A vegetation index of biotic integrity for small-order streams in southwest Montana and a floristic quality assessment for western Montana wetlands

Abstract

This study evaluated the relationship between grazing-related disturbances and vegetation in firstthrough third-order montane streams in southwestern Montana. Eight vegetation metrics (relative cover of native graminoids, relative cover of exotic species, relative cover of hydrophytes, cover-weighted floristic quality index, coverweighted mean bank stability rating, absolute combined cover of seedling and young willows, and willow seedling density) were found to respond to grazing-related disturbances. These metrics were combined into a multimetric index, the vegetation index of biotic integrity (VIBI), which responded strongly to a grazing-associated disturbance gradient. VIBI scoring thresholds were established that differentiated among three condition classes: reference condition, moderately impaired, and severely impaired. The VIBI can be used as an evaluation tool to assess riparian area condition. Coefficients of conservatism, which form the basis for floristic quality assessments, were assigned by an expert panel for plant species likely to occur in western Montana wetlands.