United States 

Department of 

Agriculture 

Forest Service 

Northeastern Forest 

Experiment Station 

Research Paper NE-680 

Acorn Production in Northern 

Red Oak Stands in 

Northwestern Pennsylvania 

L. R. Auchmoody 

H. Clay Smith 

Russell S. Walters 
Abstract 

Northern red oak acorn production was measured in 21 maturing stands on good 

sites in northwestern Pennsylvania. The number of acorns produced per acre varied 

from a low of 7,000 in a poor seed year to nearly 273,000 in a bumper year. Some 

acorns were produced in all years. In no year was there consistently good acorn 

production at all areas, nor was there a good crop for more than 2 consecutive years 

at any location. Acorn production was not related to the mean diameter and range of 

basal area of red oak trees in the experimental stands. Freezing temperatures when 

oaks were in flower was a major factor affecting acorn production on the Allegheny 

Plateau. 

The Authors 

L. R. AUCHMOODY is a research forester and principal soil scientist at the 

Northeastern Forest Experiment Station's Forestry Sciences Laboratory, Warren, 

Pennsylvania. He holds B.S. and M.S. degrees from the State University of New 

York College of Forestry, and a Ph.D. from North Carolina State University at 

Raleigh. He conducts research on site evaluation, forest nutrition, and regeneration 

of oaks and Allegheny hardwoods. 

H. CLAY SMITH is project leader and principal silviculturist at the Northeastern 

Forest Experiment Station's Timber and Watershed Laboratory, Parsons, West 

Virginia. He received his B.S. and MS. degrees from West Virginia and Purdue 

Universities, and joined the Northeastern Forest Experiment Station in 1962. He has 

conducted extensive silvicultural research in Vermont and West Virginia. 

RUSSELL S. WALTERS is principal silviculturist and research forester at the 

Northeastern Forest Experiment Station's Forestry Sciences Laboratory, Warren, 

Pennsylvania. He holds a B.S. from Michigan State University, an M.S. from Oregon 

State University, and a Ph.D. from the State University of New York College of 

Forestry. He conducts research on silviculture and regeneration of oaks and 

Allegheny hardwoods. 

Acknowledgment 

The authors wish to thank Jimmy Galford, research entomologist, U.S. Department 

of Agriculture, Forest Service, (retired) and Perry Fox, forestry technician, U.S. 

Department of Agriculture, Forest Service, for collecting the acorn cap data used in 

this study. Study areas on the Moshannon State Forest were made available by the 

Pennsylvania Bureau of Forestry and the Allegheny National Forest by the U.S. 

Department of Agriculture, Forest Service. Additional support also was provided by 

Paul Augustine, Ed Richards, and Lee Warren of the Moshannon State Forest. 

Manuscript received for publication 7 June 1993 

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Introduction 

Production of northern red oak (Quercus rubra L.) acorns is 

essential for establishing abundant advanced red oak 

regeneration. Acorns also are an important food supply for 

deer, squirrels, turkeys, and many other wildlife species. 

Therefore, estimates of acorn crop size, periodicity of acorn 

crops, and knowledge of the variables that can affect acorn 

production are important to forest and wildlife managers alike. 

Reproduction of northern red oak after cutting comes from 

advanced seedlings, seedling sprouts, and stump sprouts. In 

northwestern Pennsylvania, however, few advanced red oak 

seedlings occur in mature red oak stands on good sites. 

While predation of acorns and young seedlings by deer, 

insects, and small mammals contribute to the lack of 

advanced seedlings, poor acorn crops also are a significant 

limitation for advanced regeneration. 

In 1988 the Northeastern Forest Experiment Station began 

studying the limitations for red oak seedling establishment in 

northwestern Pennsylvania. One of the studied limitations 

was acorn production. Reported in this paper is northern red 

oak acorn production and flowering observations during 4 

years in one research area, and 2 years at a second area. 

Also reported are relationships between acorn production 

and red oak stand basal area and red oak stand diameter. 

