The initial surface treatment of 2.2 Kg/ha
(21b/a) was calculated to be approximately equivalent to a
concentration of 2.2 ppmw mixed uniformly in the surface
6 inches of the soil. The logarithm of the concentration
in nanograms per gram of dry soil (ppb) plotted against
time conforms to a pseudo first order reaction consisting
of two phases. The concentration of simazine decreased
rapidly during the first phase. During the second phase,
dissipation continued at a slower, ever decreasing rate.
Only 1.5% of the simazine applied remained in the 0-3 in.
depth after 120 days. The amount of simazine in the 3-6
in. depth increased during the first 30 days and remained
approximately constant for the next 30 days. After this
period, simazine concentration decreased continuously to
almost undetectable levels 120 days following application.
The average concentration of Simazine in the two depths of
soil can be seen in Figure 2.

The dissipation of simazine from both depths might
have been the result of leaching, microbial degradation
or adsorption to organic and/or inorganic soil colloids.
Plant uptake may also account for dissipation.

Similar disappearance curves, consisting of two
distinct phases, have been obtained for simazine by other

investigators (Roadhouse and Birk, 1961; Talbert and

 

52

 

 

4' " - — - — 0 - 3 in
an. o — o — a- 6 in
\
\\\

3« \
t \
o \
o.
E \s
2 \\
Q ‘\‘
h ‘s‘
Q. 2 " ~“
E ~“\
fi ‘ ‘\ \‘\
Q ".~.‘ ‘~
2 '\.\
O ‘ \u,‘
0 ’\.‘_

q .\.

8 I \. ~
0
0
.4

O- T t I v

30 60 90 I20
TIME [days]

Figure l. Curves showing the disappearance of simazine

from two depths of a sandy loam soil after
application of 2.2 Kg/ha (2 1b/a). Points
are average of seven replications.

‘I

 

53

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2.0;; a 7" 0 3m
'3‘ ' B 3-6 in
/
é
2
4
E / //
.5: / y
a 2 4
a / 2
4 4
. 0 A at

Figure 2. Average concentration of simazine in two depths
of a sandy loam soil following application of
2.2 Kg/ha (2 1b/a).

54

Fletchall, 1964). Others have shown the existence of a
lag phase in the disappearance of simazine (Burnside gt gt.,
1961; Holly and Roberts, 1963). This lag phase is usually
attributed to unfavorable weather conditions or adaptation
of organisms that are effective in degredation.

Some studies have indicated relative resistence of
simazine to leaching (Ashton, 1961; Roadhouse and Birk,
1961; Harris, 1967). Burnside gt gt. (1961) studying
leaching of simazine in a silt loam soil found that the
depth to which simazine moved was not great but it in-
creased with amount of water applied.

The majority of evidence indicates that slow micro-
biological decomposition is the principal process involved
in the dissipation of simazine (Burnside gt gt., 1961;
Rabag and McCollum, 1961; Talbert and Fletchall, 1964;
Kaufman gt gt., 1965). Inactivation has been shown to
occur during the warm moist period of the year and cease
during dry, cool periods, coinciding with favorable condi-
tions for microbial growth.

A number of investigators have correlated the phy-
totoxicity of triazine herbicides with soil prOperties
(Sheets gt gt., 1962; Nearpass, 1965; Upchurch, 1966;
Hance gt gt., 1968).

The most important soil properties appear to be
organic matter, soil acidity and Clay content. Uptake and
degredation of simazine by red and white pine seedlings

has been studied by Freeman gt gt. (1964) and Dhillon gt

 

55

gt. (1968). The importance of soil properties and plant
uptake in the dissipation of simazine, however, requires
more detailed investigation than was possible in the pres-

ent study.

 

CHAPTER VI

CONCLUSIONS AND RECOMMENDATIONS

The establishment of a new timber stand requires
creation and maintenance of favorable conditions for
growth. Failures of reforestation programs have often
been associated with the competitive influence of her-
baceous vegetation that compete with the seedlings for
moisture, space, nutrients and light. Manipulation of
existing vegetation Imus been shown to minimize the sever-
ity of the habitat and improve survival and growth of the
seedlings.

The primary objective of this study was to examine
the effects of competition control on survival and field
growth of Scotch pine seedlings at the end of the first
growing season.

Seedlings were machine planted and subjected to five
treatments: 1) No competition control, 2) elimination of
shading from weeds, controlling competition for light,

3) competition control with simazine + glyphosate, 4) com-
petition control with glyphosate and 5) mechanical weed
control.

