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This is to certify that the

thesis entitled

PRODUCTION AND TTTILIZATION OF
ACORNS IN CLINTON COUNTY, MICHIGAN

presented b1]

LOUIS J. VERME

has been accepted towards fulfillment

of the requirements for

M S d H- Fisheries
69W 'SnT—m ldl 1 1‘6

 
   

Major professur

Date March L8, 1955

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PLACE IN RETURN BOX to remove this checkout from your record.
TO AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

DATE DUE DATE DUE DATE DUE

 

OCT 1 2 2008

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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PRODUCTION AND UTILIZATION OF ACORNS
IN CLINTON COUNTY, MICHIGAN

BY

Louis Joseph Verme

A THESIS

Submitted to the School of Graduate Studies of Michigan
State College of Agriculture and Applied Science
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Fisheries and Wildlife

1953

ACKNOWLEDGEMENTS

The author expresses his sincere gratitude to
Dr. Leslie W. Gysel, under whose guidance this
investigation was undertaken, for invaluable aid
in initiating the study, and also for providing
certain materials and data obtained by him. His
constant encouragement and helpful criticism during
the field work and manuscript preparation are
gratefully acknowledged.

I also WiSh to thank Dr. Don W. Hayne for
generously providing the equipment and facilities
used in the acorn feeding eXperiment.

Thanks are also due to Dr. C. T. Black,
biologist in charge of the Rose Lake Wildlife
Experiment Station. for his excellent c00peration
I during the investigation, particularly in the
collection of chipmunk live-trapping data.

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TABLE OF CONTENTS

I. INTRODUCTION . . . .
II. REVIEW OF LITERATURE . .
III. DESCRIPTION OF STUDY AREAS .
IV. ANALYSIS OF SOKE FACTORS INFLUENCING ACORN
PRODUCTION . . . . . . . . . . . . . . .
Materials and Methods . . . . .
Results and Discussion . . . . . . . .
Crown structure and acorn production
Interior trees . . . . . .
Border trees . . . . . . . .
Acorn production variations and
comparative yield of study trees . .
Fruiting cycle . . . . . . . . . .
Individual variation . . . . .
Species and area differences . . .
Comparative production of interior,
border. and isolated trees . . .
V. THE USE OF TRAPPING DATA FOR ACORN
PRODUCTION ESTIMATIONS . . . . . . .
Materials and Methods . . . . .
Results and Discussion . . . . . .
Period of acorn fall based on trap

collections . . . . . . . . . . . . .

Page

ll
10
l4
l4
14
21

TABLE OF CONTENTS (Continued)

Composition of the 1952 acorn crOp .

Variations in trap and quadrat collections.

Trap-pairs .

Trap-quadrat pairs . . .

Acorn production estimation from crown

acorn counts and trap collection ratios

VI.

CERTAIN SMALL MAMMALS

Materials and Methods

Results

Chipmunk pOpulation estimate
Acorn feeding experiments

Effects of competition for acorns

SUMMARY . . . .
LITERATURE CITED

and Discussion .

POPULATION SIZE AND ACORN UTILIZATION OF

54

58

. 60

6O
64
68
72

LIST OF TABLES
Table Page

1. Distribution of Acorn Production, Number
of Limbs, and Acorns Per Limb of Interior
Trees, from Crown Counts . . . . . . . . . 15

2. Number, Range, and Mean Diameters and
Lengths of Interior Tree Crown Limbs
of Five Sample Trees for Each Spcies . . . l7

5. Distribution of Acorn Production, Number
of Limbs, and Acorns Per Limb of Border
Trees, from Crown Counts . . . . . . . . . 22

4. Tree Measurements and Acorn Production of
Interior Study Trees . . . . . . . . . . . 50

5. Comparative Acorn Production of Interior,
Border, and Isolated Trees, Based on
Crown and Trap Counts, and Ground
Estimation . . . . . . . . . . . . . . . . 55

6. Composition of the 1952 Acorn Crop, Based
on Trap Collections, September 15 to
OCtOber 24 O O O O O O O O O O O O O O O O 45

7. Number of Acorns and Cups in Traps and
Ground Quadrats, Collected September 2
to October 24 . . . . . . . . . . . . . . . 52

8. Proportion of the Acorn Crop Determined
by Tree Counts to that Measured by
Trapping . . . . . . . . . . . . . . . . . 55

9. Results of Live-Trapping at Rose Lake
Woodlot 6 during October 6 to 17 . . . . . 61

lO. Species and Number of Acorns Fed, Total,
and Daily Average Food Consumption of
Captive Chipmunks and White-Footed Mice . . 65

LIST OF FIGURES
Figure Page

1. Average Crown Conformation and Acorn
Producing Area of Sample Trees in
the Interior of Forest Stands . . . . . . l9

2. Crown Conformation and Acorn Producing
Area of Typical Border Black Oaks,
Rose Lake Woodlot l . . . . . . . . . . . 25

5. Acorn Trap in Operation on South Border
of Rose Lake Woodlot l . . . . . . . . . 41

4. Period of Acorn Fall Determined from
Trap Collections: Counts Exclusive of
Small Size Acorns . . . . . . . . . . . . 45

I. INTRODUCTION

Members of the genus Quercus have great commercial
importance and considerable silvicultural study has been
accorded them. A concomitant value, but one generally
less recognized, is oak mast production as food for wild-
life. Although often of vital importance to foresters
and wildlife biologists alike, little is known concerning
either acorn production or utilization. Basic, quanti-
tative data are urgengly needed, since these will materially
aid the deveIOpment of intensive oak forest management,
whether for timber or game.

This study is an outgrowth of a long-term acorn
investigation recently initiated at Michigan State
College. The author attempted to determine some of
the lesser known, but none-the-less important factors.
influencing acorn production and utilization. These
include: (1) amounts and variations in acorn production
of individual trees, and Species and Site differences.
The data were obtained largely by acorn counts of tree
crowns; (2) quantitative measurements of the acorn creps
as determined from seed trapping activities, and. (5)

animal utilization of acorn mast, particularly rodent

competition, obtained from population studies and acorn
feeding experiments. .

The study was conducted on two areas, approximately
40 miles apart, at Rose Lake and Maple Rapids, in Clinton
County, Michigan. Both areas have upland oak-hickory
forest types, although each differs strikingly in stand
composition, land-use, and soils.

The field work began during late summer and continued
through the fall months of 1952. Following the selection
of sample trees, acorn counts of tree crowns were
initiated and occupied most of September. Acorn trapping
activities ran concurrently but extended into mid-October.
The studies on animal papulations and acorn utilization

were conducted during the months of October and November.

II. REVIEW OF LITERATURE

Surprisingly few data are available concerning acorn
production. Much of the literature extent is based upon
short—term studies or observations. Interest in forest
tree seed production received initial impetus in Germany
in the years between 1870 and 1900 (Baker, 1950). Oak
mast studies are of particular interest to foresters
because oak stand regeneration is often inadequate.
Korstian (1927) investigated some of the factors affect-
ing germination and early survival of oaks in the southern
Appalachian region and attempted to obtain quantitative
data on production and biotic agencies reaponsible for
destruction of the crop. Similar studies were conducted
by Wood (1954, 1938) for chestnut oak in New Jersey.

The most comprehensive and authoritative acorn study
resulted from a 7-year investigation of five oak Species
in the southern Appalachians by Downs and McQuilkin (1944).

Additional studies, although of limited scepe, were
conducted by Cypert and Webster (1948), and Cypert (1951).
Baker (1950) summarized the various investigations
concerning seed production and presents an excellent

discussion on the topic.

Quantitative measurements of acorn crops have been
attempted. The most common method is based upon crown
sampling by open, ground quadrats, variously delineated,
and yielding a proportion of the total crop (Korstian,
1927; Wood, 1934; Allen and McGinley, 1947; and Cypert
and Webster, 1948). The data obtained are subject to
serious error, however, due to animal utilization. More
reliable data accrues from sampling by Specially con-
structed ”seed traps” (Wood, 1958; Downs and McQuilkin,
1944; Easley and Chaiken, 1951; and Cypert, 1951),
since they tend to exclude most animals.

The utilization of acorns by wildlife, although
often of great importance, has not received the study
commensurate with its scape and value. When available,
acorns constitute a staple food for many game animals.
Van Dersal (1958, 1940), and Martin, et a1. (1951)
summarized the many separate studies and records of
acorn utilization by wildlife. Animal consumption of
acorns often has a deleterious affect upon oak regener-
ation, depending upon the magnitude of the acorn crop
and the animal pOpulation present (Korstian, 1927;
Wood, 1954, 1958; Downs and McQuilkin, 1944: Cypert
and Webster, 1947; Baker, 1950). Additional studies on

population densities and acorn utilization of small

5
mammals have been reported by Hamilton (1941), Allen (1945),
Baumgras (1944), and Burt (1940, 1948). An excellent
report on small mammal ecology at Rose Lake, Michigan,

is that of Linduska (1950).

III. DESCRIPTION OF STUDY AREAS

Clinton county lies in the south-central part of
the Lower Peninsula of Michigan. The land surface and
soils differ greatly within the county, ranging from
well-drained uplands to swampy depressions. The Rose
Lake area is located in the southeast corner of the
county. This vicinity is characterized by undulating
to hilly topography. The soils are varied, but consist
mostly of well-drained sandy loans and loamy sands,
developed from calcareous glacial parent materials
deposited as terminal moraines and till plains. Natural
fertility and water retention is usually low (Johnsgard,
et a1. 1942). The woodlands generally consist of mixed
hardwoods,-although upland oak and oak-hickory forest
types predominate.

