Differences in Townsend's Chipmunk Populations between Second- and Old-growth Forests in Western Oregon

Because Townsend's chipmunks (Tomias townsendii) may be important in maintaining natural ecosystem processes in forests in the central Oregon Cascade Range, we compared their population characteristics in young second-growth and old-growth forests. We live-trapped Townsend's chipmunks in 5 young (30-60 yr old) second-growth and 5 old-growth (>400 yr old) Douglas-fir (Pseudotsuga menziesii) stands during spring and autumn 1987-90 in western Oregon. We tested the null hypothesis of no difference in characteristics of chipmunk populations in these 2 stand age-classes. Densities ranged from 0.4 to 10.3 chipmunks/ha and were greater (P < 0.05) in old-growth ( ± SE, 5.1 ± 0.4) than in second-growth (2.8 ± 0.3) stands. Chipmunk densities were related to large (≥50 cm diam at breast height [dbh]) snags in oldgrowth (P = 0.002) but not in second-growth (P = 0.6) stands. Chipmunks in old-growth stands moved shorter (P = 0.03) distances in autumn and had a greater proportion of young-of-the-year (P = 0.007) than those in second-growth stands. These differences suggest that old-growth stands provide better habitat for Townsend's chipmunks than young second-growth stands, and may reflect important functional differences in food chains and energy flow between the different stand age-classes. J. WILDL. MANAGE. 57(2):365-373 x Timber harvesting in the Pacific Northwest has changed much of the landscape from oldgrowth coniferous forests to young; secondgrowth forests; <13% of old-growth forests remains (Booth 1991). Short logging rotations (e.g., removal of timber at <80 yr) and even-aged management practices do not allow these forests to attain ecological characteristics of older forests. Old-growth forests provide unique habitat for a variety of wildlife species (Meslow et al. 1981, Ruggiero et al. 1991) and also may provide optimum habitat for species that are of particular ecological importance. For example, several species of small mammals are believed to be important dispersers of mycorrhizal fungi (Maser et al. 1978), and some of these species may attain greater densities in old than young forests (Corn and Bury 1991, Gilbert and Allwine 1991, West 1991). Previous investigators (Nelson 1989; Buchanan et al. 1990, Corn and Bury 1991, Gilbert and Allwine 1991, West 1991) compared wildlife populations in old-growth coniferous forests with those in naturally regenerated (i.e., after wildfire), unmanaged young stands (<80 yr old), but few have investigated populations in managed second-growth stands after canopy closure, despite the fact that these stands increasingly dominate forested landscapes in this region. One of the most prevalent small mammal species in old-growth forests in the Pacific Northwest is Townsend's chipmunk. The abundance and population dynamics of Townsend's chipmunks may be important in maintaining natural ecosystem processes. In coniferous forests of the central Oregon Cascade Range; Townsend's chipmunks often compose the largest proportion of small-mammal biomass (Doyle 1990) and are prey for both mammalian and avian predators (Maser 1981:150', Reynolds and Meslow 1984, Toweill and Anthony 1988). In this paper, we report differences in demographic characteristics between Townsend's chipmunk populations in young second-growth and old-growth coniferous forests in the central Oregon Cascades. We thank G. S. Miller for logistical support throughout the study; D. A. DellaSala for help with study design; M. T. Brown for coordinating the 1989 field season; S. K. Albert, M. T. Brown, T. D. Buchholz, D. A. DellaSala, S. M. Desimone, M. Fishman, J. D. Hall, M. C. Hansen, B. C. Latta, R. S. Lutz, N. V. Marr, G. R. Orth, K. A. Swindle, and M. Vander Heyden for their dedicated field assistance; W. M. Block, A. B. Carey, B. E. Coblentz, W. C. McComb, M. L. Morrison, R. S. Ostfeld, T. A. Spies, R. J. Steidl, T. P. Sullivan, and B. J. Verts for helpful comments on earlier drafts;and the staff of the H. J. Andrews Experimental Forest and Willamette National Forest for accommodations at the field site and assistance with locating and securing