Ecological scale and forest development: Squirrels, dietary fungi, and vascular plants in managed and unmanaged forests

Understanding ecological processes and their spatial scales is key to manag ing ecosystems for biodiversity, especially for species associated with lat e-seral forest. We focused on 2 species of squirrel (Sciuridae: northern fl ying squirrel, Glaucomys sabrinus, and Townsend's chipmunk, Tamias townsend ii) in a cross-sectional survey of managed and natural stands in southweste rn Oregon during 1985-59. We measured vegetation and abundances of squirrel s at >2,000 points in 19 stands in 3 seral stages. We described the diets o f die squirrels in the stands. We analyzed data at point, stand, and stage scales to identify key processes contributing to biodiversity and scales at which emergent properties (synergistic effects) appeared. Four factors (crown-class differentiation, decadence, canopy stratification , and understory development) accounted for 63% of variance in vegetation s tructure. Decadence contributed to variation mostly in late-seral forest. W ithin stands, most habitat variables were poorly correlated. Across stands many variables were highly correlated, suggesting forests developed emergen t properties above the point level but at or below stand level (16 ha). Pla nt species composition was summarized by 21 vegetation site types. Stands h ad 7-19 site types arrayed in fine scale (point and soups of points 40 m ap art). Site types were used to measure habitat habitat breadth (within-stand heterogeneity resulting from disturbance and forest development). Vegetati on structure varied on a 0.5-ha scale. Stand-level characteristics were mor e influential than nominal seral stage for a variety of organisms. Late-ser al forests were more moist and complex with greater habitat breadth than 40 -70-year managed stands. Structural factors, moisture-temperature gradient values (MGV), and habitat breadth were used to describe the habitat space potentially available to s quirrels. Correlations between squirrels and habitat variables within stand s were low linear regressions explained <20% of the within-stand variance i n squirrel captures, but logistic regressions correctly classified 74 and 8 8% of the points according to usage (used, not used) by flying squirrels an d chipmunks, respectively. Compared to available habitat space, the realize d habitat of flying squirrels had high decadence and complex canopies. The realized habitat of chipmunks had complex canopies and large, dominant tree s. Overall, chipmunks were less selective than flying squirrels and used 83 % of the habitat space compared to 59% by flying squirrels. Among stands, v ariance in carrying capacity of Eying squirrels Mas Lest explained (70%) by decadence, habitat breadth, and MGV. For chipmunks, decadence and canopy s tratification provided the Lest model (72% of variance explained). Both squ irrels had mycologically diverse diets; richness was correlated with decade nce and canopy stratification. Major dietary fungi were associated with woo dy debris. Flying squirrels had higher carrying capacities and overlap amon g foraging patches of individuals, but smaller foraging patches, in late se ral forest than in managed stands. Squirrels were more abundant in late ser al forest than in managed forests. Abundance in some stands deviated marked ly from the stage mean-stand character was more influential than nominal se ral stage. The 4 structural factors each represented all important ecological process; decadence and canopy stratification apparently had profound influences on other life forms. Carefully timed variable-density thinnings could accelera te crown-class differentiation, canopy stratification, and understory devel opment and increase habitat breadth. Management of decadence is more proble matic and may require various interventions, in eluding inducing decay in l ive trees, conserving biological legacies from previous stands, and ensurin g recruitment of coarse woody debris.