The topography in the vicinity of Maple Rapids is
slightly undulating to gently rolling. Most of the
soils present have developed from calcareous glacial
drift. A.high clay content insures water retention
during the growing season. Most of the woodlots in
this region are composed of upland oak-hickory forest

types.

The climate is temperate, with winters moderately
cold and summers mild. The average annual rainfall of
about 50 inches is fairly uniformly distributed through-
out the year.

One of the study areas was located on the property
of the Rose Lake Wildlife Experiment Station, and lies
in Section 25, T5N, RIW (Bath Township). This area,
designated as Rose Lake woodlot 6, is a l2-acre woods.
Only the eastern half was suitable for study; the
western portion consists mostly of immature timber.
White oak (93ercug g1pg)l is the dominant tree species
in the woodlot, with black oak (Quercgs yeluting) and
pignut hickory (Q§£z§,ovali§) codominant and of secondary
importance. Most of the white oaks are large, ranging
70 to 85 feet high and 20 to 25 inches in diameter.

Ages vary from 150 to 200 or more years. The black

oaks are generally smaller. The average diameter of

11 trees was 16.9 inches, and ranged from 14.2 to 21.2
inches. Height is very similar to that of white oak,
averaging 74.7 feet. The trees age from 75 to 150 years
old, but are thrifty and growing more rapidly than white
oak. Crown vigor is good for both species, but the

 

1 Common and scientific names of woody plants are
according to Gray's Manual of Botany, 8th Edition
(Fernald, 1950).

8

crowns of black oak are smaller than the white oak. The
stand has approximately normal stocking. A number of
decadent white oaks are present and in some instances
excessive crowns have developed, due to openings in the
stand.

A dense understory has developed on the area follow-
ing cessation of grazing in 1958 (Linduska, 1950). Black
Cherry (Egunus,§erotina) and sassafras (Sassafggsyalbidum)
are in great abundance. Scattered clumps of blackberry
(Rubu§,_p,), wild rose (Egan _p.), and ground juniper
(Junipegus communis) are also present, but are slowly
being eliminated. A ground cover of June grass sod
(£9g,pratensi§) is present on much of the area but
considerable leaf litter has accumulated.

The topography is undulating to rolling, and the
soil consists of Bellefontaine sandy loam - a medium to
good black oak site (Gysel and Arend, 1955).

A second woodlot (number 1) was used for border tree
studies, since well-developed borders were lacking in the
former. This woodlot consists mostly of a pure stand of
even-aged (about 100 years) black oak of moderate to
good stocking on soil similar to that of woodlot 6. A
partial selection cut in 1949 removed some of the timber.

9

White oak, pignut and shagbark hickory (Carya ovate) are

 

codominant but of lesser importance. The woodlot has
well-deveIOped borders dominated by black and white oak.
The fields surrounding the woodlot are in row crops or
pasture.

The second study area is located in Section 10, TSN,
R5W, one mile east of Maple Rapids, Michigan. It is
approximately 40 miles north and west of the Rose Lake
area. This 40-acre woodlot, locally known as the Lansing
Woods, is a remnant stand of virgin timber. White oak
dominates the stand in size and stocking. Many of the
trees are 150 to 500 years or more in age. Diameters
of sample trees ranged from 20.0 to 50.4 inches and
averaged 22.7 inches. Many larger trees are present.
Tree heights averaged 81.7 feet and varied from 78 to
91 feet high. These trees have thrifty, well-formed
, crowns and long, clear boles. Growth rate is fair, but
generally best in the smaller trees. Red Oak (Quercgg
IEDEQ) is codominant and an important component of the
stand. It is slightly taller than the white oak (average
84.0 feet) but the diameter range of 10 trees was
considerably smaller, 15.7 to 20.5 inches. The tree

crowns are small, columnar, and thrifty. Growth rate

10

is excellent - average diameter increment was slightly
less than two inches during the past ten years. Red oak
generally occupies the lower, but well-drained sites,
which may be Optimum for this species. Shagbark hickory,
white ash (Fraxinus americana), swamp white oak (Quercus
bicolor), black oak, and elm (Ulmus americana) are co-
dominants and commonly interspersed throughout the stand.

All borders are dominated by huge white oaks, although
red, black, and Jack oak (Quercus ellipsoidalis) also occur.

A dense, heterogeneous understory is present and is
probably the result of the generally open canopy and site
fertility. Hawthorn (Crataegus §p,), shadbush (Amelanchier
sp,), and witherod (Viburnum cassinoides) are the most
common shrubs.

A thick accumulation of leaf litter is present over
most of the woodlot, but June grass has encroached onto
the south border. The topography is undulating to rolling
and the soil consists of Miami silt loam. This is a good
to very good oak site (Gysel and Arend, 1955). Intensive
farming for row crops and livestock characterizes the
general vicinity of Maple Rapids.

Little if any timber has been removed in the past;
however, cutting operations were initiated during the

current year under an experimental management program.

IV. ANALYSIS OF SOME FACTORS
INFLUENCING ACORN PRODUCTION
A number of factors are believed to influence forest
tree seed production; however, their effects upon fruiting
and seed development are poorly understood. Among the
factors often considered are light conditions, site
fertility, climate, and tree genetics. In this study,
the effects of light upon acorn production were determined
from crown counts of acorns, in relation to crown aspect.
Site influence was evaluated from the variations in Species
production between the study areas, according to their
site classes. Genetic factors were expressed as production

variations of individual trees.

Materials and Methods

After a preliminary study, 10 trees of white oak and
11 black oaks were selected at Rose Lake woodlot 6. Ten
trees each of white and red oak were chosen at Maple
Rapids. This group constitutes a sample upon which long-
term acorn studies will be based. The criteria for
individual tree selection were adOpted from Downs and
McQuilkin (1944). Their study revealed acorn production

differences were generally correlated with bole diameters.

12
The bulk of the acorns for white oak were produced by
trees 20 to 52 inches d.b.h., with greatest production
at about 26 inches. That for red oak was 16 to 25 inches
and was best for 21 inch trees. Black oak production
increased prOportionately with diameter. Crown size and
thrift were also related to production potential. The
larger crowned trees generally produced the largest crops,
particularly if growth was vigorous.

In the present study white oaks were restricted to
trees 50 inches d.b.h. or under. Most of the red and
black oaks ranged from 15 to 22 inches, and were the
largest trees available. All trees selected possessed
medium-sized, thrifty crowns, as Opposed to excessively
large or small forms. Crown symmetry was also considered
Since it affected trap placement. Measurements of sample
trees are presented in Table 4.

In order to correlate acorn production with crown
structure, five trees of each Species, for both sites,
were chosen for special study. The trees were ascended
by means of a loo-foot half-inch manila rope and crowns
were inSpected by climbing the main branches. Selection
of trees was related to ease of crown accessability;

i.e., one large limb within 50 feet of the ground. Upon

l5
entering the crown all limbs were numbered and diameters
(2 inch minimum) and lengths estimated and recorded.
All limbs were designated as ”exposed” or “lower” crown
branches. Limb position relative to origin on the trunk
was the criterion used; however, in some instances general
limb condition as indicated by natural pruning was used,
since this was a reflection of light quality and intensity.

In addition, the crown was divided into four 90 degree
quadrants and each limb classified as north facing, south
facing, etc., on the basis of point of origin and sub-
sequent growth habit. Arbitrary designations often
resulted, particularly with twin-headed crowns. Errors
in judgment are considered compensatory.

Acorn counts were conducted for all limbs, starting
at the t0p and descending. The foliage of each limb was
carefully scrutinized and counts of well-developed acorns
recorded. The observer was usually within a few feet of
the acorn bearing outer branchlets, but this varied with
accessibility and safety. Most acorns were visible and
easily discernible. Slight air currents often revealed
acorns hidden by foliage. An estimated 5 to 10 percent
of the acorns were probably not counted, depending upon
tree Species and size of crown, thus the counts may

sometimes be low.

14

In a year of high production a sampling method would
have been desirable Since individual counts are laborious
and time consuming. Preliminary study showed close agree-
ment between sample area counts and total limb counts.

The trees at Rose Lake woodlot 6 were censused
between September 7 and 11, and those at Maple Rapids
September 16 to 19. In addition, 8 black and 4 white
oak border trees (woodlot 1) were climbed from September
12 to 15. Six Naple Rapids border trees (5 each of red
and white oak) were censused during September 20 to 25.

Several others were climbed for observation.
Results and Discussion
Crown Structure and Acorn Production

Interior trees

Analysis of Table 1 reveals striking differences in
quantity of seed produced between the eXposed and lower
crown categories of sample trees. Although there is
considerable variation among species, the trends are
generally similar. Individual tree counts are in close
agreement with aggregate production of the group. Total
eXposed crown production was 5.4 times greater than
lower crown yield for Rose Lake white oak, 11.2 times
greater for black oak, 5.5 times greater for Maple Rapids
white oak, and 5.6 times greater for red oak.

