Final Report Summary - PASTFORWARD (Development trajectories of temperate forest plant communities under global change: combining hindsight and forecasting (PASTFORWARD))
The last decades are characterized by an upsurge of research on the impacts of global environmental changes on forests. Climate warming, atmospheric deposition of acidifying and eutrophying pollutants and land-use change are three of the most important threats to biodiversity in temperate forests. However, most studies focused on the effects of single factors over short time periods, such that our ability to predict the combined effects of multiple global change drivers over longer time periods remains rudimentary. The lack of knowledge on effects of global change drivers on forest herb layer communities is particularly striking, since the herb layer contains the largest part of vascular plant diversity in temperate forests and provides key ecosystem services. Therefore PASTFORWARD aimed at building an integrative understanding of the combined effects of land-use change, atmospheric deposition and climate warming on forest herb layer communities using three complementary data sources (a large database with >1800 resurveyed vegetation plots, field measurements in a pan-European network of 192 resurvey plots, and a multi-factor experiment) combined with ecosystem modelling. By applying this combination of methods we showed that over time large changes in understorey community composition, not in diversity, have taken place resulting in an altered functional signature. Past land use, climate warming, and atmospheric pollutant deposition had a variable impact on herb layer changes, but the effect of changes in canopy composition - and light availability in particular - was very strong and consistent. We also found that forest canopy changes can buffer or accelerate the changes caused by the other global change drivers. Since the canopy layer can be managed by humans, the results of PASTFORWARD will help forest managers and policy makers in taking more informed decisions on how to combine resource extraction with biodiversity conservation in an era of environmental change.