Document: AMY-3-76-9

Landscape patterns in the distribution of riparian plant associations and ecosystem types in the California Sierra Nevada.

MERRILL, A.G.* and T.L.BENNING

U.C. Berkeley , Berkeley, CA 94720 ¹

Abstract:
Recognition of riparian zones as valuable habitat and important modulators of stream water flow and chemistry has led to growing interest in riparian habitat classification. Classifications that reflect differences in ecosystem function can be used to prioritize preservation and restoration efforts and to develop landscape scale models of ecological processes. The dynamic nature of streamside environments complicates development of traditional classifications based only on plant species distribution. We examined patterns in riparian physical conditions as well as plant species distribution in order to identify the physical and vegetative factors that contribute the greatest variation in streamside environments. We collected data on plant species cover and abiotic variables in 144 riparian plots throughout the Lake Tahoe Basin. We identified five riparian plant associations using cluster analysis of plot species data (TWINSPAN). Through canonical correspondence analysis of plant and abiotic data, we identified seven abiotic variables that are principle correlates with riparian plant associations: Geofluvial surface, stream gradient and width (associated with position in the watershed), parent material, valley shape, channel bed material, and surface soil texture. We used a clustering algorithm that incorporates canonical correspondence analysis of both species and abiotic data to classify the sites into 14 distinct ecosystem types. We tested the usefulness of this classification in deciphering different functional attributes, in this case differences in N dynamics, in the riparian landscape. Differences in net N mineralization, nitrification, and potential denitrification among 5 ecosystem types (n=4, p<.0.05) were significant within one watershed of Lake Tahoe. These results suggest that ecosystem type classifications, when based on abiotic as well as vegetative characteristics, may be useful in determining variation in functional attributes at the ecosystem/landscape scale.

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This abstract is being presented at: 10:30 AM in session:
RIPARIAN ECOLOGY