Small mammals in young forests: implications for management for sustainability

Small mammals have been proposed as indicators of sustainability in forests in the Pacific Northwest and elsewhere. Mammal community composition and s pecies abundances purportedly result from interactions among species, fores t-floor characteristics, large coarse woody debris, understory vegetation, and overstory composition. Coarse woody debris is thought to be particularl y important because of its diverse ecological functions; covers from 10 to 15% have been recommended based on retrospective studies of forests and sma ll mammals. Unfortunately, ecological correlations are not necessarily indi cative of causal relationships and magnitudes depend on composition of fini te, usually non-random, cross-sectional samples. Retrospective studies must be replicated to confirm relationships. We conducted a large-scale, cross- sectional survey of 30- to 70-year-old coniferous forests in western Washin gton to determine if previously reported relationships would hold with an u nrelated, larger sample. Coarse woody debris cover was 8.3 +/- 0.6% ((x) ov er bar +/- S.E., n = 8 blocks of forest, range 4-13%). Understory cover was too low (18 +/- 8% for shrubs) to allow examining interactions between und erstory and coarse woody debris. Overstory composition covaried with coarse woody debris. One or two of four statistically extracted habitat factors ( overstory composition, herbaceous cover, abundance of Acer circinatum, and abundance of Acer macrophyllum) accounted for 18-70% of variance in abundan ce of I I mammal species. Our results support hypotheses that: (1) biocompl exity resulting from interactions of decadence, understory development, and overstory composition provides pre-interactive niche diversification with predictable, diverse, small-mammal communities; (2) these communities incor porate numerous species and multiple trophic pathways, and thus, their inte grity measures resiliency and sustainability. Published by Elsevier Science B.V.