Document: AYN-3-40-21

Vegetation dynamics in meadows of the Sierra Nevada, California.

SHLISKY, A.J.* and B.ALLEN-DIAZ

University of California, Berkeley, USA ¹

Abstract:
Understanding the complex patterns and processes of vegetation change requires empirically-based induction from an understanding of local habitats, populations, and disturbance regimes, rather than deduction from broad generalizations about successional processes. In the past, many have assumed, based on Clementsian views of succession, that meadow ecosystems grazed by livestock resiliently return toward climax after removal of livestock, or after stocking rate reduction, and conversely retrogress toward early seral stages with increased grazing pressure. We used a 40-year permanent vegetation plot record of sixteen meadows on the Tahoe and Sierra National Forests, California, and associated environmental data to develop a floristically-based classification of meadow communities, and determine important relationships between environmental variables and meadow type transitions through time. Each meadow-year observation was associated with 10 environmental variables. Community types from 81 plots were defined using TWINSPAN. Meadow community types were separated along environmental and grazing intensity gradients using detrended correspondence analysis (DCA), classification and regression tree analysis (CART), and canonical correspondence analysis (CCA). Community classification resulted in five meadow types. A regional pattern appeared in community types based on minimum annual air temperatures, separating types found on the Tahoe versus the Sierra National Forests. Most between-type transitions were associated with precipitation, snow water content, and duration of livestock use. Shifts in livestock intensity through time tended to be associated with within-type changes in species composition or abundance, but were not strongly correlated with transitions between meadow types. Results of this study fail to support a linear model of meadow change considering grazing alone. Differences in environmental variables important at the regional versus local scales highlight the need to evaluate the consistency between the scale of community identification and the choice of associated environmental factors.

Keywords: vegetation dynamics, meadows, livestock grazing, plant community classification

This abstract is being presented at: 9:15 AM in session:
Oral Session #59: Plant Communities: Vegetative Analysis.