RESPONSE OF TOWNSEND’S AND SISKIYOU CHIPMUNKS TO VARIABLE
RETENTION LOGGING IN THREE PACIFIC NORTHWEST FOREST EXPERIMENTAL
BLOCKS.
Randall J. Wilk, Tom Manning, and Winston P. Smith.
U.S.D.A. Forest Service, Pacific Northwest Research Station, Olympia Forestry
Sciences Laboratory, 3625 93rd Avenue, SW, Olympia, Washington 98512 (RJW,
WPS); Department of Forest Ecosystems and Society, 321 Richardson Hall, Oregon
State University, Corvallis, Oregon 97331 (TM)
rwilk@fs.fed.us
We used live-trapping to assess the effect of variable retention logging on the
Townsend’s chipmunk (Tamias townsendii) in two randomized experimental blocks in
western Washington, and the Siskiyou chipmunk (T. siskiyou) in one block in western
Oregon. We compared change of population attributes in unlogged controls (100%
aggregated [A]) with logged treatments: 75%A with trees removed from 1-ha circular
removal patches; 40%A and 15%A (trees retained in 1-ha aggregates); and 40%
dispersed (D) and 15%D retention (retained trees dispersed). From the retained forest
canopy, we expected no detectable effects in units with ≥40% retention and a decline in
density for 15% retention. The logging change in mean maximum distances moved was
small and did not influence the effective trapping area in treatments. Density shift derived primarily from the minimum number of individuals known alive - was largely
negative, especially for T. siskiyou, with -66% change in treatments compared to -56%
in the control. The 40% and 15% retentions declined -84% and -54%, respectively.
Corresponding values for T. townsendii were -33% across treatments and -20% in
controls, and -45% and -38% in the 40 and 15% retentions, respectively. The
percentages of females declined in treatments and increased in controls for T. siskiyou
and varied across categories for T. townsendii. Mean body mass generally increased
(T. townsendii), especially in ≥40% treatments. The overall mean percentage of
reproductive females was small (T. townsendii) because we trapped in late season, but
increases occurred in some treatments. Higher percentages of young-of-the-year were
associated with higher percentages of reproductive females. Differences between
species may be attributed to the variability of forest stands in each block, small
samples, and unique ecological requirements of each species.