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    Author(s): A.B. Carey; J. Kershner; B. Biswell; L.S. Dominguez de Toledo
    Date: 1999
    Source: Wildlife Monographs. 142: 1-71
    Publication Series: Scientific Journal (JRNL)
    PDF: View PDF  (7.69 MB)

    Description

    Understanding ecological processes and their spatial scales is key to managing ecosystems for biodiversity, especially for species associated with late-seral forest. We focused on 2 species of squirrel (Sciuridae: northern flying squirrel, Glaucomys sabrinus, and Townsend's chipmunk, Tamias townsendii) in a crosssectional survey of managed and natural stands in southwestern Oregon during 1985-89. We measured vegetation and abundances of squirrels at >2,000 points in 19 stands in 3 seral stages. We described the diets of the 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 structure. Decadence contributed to variation mostly in late seral forest. Within stands, most habitat variables were poorly correlated. Across stands many variables were highly correlated, suggesting forests developed emergent properties above the point level but at or below stand level (16 ha). Plant species composition was summarized by 21 vegetation site types. Stands had 7-19 site types arrayed in fine scale (point and groups of points 40 m apart). Site types were used to measure habitat breadth (within-stand heterogeneity resulting from disturbance and forest development). Vegetation structure varied on a 0.5 ha scale. Stand-level characteristics were more influential than nominal seral stage for a variety of organisms. Late-seral forests were more moist and complex with greater habitat breadth than 40-70-year-old managed stands.

    Structural factors, moisture-temperature gradient values (MGV), and habitat breadth were used to describe the habitat space potentially available to squirrels. Correlations between squirrels and habitat variables within stands were low. Linear regressions explained <20% of the within-stand variance in squirrel captures, but logistic regressions correctly classified 74 and 88% of the points according to usage (used, not used) by flying squirrels and chipmunks, respectively. Compared to available habitat space, the realized habitat of flying squirrels had high decadence and complex canopies. The realized habitat of chipmunks had complex canopies and large, dominant trees. Overall, chipmunks were less selective than flying squirrels and used 83% of the habitat space compared to 59% by flying squirrels. Among stands, variance in carrying capacity of flying squirrels was best explained (70%) by decadence, habitat breadth, and MGV. For chipmunks, decadence and canopy stratification provided the best model (72% of variance explained). Both squirrels had mycologically diverse diets; richness was correlated with decadence and canopy stratification. Major dietary fungi were associated with woody debris. Flying squirrels had higher carrying capacities and overlap among foraging patches of individuals, but smaller foraging patches, in late-seral forest than in managed stands. Squirrels were more abundant in late-seral forest than in managed forests. Abundance in some stands deviated markedly from the stage mean-stand character was more influential than nominal seral stage.

    The 4 structural factors each represented an important ecological process; decadence and canopy stratification apparently had profound influences on other life forms. Carefully timed variable-density thinnings could accelerate crown-class differentiation, canopy stratification, and understory development and increase habitat breadth. Management of decadence is more problematic and may require various interventions, including inducing decay in live trees, conserving biological legacies from previous stands, and ensuring recruitment of coarse woody debris.

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    Citation

    Carey, A.B.; Kershner, J.; Biswell, B.; Dominguez de Toledo, L.S. 1999. Ecological scale and forest development: squirrels, dietary fungi, and vascular plants in managed and unmanaged forests. Wildlife Monographs. 142: 1-71

    Keywords

    ecological scale, forest development, Glaucomys sabrinus, habitat, northern flying squirrel, Oregon, Tamias townsendii, Townsend's chipmunk

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