United States 

Department of 

Agriculture Planting Northern Red Oak Acorns: 

Forest Service IS Size and Planting Depth Important? 

Northeastern Forest 

Experiment Station 

Research Paper NE-693 L. R. Auchmoodv J 

H. Clay Smith 

Russell S. Walters 
A study was conducted in northern Pennsylvania to determine whether predation 

by smaH rnammalls and insects is related to the size of red oak acorns. Three 

sizes of acorns were used along with o planting techniques and three Ievek of 

overstory shading. Three-year results indicated that acorn size is not a factor in 

rn size did not affect &year survival. Although 

different after 3 years, the differences were too 

small for practical use. 

8. R. AUCHMOODV (retired) was a research forester and principal soil scientist at 

Northeastern Forest Ex Station's Forestry Sciences Laboratory, 

rren, Pennsylvania. He S. and M.S. degrees from the State University 

of Forestry, and a h.D. degree from North Carolina State 

SMITH (retired) was roject leader and principal silviculturist at the 

ortheastern Forest Experiment Station's Timber and atershed Laboratory, 

Parsons, West Virginia. .S. and MS. degrees from West Virginia 

and Purdue Universities, and joined the Northeastern Forest Experiment Station in 

1962. 

RUSSELL S. WALTERS (retired) was principal silviculturist and research forester 

at the Northeastern Forest Experiment Station's Forestry Sciences Laboratory, 

Warren, Pennsylvania. He received a B.S. degree from Michigan State University, 

an M.S. degree from Oregon State University, and a Ph.B. degree from the State 

University of New York, College of Forestry. 

Manuscript received for publication 12 April 1994 

USDA FOREST SERVICE 

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September 1 994 
Introduction 

Due to the wide geographic range of oaks, acorn seed 

crops vary greatly in the quantity and size of acorns that 

are produced for the same species. Average acorn size in 

one portion of the range may be twice as large as large 

seed from another portion of the range (Tourmey and 

Korstian 1947). Does acorn size really matter? Is there 

some advantage lo selecting smaller or larger acorns for 

artificial regeneration of oaks? Does the size of an acorn 

influence seed germination or seedling survival? Similar 

questions can be asked about acorn consumption and 

predation. Do small mammals or insects prefer smaller or 

larger acorns? 

There are a number of available publications indicating that 

acorn seed size or weight has a positive relationship with 

such factors as germination, seedling survival, and seedling 

height. Other information indicates acorn size has little or 

no effect. Some researchers conclude that genetic 

differences are more significant than acorn seed size. Early 

literature reported that there was considerably more 

information on seed size and weight of agricultural and 

garden seeds than of seeds of forest trees (Cummings 

191 4; Korstian 1927; Schmidt 1924). 

When using acorns for artificial regeneration, we often pick 

the larger, heavier, "better looking" acorns. Realistically, 

larger acorns presumably have greater quantities of stored 

nutrients (food reserve), implying larger, more vigorous 

seedlings with a better chance of early survival. Thus, seed 

weight (size) should play an important role in the selection 

of forest-tree seeds. 

European foresters have iong recognized that heavier and 

larger seed results in higher germination and seedling 

survival. The concern is, then, how long does this 

advantage persist? Clements et a!. (1929) indicated a 

height-growth advantage that tended to be cumulative. 

Tree seedlings that are able to quickly get their crowns 

above the competition usualiy are more favorably situated 

to continue to be competitive (McComb 1934; Korstian 

1927). Hauch (1 923) and Tourmey and Korstian (1 947) 

indicated that the variation in tree size and vigor persists 

throughout the life of oaks. Cieslar (1896) indicated the 

early height-growth advantage for oaks from larger acorns 

persisted for 18 growing seasons. 

However, much of the information in the literature is based 

on 1- to 2-year studies. Korstian (1 927) reported that 

larger acorns of northern red oak (Quercus rubra L.), black 

oak (Q. velutina L.), chestnut oak (Q. prinus L.), and 

scarlet oak (Q. coccinea L.) should provide additional 

germination and greater seedling vigor. Seedlings from 

large chestnut oak acorns had significantly more extensive 

roots (McComb 1934). Conversely, Tecklin and McCreary 

(1991) reported that root length for blue oaks was not 

affected by acorn size. Larger acorns result in greater 

weights of seedling roots and tops (Korstian 1927; 

Matsuda and McBride 1986; McComb 1934; Tecklin and 

McCreary 1991). Also, acorn size can be an important 

factor influencing the extent of the range of plant species 

that expanded or whose range shifted following climatic 

changes. Aizen and Patterson (1 990) reported a positive 

correlation between acorn size and the geographic range of 

oaks in Eastern North America (large-seeded oaks have a 

greater geographic range than smaller seeded oaks). Also 

reporting positive results when evaluating larger versus 

smaller acorns were Eytingen (1 91 5), Cummings (1 91 4, 

Kiesselbach and Helm (1 91 7), Renich (1 WI), and Baranski 

(1 975). 