15

 

 

 

 

 

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These differences represent the innately greater
production of upper crown limbs. Number or size of
limbs is not a factor. Table 2 shows slightly greater
numbers of upper crown limbs for Maple Rapids trees,
but Rose Lake trees have more lower branches. Although
not expected, the diameters of upper and lower limbs
are remarkably Similar. No difference in size exists
for Rose Lake trees; the lower limbs of Maple Rapids
trees are only slightly larger than the upper limbs
(.8 and 1.0 inch greater diameter for red and white
oak, reSpectively). Lower limbs averaged slightly
longer than their counterparts. The difference was
greatest for red oak (9.6 feet).

Average production per limb also varies but is
directly related to tree yield. The highest producing
black oak had an average exposed limb yield of 229.8
acorns but only 9.8 acorns per lower limb. The average
production for all black oaks was 62.1 and 4.8 acorns
per exposed and lower limb. Average production per
branch for all trees is closely similar to total upper-
lower crown acorn ratios of a group. The data appear
to confirm the contention that production of high-forest
trees in closed stands is confined to tops of trees

(Toumey and Korstian, 1947).

17
Table 2
Number, Range, and mean Diameters and

Lengths of Interior Tree Crown Limbs
of Five Sample Trees for Each Species

 

 

 

Exposed Crown _ Lower Cgogg II—
Total Total
No. Diameter Length . No. Diameter Length
of (inches) f at of (incheg) e
Species Limb: Rggge Megg Rgnge an Limbs Range Mean Rgngg Mean
White .
Oak 22 5-8 4.9 6-55 17.5 28 2-8 5.0 10-52 19.1
Black
Oak 21 5-8 5.9 6-50 11.4 24 2-6 4.0 6-55 15.2
White
Oak 56 5-10 5.4 10-54 20.6 52 5-10 6.2 8-50 26.5

Red Oak 24 5-6 4.0 12-25 17.3 18 5-9 5.0 15-44 26.9

 

18

Limb aSpect (azimuth) also modifies production as
noted in Table 1. Average per limb production is a
better index than total yield since the number of limbs
is considered. South facing eXposed crown limbs usually
produced the greatest quantity of acorns. Average limb
production for all black oaks was, south 150.6 and north
52.1 acorns - a 4 to 1 ratio. West limbs produced 58.8
acorns to 8.2 per east limb. Maple Rapids white oak,
averaged 67.4 acorns per south limb and 25.7 for north;
the west face production was 48.8 to 50.5 acorns per
east limb. The lower aSpect ratios of white oak probably
represent differences in crown deve10pment; i.e., larger,
more open form.

Lower crown production does not appear to be
correlated with limb azimuth, since no definite trend
is discernible. This is SXpected because most of the
light reaching this level is diffused and equally
distributed.

Interpretation of acorn production as modified by
crown position is best illustrated by Figure l. The
crown diagrams are based upon average measurements of
individual study trees (Table 4). Crown measurements

were obtained after leaf-fall was completed. The outlines

 

 

 

 

 

 

 

 

 

 

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20
are drawn to scale and represent real differences in
conformation among Species and between sites. The
relative acorn producing areas are based on data from
Table l, and graphically illustrate the effects of
insolation upon seed production. Although the diagrams
represent south-north aSpects, a somewhat similar
relationship exists for west-east faces.

The shading effects of contiguous trees (abutting
crowns) delimits the height of eXposed crown and is
eXpreSSed in foliage changes; i.e., lower limbs have
large, thin, verdent leaves. Severe pruning is often
evident in the lower limbs. ‘White oak lower limbs have
higher shade tolerance and therefore a deeper lower crown.
Foliage densities also modify production and result in
lower north and east upper crown production through light
energy interception by the reverse face. Depth of light
penetration varies with foliage density and differs within
Species and sites.

According to Baker (1950), and Toumey and Kbrstian
(1947), insolation directly affects seed production since
a high rate of photosynthesis and rapid accumulation of
carbohydrates is favored by high temperatures and plenty
of light. A.high food reserve (starch) seems necessany

for adequate flowering and bud formation. Solar energy

21
as heat may directly affect flower and bud survival.
Wood (1958) believes there is a physiological limit to
the number of acorns that can be supported by a tree.
The low production of the lower crown is probably due to
the inability of the shaded foliage to produce reserve
food in excess of the amounts needed for subsistence and

growth.

Border trees

Adequate data for border tree analyses are limited
to the black oak of woodlot l at Rose Lake (Table 5).
Exposed and lower crown categories were not feasible for
border oaks since all portions of the crown are considered
exposed. However, the data showed a decidedly greater
production of acorns born on the upper limbs of the trees.
For example, one south border black oak had 7 upper crown
limbs which averaged 81.5 acorns per limb (total 569).
while 15 lower limbs produced only 52.2 acorns per limb,
with a total yield of 475. Similar trends were noted
for all border trees regardless of aspect. Figure 2
illustrates the relation of crown surface and acorn
production for north and south border black oaks.

ASpect differences in border production of black

oak are correlated with number of limbs and are a function

22

 

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Acorn
Producing
Area

 

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A A l A
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24
of border exposure. The south face of a south border tree
always had relatively more limbs than any other face,
consequently total production was greater. Average
production per limb. however, was only slightly higher
for south limbs (42.0 acorns) than west (40.2). but about
twice as high as north (28.3) or east (22.7). The side
Opposite the border eXposure was always lowest in either
category. The production of north border black oak was
considerably lower than south or west border trees.
therefore the production trends according to aspect could
not be accurately interpreted.

White oak border trees (woodlot l) were few and
produced poorly. North border trees have shade tolerant
lower limbs that usually extend outward, forming extensive
canopies. An excellent example of insolation effect was
noted for one white oak. A lower limb, estimated at
one-eighth the total crown area, projected beyond the
northwest corner of the woodlot and accounted for 112
of the 171 acorns (65.5 per cent) tallied for the tree.

Maple Rapids border white oaks were extremely large,
but did not have high production commensurate with size.
Only 2 of 8 trees climbed were producing well, the others
largely failed. Disposition of acorns were similar to

that of black oak at Rose Lake.

25

Crown formation and growth habit differences of
border black oaks are presented in Figure 2 and are based
upon average tree measurements. Although these trees are
similar in age, bole diameter, and height, growth form
varies greatly and seem to reflect reSponses to light.
The north border trees are severely pruned; the limbs are
few and widespreading. Acorn production appears to be
sacrified in favor of tree growth. The extremely poor
conditions of these trees suggest that other factors may
be influencing growth form. South border trees contain
many large lower limbs which develOp numerous branchlets
and dense foliage. West and east border trees are
intermediate in stature: west trees are similar to south
border form, and east trees closely allied to north.

Acorn Production Variations and
Comparative Yield of Study Trees

Fruiting gycleg

Annual variations in seed production are commonly
observed in oaks. The fluctuations are often striking
in occurrence and a cyclic phenomenon has been ascribed
to them. A.uniform cycle does not appear to exist,
however. Baker (1950) reports a 5 to 6 year peak
production for European oak between 1874 and 1893,

26

but alternate year highs are indicated. Wood (1954)
observed high production for chestnut oak during 1928,
followed by two years of low yield. For oaks in general,
Van Dersal (1958) believes full crops are borne at
intervals of 8 to 10 years, but some seed is produced
almost annually. Downs and McQuilkin (1944) reported

a peak production for 1958 and 1942 during their seven
year study, but concluded that a longer period is needed
to determine the periodicity of the cycle (5 to 4 years)
if it exists. Allen (1945) believes an alternate year
production is evident among individual trees, thus some
seed is produced almost every year. A.1imited amount of
acorn crOp data has been obtained by the Rose Lake Station
since 1959. The sampling method is that of Allen and
McGinley (1947) but has been variously modified since
its inception. Only a few (mostly isolated) trees
constitute the sample. The success of the acorn cr0ps
I{are given below. A peak crop is indicated once in 5 to

4 years but it is not consistent.

 

 

 

 

Xgar Crop Year ngp
‘1959 Excellent, all oaks 1946 Very poor, all oaks
1940 Very poor, all oaks 1947 Poor, all oaks
'1941 Good, red oak ex- 1948 Fair, black oak
ceptional *1949 Good, all oaks
1942 Fair, white oak failed 1950 Fair, red and white oak
1945 Poor, red oak fair 1951 Poor, red oak exceptional
1944 Poor, all oaks 1952 Poor, red and white oak

1945 No data failed

 

27

Note that 1952 was considered a poor year, particularly
for white and red oak. Some seed was produced by Nbple
Rapids white oak, and black oak. Acorn crOp failures

are the rule rather than the exception, thus data obtained
during a poor year are significant.

The cycles have been explained on the basis of the
carbon-nitrogen ratio theory. A.favorable (carbon) ratio
results in reserve food accumulation, and this is expressed
in high flower production. After a tree produces a heavy
crop of seed it usually requires a period of several years
for the accumulation of sufficient food reserve to make
another heavy seed year possible (Toumey and Korstian,
1947). Baker (1950) largely repudiates this concept
because greatly increased seed production has been noted
following application of nitrogenous fertilizer (Chandler,
1958, Detweiler, 1945).

