Plant Community Composition and Biomass on Calcareous and Siliceous Substrates in the Northern French Alps: Comparative Effects of Soil Chemistry and Water Status

Abstract

Floristic differences between alpine communities on calcareous and siliceous rocks have been mainly attributed to soil chemical properties in the European Alps. In contrast, water availability and temperature, factors that correlate with calcareous and siliceous substrates, have received more attention in other mountain ranges. To compare the relative importance of soil chemical versus physical factors for explaining differences in floristic composition between communities from calcareous and siliceous rocks, we conducted a fine-scale correlative study in the northern French Alps, in which the effects of topographic variations were compared on dolomitic limestone (calcareous) and gneiss (siliceous). We analyzed 192 plots with correspondence analysis (CA) and canonical correspondence analysis (CCA) using a matrix of 20 environmental variables including snow melt dates and water availability. We also measured aboveground biomass and available nitrogen and phosphorus for a subset of the plots. Species composition, aboveground biomass, and species richness were highly correlated with substrate type. However water availability, not substrate chemistry, appeared to drive differences in community composition, biomass, and richness. Siliceous substrates appeared to be more mesic because of the water supplied at the subsurface level. Conversely calcareous soils were drier, probably because of the higher porosity of the rock.