Study Areas 

Study installations are located on the Moshannon State 

Forest and the Allegheny National Forest within the 

unglaciated section of the Allegheny Plateau in northwestern 

Pennsylvania. At the Moshannon installation, there were 

three study areas where acorn production was measured, 

and on the Allegheny National Forest there were four areas. 

Each study area consisted of three 4-acre stands (1 2 acres 

total) fenced to exclude deer. 

Each 12-acre area was characterized by uniform, 

gently-rolling topography. Elevations among the areas 

ranged from about 1,500 to 2,300 feet, though all but one 

were above 1,700 feet (Table 1). The regional climate is cool 

and moist, with precipitation averaging nearly 4 inches per 

month during the growing season. The growing season 

length is approximately 130 days, with an average air 

temperature of 60°F. Late spring freezes are common 

through early June, particularly above 1,700 feet, and are 

known to be a critical factor for acorn production in some 

years (Grisez 1975). Because of ample rainfall, cool summer 

temperatures, and much cloud cover, soil moisture usually 

remains plentiful until late in the growing season. Snow cover 

prevails from December through mid-March. 

Soils vary somewhat among the areas, but none of the sites 

has any important physical soil limitations for red oak 

development or acorn production. Soil texture ranges from 

sandy loam to silty clay loam, and the effective soil depth 

varies from approximately 24 to 30 inches. Humus.types are 

duff mulls. 

Each of the experimental stands, except for Keller Road 

(Table I), originated after clearcutting, and is even aged and 

dominated by northern red oak in the overstory. The Keller 

Road site is uneven aged and has less red oak than the other 

sites, although the red oak trees there are larger and older. 

Site index for red oak at age 50 varied from 63 to 79 among 

the seven areas. Common associated species in the study 

areas were white oak (Quercus alba L.), black oak (Quercus 

velutina Lam.), chestnut oak (Quercus prinus L.), red maple 

(Acer rubrum L.), sugar maple (Acer saccharurn Marsh.), 

American beech (Fagus grandifolia Ehrh.), black cherry 

(Prunus serotina Ehrh.), white ash (Fraxinus americana L.), 

and cucum bertree (Magnolia acuminata L.). 

Table 1. - Description of the areas where northern red oak production was measured. Each study area 

includes three &acrestands, for a total of 12 acres 

Elevation Site Soil Red oak Red oak Red oak Even 

Study area (ft) index series stand age basal areaa diametera aged 

---------- Moshannon State Forest ---------- 

Smith Road 2,300 63 HazletonICookport 82 70.5 14.1 Yes 

Gordon Road 1,850 75 RayneIGilpin 82 75.9 20.3 Yes 

Snotrail 1,700 73 WhartonIGilpin 78 73.4 17.6 Yes 

---------- Allegheny National Forest ---------- 

Route 337 1,860 74 HazletonICookport 76 54.4 16.3 Yes 

Keller Road 1,530 75 Cavode 109 24.7 22.2 No 

Buehler Corners 1,720 79 HazletonICookport 72 78.2 16.8 Yes 

Whistletown 1,750 79 HazletonICookport 76 97.5 15.3 Yes 

a For trees 1.0 inches d.b.h. and larger. 
The basic plot design was the same for each of the study 

areas. At the Moshannon State Forest, acorn production was 

estimated annually at three areas over a 4-year period, and 

annually on the Allegheny National Forest at four areas for a 

2-year period. At each area, acorn production was measured 

in three 4-acre stands providing estimates from a total of 84 

acres. One stand at each area was uncut, one had its 

overstory density reduced to 60 percent relative density, and 

one had its overstory density reduced to 40 percent relative 

density. Cutting procedures in the 60- and 40-percent stands 

retained all of the northern red oaks large enough to produce 

acorns, so there was minimal effect from the cutting 

treatments on the potential of the different stands to supply 

acorns. All measurement sites initially were located in 

uniform, fully-stocked stands before cutting, and ail were 

fenced to exclude deer. 

