Early-melting snowpatch plant communities are transitioning into novel ecosystems

Snowpatch plant community distribution and composition is strongly tied to the duration of long-lasting snow cover in alpine areas; they are vulnerable to global climatic changes that result in warmer temperatures and longer growing seasons. We used a multi-decadal revisitation study to quantify early-melting snowpatch floristic and functional diversity change in southern Australia, and document shrub size-class distributions over time to detect evidence for their encroachment patterns into snowpatches, a key prediction with climatic change. Early-melting snowpatches have declined in areal extent, changed in species composition, shrub and tussock grass cover has increased, but the effects of these changes on functional trait diversity were less clear. Species gains accounted for most of the floristic change observed. Shrub recruitment into early-melting snowpatches is ongoing by most shrub species. Biotic differentiation is occurring; many early-melting snowpatches are transitioning to a novel community with changed composition and taller vegetation structure, but there is little evidence for species loss having occurred. Given enough time, however, the long-term loss of snowpatch species is likely (i.e. biotic homogenisation) if taller shrubs outcompete short-statured snowpatch species. We believe that the changes observed provide evidence that this alpine ecosystem is on the verge of collapse.