Vol. 22, No. 9 
Page 2 
This month we consider the short-term effects of selection cutting on the 
availability of shelter and food for squirrels and recommend ways to minimize 
the effects of selection cutting on squirrels. 
The selection cuts we studied did not include cull-tree removal as a part 
of forest management. Removal of these trees can reduce the number of tree 
cavities available for use by squirrels. 
We did examine the impact of intensive cull-tree removal on tree cavity 
abundance on 4 areas on the Kaskaskia Experimental Forest, an 876 ha research 
forest maintained by the U.S. Forest Service in Hardin County, Illinois. In 
2 mixed hardwood stands totaling 10 ha, an average of 133 inoperable (no 
saleable timber products) or cull trees per ha were removed; in 2 comparable 
stands totaling 15 ha, no cull or inoperable trees were removed. Periodic 
selection cuts had also removed an average of 30 trees from each area. We 
found a 5-fold difference in the number of tree cavities between treatments 
(cull removal), with treated stands averaging only 4 cavities per ha and 
untreated stands 21 cavities per ha. Thus, wherever cull-tree removal is 
practiced, some trees containing cavities should be retained for wildlife use. 
The number of trees with cavities that should be retained for squirrel 
shelter is difficult to determine, because denning needs are not well documented 
for gray and fox squirrels. Gray squirrels are more likely to need tree 
cavities for shelter than are fox squirrels, who often prefer leaf nests. 
Radio-tracking studies have shown that both species utilize from 1 to 9 
shelters (tree cavities or leaf nests) scattered throughout their home range. 
One study in North Carolina showed that 2-3 tree cavities per acre were needed 
to sustain high densities of gray squirrels. 
We believe that retention of 3-4 living trees with suitable cavities for 
squirrel denning ( 3 - to 5-inch diameter entrance hole) is a reasonable guide for 
use in marking stands for a selection cut. 
In Illinois, black oak, sugar maple, basswood, beech, cottonwood, sassafras, 
and elm have been found to form cavities readily and are the best species to 
retain to provide for present and future cavity formation. 
To provide adequate food for squirrels in those forests where management 
for both timber and squirrels is important, we recommend that stands marked 
for selection cutting retain a mix of oak, hickory, and walnut close to that 
shown in Table 1. Not all stands contain each of the species shown in Table 1, 
but most stands in Illinois contain at least 2 and usually all of these species. 
Post and bur oaks may be substituted for white oak, scarlet oak for black oak, 
and pignut hickory for mockernut using the same stocking rates shown in Table 1. 
Trees selected to remain in the stand should be dominant or codominant in the 
canopy and should be proven seed producers (look for old nuts or shells under 
the tree). A good species mix will also minimize the possibility of a seed 
failure due to late spring frosts. 
