Recent 5-years plant colonization in proglacial forelands has been faster than expected in two Gran Paradiso National Park study sites (Italian Alps)

Plant colonization in glacier forelands has been studied for decades, mainly with the chronosequence approach (Pickett 1989) and less frequently by revisiting permanent plots (Fickert and Grüninger 2018). However, the latter approach can provide more reliable information on vegetation dynamics and climate change effects. By revisiting permanent plots in two proglacial chronosequences in the Gran Paradiso National Park, spanning 5 to 165 years from deglaciation (Mainetti et al. 2021), this study aims to scrutinize how quickly vegetation colonization is occurring in present years. Thirty-six vegetation plots were surveyed in 2016-2017 and revisited in 2021-2022. The speed of colonization was computed as the ratio between the increments in vegetation cover and species richness recorded in the last five years on permanent plots and those observed along the chronosequence. Results showed that vegetation cover and species richness increased up to 17-19 and 14-21 times faster in recent years than predicted by the chronosequence, respectively. Such rapid dynamics are likely related to climatic changes, e.g. higher summer temperatures and longer growing season, that favor the colonization from species of lower elevations. Further revisiting of such permanent plots in alpine proglacial forelands is necessary to better understand and strengthen these findings.