Changes in biodiversity and vegetation composition in the central <scp>S</scp>wiss <scp>A</scp>lps during the transition from pristine forest to first farming

Abstract

Abstract Aim We investigate the response of vegetation composition and plant diversity to increasing land clearance, burning and agriculture at the M esolithic– N eolithic transition ( c . 6400–5000 bc ) when first farming was introduced. Location The V alais, a dry alpine valley in S witzerland. Methods We combine high‐resolution pollen, microscopic charcoal and sedimentological data to reconstruct past vegetation, fire and land use. Pollen evenness, rarefaction‐based and accumulation‐based palynological richness analyses were used to reconstruct past trends in plant diversity. Results Our results show that from c . 5500 cal. yr bc , slash‐and‐burn activities created a more open landscape for agriculture, at the expense of P inus and B etula forests. Land clearance by slash‐and‐burn promoted diverse grassland ecosystems, while on the long term it reduced woodland and forest diversity, affecting important tree species such as U lmus and T ilia . Main conclusions Understanding the resilience of Alpine ecosystems to past disturbance variability is relevant for future nature conservation plans. Our study suggests that forecasted land abandonment in the Alps will lead to pre‐ N eolithic conditions, with significant biodiversity losses in abandoned grassland ecosystems. Thus, management measures for biodiversity, such as ecological compensation areas, are needed in agricultural landscapes with a millennial history of human impact, such as the non‐boreal European lowlands. Our study supports the hypothesis that species coexistence is maximized at an intermediate level of disturbances. For instance, species richness decreased when fire exceeded the quasi‐natural variability observed during the Mesolithic times. Under a more natural disturbance regime, rather closed P inus sylvestris and mixed oak forests would prevail.