Climatic conditions such as spring frosts, exception-
ally dry or wet summers, etc., may directly affect seed
production through pollination failure and flower bud
mortality. Inadequate fertilization was not found to be
significant in chestnut oak flowering, according to Wood
(1958). He observed a progressing mortality (99.5 percent)
from time of fertilization to acorn maturity. Baker (1950)

28
ibelieves that the destruction of a potentially heavy crap
prevents the eXpenditure of stored nutrients, or otherwise
upsets the normal cycle, and commonly calls forth a heavy
crop the following year. During crown counts the author
observed several low producing black oak trees whose
branches contained numerous small, dead acorns (often

5 or more per cluster), indicating a high summer mortality.
High acorn flower counts were noted for these trees,

thereby substantiating Baker's observation.

individual variation

Seed production is greatly affected by crown class
(dominance) and reflects the direct stimulus of light
upon size and thriftiness of tree crowns (Toumey and
Korstian, 1947; Baker, 1950; Cypert, 1951). Downs and
McQuilkin (1944) state that “within a Species, intensity
of acorn production per unit of crown volume is approxi-
mately the same for all trees, and that total acorn
production therefore is related directly to size of
crown, and indirectly to d.b.h.” However, they did not
find high acorn production to be consistently correlated
with such tree characteristics as d.b.h., crown diameter,

age, or growth rate.

29

Attempts to relate acorn production to tree develop-
ment in the areas studied generally indicate positive
correlation, although wide discrepancies occur (Table 4).
The highest producing black oak has the largest crown
diameter and is above average in all categories except
growth rate. The second highest producer, however, is
below average in all categories but has the best growth
rate. The highest producing Maple Rapids white oaks also
possessed the largest crowns, and were above average in
all other classes. Several large crowned trees produced
low acorn crOps, however. Downs and McQuilkin (1944)
found that well-formed, thrifty crowns were the best
producers. A.favorable crown position in the canOpy
is expressed in increased bole increment and therefore
a larger d.b.h. This is true for Maple Rapids white oak,
but not for black oak. Apparently, no single, valid
criterion exists for judging the potential production
for all trees.

The possibility exists, that genetic factors also
control seed production. It has been observed that some
trees consistently bear good crops of seed, even in poor

years, while others are “vegetative" and usually fail

50
Table 4"

Tree Measurements and Acorn Production
of Interior Study Trees

 

 

 

 

 

 

 

Species Radial Cgown Total
and Growth Height Diameter Acorns
Locali- Tree 10 Ex- Maxi- Ex- Per
ty No. Years Age D.B.H. Height Totgl Posed mum Posed Tree
mm. Yeags Inches Feet Feet Feet Feet Feet Number
White 1 - - 25.0 68 28 20 57.5 26.6 64
Oak 2 14 195 22.2 70 22 20 52.6 22.1 8
Rose 5 - - 25.5 72 27 17 50.0 21.5 57*
Lake 4 - - 20.8 86 5O 15 28.5 25.0 15
5 8 198 20. 6 84 25 25 26. 0 24.1 19*
6 10 185 20.5 76 26 16 58.5 27.5 19*
7 - - 20.2 77 ,25 10 24.5 10.5 97
8 15 192 25.8 81 58 15 54.7 28.1 58*
9 - - 25.0 77 27 17 54.0 50.0 57*
10 _15 120 14.7 76 21_T 10 17.2 .17.2 56
Mean :12 178 pglg4 76.7 26.7 _16.5 50.5 25.4 40.8
Black 1 16 75 15.6 81 26 16 55.2 21.9 59
Rose 5 - - 16.0 66 24 24 50.5 25.5 500*
Lake 4 ~ - 20.7 86 26 26 50.5 27.5 75*
5 15 96 16.8 87 24 24 56.1 55.0 150*
6 - - 17.2 7O l7 17 29.5 25.7 25
7 14 124 21.2 79 16 10 40.0 28.9 1,525*
8 19 82 18.2 86 28 18 52.5 26.8 50
9 - - 14.2 57 19 19 26.5 26.5 158
10 20 85 14.2 65 14 14 25.9 24.6 1 188
11 - - 14.8 70 .15 10_ 17.0 .17.0 -
Mean 16.4 92 p16.9 74.7 21.9 18.0 50.0 25.7 408.0
Oak 2 12 - 50.4 87 28 18 42.1 40.7 1,989
Maple 5 7 - 22.6 85 2O 10 54.4 52.5 155*“
Rapids 4 , 11 - 20.1 79 2O 14 28.0 25.1 88**
5 15 202 21.5 78 27 20 55.6 52.2 28
6 9 168 20.4 88 22 12 41.8 41.8 88w“x
7- 9 - 25.5 91 50 12 44.5 52.9 670
8 11 248 20.0 78 28 8 57.9 .18.8 117
'9 12 - 19.8 78 24 12 52.8 25.4 25
10 - - 21.9 p15» 20 10 40.0 5414;? 77*
Mean 10.4 209 22.7 81.7 24.1 15.8 57.8 51.8 549.0

 

 

 

 

 

 

 

*Estimates computed from trap collections
iWRevised acorn counts due to previous fall

Table 4 (Continued)

Bl

 

 

 

 

 

 

 

 

Species Radial flu Crown Total
and Growth Height Diameter Acorns
Locali- Tree 10 Ex- Maxi- Ex- Per
ty No. ,Xgars YAge D.B.H. Height Total Posed mum Posed Tree
__ mm. ears Inches Feet Feet Feet Feet Feet Numbgg
Red Oak 1 2O 88 19.9 82 25 25 52.4 52.4 -
Maple 2 ll - 16.7 85 27 15 28.4 25.4 10
Rapids 5 17 ~ 16.0 76 22 15 28.9 24.2 12
5 54 - 20.5 80 18 15 55.9 24.9 44
6 26 76 17.1 88 27 17 55.4 24.5 27
7 - - 18.7 85 19 10 28.8 28.8 55
8 29 - 17.8 74 55 15 55.5 27.9 -
9 59 51 15.7 82 57 20 27.5 27.5 -
10 12 66 16.5 88 15 2O 24;§p 22.9 -
Mean 22.4 75 17.6 84.0 24.5 15.8 50.0 26.5 25.2

 

52

to produce (Wood, 1954, 1958; Toumey and Korstian, 1947;
Cypert and Webster, 1947; Baker, 1950, and Cypert, 1951).

Border tree production is generally correlated with
light intensity. Greater insolation for south border
black oaks results in a larger crown volume than that of
(north border trees (Figure 2). Crown thrift is eXpressed
in increased growth rate in the south-facing trees. The
west border black oaks are generally smaller trees but
are vigorous and have thrifty crowns; they are intermediate
in production. White oak production at Maple Rapids is
not related to crown volume but may be due to insolation,
per so, since all trees are overmature and therefore
lack vigor. High acorn production was counted on two of
the three south and west border trees censused. Similar
east and north border trees had consistently low pro-

duction.

Species and area differegces

The trap data presented in Table 7 reveals an obvious
production differential between Species. Total trap
collections were 7.4 times greater for Rose Lake interior
black oak compared to white oak. Estimated acorn pro-
duction (Table 4), based on crown counts and trap

collections (see page56 ), was 10 times greatemfor

54
black oak (408.0 acorns per tree) than it was for white
oak (40.8 acorns). Similarly, Maple Rapids white oak
trap counts exceeded those of Rose Lake white oak by
8.6 times. Estimated average production was 549.0 acorns
per tree for the former and 40.8 for the latter, also an
8.6 to 1 ratio. The red oak crop was almost a complete
failure, in this reSpect it closely approximated that of
Rose Lake white oak.

Adequate explanation of the production differences
noted is not feasible because the factors reSponsible are
poorly understood. Several facts are evident, however.
Within an area, acorn production varies considerably
between species for any one year. Although it cannot
be predicted, the production trend of Rose Lake may be
reversed in 1955. This tendency is highly improbable
for Maple Rapids since another fail year is predicted
for red oak on the basis of flower counts. Judging from
acorn and cup remains red oak produced an exceptionally
good crOp in 1951. Although 1952 was a poor production
year, some few trees bore moderate crops; this is con-
sidered normal (Baker, 1950).

White oak production differences between areas may
be due to soil, or to climatic conditions; i.e., frosts,

other
etc. The effects of local soil and/site influences upon

55
seed production has not been determined. Site quality
may have a direct influence in that it helps determine
the amounts of food materials stored in a tree. Seed
production requires large amounts of potash and nitrogen.
Soils deficient in these elements produce trees which
yield small, inferior craps of seed (Toumey and Korstian,
1947). Site may also influence stand density and crown
differentiation (Baker, 1950). The Rose Lake site is
considered medium.for oak. Site quality is greatly
superior at Maple Rapids and is probably optimum for
both red and white oak.

 

Comparative prodaction of interior. border, aag isolated
tress. »

It is commonly stated that border or isolated trees
usually produce earlier, larger, and more consistent crops
of acorns than do forest-grown trees (Wood, 1954, 1958;
Toumey and Korstian, 1947; Cypert and Webster, 1948;
Baker, 1950). Allen and McGinley (1947) believe that
interior woodlot trees are unimportant as acorn producers;
the bulk of the acorn crop of value to wildlife, according
to them, is produced by isolated and border trees.

The author believes such statements are unjustified

and unsupported by data. Table 5 presents a summary of

55

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36

observed acorn production for the growth form categories
in question, based upon tree counts, trap collections,
and ground observations (see page 56 for latter method).

The crop failure of Rose Lake white oak, and for
red oak, was not confined to interior trees but extended
to border and single trees as well. Only one of 45 white
oak samples in the vicinity of Rose Lake had a high acorn
crop. Similarly, of 21 red oaks only one was productive.
The prOportion of high producing black oak trees in
interiors and borders is approximately equal (6.4 to 6.7
percent). All isolated trees sampled (6) failed to produce
seed in quantity, although all were large crowned trees.
Furthermore, acorn production of interior trees was
greater, in both individual production and average per
tree, than it was for border trees. It is of interest
to note that of the 7 high producing border trees listed,
5 were located on a north border (Okemos Woods), 5 of
these were contiguous along 40.feet of border, indicating
possible inherent genetic characteristics.