Competition control had a pronounced effect on

56

 

57

seedling growth and survival. Increased survival, height

growth and diameter resulted from competition control

with simazine + glyphosate, with only glyphosate and with

mechanical weed control. No significant differences were

observed among these three methods of competition control.
Other factors such as cost and environmental disturbances

should be considered in selecting a practice. Elimination
of shading from weeds did not increase survival or growth,
indicating that competition :fin: water is likely to be the
most important competitive factor on this particular site.
Nutrient differences were taken into account by the exper-
imental design used.

Plant moisture stress measurements in three repre-
sentative treatments (control, competition control with
glyphosate and mechanical weed control), showed that mois-
ture stress was higher where competing vegetation had not
been removed and lower where competition was controlled
mechanically. This is an indication of the relationship
between competition control and soil moisture availability.
More detailed investigations are needed to provide a better
understanding of the moisture relations for that site. Soil
moisture relations should be thoroughly investigated as
well as effects of sunshine and humidity.

The individual tree evaluation, done shortly after
planting, and based on diameter size and bud conditions
was used as an index of seedling quality. Results showed

that seedlings with large diameter size (0.60 cm or more)

58

always had the best survival and growth regardless of com—
petition control. Buds with good physical appearance also
resulted in better survival. Weeding resulted in signifi—
cant increased survival and growth of medium and small
seedlings.

The results suggest that high quality planting stock
and control of competing vegetation assure better survival
and growth of Scotch pine seedlings during the first grow-
ing season and that most of the response would be on medium
and small seedlings.

The same responses were obtained with different
methods of competition control. Cost analysis would be
advisable before selecting a method.

The planting technique, evaluated by the depth of
planting did not show significant influence on survival.

A secondary objective of this study was to determine
the persistence of the herbicide simazine in the soil as
well as its rate of disappearance. Only 1.5% of the
applied rate of 2.2 kg/ha (2 lb/a) remained in the top
0-3 in. of soil after 120 days. In the same period concen-
tration of simazine in the 3-6 in. depth decreased to al-
most undetectable levels. Results indicate that if control
of vegetation is required for more than one growing season
higher rates of simazine should be applied. Further in~
vestigations would be needed to assess influence of soil
properties, microbial degradation and uptake of herbicide

by Scotch pine on the dissipation of simazine from the

 

59

soil. These are important factors when control of un-

wanted vegetation is needed for longer periods.

 

 

 

BIBLIOGRAPHY

BIBLIOGRAPHY

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Bell, L. E. and D. P. White. 1966. Technical Manual for
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Brady, N. C. 1974. The Nature and Property of Soils.
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Brown, J. H. 1969. Effect of root pruning and provenance
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Chapmann, A. G. and R. D. Wray. 1957. Christmas Trees
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Dhillon, P. 8.; W. R. Byrnes and C. Merrit. 1968. Sima-
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Freeman, F. W.; D. P. White and M. J. Bukovac. 1964.
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Harris, C. I. 1967. Movement of Herbicides in soil.
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1967. Past, Present and Future uses of Her-
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APPENDICES

 

 

APPENDIX A

PROCEDURE FOR EXTRACTION OF SIMAZINE

RESIDUES FROM SOIL SAMPLES

 

b)

C)

f)

APPENDIX A

PROCEDURE FOR EXTRACTION OF SIMAZINE

RESIDUES FROM SOIL SAMPLES

Weight approximately 50 g of soil, add 10 ml of dis-
tilled water and let stand over night.

Add 80 m1 hexane-acetone (1:1) solvent, shake for 15
minutes and decant liquid into a separatory funnel.
Repeat the above procedure two more times using 40 m1
of solvent. Use vacuum filtration after the last
shaking.

Add 15 ml of 1% NaCl in water to the separatory funnel,
shake for 10 seconds. Discard the water layer (lower
layer).

Dry the hexane layer with 15-20 g of anhydrous NaZSO4.
Wash the funnel two times with 5 ml hexane. Add

wash to extract.

Concentrate the filtrate using a rotatory evaporator
to about 2 or 3 ml. Put the concentrate in a 10 ml
volumetric flask and add hexane washings to bring to
10 ml.

Proceed to Clean-up of extract.

The recovery of the extraction procedure was

66

67

determined by fortification of a soil sample with 4 m1
of a standard simazine solution (20 ppm in benzene). The

recovery was 78%.

