Vegetation trajectories in proglacial primary successions within Gran Paradiso National Park: a comparison between siliceous and calcareous substrates

Abstract

Global warming has a major impact on alpine environments and glacier retreat is the most noticeable consequence of rising temperatures. Ice-free screes and moraines are subjected to the colonisation of biota thus providing a unique opportunity for the study of primary successions. Plant primary succession trajectories depend on several environmental factors but bedrock type is one the most important driver of changes. We studied the primary plant successions along two proglacial chronosequences, i.e. on siliceous and calcareous substrates, within the Gran Paradiso National Park (North-Western Italy). Both the chronosequences encompassed about 200 years and were located at high elevation (2450-3000 m a.s.l.). We focused on three functional species pools, namely early-successional pioneer, late-successional grassland, and companion species. Plant species and phytosociological communities were recognised as indicators of several environmental features, such as sediment mobility and particle size. Despite the calcareous substrate generally host more plant species, we found a greater species richness and diversity in the gneissic chronosequence. The higher heterogeneity of the siliceous debris likely promoted plant establishment and vegetation development towards climax community, even if it was not reached. Conversely, the calcareous chronosequence showed higher plant covers in the more developed stages, but still dominated by several pioneer species.