Some investigators have reported that size or weight of red 

oak acorns was not as significant as previously indicated. 

In France, Aissa (1 983) found that large Q. ilex acorns had 

no advantage of root size during germination. In reviewing 

several studies, Bonner (1988) suggested that the 

advantage of seed size may not persist, and that genetic 

factors may be more important. 

Predation of red oak acorns by mammals and insects was 

reported by Korstian (1927) who found in a North Carolina 

study that acorns were destroyed by animals (56.5 percent) 

and insect larvae (24.2 percent). Similar comparisons 

were reported for acorns from white, chestnut, and black 

oak. Acorns provide highly nutritious food for numerous 

species of wildlife and constitute both a fall and winter food 

source. In a Michigan study, Verne (1957) found that white, 

black, and scarlet oak acorns were most preferred by 

chipmunks (Tamias striatus) and white-footed mice 

(Peromegscus lencopses). Red oak acorns were least 

preferred. 

Methods 

The objective of this study was to determine the effect of 

size of northern red oak acorns on populations of small 

mammals and insects, germination and seedling survival, 

and height growth. Other treatments superimposed on the 

acorn-size treatments were depth of planting and overstory 

density. 

Three acorn-size treatments and two sowing depths were 

evaluated. Acorn sizes were small, medium, and large. 

Acorn green weights for each size class were large, more 

than 5.5 grams; medium, 3.5 to 5.5 grams; and small, less 

than 3.5 grams. Acorns were float-tested and examined for 

weevil infestation prior to sowing; only sound, uninfected 

acorns were used. The acorns were sown in early 

November to two soil depths--on the soil surface and 1 inch 

beneath the soil surface. For each acorn-size plot there 

were three rows of surface-sown acorns and three rows of 

subsurface-sown acorns. Each row contained 14 acorns. 

The acorns were planted 4 inches apart and rows were 1 

foot apart. The subsurface acorns were pushed 1 inch into 

the mineral soil. For the surface-sown acorns, the current 

year's litter was pulled back and acorns were pressed into 

the top of the previous season's litter. All acorns were 

covered with an amount of the current year's litter that was 

representative of the treatment plot. During the first year, 

acorns were examined three times to determine viability or 

causes of mortality and thereafter checked annuaily to trace 

seedling development. In this paper we report 3-year 

survival. 
The study was conducted in north-central Pennsylvania on 

the unglaciated Allegheny Plateau on the Moshannon State 

Forest in commercial-size northern red oak stands. 

Elevations ranged from 1,700 and 2,300 feet. Precipitation 

averaged nearly 4 inches per month during the growing 

season. The region's climate is coos and moist, with a 

growing season of approximately 130 days. The average 

air temperature during the growing season is 60°F, though 

late freezes are common thr June. Because of ample 

rainfall, cool summer tempe 

cover, soil moisture usually remains plentiful until late in the 

growing season. Snow cover prevails from December 

through mid-March. Each study area consisted of three 

4-acre stands (12 acres total). Ail 36 acres were fenced to 

exclude deer. 

Each study area was characterized by uniform, gently 

rolling topography. Althou h soils varied among areas, 

none has important physica! limitations for the development 

of red oak or production of acorns. Soil textures range from 

sandy loam to silty clay loam; the effective soil depth ranges 

from about 24 to 30 inches. Humus types are duff mull. 

Each of the even-aged stands originated after clearcutting 

and is dominated by northern red oak in the overstory. Site 

index for red oak at age 50 ranges from 63 to 75 among the 

three areas. Common associated species are red maple 

(Acer rubrum L.), sugar maple (A. saccharum Marsh.), 

black cherry (Prinus serotha Ehrh.), white oak (Quercus 

alba L.), and white ash (Fraxinus americana L.). Along with 

northern red oak, these species make up 95 percent of the 

stand basal area, 

The basic experimental units within each study area are 

three 4-acre cutting plots with installations located only in 

plots that are fenced (electric) to protect acorns from deer 

predation. The overstory in each 4-acre plot was treated 

with one of three relative-densiv levels: 100 percent (no 

cutting), 60 percent, an 

plot, four acorn-size plots (14 x 14 feet) were established. 