 

APPENDIX B

ONE-WAY ANALYSES OF VARIANCE TABLES

 

APPENDIX B

ONE-WAY ANALYSES OF VARIANCE TABLES

 

 

Table B1. Analysis of Variance for Survival

Source DF SS MS F—Ratio
Treatments 4 3802.0148 950.5037 28.1596**
Blocks 6 129.5674 21.5946

Residual 24 810.1003 33.7542

Total 34 4741.6825

 

**Significant at 1% probability level.

68

 

69

Table B2. Analysis of Variance by Initial Diameter Size
- for Survival

 

 

 

 

Source DF SS MS F-Ratio
SMALL
Treatment 4 2834.7144 708.67.86 4.1556**
Block 6 499.2668 83.2114
Residual 24 4092.7659 170.5319
Total 34 7426.7471
ME D IUM
Treatment 4 2437.3804 609.3451 9.3455**
Block 6 334.8886 55.8148
Residual 24 1564.8564 65.2024
Total 34 4337.1257
LARGE
Treatment 4 436.2037 109.0509 1.9950 ns
Block 6 348.8971 58.1495
Residual 24 819.9270 54.6618
Total 34 1605.0278

 

**Significant at 1% probability level.

ns - non significant

70

Table B3. Analysis of Variance for Initial Height

 

 

Source DF SS MS F-Ratio
Between groups 4 413.6537 103.4134 5.3348**
Within groups 965 18706.3313 19.3848

Total 969 19119.9850

 

**Significant at 1% probability level.

Table B4. Analysis of Variance for Total Height

 

 

Source DF SS MS F-Ratio
Treatment 4 355.3439 88.8360 33.0342**
Blocks 6 75.0819 12.5136

Residual' 24 64.5411 2.5892

Total 34 494.9669

 

**Significant at 1% probability level.

 

71

 

 

 

 

Table B5. Analysis of Variance by Initial Diameter Size
for Total Height
Source DF SS MS F-Ratio
SMALL
Treatment 4 255.2121 63.8030 8.4981**
Block 6 91.7602 15.2934
Residual 24 180.1899 7.50791
Total 34 527.1622
MEDIUM
Treatment 4 292.2135 73.0534 17.6584**
Block 6 22.6440 3.7740
Residual 24 99.2889 4.1370
Total 34 414.1464
LARGE
Treatment 4 157.6566 39.4141 1.6357 ns
Block 6 178.7929 29.7988
Residual 24 361.4366 24.0958
Total 34 697.8861

 

**Significant at 1% probability level.

ns - non significant

 

 

 

72

Table B6. Analysis of Variance for Height Growth

 

 

Source DF SS MS F-Ratio
Treatment 4 295.5874 73.8969 35.6980**
Block 6 18.0491 3.0082

Residual 24 49.6812 2.0700

Total 34 363.3177

 

**Significant at 1% probability level.

 

73

 

 

 

 

Table B7. Analysis of Variance by Initial Diameter Size
for Height Growth
Source DF SS MS F-Ratio
SMALL
Treatment 4 191.2175 47.8044 11.2439**
Block 6 33.1278 5.5213
Residual 24 102.0382 4.2516
Total 34 326.3835
MEDIUM
Treatment 4 376.9671 94.2418 33.4665**
Block 6 28.9800 4.8300
Residual 24 67.5842 2.8160
Total 34 473.5313
LARGE
Treatment 4 200.1018 50.0255 3.4631 ns
Block 6 34.7119 5.7853
Residual 24 216.6826 14.4455
Total 34 415.4963

 

**Significant at 1% probability level.

ns - non significant

 

74

 

 

Table B8. Analysis of Variance for Diameter at the End
of the First Growing Season

Source DF SS MS F-Ratio

Treatment 4 35.5927 838982 32.5655**

Block 6 3.0635 .5106

Residual 24 6.5577 .2732

Total 34 45.2139

 

**Significant at 1% probability level.

 

 

75

 

 

 

 

Table B9. Analysis of Variance by Initial Diameter Size
for Diameter at the End of the First Growing
Season
Source DF SS MS F-Ratio
SMALL
Treatment 4 40.4325 10.1081 7.3387**
Block 6 13.6094 2.2682
Residual 24 33.0569 1.3774
Total 34 87.0988
MEDIUM
Treatment 4 25.1521 6.2880 35.6211**
Block 6 .9502 .1584
Residual 24 4.2366 .1765
Total 34 30.3389
LARGE
Treatment 4 15.0109 3.7527 2.3910 ns
Block 6 18.9481 3.1580
Residual 24 23.5426 1.5695
Total 34 57.5016

 

**Significant at 1% probability level.

ns - non significant

 

76

 

 

Table B10. Analysis of Variance for Plant Moisture Stress
Measurements

Source DF SS MS F-Ratio

Treatment 2 13.8017 6.9008 4.8351**

Blocks 6 12.0062 2.0010

Residual 12 17.1268 1.4272

Total 20 42.9347

 

**Significant at 1% probability level.

 

APPENDIX C

COMMON,TRADE AND CHEMICAL NAME OF HERBICIDES

AND RESPECTIVE MANUFACTURES

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