Glacial loss and its effect on riparian vegetation of alpine streams

Abstract

Abstract Rising global temperature is expected to increase alpine glacier mass loss with cascading effects on alpine habitats and biota. Currently, there is limited information on the effects of climate change on alpine riparian vegetation including quantitative assessments of geophysical habitat context. We measured geomorphic conditions and riparian vegetation composition of alpine streams across a chronosequence of sites supported hydrologically by glaciers, permanent snowfields (PS) and seasonal snowfields (SS) in Glacier National Park (GNP), Montana, USA. Responses in the system to possible climate‐driven shifts in hydrologic regime were identified using multivariate analyses. Glacier‐fed streams had higher discharge and stream power and lower substrate stability than streams fed by PS and SS. Streams fed by PS supported a higher number of species than other stream types. Glacier‐fed streams were characterised by higher abundance of disturbance‐adapted shrub species than PS and SS. By applying projections from climate models that forecast total glacial loss in GNP by 2030 to our data, we predict that stream geophysical conditions will shift, resulting in a loss of physical habitat for shrub species, an increase in habitat for herbaceous species, and ultimately a homogenisation of riparian communities in the alpine zone. Our study identifies glaciers as drivers of alpine riverine ecosystems and highlights the importance of examining geophysical habitat linked to hydrologic regimes and glaciers to better understand the impacts to biota under future climate scenarios. We provide a framework for relating fluvial biological and hydrogeomorphic processes in the context of alpine glacial recession.