Acorn production was estimated indirectly from acorn cap 

counts taken in each 4-acre stand, as recommended by 

Shaw (1 974). Cap counts for acorns that matured in the 

previous fall were completed by the following June after all 

caps had fallen and before starting to decompose. The 

sampling procedure used to estimate the 1988 acorn crop 

consisted of randomly selecting 10 large red oaks in each 

4-acre stand, then counting the acorn caps on four 

1 -square-foot plots beneath each tree. Trees were selected 

without previous knowledge of their acorn production. Thus, 

in each 4-acre stand there were 40 acorn cap plots for a total 

of 120 plots per area. In the following years, acorn cap 

counts were conducted on 30 systematically located, 1 - 

foot-square plots in each 4-acre stand, for a total of 90 plots 

per area. 

Results 

Northern Red Oak Acorn Production 

The number of northern red oak acorns produced annually 

over a 4-year period at the Moshannon sites and over a 

2-year period at the Allegheny National Forest sites are given 

in Table 2. Some acorns were produced each year at all of 

the areas, but there was great variation from area to area 

within the same year, and among study areas in different 

years. Production varied from a low of about 7,000 acorns at 

the Whistletown area in 1990 to a high of nearly 273,000 in 

the same year at Smith Road (Table 2). In no year was there 

consistently good production (>I 25 M acornslacre) at all 

areas, nor was there a good crop for more than two 

consecutive years at any location. Acorn production in 1991 

was uniformly poor, the result of a wide-spread hard freeze in 

1990 when oaks were in flower. 

Acorn Production and Stand Parameters 

Relationships between annual acorn production and mean 

residual red oak stand diameter and red oak stand basal 

area were examined using multiple regression analyses. 

Data were from 9 stands on the Moshannon State Forest and 

12 stands on the Allegheny National Forest. 

Analyses using all 21 sites showed no regional relationships 

between acorn production and stand diameter (mean red oak 

diameter) or between acorn production and the quantity of 

red oak present in the stands (red oak stand basal area) in 

either 1990 or 1991, the two years data were available for all 

sites. Instead, 1990 acorn production was strongly site 

related, with two areas having good or bumper crops and 

most of the remaining sites having poor crops regardless of 

tree size or the quantity of red oak present. In 1991, a 

uniformly poor year for acorn production region-wide, only 

one site produced more than 80 M acorns per acre, and 

there was no relationship between acorn production and 

stand parameters on the other sites. 

Regression analyses of acorn production on the Moshannon 

State Forest also showed that acorn production was strongly 

site related, and not related to either red oak tree size or 

basal area in the individual stands. The relationships 

between acorn production and mean red oak stand diameter 

over the 4-year period are shown in Figure 1. Although a 

positive relationship between acorn production and red oak 

Table 2.-Number of acorns per acre produced at seven areas in northwestern Pennsylvania 

Study area 1988 1989 1990 1991 

---------- Moshannon State Forest ---------- 

Smith Road 49,368 (6,l 42)a 133,584 (1 4,253) 272,979 (1 8,182) 22,748 (6,502) 

Gordon Road 127,776 (1 1,805) 143,458 (1 6,754) 69'21 2 (7,815) 22,264 (3,658) 

Snotrail 135,036 (1 2,763) 38,188 (7,597) 45,012 (7,740) 30,976 (4,927) 

---------- Allegheny National Forest ---------- 

Route 337 --- --- 128,744 (1 6,023) 53,240 (9,280) 

Keller Road --- --- 1 6,456 (3,240) 49,368 (8,323) 

Buehler Corners --- --- 20,812 (3,525) 49,368 (6,645) 

Whistletown --- --- 6,776 (2,567) 81,312 (8,793) 

a Standard error of mean in parentheses, 
NORTHERN RED OAK MEAN DIAMETER (inches) 

Figure 1 .-Northern red oak acorn production and the average stand diameter of red oak during 4 years on 

the Moshannon State Forest. Points with the same symbol are from the same study area (S = Smith Road, 

G = Gordon Road, ST = Snotrail). Acorn production was related to location, not directly to stand diameter. 

