March, 1994, TB-NC-1
HOW TO MANAGE OAK FORESTS FOR ACORN PRODUCTION
Paul S. Johnson, Principal Silviculturist
Importance of Acorns
Oak forests are life support systems for the many animals that live in
them. Acorns, a staple product of oaks forests, are eaten by many
species of birds and mammals including deer, bear, squirrels, mice,
rabbits, foxes, raccoons, grackles, turkey, grouse, quail, blue jays,
woodpeckers, and waterfowl. The population and health of wildlife
often rise and fall with the cyclic production of acorns. Acorns'
importance to wildlife is related to several factors including their
widespread occurrence, palatability, nutritiousness, and availability
during the critical fall and winter period. It would seem natural,
then, that some oak stands and perhaps extensive forests be managed
primarily for acorn production. Even though our knowledge of acorn
production is incomplete, we have enough information to make reasoned
decisions on the management of oak stands for acorn production.
What We Know About Acorn Production
Acorns of trees in the white oak group (subgenus Lepidobalanus) mature
in 3 months; those in the red oak group (subgenus Erythrobalanus)
require 15 months (two growing seasons). However, in both species
groups, acorn production is relatively unpredictable from year to
year. On the average, most species produce a good crop of acorns one
year in three or four (Beck 1977, Christisen and Kearby 1984, Downs and
McQuilkin 1944, Goodrum et al. 1971). In years of low or moderate
acorn production, most acorns are consumed by insects. Moreover, the
production of acorns differs among species. Some species are
inherently better acorn producers than others, and different species
tend to produce good acorn crops in different years. Although
environmental factors unfavorable to acorn production such as late
spring frost and summer drought tend to obscure inherent periodicity
(cycles) in production, new evidence suggests that such periodicity
occurs at 2-, 3-, and 4-year intervals for black, white, and northern
red oaks, respectively (Sork et al. 1993).
Other factors being equal, trees of large diameter produce more acorns
than trees of small diameter. However, in some species, production
declines after the tree reaches a threshold diameter (fig. 1). Oaks
with crowns fully exposed to light, such as dominant and codominant
trees, produce more acorns than trees with crowns totally or partially
shaded. In the white oak group, when one tree produces well, all of
the potential acorn-producing trees in the population tend to produce
well. In contrast, in the red oak group, some producers yield well in
a given year while others do not. In addition, only a relatively small
proportion of trees are inherently good seed producers. For example,
among white oaks in Pennsylvania, only 30 percent of large, healthy
trees produced any acorns even in good seed years (Sharp 1958) and an
even smaller proportion produced a good crop in those years (Sharp and
|Figure 1. Average annual acorn production per tree in relation to
d.b.h. in the southern Appalachians. (Based on a 7-year study: Downs 1944.)
Substantial gains in acorn production of established stands may be
obtained by following these guidelines:
- Before the first thinning, identify and reserve the good acorn
producers in each stand. To do this, you'll need to observe and keep
records for 5 years or more. If that is impractical, roughly assess
the acorn-producing capacity of individual trees by observing
production during a single year in which a good to excellent acorn crop
occurs for one or more of the major species present. However, in the
red oak group, many good producers may be overlooked in a single year
because not all trees of those species may produce well in the same
year. Criteria for identifying good producers are given by Sharp
(1958) (table 1). The best time to rank trees in the oak-hickory
region is from August 10 to 25, before acorn predators begin to eat or
cache many acorns. Acorns are best observed with binoculars on bright
days when they are silhouetted against the sky (Sharp 1958).
|Table 1. -A ranking of acorn production for
1Adapted from Sharp
(1958). Note that in any one year, excellent producers may not reach their
potential because of unfavorable environmental factors.
2Based on the terminal
24 inches of healthy branches in the upper one-third of the crown.
