Vol. 2k, Mo. 1 
Page 2 
Ecology and Management of Squirrels - W-66-R 
C. M. Nixon, 
L. P. Hansen 
* 
Although logging is not a major management program on the state-owned 
public forests of Illinois, commercial logging is an important influence on 
squirrel abundance on private lands and the Shawnee National Forest. Our 
research has concentrated on determining the effects of clear-cutting and 
selection cutting on squirrels. 
Selection cutting, or the removal of individual or small groups of mature 
trees, is practiced on hundreds of acres of 111inois forest land each year and 
is often followed by removal of cull trees. We studied the short-term U 
years postlogging) response of squirrels to selection cutting without cull-tree 
removal on 3 hardwood tracts: 2 on the Shawnee National Forest and 1 on private 
land in Central Illinois. Logging removed 37%, k5% 9 and 55% of the basal area 
(a measure of density) of trees larger than 12 inches dbh on the 3 areas. Tree 
cavities suitable for sheltering squirrels were reduced on all study areas, 5.% 
of those offering all-weather shelter and 29% of those offering escape only. 
To relate the loss of food-producing trees to squirrel needs, we developed 
a crude stocking guide, which provided a minimum density for the principal 
squirrel-food producers larger than 
on our information on squirrel food 
densities in Illinois (1-2 per acre 
the Midwest. If we use our 3 study 
abundance, areas 1 and 3 apparently 
seed whereas area 2 was short of 
area 2 also supported k beeches, 
10 inches in diameter. The guide is based 
consumption in winter, average squirrel 
in winter), and average tree seed yields in 
areas as an indication of postcutting food 
had an adequate number of trees producing 
oaks and black walnut (Table 1). Fortunately, 
7 red oaks, and 2 sugar maples per acre-- 
species also known to supply food for squirrels. 
Selective logging had no apparent effect on squirrel densities, breeding 
rates, or the annual survival of marked adult males. Recovery rates for marked 
adult females were significantly reduced (P < 0.025) the year of logging when 
>k0% of the merchantable volume was cut, but recovery rates of marked adult 
females increased to precutting levels the first year after logging. More 
squirrels were captured after logging than before logging on all 3 areas, 
possibly due to increased foraging by squirrels in logged areas. Adult male 
fox squirrels avoided the centers of the logged areas whereas gray squirrels 
were attracted to the cuts. 
In a selection cut, if a minimum number of trees >25 cm dbh with a species 
mix close to that shown in Table 1 is retained, they should provide sufficient 
storable tree seed to maintain densities of 1-2 squirrels per acre. Trees to 
be retained should be selected during falls of good seed years so that only 
proven seed producers are saved. A good species mix will also minimize the 
effects of any seed failures due to late spring frosts. 
Food supplies for squirrels should improve on our study areas. The 
increased light, water, and nutrients available to the residual trees should 
increase seed production beginning 2-5 years after logging. Squirrel numbers 
were not reduced by removals of up to 55% of the basal area of merchanta e 
trees, at least for 1-2 years after logging, but removals greater than W ot 
the merchantable volumes may be expected to reduce the number of breeding 
females the year of logging. 
