PARENT SESSION
Poster Session #44: Plant Ecology II.
Friday, August 10, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

Factors that influence the distribution and abundance of shrubs in coastal Oregon forests.

Kerns, Becky¹, ¹

ABSTRACT- In the Pacific Northwest, information regarding the distribution and abundance of understory vegetation, and relationships between understory vegetation and land management, stand development, and environmental factors, is limited. My objectives were to examine trends in shrub distribution and abundance and identify overstory, environmental, and disturbance factors associated with total and deciduous shrub cover and individual shrub species cover. Data were acquired from grids of field plots established by forest inventories and research programs and included overstory tree plot measurements and mapped environmental data. For regression model development, data were portioned into two sets, with 25% of the data reserved for model cross-validation. Total and deciduous shrub cover were more strongly correlated with overstory tree variables than with environmental variables. Basal area of Tsuga heterophylla and density of shade tolerant trees provided the strongest relationships (negative) with total and deciduous shrub cover. However, models developed at the landscape scale were not strong in terms of predictive power (r² < 0.3). Environmental variables such as moisture stress during the growing season and mean December minimum temperature, were important in models for particular shrub species such as Vaccinium parvifolium and Berberis nervosa. Predicting shrub distribution and abundance was highly dependent on landownership, land management and disturbance history. Incorporation of these variables provided better predictions and insight into factors that control shrub abundance in coastal Oregon forests.

KEY WORDS: understory, regression, models