A multi-scale assessment of avian diversity following rewatering, Owens River Gorge, California

ABSTRACT

We employ a multi-scale approach to examine the evolving spatial patterns of avian diversity following rewatering (1991-1999) of the Owens River Gorge in eastern California.  We based our analysis on three independent data sets representing 18 canyon locations (4 reference and 14 rewatered) consisting of bird counts, measures of landscape variation (canyon dimensions), and vegetation structure and composition (foliage height diversity, total vegetation volume, and plant species diversity).  We analyzed our data by grouping sites according to bird diversity and environmental factors using Sørenson's similarity index and cluster analysis, and by employing correlation (Spearman rank) and regression (multiple and backward stepwise) procedures to determine the relative importance of environmental factors on avian diversity at different spatial scales.  Our results reveal: 1) valley bottom width determines the extent of riparian vegetation (r_s = .73, p < .01) and indirectly, bird species diversity (r_s = .52, p < .05) at the landscape scale and 2) avian diversity at the habitat scale is most strongly correlated with plant species diversity (r_s = .57, p < .05).   These results indicate avian diversity is responding to habit restoration resulting from the rewatering of the Owens River Gorge but is spatially constrained by canyon dimensions that limit the area of riparian habitat and indirectly, plant species diversity.  We suggest future evaluations of stream restoration and its role on animal communities consider the merits of a multi-scale analysis.