The production trend for Maple Rapids white oak is
comparable to that of black oak, although fewer trees
were sampled. The production differential between high
producing interior and border trees is minor (11.1 and

15.4 percent, reapectively). It is noted that approximately

57
one out of 5 trees had medium or better production; for
black oak this ratio was one to 6 or 7 trees. The
significance, if any, is not known.

The summary for all species and areas combined is
in general agreement with the above analyses. It is
concluded therefore, that superior location of border
or single-trees, with regard to insolation and root
competition, does not necessarily result in increased
production, per se. The crowns of these trees are
usually larger than interior trees, but the assumption
that acorns are evenly distributed over the entire crown
has been diaproved. Tree vigor, including crown thrift,
can also be high for interior trees, with suitable sites
and stocking. This is apparently true for black oak,
and possibly for Maple Rapids white oak, even though the
latter is a virgin stand. In addition, the total acorn
production of a woodlot interior is considerably greater
than it is for borders. According to Gysel and Arend
(1955), the average woodlot on medium to good site contains
60 to 80 trees, 12 inches d.b.h. or over, per acre. On
this basis, there are between 720 and 960 trees (mostly
black oak) in the interior portion of woodlot 1 (12 acres).

Only 41 border oaks were recorded from the perimeter of

58
this woods. Even if average production per interior tree
were lower than that for border trees, the total interior
production would still be overwhelmingly greater. Further-
more, single-trees are often few and isolated. The value
of these trees in providing acorn food for animals of low
cruising radius is negligible, although Allen (1945)
noted some squirrel utilization of these acorns during
late winter.

The large acorn crops often noted for single-trees
(includes fencerows) may not represent natural conditions.
Allen (1945) records a large white oak that annually
produced at least one bushel of acorns (approximately
10,500) between 1957 and 1959. The author also observed
comparable production for a white oak growing within a
wheat field, but concluded that application of nitrogenous

fertilizer probably induced the copious acorn crOp.

V. THE USE OF TRAPPING DATA
FOR ACORN PRODUCTION ESTIMATIONS

Sampling methods are commonly used for estimating
acorn-crops. Sample collections are useful in providing
a basis for calculating total tree yield, composition
of the cr0p, and utilization by wildlife. The most
commonly employed method has been that of selecting a
sample area on the ground beneath a tree crown and
collecting or counting the fallen acorns. These ground
quadrats are usually arbitrarily located, and variously
delineated (Korstian, 1927; Wood, 1954; Allen and McGinley,
1947; Cypert and Webster, 1948). The total yield is
calculated from the prOportion of the known sample area
to that of the total crown. Estimation of tree yield
by this method would generally produce accurate results
since a total segment of the crown is considered. However,
animal activity is often great and undoubtedly affects
the validity of the counts.

In order to obviate this factor, Specially constructed
I'seed traps” have been devised for use in obtaining un-
biased acorn samples, (Wood, 1958; Downs and McQuilkin,

1944; Cypert, 1951, and Easley and Chaiken, 1951). The

4O

traps are usually 1/4 mil-acre in area and covered with
hardware cloth to exclude animals. Many of these traps

are expensive to build, usually bulky, and often not
completely animal (rodent) proof, this is particularly

true of those constructed by Downs and McQuilkin. Estimates
of acorn yield are usually determined from the relationship

of trap collections and tree crown-trap volume ratios.

Materials and Methods

A modification of the seed trap reported by Easley
and Chaiken (1951) was developed for a long term acorn
production investigation and was used in this investigation.
The trap body consists of triangular sections of treated
canvas sewn together in pyramidal form. It is supported
by a welded frame of quarter-inch steel rods, each 5.5
feet in length, producing a trap 1/4 mil-acre in area.

A collection basket made of stapled fly-screening is
attached to the funneled lower body by means of a wire
pin. The trap mouth is covered with one or two inch mesh
galvanized wire, the latter was used for red oak. The
trap is elevated into position by means of four soft-

wood stakes. The completed unit is shown in Figure 5.

 

 

Figure 5. Acorn trap in operation on south border of
Rose Lake woodlot 1.

Two traps were placed under each tree. Consideration
was given to crown symmetry and limb position. The traps
usually sampled dissimilar portions of the crown; i.e.,
dense and Sparse foliage. Uhdesirable trap position
necessitated a slight relocation of several traps soon
after collecting Operations had begun.

In close proximity to each trap a stake was placed
marking the center of a circular 1/4 mil-acre (22.5 inch

radius) open-quadrat. The ground litter within the

42
quadrat area was searched for fallen acorns and cups.
These were recorded and ejected from the plot.

Traps at Rose Lake woodlot 6 were placed in operation
between August 28 and September 2 and first checked on
September 8. Trapping operations at Maple Rapids began
during September 5 to 5. Traps were visited at weekly
intervals (one day lag for Maple Rapids), checked, and
emptied. Acorns collected were sorted according to the
classes given in Table 6.

In addition, traps were also placed under six black
oaks on the north and south border of Rose Lake woodlot 1.
For each tree one trap and quadrat was located on the
border side, the other was interior. Trapping began on

September 11 and was first checked on September 22.

Basalts aag Discaaaioa

Period of Acorn Fall Based
Upon Trap Collections
A generally uniform trend for all Species is noted

for weekly trap collections in Figure 4. The peak fall
period occurred during the week of September 8 to 16.
Forty percent of the Maple Rapids white oak acorns fell
during this period. Forty-four percent more fell during
the following 5 weeks, thereafter the fall ceased abruptly-

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44
The peak for black oak was protracted into a 5 week period,
September 8 to 29. Although the data are limited, border
black oak fall appears similar to that for interior trees.

The fall period for mature acorns is modified by
several factors, among which are climate (abscission
formation), wind, insect damage, and animal activity.
Cypert and Webster (1948) found a wide range of dates of
acorn dropping for individual trees as well as seasonal
variations. Downs and McQuilkin (1944) stated that the
period of drop tends to lengthen with larger crops but
75 percent of the drOp, whether heavy or light, occurs
in about a month. Poorly developed, wormy acorns begin
to fall about a month earlier (Toumey and Korstian, 1947).
This was particularly evident for red oak during the
current year.

Korstian (1927) and Wood (1958) state that acorns
are normally shed somewhat in advance of the cups. However,
the weekly trap data of this study revealed close corre-
lation between acorn and cup fall. Animal activity may
have heightened the cup fall.

Composition of the 1952 Acorn Crop

Analysis of the acorn crop is limited to trap
collection data presented in Table 6. The most striking

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46
feature of the crop was the uniformly high incidence of
damage. This ranged from 100 percent for Rose Lake white
and border black oaks, to 78.2 percent for Maple Rapids
white oak. Conversely, sound, average size acorns were
almost non-existent. Insects were largely responsible
for the crop destruction. This was determined by actual
cutting tests of collected acorns. Larval activities
were noted in 80.0 to 61.5 percent of the white oak acorns,
and in approximately 64 percent of all black oak. The
low incidence (57.2 percent) for red oak appears in-
congruous with general observations, but may be due to
the low numbers of the sample.

Degree of insect infestations apparently varies
considerably between Species. locale, and perhaps year
and size of crOp. Korstian (1927) reported an average
of 18 percent insect damage for 4 Species of oak in the
southern Appalachians. Incidence was highest in black
oak (27.7 percent) and lowest'in white oak (10.6 percent).
According to Kautz and Liming (1959) the 1937 Missouri -
acorn crOp was 98 percent defective. of which 67 percent
was attributable to insects. Downs and McQuilkin (1944)
found insect damage to average 60 percent for all oaks.)

and believe that Species differences are due to chance.

47
Linduska (1950) reported a noted Species preference by
insects for RoSe Lake oak during 1941. The incidence
was highest in black oak (81 percent), followed by white
oak (67 percent), and only 7 percent for red oak. His
assertion that the high tannin content of red oak may
prove distasteful to insects is not substantiated. The
possibility exists that low acorn production increases
the incidence of insect infestation.

Three main groups of insects are known to damage
acorns; these are (l) nut weevils or curculios, (2)
moth larva, and (3) gall forming cynipids (Korstian,
1927). Curculios of the genus Balanings appear to be
the most destructive. As many as 4 large larvae per
acorn were removed from white oak acorns collected at
Rose Lake.

Although insects often totally destroy acorns,
72.3 percent of the Maple Rapids white oak acorns
damaged had more than one-half the endOSperm intact.

It was substantially lower (46.0 percent) for interior
black oak. Germination of weeviled acorns is poor,
particularly if the embryo has been damaged. The per-
centage of normal seedlings develOping from weeviled

acorns is practically negligible (Korstian, 1927).

48

Animal damaged acorns from trap collections repre-
sent tree foraging activities. This would include squirrel
and bird harvesting but not that of chipmunks. In many
instances great quantities of acorn and cup fragments
were collected from the traps which could not be
evaluated. The variation in incidence of damage was
remarkably uniform between Species and areas. It ranged
from 20.0 percent for interior black oak to 10.5 percent
for Maple Rapids white oak. Animal damaged acorns are
probably those dropped or collected by animals but found
to be worthless as food. Sound, or slightly damaged
acorns are either consumed in the tree, dropped to the
ground intact, or carried away. The amount of acorns
removed from trees is indicated from empty cup tallies.
For example, 23 damaged acorns were tallied for black
oak, but 48 cups were collected --- 54 percent of the
average acorn crOp was not retrieved by the traps.