- During thinning, retain a mixture of oak species to minimize the
impact of the large year-to-year fluctuation in acorn production in any
- Thin around the identified acorn producers to expose their crowns
to full light on all sides. This facilitates crown expansion and
increases branch density. Branch density increases acorn production
per unit of crown area because of the increase in numbers (density) of
acorn- bearing branches (Verme 1953). Among the potential acorn
producers, dominant and codominant trees will be the most efficient
producers. Area-wide thinning is not necessary because only 20 or
fewer good seed producers are likely to occur per acre even in pure oak
stands. But because these seed producers typically will be dominant
and codominant trees, they may account for proportionately more basal
area and stocking than their numbers alone indicate.
- Increase or decrease the rotation (or in uneven-age management,
maximum tree diameter) to include the tree diameter of maximum acorn
production of the predominant species in each stand. For example,
production in northern red oak peaks when tree d.b.h. reaches 20 inches
and then it declines in larger trees (fig. 1). In contrast, white oak
production is maximized at about 26 inches. Many other species,
however, do not exhibit well-defined diameter-related peaks in
production, at least within the diameter ranges that have been reported
(Downs 1944, Goodrum et al. 1971). Large, senescent trees are usually
poor acorn producers (Huntley 1983).
The above guidelines are similar to those presented by Beck (1989).
They also are consistent with managing oak forests as life support
- Beck, Donald E.
- 1977. Twelve-year acorn yield in
southern Appalachian oaks. Res. Note SE- 244. Asheville, NC: U.S.
Department of Agriculture, Forest Service, Southeastern Forest
Experiment Station. 8 p.
- Beck, Donald E.
- 1989. Managing mast
production/capability. In: McGee. C.E., ed. Proceedings of the
workshop: Southern Appalachian mast management; 1989 August 14-16;
Knoxville, TN. Knoxville, TN: University of Tennessee: 24.
- Christisen, Donald M.; Kearby, William H.
Mast measurement and production in Missouri (with special reference to
acorns). Terrestrial Ser. 13. Jefferson City, MO: Missouri Department
of Conservation. 34 p.
- Downs, Albert A.
- 1944. Estimating acorn crops for
wildlife in the southern Appalachians. Journal of Wildlife Management.
- Downs, Albert A.; McQuilkin, William E.
- 1944. Seed production of southern Appalachian oaks. Journal of
Forestry. 42(12): 913-920.
- 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): 520-532.
- Huntley, Jimmy C.
- 1983. Squirrel den tree management; reducing
incompatibility with timber production in upland hardwoods. In: Jones,
Earle P., Jr., ed. Proceedings, 2nd biennial southern silvicultural
research conference; 1982 November 4-5; Atlanta, GA. Gen. Tech. Rep.
SE-24. Asheville, NC: U.S. Department of Agriculture, Forest Service,
Southeastern Forest Experiment Station: 488-495.
- Sharp, Ward M.
- 1958. Evaluating mast yields in the
oaks. Bull. 635. University Park, PA: Pennsylvania State University,
College of Agriculture, Agricultural Experiment Station. 22 p.
- Sharp, Ward M.; Sprague, Vance G.
- 1967. Flowering
and fruiting in the white oaks: pistillate flowering, acorn
development, weather, and yields. Ecology. 48(2): 243-251.
- Sork, Victoria L.; Bramble, Judy.
- 1993. Ecology of
mast-fruiting in three species of North American deciduous oaks.
Ecology. 74(2): 528-541.
- Verme, Louis J.
1953. Production and utilization of acorns in Clinton County, Michigan.
East Lansing, MI: Michigan State University. 77 p. Thesis.
The United States Department of Agriculture (USDA) prohibits
discrimination in its programs on the basis of race, color, national
origin, sex, religion, disability, political beliefs and martial or
familial status. (Not all prohibited bases apply to all programs.) Persons
with disabilities who require alternative means for communication of
program information ( braile, large print, audiotape, etc. ) should contact
the USDA Office of Communications (202) 720-5881 (voice) or (202) 720-7808
To file a complaint, write the Secretary of Agriculture, U. S.
Department of Agriculture, Washington, D. C. 20250, or call (202) 720-7327
(voice) or (202) 720-1127 (TDD). USDA is an equal employment opportunity
Copyright © 1998, USDA Forest Service