Two of these plots were protected from pilferage of seed by 

small mammals and two were [eft unprotected. Acorn-size 

plots were located in areas that were representative of the 

level of overstory light that reached the forest floor beneath 

the different overstory levels. These small-acorn plots 

always were located well away from the perimeter of the 

larger 4-acre plot to avoid edge effects. Data were 

analyzed using chi-square analysis and analysis of variance 

split/split/split plot techniques with significant differences 

tested at the 1-percent !eve%. All treatments were assigned 

at random. 

Acorn size did not affect predation and consumption of 

acorns by small mammals in the unprotected plots. There 

was no preference for acorns of different size that were 

readily available on the soil surface or for the less 

conspicuous acorns located 1 inch beneath the surface 

(Table 1). Placement beneath the soil simu[ates caching by 

small mammals and heips protect the acorn from insect 

attacks and desiccation, and may reduce pilferage by small 

mammals. Small mammals consumed about 91 percent of 

the acorns that were placed on the surface and about 34 

percent of those beneath the surface. 

installed, it was a good acorn crop yea 

would have expected more acorns to have been consumed. 

Observations suggest that the major p 

chipmunks and white-footed mice. Co 

by gray squirrels (Sciurus caroiiraensis) 

(Tamiasciurus hudsonicus) was minor, probably because of 

their low population levels in 1989 when the acorns were 

sown. 

There were no significant differences in small-mammal 

preferences for acorns of different: size among the three 

overstory densities. This was true for acorns placed on the 

soil surface and beneath it. 

Acorn placement 

Acorn size Surface Subsurface 

Number Percent Number Percent 

Small 696 92 271 36 

Medium 708 94 246 33 

Large 

aMaximum number of acorns available for predation was 

756 per treatment; plots not protected from small 

mammals. 

lnsect infestation 

There were no significant differences in insect infestation 

rates that were attributed to acorn size for either surface or 

subsurface placed acorns (Table 2). Insects infested about 

40 percent of the acorns on the surface and about 25 

percent of the acorns beneath the soil surface. Insect 

infestation was primarily from ground weevils 

(Conotracheius posticafus Buheman) and to lesser extent 

from nitidusids (Stelidofa octomaculata (Say)), which 

collectively accounted for 97 percent of all damage. 

lnsect infestation of northern red oak acorns by weevils 

and nitidulids is nearly always fatal. Of the 4,536 acorns 

that were sampled in this part of the study, 1,405 

Table 2 ns destroyed or infeste 

size an rnenl" 

Acorn placement 

Acorn size Surface Subsurface 

Number Percent Number Percent 

Small 291 3€Ib 176 2sb 

Medium 299 40 187 25 

Large 306 40 146 19 

aMaximum number of acorns available for predation was 

756 per treatment; plots protected from small mammals. 

b~o significant differences among acorn-size treatments. 
(31 percent) became infested. None of the infested acorns 

produced a seedling. Thus, regardless of size, virtually all 

acorns that become infested with insects die. Insect 

infestation of small, medium, or large acorns was 

unaffected by light levels resulting from the overstory 

treatments. 

Thirty-five percent of the subsurface acorns were infested 

with insects; an average of 23 percent of these planted 

acorns were lost to predation by small mammals. This 

means about 50 percent of the subsurface acorns would be 

available for germinating seedlings. 

Too many surface acorns (90 percent) were destroyed by 

chipmunks and mice in the unprotected small-mammal 

treatment areas and too many surface acorns (39 percent) 

were lost to insects in the protected treatment for 

meaningful statistical analysis. Therefore, the effects of 

acorn size were analyzed only for the protected subsurface 

treatments. 

Acorn size did not significantly affect seedling survival 

during the first and third years after germination (Fig. I). 

For the 2-year data, survival was significantly higher for the 

larger acorns compared to medium or small ones. 

However, this trend was not evident in the 3-year data. 

Also, seedling survival was not affected by initial acorn size 

for the three overstory density levels. 

Total Height Growth 

Height data were used only for subsurface acorns that were 

protected. In all, 2,268 of these acorns were available for 

analysis. 

There were small increases in seedling height with acorns 

of increasing size (Fig. 2). These increases were similar 

over all light levels and were consistent during each of the 3 

years. At the end of 3 years, the maximum difference in the 

annual gain in seedling height growth of increasingly larger 

acorns was 0.5 foot among the small, medium, and large 

acorns at any time during the study period. Although these 

differences are statistically significant, the actual differences 

in height are so small that they are of little practical value. 