Forty percent of the Maple Rapids white oak were
similarly affected. Birds, as well as Squirrels, may
have been reSponsible.

The determination of acorn utilization by animals
based upon open quadrat data has been commonly attempted
(Korstian, 1927; Wood, 1954, 1938; Downs and McQuilkin,
1944, Cypert and Webster, 1948). In practice, the

49
number of empty cups found (not ordinarily carried away)
remaining in the quadrat has represented the amount of
animal depredation. By this method Korstian (1927) found
animal utilization to average 68 percent for 4 Species of
oak. A high deer and mouse population was reSponsible.
Wood (1938) noted that as high as one-half of the newly
fallen chestnut oak crOp was removed by squirrels; Pine
mice were responsible for destruction of acorns during
winter. Downs and McQuilkin (1944) reported a 24 percent
average utilization of acorns by sciurids, mice, and deer;
the latter were the worst offenders. Cypert and Webster
(l948) observed bird depredations amounting to 13.8 and
12.8 percent of the entire water and willow oak crop in
Arkansas, in 1939 and 1940.

Theoretically, the number of trapped acorns is
expected to be greater than that for ground quadrat
collections. In this study, however, twice as many
damaged acorns were noted for Open plots than for traps,
equaling 23.2 to 43.7 percent of the total average Size
.quadrat acorns counted. Empty cup counts were obviously
also distorted. Thus, black oak cups were 2.4 times as
abundant in Open quadrats as in traps. The greater
amounts of acorns and cups within the quadrat was not

expected, their true relationships are conjectural;

50
therefore adequate analysis of animal utilization from
Open quadrats is impossible. The use of this method may
be considerably more complex than has been previously
believed. The problem is discussed further on page 5‘.

Damage from fungi was generally of minor importance
(Table 6), ranging from O to 18.4 percent. It averages
about 6 percent of the crop for interior black oak and
Maple Rapids white. Incidence of fungi within acorns
may be related to insect damage, because fungi Spores
may conceivably enter through ovipositor scars. Korstian
(1927) found a very low incidence of fungus (Penicillium)
in newly fallen acorns although it averaged 10 percent
as a mortality factor during germination. Kautz and
Liming (1939) reported a 16 percent acorn decay but did
not Specify the cause.

Small size acorns result from a cessation of growth
develOpment. The highest incidence occurred in Rose Lake
whiteoak (39.5 percent) and appears correlated with the
crop failure, suggesting a lower limit of physiological
condition. It was also high for Maple Rapids white oak
(23.8 percent), but only 10.0 and 15.1 percent for
interior and border black oak, reapectively. Climatic

conditions may account for these Species differences.

Variations in Trap and Quadrat Collections

Trap-pairs

The variations existing between trap-pair collections
(Table 7) represents differential crown sampling due to
A trap position. The higher totals of a pair may be corre-
lated with greater production of the denser crown area
sampled, but cannot be stated with certainty. The use
of a single trap per tree (Cypert, 1951) may be Justified
Since the differences between traps is often small. For
high producing trees, the collection differences vary

about 10 to 25 percent between members of a trap-pair.

Eggp-guadratfpairs

The differences noted between complimentary trap and
quadrat collections in Table 7 are not readily explained.
As previously mentioned, open quadrats have been used to
determine the degree of animal utilization. The validity
of the data is based upon the belief that acorn and cup
fall collections are normally distributed. This was not
true for the present study. The higher quadrat counts
may be explained as follows:

(1) Some acorns falling onto the trap periphery
rebounded over the trap edge, thus lowering the collection

counts. Quadrats lying in close proximity to a trap edge

52

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55
may have received some of these acorns. raising their
counts. Trap tests revealed a low probability for this
phenomenon.

(2) The quadrats may not have been entirely cleared
of previous acorn and cup fall due to the heavy leaf
litter often present on the plot area. The litter was
not excessively disturbed in the original search; acorns
present may have been subsequently found and recorded.

(3) Animal activity may have abnormally affected
the normal distribution of acorns on the ground. A high
chipmunk population existed in woodlot 6. Several dens
were located near or within the quadrats under high
producing black oaks. High densities of squirrels and
mice were noted for Maple Rapids. The ground beneath
some white oaks was often a labyrinth of mouse tunnels.
The feeding and caching activities of these small animals
may have invalidated the quadrat counts under these trees
because of local acorn concentrations.

The possibility that trap collections were rifled
by animals is remote. Experimentation with sound, marked
acorns during the study proved the traps to be almost
completely animal proof during the weekly periods. Marked
acorns within the Open quadrats quickly disappeared or

were broken by animals. The fact that Rose Lake white

54
oak was comparatively immune to the phenomenon indicates
that animal activity was the major cause of the higher
plot counts. The animals were obviously not interested

in the low acorn production of this Species.

Acorn Production Estimation from Crown
Acorn Counts and Trap Collection Ratios

A method was devised for estimating individual tree
production from the relationship of total sample tree
acorn counts and trap collections. The calculations of
total tree production retrieved by trapping are presented
in Table 8. Percentage of trap returns are more variable,
and usually higher, for low producing trees. The per-
centage of returns for high producing trees is remarkably
uniform, varying from 3.4 percent for black oak number 10,
to 5.3 percent for border black oak number 16. The low
percent of the former tree may be due to its narrow,
conical crown form. For the 5 interior black oaks the
range is 5.4 to 6.7 percent and averaged 4.0 percent.
South border oaks average 5.5 percent trap returns and
vary from 3.8 to 6.5 percent. Maple Rapids white oak
traps retrieved 5.8 to 5.5 percent of the total counted

production, and averaged 4.6 percent.

55
Table 8 J”

PrOportion of the Acorn CrOp Determined
by Tree Counts to that Measured by Trapping*

 

 

 

 

 

 

 

 

Bose Lake: ‘ White Oak Black can t
Tree Number 1 7 10 Totals 1 6 8 9 p10 TotaLs
Tree Counts: I . .
Number of Acorns 74 98 56 208 59 25 50 158 1,188 1,420
Trap Collections: ‘
Number of Acorns 2 7 5 12 2 5 2 8 40 57
Percent Retrieved , '
by Traps 2.7 7.1 8.5 5.7 5.1 5.0 6.7 5.8 5.4 4.0
yaple Rapids: White Oak**;_ : Black Oak {Borde22+
Tree Number 2 5 7 8 Totalsw 1; 16 17 Totals

 

Tree Counts:
Number of Acornsl,565 19 459 80 1,921 552 1,044 104 1,500

Trap Collections:
Number of Acorns 62 1 22 5 88 25 55 4 82

Percent Retrieved
by Traps 4.5 5.5 4.8 5.8 4.6 6.5 5.5 5.8 5.5

 

“Exclusive of small size
**Counts and trap data after September 15
+South border of woodlot 1

56

The data can be used for estimating total tree
production from average trap return percentages. This
is obtained by dividing trap collections by the average
percent total trap returns. The estimated production
in Table 4 was obtained by this method. For example,
the total trap collections for black oak number 7 amounted
to 61 acorns, this, divided by .04 (the 4 percent average
trap returns), equals 1,525 acorns. Deviations from true
production are eXpected to be compensatory. Whether ratio
changes will occur following high production cannot be
stated; however, similar relationships should be operative.
Although crown counts are difficult to obtain, the ease
and accuracy with which production estimates are obtained
by this technique warrants its use.

Detailed data on acorn production may not be needed.
Often, general observation indices, depicting year-to-year
trends, are sufficient. The data from Table 5 result
largely from ground observation of acorn fall, particularly
for border and isolated trees. Relative abundance of cups,
acorn fragments, and weeviled acorns (not ordinarily
removed by wildlife) provided the basis for the high,
medium, and low categories. Annual resampling of

selected trees, checked at weekly intervals during

El

57

acorn fall, should provide adequate indices to acorn
production and animal utilization. A similar mast index
has been devised and is currently in use in West Virginia

(Uhlig and Wilson, 1952).

VI. POPULATION SIZE AND ACORN UTILIZATION
OF CERTAIN SMALL MAMMALS
Observations during September indicated an abnormally

high eastern chipmunk (Tamias striatus rufescens)l
population was present in Rose Lake woodlot 6. Signs of
high densities of white-footed mice (Peromyscus leucopgs
nogeboracensis) were also noted for Maple Rapids. Since
the acorn crop was poor, the author believed that severe
competition for acorns would develop during the fall
between these Species and other mast-eating game animals.
In order to determine the possible extent of this food
competition, a line-trapping study for the estimation
of chipmunk population size was conducted at Rose Lake
during October. In addition, an acorn feeding experiment
was devised to test the consumption and preference of
acorns by chipmunks and mice. The results of these
studies were intended to provide data upon Which an

analysis of acorn competition could be made.
Materials and methods

Cooperation was obtained from the Rose Lake Station

staff for the collection of chipmunk data during the

 

1 Common and scientific names of mammals are according
to Mammals of Michigan, Burt (1948).

59

normal course of pre-hunting season animal population
studies. Population estimates are derived from line-
trapping data through the use of tagged-untagged ratios,
or from hunting season kill-ratios.

