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Influences of watershed geomorphology on extent and composition of riparian vegetation

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Abstract

Question

How strongly do watershed morphometry and geology influence the extent and composition of vegetation along riparian corridors?

Location

Eighteen upland watersheds in central Nevada, USA.

Methods

Watershed (drainage basin) morphometry and geology were derived from digital data sets (DEMs and geologic maps). Riparian corridors were classified into five vegetation types (riparian forest, riparian shrub, wet/mesic meadow, dry meadow and shrub dry meadow) using high-resolution aerial photography. Regression and multivariate analyses were used to relate geomorphic characteristics to riparian vegetation extent and composition.

Results

Riparian extent ranged from 0.4% to 3.6% of watershed area, was positively related to percentage intrusive bedrock and drainage density, and was negatively related to percentage carbonate bedrock and relative stream power. Riparian forest and shrub types occupied more than 75% of the riparian corridor in 12 of 18 watersheds; meadow types comprised a smaller proportion. Watershed size, topography and geology were important in predicting riparian composition. Riparian forest and shrub types were more abundant in small, rugged watersheds of high relief. Meadow types were more abundant in large, low gradient and less rugged watersheds. The importance of woody vegetation increased with more volcanic and intrusive bedrock, whereas meadow vegetation increased with increasing alluvium, carbonate and metasedimentary rock types.

Conclusions

Watershed geomorphology significantly constrains extent and abundance of woody versus herbaceous vegetation within the riparian corridor. Watershed variables related to riparian vegetation are likely indicators of run-off regimes or water and sediment transport. Consideration of relationships between watershed-scale geomorphology and riparian vegetation can improve prediction and inform restoration efforts.

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