NORTHERN RED OAK MEAN DIAMETER (INCHES) 

Figure 2.-Northern red oak acorn production and the average stand diameter of red oak during a 2-year 

period on the Ailegheny National Forest. Acorn production was related to location, not directly to stand 

diameter. 
diameter is suggested in 1988 (Fig. 1) and a negative 

relationship is suggested in 1990, these are caused by 

differences in acorn production among the areas, and not 

from differences in stand diameters. For example, the Smith 

Road stands (Fig. 1) had the smallest mean red oak 

diameters, yet in 1990, those stands had the largest acorn 

crop and in 1988, the poorest. No relationships between 

acorn production and stand diameter were indicated for 1989 

or 1991 (Fig. 1). Further evaluation also showed that acorn 

production in stands from within a given area were similar 

and that no consistent relationship was found between acorn 

production and red oak stand diameter during the 4-year 

period at any of the three areas. 

The relationships between acorn production and stand 

parameters on the Allegheny National Forest were similar to 

those on the Moshannon State Forest (Fig. 2). In 1990 one 

area had a good acorn crop and the remaining three areas 

were poor, regardless of their diameter or the quantity of red 

oak basal area in the stands. In 1991, two of the study stands 

at the Whistletown site had fair crops, while ail other sites 

had poor crops regardless of stand parameters. 

Flower Production 

Observations of red oak flowering were made annually at 

each of the seven areas, though no quantitative data were 

actually collected. Abundant male flowers (catkins) with some 

year-to-year variation were observed in each of the 4 years, 

suggesting that male flower production is not a limiting factor 

for acorn production. Female flowers also were present each 

year on fallen branches; however, these limited observations 

were not adequate to assess year-to-year variation. In 3 of 

the 5 observation years, spring freezes destroyed most of the. 

flower crops at most study areas (1 988, 1990, 1992). 

Acorn Crop Ratings 

During the 4-year measurement period, acorn crops from the 

21 study stands varied from zero to more than 31 2,000 

acorns per acre. From subjective ratings of acorn abundance 

and the estimated number of acorns present from cap counts 

in the same stands, a simple acorn crop rating guide was 

developed (Table 3). 

Quick estimates of the acorn crop rating and actual acorn 

numbers can be made from estimates of the number of 

acorns or the acorn caps per square foot. At least 30 

Table 3.-Guide for rating northern red oak acorn crops 

Subjective Actual Approximate 

crop rating acornslacre acorns 1 ft 

Bumper >250,000 5 + 

Good 125 - 250,000 3-5 

Fair 65 - 125,000 1.5-3 

Poor 20 - 65,000 0.5 - 1.5 

Trace to none <20,000 0-1.5 

square-foot samples are recommended. With a little 

experience, the number of acorns per square foot can be 

estimated at a glance near the termination of peak acorn fall, 

but plots are required for cap counts since the caps become 

embedded in the litter and are difficult to see. If acorn 

estimates are made where deer and small mammal 

populations are high, some acorns will be consumed quickly 

or cached, causing subsequent low estimates of the total 

crop. In theses cases it is best to use the acorn cap 

technique after all caps have fallen to the ground, since cap 

numbers are much less affected by wildlife consumption. 

Acorn production estimates are important for their value in 

wildlife management and as a means for establishing oak 

reproduction. Trapping and ground counting of acorns are 

the methods commonly used to estimate acorn production. 

The accuracy of these techniques, though, can be affected 

by the uneven dispersal pattern that requires a prohibited 

large number of traps, and also by consumption of acorns by 

deer, small mammals, and birds during the dispersal period. 

For example, it rarely is possible with traps to sample 

adequately the uneven distribution of acorns, which, because 

of their weight, remain concentrated beneath mother trees. 

Acorns caught in traps also are subject to significant pilferage 

by predators. Ground surveys, as well, are subject to serious 

underestimates because predators rapidly consume acorns 

throughout the dispersal period. 