A total of 12, permanently stationed box traps,
Spaced one to the acre in grid pattern, were Operative
in woodlot 6 during a 10 day period, October 6 to 17,
for a total of 120.5 trap days. The traps were checked
twice daily. All animals captured were ear-tagged, the
weight, age, and sex noted, and released. Ear corn and
dried herring were used as bait. The weather during
this period was mostly clear and cool.

The acorn feeding eXperiment began on October 18.

A total of 5 chipmunks and 4 mice were captured in box-
traps and confined in cages at the Michigan State College
animal house (Table 10). The chipmunks were confined in
experimental rat cages. The cages measured 18 inches on
the Side. One chipmunk was later transferred to a
commercial type squirrel cage, complete with rotary
exerciser. The mice cages were cylindrical, 5 inches
high and 8 inches in diameter. Wood shavings and cotton
batting were provided for nesting. Water was available

at all times. The animals were examined every day and

60
fed periodically, depending upon the quantity of food
remaining. Acorns were the only food provided during
the study. An attempt was made to feed only well-deveIOped,
sound acorns; however, this was not always possible. Four
Species of acorns were collected. These were placed in
quart Jars and subjected to room temperature for several
days. At the end of this period almost all weevil larva
had emerged from the acorns. Acorns without emergence
holes were checked, and fed to the animals.

The animals were kept at room temperature, ventilation
and light were provided by several windows. Except when
fed, the animals were not disturbed. Although the cages
were small the animals appeared healthy and vigorous.
Examination of several sacrificed Specimens at the end
of the study did not reveal symptoms of malnutrition.

As late as November 15, none of the chipmunks showed signs

of torpidity.

Results and Discussion

Chipmunk Population Estimate

Results of the live-trapping program are presented
in Table 9. The high frequency of chipmunk capture
reveals the relatively greater abundance of this Species

to other sciurids in the woodlot.

61
Table 9

Results of Live-Trapping at Rose Lake
Woodlot 6 During October 6 to 17*

 

Number of Individuals

 

 

 

New Previous
Species Records Records, Recabtures Total
Eastern Chipmunk 16 5 25 46
Red Squirrel 5 - - 5
Southern Flying
Squirrel l 1 - 2
Fox Squirrel 2 5 1 6

 

*Twelve traps Operating for 205.5 trap days

62

Estimation of the chipmunk population, calculated
from tagged-untagged ratios (Hayne, 1949), proved un-
satisfactory. The highest estimate obtained was 28
chipmunks, or 2.5 animals per acre for the 12-acre woods.
This density appeared incongruous with field observations,
a much higher population was indicated. In lieu of the
above estimate, a population size of approximately 7
chipmunks per acre was ascribed to the 6-acre portion
of the woodlot. This was believed to be the best estimate
of the actual density prevalent on the area, and was not
considered excessive. Bole (1959) reported a high density
of 8.7 per acre for upland fOreSts in Ohio during 1955.
Burt (1940) found populations of 2.4 and 5.6 per acre
in two oak-hickory woodlots in southern Michigan, but
believes September populations may average 4 to 5 per
acre after the second litter appears above ground (1948).
Linduska (1950) observed densities of 2.0 to 2.5 chipmunks
per acre for a 25-acre woodlot during a low population
period.

The cause of this high density is not clear. However,
approximately three times as many chipmunks were handled
during the 1952 trapping period as in 1951, indicating
an 'irruptive" type fluctuation. The phenomenon did not
appear to be restricted to the Rose Lake area, but was

more widespread.

65

Estimates of other sciurids was not attempted, but
observations of them deserve mention, Since they are also
important competitors for acorns. The Six red squirrels
(Tamiasciuru§_hudsonicus loguax) trapped may represent
a minimum population of one per 2 acres. Linduska (1950)
reported a maximum of 2 per acre for woodlot 6 during
1940. During this period, flying squirrel (Glaucomys
volans volans) densities were one per acre for this
woodlot; however, Linduska expressed doubt as to efficiency
of the box-traps. Burt (1948) states that groups of 20
or more may band together in a single den during winter.

POpulation data were not collected for white footed
mice. High densities were believed to exist in Maple
Rapids. Numerous burrows, and other Signs of activity,
were noted. Mice were frequently captured in box-traps
during a preliminary study. Burt (1940) found mice
pOpulations to vary from a spring low of 5.0 per acre
to 10 or 15 per acre in November. Linduska (1950)
reported a density at 7.6 mice per acre in woodlot 1
during October.

Of the mast-eating game animals, fox Squirrels
(Sciurus nigra rufiventer) are probably most directly

affected by acorn competition. Significantly, fox

64
squirrel populations were low in woodlot 6 during 1952.
Less than one squirrel per two acres was removed from
this woodlot during the hunting season, although gun
pressure was high. All other sciurids were probably
near peak densities. Linduska (1950) found similar
inverse trends Operating during his 1940-42 Rose Lake
study. Although food competition may be a limiting
factor, there is evidence to indicate a 4-year cycle
of abundance for Rose Lake fox squirrels.1 The fox
squirrel population at Maple Rapids was believed to be
high. Many tree dens and leaf nests were present in
this woodlot and fox squirrels were commonly seen during
the study. One hunter interviewed reported killing 19
squirrels during the 1951 hunting season - almost 1
Squirrel per 2 acres. The population for this woods
is probably between one and two per acre. Chipmunks
were not present in the woodlot, although flying squirrels

were noted.
Acorn Feeding EXperiments

The data obtained from this study, presented in
Tablelfi are of considerable importance since comparable

information is lacking. During the 98 chipmunk days

 

1 Oral communique with Dr. c. T. Black.

65

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66
of feeding, the average consumption was 6.1 acorns per
individual per day. Slight variations are noted, the
high 6.8 daily average of one chipmunk is probably the
result of greater energy expenditure, since this animal
had use of the rotary exerciser cage. The lowest individual
average consumption (5.5 acorns per day) resulted from a
distaste for red oak acorns rather than a lower food
requirement. The data for red oak utilization are mis-
leading. It was soon evident that acorns of this Species
were not being eaten. From November 5 to 9 no additional
acorns were fed in order to encourage consumption of
accumulated red oak acOrns. These were subsequently
eaten, except as noted. No ill effects were observed.
Baumgras (1944) reported that 2 of 5 fox squirrels died
within 10 days when fed this Species. He believes the
high tannin content of red oak is unpalatable for fox
squirrels. The tannin content appears to vary with
region of acorn origin, according to Korstian (1927),
and may often be considerably lower than that of White
oak. Urban.fox squirrels greedily consumed red oak
acorns, even though other foods were available. Baumgras
noted a slight loss of weight (2.6 grams per day) for
test Squirrels fed red oak acorns, but the loss was

greatest (5.2 grams per day) with a corn diet.

67
All white and black oak acorns fed were readily
consumed. Although both Species were sound and well-
formed, white oak acorns were approximately twice as
large as the black. Observations during feeding indicated
white oak acorns were preferred. They were invariably
eaten first, although both were supplied in equal numbers.
Baumgras (1944) believes that the higher utilization of
this Species by fox squirrels represents a lower food
value for white oak.
During the last 5 days of the experiment one lot
of 50 scarlet oak acorns (Quercus goccinea) were fed to
each chipmunk. All but 5 of the 120 acorns fed were
consumed during this period - 5.8 acorns per day per
chipmunk - only Slightly less than maximum consumption.
Average consumption for mice was 1.8 acorns per
day, and was remarkably constant (Table 10). All but
two white, and all black oak acorns fed were eaten.
White oak acorns were eaten first, but preference may
have been due to the softer tests of this Species. 0f
the 12 scarlet oak acorns fed, consumption was maximum
(2.0) for one individual, but not for the other (1.2 acorns
per day). The latter may represent availability of uneaten

food. Red oak acorns presented a major problem because

68

of their large size. About half of the number fed were
breached, however, and one-fourth to one-third of each
endOSperm eaten. In feeding, a small hole was chewed
at the base of the acorn and gradually enlarged to allow
extraction of endOSperm fragments.

Hamilton (1941) States that under natural conditions,
adult deer mice eat about 6 grams of food daily. This

is equivalent to approximately 2 white oak acorns.
Effects of Competition for Acorns

The Significance of the pOpulation and food habit
studies lies in analysis of the possible deleterious
effects imposed upon mast-eating game animals by competing
small mammals. Oak regeneration is also directly related
to acorn utilization by these animals, and may often be
Severely curtailed (Korstian, 1927; Wood, 1954, 1958;
Downs and McQuilkin, 1944; and Baker, 1950).

Acorns provide substantial food for numerous wild-
life Species and therefore rate a position at the top
of the wildlife food list, not only because they are a
preferred food item, but because they constitute a
staple fall and winter food for many game animals
(Van Dersal, 1958, 1940; Martin, et al., 1951). Acorns

69

are not always abundant or available to game animals.
During a poor crOp year the lack of food may prove
critical. Allen (1945) noted a marked fox squirrel
mortality and debilitation following an oak crop failure
in Allegan County, Michigan. Linduska (1950) observed

a food Shortage existing in Rose Lake woodlots during

an acorn failure in 1940, but not the two following
years. He believes no marked incompatability exists
between the woodland rodent Species, but noted that all
were in direct competition for the same foods, and except
for chipmunks, for the same nesting sites.

