Meadows are critical biodiversity hotspots within montane landscapes, and there is much interest in monitoring and restoring degraded meadows. Understanding the mechanistic relationships between hydrology and biodiversity in meadow ecosystems is very important, but many existing assessment tools use a one-time, visual survey of physical habitat and may not account for ecological processes. For example, the non-profit organization American Rivers developed a rapid assessment scorecard based on six qualitative observations (bank height, bank stability, presence of gullies, vegetation cover, bare ground, and conifer or upland shrub encroachment) that is being widely used in the Sierra Nevada to prioritize meadows for restoration and can be completed in several hours. I conducted a field experiment that examines stream hydrology and the biodiversity of plants and aquatic invertebrates in healthy and degraded meadows of the Lake Tahoe Basin, California. I predicted measures of hydrologic functions (e.g., magnitude of summer streamflow decline, water temperature) and geomorphology (e.g., channel cross-section form) will be more strongly correlated with aquatic and terrestrial biodiversity than rapid assessments of habitat conditions in montane meadows.
Results/Conclusions:
Biodiversity of the aquatic invertebrates and terrestrial vegetation was lower in meadows with incised stream channels. In particular, the abundance of the larval aquatic insects Simuliidae (blackflies), Baetis mayflies, and Plecoptera (stoneflies) were significantly lower in incised streams. Incised streams had lower richness and abundance of plants characteristic of hydric habitats, such as Salix (willow) and many forbs, and greater abundance of grasses. Incised streams also experienced greater declines in streamflow over the summer season, and warmer water temperatures during the late summer. We conclude that strong linkages between channel geomorphology, hydrology, and riparian and aquatic biodiversity exist in our study system. The meadow scorecard did not capture the complex eco-hydrologic processes of meadow ecosystems, resulting in weaker correlations with the ecological and hydrological functions of the montane meadow. Assessment methodologies that focus more on ecological processes and the function of hydrological and ecological attributes may be needed in order to understand about the needs and benefits of meadow restoration projects.