The cap counting technique offers a way to minimize these 

problems. It allows use of a large number of inexpensive 

temporary plots to sample thoroughly uneven acorn 

distributions, and because acorn caps are not eaten by small 

mammals, primarily avoids underestimates from predator 

consumption. Additionally, cap counts can be conducted over 

a much longer period and are not restricted to a short interval 

at dispersal. 

Estimates of northern red oak acorn production at the seven 

areas varied from approximately 7,000 to nearly 273,000 

acorns per acre during the measurement period. These 

values encompass the range of red oak acorn production 

reported in the literature, but substantially exceed the 

reported values where exceptionally good or bumper crops 

occurred. In comparison to our estimates, Gysel (1 957) 

reported 30,600 northern red oak acorns per acre as the 

4-year average for good sites in Michigan. In the southern 

Appalachians, Beck and Olson (1 968) measured 6,600 to 

94,600 acorns per acre for several species of oaks. In a 

review of acorn production, McQuilken (1 983) concluded that 

annual acorn crops ranged from none in poor years to more 

than 100,000 in good years, Barni (1 980) reported annual 

averages of 31,074; I 1 ,I 64; and 40,199 acorns per acre in 

north central Pennsylvania, from 1977 to 1979, respectively. 

We feel that our higher estimates may be due not only to the 

inclusion of exceptionally good crop years during the 

measurement period, but also to estimates made from acorn 

cap counts in stands where deer were excluded, resulting in 

estimates unaffected by predator consumption. 
We experienced much variation in acorn production among 

the different sites and from year to year, regardless of the 

diameter or quantity, of red oak in the stands. This variation 

agrees with a common conclusion drawn from the literature 

that acorn crops are sporadic, infrequent, and unpredictable 

(Sharp and Chisman 1961; Watt 1979; McQuilken 1983). 

The reasons for this variation are not known, though there 

have been many attempts to determine the causes. In the 

present study, all of the stands were above the minimum 

seed-bearing size and age, and all were well stocked with red 

oak. Thus, in this study, tree age and size and stocking of red 

oak should not have been important factors limiting acorn 

production. In addition, we know good production of male 

flowers occurred annually and that female flowers were 

present each year as well. Nor did cyclic flower production 

due to physiological reasons appear to be the major cause of 

the variation. 

Weather related limitations for acorn production, particularly 

freezing temperatures when oaks are in flower, appear to be 

one of the most critical factors for acorn crops on the 

Allegheny Plateau. Oak flowers were affected by spring 

freezes in 3 of the 5 years that flowering was observed. Not 

all of the sites were affected each year, suggesting that small 

differences in elevation or the location of areas on the 

plateau may allow some areas to remain unaffected. Our 

observations agree with Goodrum et al. (1971) that low 

spring temperatures kill oak flowers. and may have an overall 

limiting effect on acorn production. Dry, desiccating winds 

during pollen dispersal combined with low temperatures 

during flowering also may adversely affect acorn production 

(Sharp and Chisman 1961). Conversely, good crops result 

when relatively wet periods are followed by warmer 

temperatures at the beginning of the flowering period. 

Finally, the study results suggest that stands with a northern 

red oak mean diameter of at least 14 inches and basal area 

of 70 square feet are above the threshold size for good acorn 

production, ,and are fully capable of producing bumper acorn 

crops. Nearly 273,000 acorns per acre were produced by 

stands with these minimum parameters in 1990, for example. 

Downs and McQuilken (1944) in the Piedmont of Georgia 

and in the Smokey Mountains of North Carolina found that 

the desirable diameter for optimum red oak acorn production 

was from 12 to 21 inches. In Michigan, Gysel (1 956) 

determined that acorn production of northern red oak 

dropped rapidly below 14 inches d.b.k. Thus, it seems that 

acorn production in northern red oak stands with a mean 

diameter of 14 inches and larger should not be influenced 

greatly by increasing stand diameter. 