A food shortage may have developed in woodlot 6
during 1952-55. Assuming a chipmunk and mouse density
of 7 per acre, the total number of black oak acorns
consumed within 60 days after acorn fall is calculated
at 5,275 sound acorns per acre, or approximately 1/4
bushel. The average production for black oak was 408
acorns per tree, or 4080 acorns with ten trees per acre.
Of this total, only 50 percent (2040) were usable as
food, due to damage. Acorn caching activities effectively
eliminates food otherwise available to game animals.

The caching propensities of chipmunks and mice are well-

known. Burt (1940) states that ”the storage of food is

 

v v— -‘_pf

70
one of the chief daily activities of eastern chipmunks.
If a supply of food is located they will work tirelessly
carrying it away to their subterranean granaries.”

Allen (1945) believes the importance of mice as food
competitors of fox squirrels have not been sufficiently
recognized.

Acorn utilization and caching by red and flying
squirrels, and passarine birds, is also significant
and adds to the deficit of food. An indication of this
is noted from the high incidence of animal damaged acorns
(20 percent) and empty cups (54 percent) trapped from
black oak trees, as previously reported.

Fortunately, small mammal pOpulationS often fluctu-
ate violently and low densities are common. The most
serious competition results from concurrent high rodent
densities and poor mast years. High rodent pOpulations
during a high yield year are probably not inimical to
oak regeneration, because the total acorn crOp may not
be consumed. The basic causes of rodent pOpulation
cycles are poorly understood, but may be due partly to
food supply. They do not appear to be synchronized
with seed-year cycles of forest trees, Since the latter

are very irregular (Baker, 1950). Whether the apparent

71
5 to 4 year cycle of fox Squirrels coincides with that
for acorns is not known.

The tremendous destruction wrought by insects
further delimits the amount of acorn food available.
Linduska (1950) believe that weevils (Balaninus an)
are the most serious competitors for the acorn crOp.

This was particularly true during 1951. Many of these
acorns are suitable as food, although they may not be
stored. Some animals may relish the larva itself.
Urban fox squirrels readily consumed weeviled acorns,
if the endOSpermS were not excessively damaged.

The total effect of acorn competition is considerable
and may regulate animal populations through limiting range
carrying capacity. Rodents, and the lesser-sciurids have
value as insect eaters, and as buffer animals for other
game Species. The buffer value of hibernating chipmunks
is probably negligible, however. These animals may be
controlled by encouraging natural predation. Unfortunately,

little can be done at this time to reduce insect damage.

SUMMARY

An investigation of some factors influencing
production and utilization of acorns, for two upland
oak-hickory woodlots at Rose Lake and Maple Rapids, in
Clinton County, Michigan, was conducted during the fall
of 1952. The areas differed widely in plant composition,
land-use, and soils. Forty trees were chosen in the two
woodlots for an investigation of the size and nature of
the acorn crOp. Twenty of these trees were selected for
study of insolation effect on crown development and
acorn production.

1. The data revealed that acorn production is
largely confined to the tOps of trees in closed stands.
The production differences are not correlated with number
or size of limbs. I

2. Greater quantities of seed were found on south
facing limbs, followed by west, east, and north. The
lower limbs were not Similarly affected.

5. Acorn production of border trees was similar
to that of interior trees. South border trees had the
greatest production. The bulk of the acorns are produced

by upper crown limbs.

75

4. The 1952 acorn crOp was low, and failed entirely
for Rose Lake white, and Maple Rapids red oak. Production
of acorns was not consistently correlated with such
characteristics as crown size, bole diameter, or growth
rate, although the larger trees usually produced the
largest acorn crops.

5. Acorn yield of open-grown, or border trees, was
neither greater nor more frequent than for forest-grown
trees.

6. The bulk of the acorns fell during a three-week
period, September 8 to 29. The fall was greatest during
the first week of this period.

7. A high incidence of acorn damage was recorded.
It ranged from 100 to 78.2 percent of the crop, depending
upon Species and site. Insect damage, mainly by acorn
weevils, was largely reSponsible, contributing 80.0 to
61.5 percent of the damage.

8. Animal damage to tree acorns accounted for 20.0
to 10.5 percent of the average-size acorns trapped; 54
to 40 percent more may have been removed from the trees
as noted from empty cups.

9. Differences in trap-pair collections resulted
from sampling of unequal foliage densities. Trap-open
quadrat pair variations were probably due to local acorn

concentrations by small mammals.

74

10. Acorn traps retrieved 4.0 to 5.5 percent of
the total production counted on sample trees. An acorn
estimation technique was devised from this data.

11. An estimated density of 7 chipmunks per acre
was ascribed to the 6-acre study area of woodlot 6.

This was based upon observations, since live-trapping
data failed to produce satisfactory results.

12. According to an acorn feeding eXperiment devised
for captive chipmunks and white-footed mice, the average
consumption for chipmunks was 6.1 acorns per day; it was
1.8 per day for the mice. Of the four acorn Species
fed, red oak was the least preferred.

15. An acorn shortage may have developed in woodlot
6 during the fall of 1952. Consumption by chipmunks and
mice is presumed to have caused a deficit over the amount

of acorns produced.

l.

6.

7.

8.

9.

10.

ll.

75

LITERATURE CITED

Allen, Durward L., 1945. Michigan fox squirrel
management. Game Div. Pub. 100 Dept. Conserv.,
Lansing.

and Howard D. McGinley, 1947. A method

 

for the year-to-year measurement of mast yields.
Jour. Wildl. Mgt. 11: 184-185.

Baker, Frederick S., 1950. Principles of Silvi- .
culture. McCraw-Hill Book Co., Inc., New York.

Baumgras, Philip, 1944. Experimental feeding of
captive fox squirrels. Jour. Wildl. Mgt.
8: 296-500.

Bole, B. P., 1959. The quadrat method of studying
small mammal populations. Sci. Pub., Cleveland
MUS. Nat. HiSto 5: 15‘270

Burt, William H., 1940. Territorial behavior and
populations of some small mammals in southern
Michigan. Misc. Pub. Mus. Zool., Univ.
Michigan, No. 45, pp. 1-58.

. 1948. The mammals of Michigan. Univ.
Michigan Press, Ann Arbor.

Chandler, R. F., 1958. The influence of nitrogenous
fertilizer application upon seed production of
certain deciduous forest trees. Jour. For.

42: 915-920.

Cypert, Eugene, 1952. Suggestions for the management
of oak forests for mast production. Mimeo. report
of the Southeastern Assoc. Game and Fish Comm.
pp. 1‘40

and Burton S. Webster, 1948. Yield and

 

use by wildlife of acorns of water and willow
oaks. Jour. Wildl. Mgt. 12: 227-251.

Detweiler, S. B., 1945. Better acorns from heavily
fertilized white oak tree. Jour. For. 41: 915-916.

12.

l5.

l4.

l5.

l6.

17.

18.

19.

20.

21.

22.

25.

76

Downs, Albert A., and W. E. McQuilkin, 1944. Seed
production of southern Appalachian oaks. Jour.
For. 42: 915-920.

Easley, L. T., and L. E. Chaiken, 1951. An eXpendable
seed trap. Jour. For. 49: 652-655.

Fernald, M. L., 1950. Gray's manual of botany.
American Book Co., New York.

Gysel, Leslie W. and John L. Arend, 1955. Oak Sites
in southern Michigan; their classification and
evaluation. Tech. Bul. No. 256. Ag. Exp. Sta.
Michigan State College, E. Lansing.

Hamilton, William J. Jr., 1941. The food of small
forest mammals in eastern United States. Jour.
Mamm. 22: 250-265.

Hayne, Don W., 1949. Two methods for estimating
populations from trapping records. Jour. Mamm.
50: 599-411.

JohnSgard, G. A., et al., 1942. 8011 survey of
Clinton County, Michigan. Pub. series 1956,
No. 12, U.S.D.A., Washington, D. C., pp. 1-71.

Kautz, L. G., and F. G. Liming, 1959. Notes on the
1957 and 1958 acorn crOps in the Missouri Ozarks.
Jour. For. 57: 904.

Korstian, Clarence F., 1927. Factors controlling
germination and early survival in oaks. Yale
Univ. SChOOl For. B11110 NO. 19, pp. 1-1150

Linduska, J. P., 1950. Ecology and land-use
relationships of small mammals on a Michigan
farm. Game Div. Dept. Conserv., Lansing,
Michigan, pp. 1-144.

Martin, A. C., Herbert S.‘Zim and Arnold L. Nelson,
1951. American wildlife and plants. McGraw-
Hill Book Co., Inc., New York.

Toumey, James W. and Clarence F. Korstian, 1947.
Foundations of silviculture; upon an ecological
basis. John Wiley and Sons, Inc., New York.

24.

26.

27.

28.

77

Uhlig, Hans G., and H. Lee Wilson, 1952. A method
of evaluating an annual mast index. Jour. Wildl.
Mgt. 16: 558-545.

Van Dersal, William R., 1958. Native woody plants
of the United States, their erosion control and
wildlife values. U.S.D.A. Misc. Pub. No. 505.

. 1940. Utilization of oaks by birds and
mammals. Jour. Wildl. Mgt. 4: 404-428.

Wood, 0. M., 1954. A brief record of seed productivity
for chestnut oak in southern New Jersey. Jour.
For. 52: 1014-1016.

. 1958. Seedling reproduction of oak in
southern New Jersey. Ecology 19: 276-295.

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