Seedling growth was slightly better in the 40-percent 

relative-density plots where more light reached the forest 

floor. Total seedling height after 3 years ranged from about 

1 foot in the 40-percent plots to about 0.5 foot for higher 

densities. During the third growing season, seedling height 

decreased slightly in the higher density plots, primarily due 

to dieback of the terminal shoot, a common characteristic of 

RD40 RD60 RD100 

Overstory Treatment 

Figure 1 .--Percent red oak seedling survival (3-year) as related to acorn size and overstory 

relative density in plots fenced (electric) to protect acorns from predation by deer. 
SM MD LG S MD LG SM MD LG 

RD40 RD60 RD100 

Overstory Treatment 

Figure 2.--Total height of red oak seedlings as related to acorn size and overstory relative 

densities in plots fenced (electric) to protect acorns from predation by deer. 

small oak seedlings growing under a shade canopy. These 

effects were unrelated to initiai acorn size. 

Summary and Csnclusions 

Results of this study indicate that initial size of acorns has 

little influence on small-mammal predation, insect 

infestations, or seedling survival. Although total seedling 

height increased significantly with an increase in acorn size, 

after 3 years, these differences were too small for practical 

use. The following are specific results from the study. 

e Size does not affect acorn predation by small mammals, 

in this case, chipmunks and mice. 

e Acorn size did not influence insect infestations. 

@ There was significantly less acorn insect damage and 

small-mammal predation of buried acorns compared to 

acorns planted on the soil surface (study installed during 

good acorn crop year). 

9 No insect-infested acorns produced a seedling. 

@ After 3 years, acorn size did not affect seedling 

survival. 

@ There was a small increase in seedling height growth with 

increased acorn size. These increases were consistent 

for all light levels. 

@ Predation of acorns on the soil surface was nearly three 

times that of acorns below the surface (91 to 34 

percent). Acorn predation was mainly by chipmunks 

and mice. 

@ Planting acorns to a depth of 1 inch resulted in a loss of 

about 50 percent to small mammals and insects. Thus, 

about half of the acorns were available for germinating 

seedlings. 

Between 19 and 40 percent of all acorns were infested 

with insects. 
We recognize and thank Jimmy Galford, retired research 

entomologist, and Perry Fox, forestry technician, 

Northeastern Forest Experiment Station, for collecting the 

acorn data used in this study. Study areas on the 

Moshannon State Forest were made available by the 

Pennsylvania Bureau of Forestry. Additional support was 

provided by Paul Augusiine, Ed Richards, and Lee Warren 

of the Moshannon State Forest. 

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332. 

Baranski, M. J. 1975. An analysis of variation within 

white oak (Ouercus alba L.). Tech. Bull. 236. 

Salisbury, NC: North Carolina Agricultural Experimental 

Station. 176 p. 

Bonner, F. T. 1988. Importance of seed size in 

germination and seedling growth. In: Kamra, S. K.; 

Ayling, R. D. comps. eds. Proceedings, IUFRB 

international symposium on forest seed problems in 

Africa 1987; 1987 August 23-September 2; Harare, 

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Agriculture Sciences, Department of Forest Genetics 

and Plant Physiology: 53-61. 

Cieslar A. 1896. Versuche iiber Aufbewahrung von 

Eicheln. Centralblatt fur das gesammte 

Forstwesenschafttiches. 22: 181 -1 88. 

Clements, F. E.; Weaver, J. E.; Hanson, H. C. 1929. Plant 

competition, an analysis of community functions. 

Publ. 398. Washington, DC: Carnegie Institute of 

Washington. 

Cummings, M. B. 1914. Large seed a factor In plant 

production. Bull. 677. Burlington, VT: Vermont 

Agricultural Experiment Station: 89-123. 

Eytingen, 6. R. 1915. (The effect of the weight of acorns 

upon the development of two-year-old seidlings.) 

Lyesopromuishiemuiii vyestnik, 196 5. No. 41 : 353-359. 

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weight and the development of 

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Brunswick, NJ: New Jersey Agricultural Experiment 

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a factor in early seedling growth of blue oaks. In: 

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November 2; Davis, CA. Gen. Tech. Rep. PSW-126. 

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corms: is size an 

Pap. NE-693. Radnor, PA: US. Department of Agriculture, Forest Service, 

Northeasiern Forest Experiment Station. 5 p. 

A study was conducted in northern Pennsylvania to determine whether 

predation by small mammals and insects is related to the size of red oak 

acorns. Three sizes of acorns were used aiong with two planting techniques 

and three levels of overstory shading. Three-year results indicated that acorn 

size is not a factor in mammal and insect predation. Acorn size did not affect 

3-year survival. Although 3-year total height growth was statisticaliy different 

after 3 years, the differences were too small for practical use. 

Keywords: Northern red oak; predation; germination; seed crops 

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