Throughout the literature, terms like "bumper," "good," and 

"poor" have been used to characterize the acorn seed crop. 

We provided a general guide for red oak seed crops as 

related to acorn production per acre. Also, we related acorn 

production to the amount of acorns (or caps) observed on a 

square foot. This approach should result in more consistent 

use of terminology and less subjectivity among forest 

managers. 

Literature Cited 

Barni, Robert T. 1980. Production and utilization of acorns 

on the Quehanna Wild Area. University Park, PA: The 

Pennsylvania State University, School of Forest 

Resources. 48 p. M.S. thesis. 

Beck, Donald E.; Olson, David F., Jr. 1968. Seed production 

in southern Appalachian oak stands. Res. Note SE-91. 

Asheville, NC: U.S. Department of Agriculture, Forest 

Service, Southeastern Forest Experiment Station. 7 p. 

Downs, Albert A.; McQuilken, William E. 1944. Seed 

production of southern Appalachian oaks. Journal of 

Forestry. 42: 91 3-920. 

Goodrum, P. D.; Reid, V. H.; Boyd, C. E. 1971. Acorn 

yields, characteristics, and management criteria of 

oaks for wildlife. Journal of Wildlife Management. 35(3): 

520-531. 

Grisez, Ted J. 1975. Flowering and seed production in 

seven hardwood species. Res. Pap. NE-315. Upper 

Darby, PA: US. Department of Agriculture, Forest Service, 

Northeastern Forest Experiment Station. 8 p. 

Gysel, Leslie W. 1956. Acorn production on good, 

medium, and poor oak sites in southern Michigan. 

Journal of Forestry. 55: 570-574. 

McQuilken, Robert A. 1983. Silvical factors affecting the 

regeneration of oaks and associated species in 

Pennsylvania. In: Finley, James; Cochran, Roe S.; Grace, 

James R., eds. Proceedings, Regenerating Hardwood 

Stands: 1983 Penn State Forestry Issues Conference; 

1983 March 15-1 6; University Park, PA. University Park, 

PA: The Pennsylvania State University: 37-56. 

Sharp, W. M.; Chisman, H. H. 1961'. Flowering and fruiting 

in the white oaks; I. Staminate flowering through 

pollen dispersal. Ecology. 42(2): 365-372. 

Shaw, M. W. 1974. The reproductive characteristics of 

oak. In: Morris, M. G.; Perrin, F. H., eds. The British oak: 

Its history and natural history. Published for the Botanical 

Society of the British Isles by E. W. Classey, Hampton, 

England: 162-1 81. 

Watt, R. F. 1979. The need for adequate advance 

regeneration in oak stands. In: Holt, H.A.; Fischer, B. C., 

eds. Regenerating Oaks in Upland Hardwood Forests. 

Proceedings of a symposium; 1979 February 22-23; West 

Lafayette, IN. West Lafayette, IN: Purdue Research 

Foundation: 1 1-1 7. 

0 Printed on Recycled Papa 

AU. 5. GOVERNMENT PRINTING OFFICE: 199 3-750- 12 3/80002 
Auchmoody, L. R.; Smith, H. Clay; Walters, Russell S. 1993. Acorn 

production in northern red oak stands in northwestern Pennsylvania. 

Res. Pap. NE-680. Radnor, PA: US. Department of Agriculture, Forest 

Service, Northeastern Forest Experiment Station. 5 p. 

Northern red oak acorn production was measured in 21 maturing stands on 

good sites in northwestern Pennsylvania. The number of acorns produced per 

acre varied from a low of 7,000 to nearly 273,000. Acorns were produced in 

all years. In no year was there consistently good acorn production at all areas, 

nor was there a good crop for more than two consecutive years at any 

location. Freezing temperatures when oaks were in flower was a major factor 

affecting acorn production on the Allegheny Plateau. 

ODC 232.31 1 : 176.1 

Keywords: acorn production, stand parameters, flowering, freezing, cap 

counts, acorn crop guide 
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