Landscape-scale vegetation homogenization in Central European sub-montane forests over the past 50years

QuestionsHow did plant species richness and spatial heterogeneity of the vegetation change across sub-montane forests over the past 50years? Did the vegetation changes reflect eutrophication, acidification and management changes, which the area underwent during the second half of the 20th century? LocationOrdinary managed forests sampled across 2500 km(2) of a typical Central European sub-montane landscape in the southern part of the Czech Republic. MethodsWe resampled 156 quasi-permanent plots sampled in the 1950s-1970s and covering the whole range of forest vegetation in the region. We compared understorey plant species richness and community composition between the surveys and tested for temporal changes in the spatial heterogeneity (-diversity) of vegetation. ResultsSpecies richness and dissimilarity in species composition among plots decreased significantly between the surveys. The vegetation of the plots also changed significantly, but there were no clear directional changes across all plots. The vegetation homogenization was driven by local extinctions of specialist species, especially competitively weak species adapted to nutrient-poor conditions. Few generalist species expanded between the surveys. ConclusionsWe found evidence of taxonomic homogenization of forest understoreys across a large sub-montane region. This vegetation homogenization was probably driven by complex landscape changes that took place in the last century. Varied traditional management regimes were replaced with largely uniform management, and the once spatially diverse landscape mosaic has become simpler. The resulting transition to species-poor and less variable vegetation was probably further accelerated by environmental eutrophication. Our results thus complement previous forest herb layer resurveys, which focused mostly on lowland forests and small nature reserves, and suggest that landscape-scale taxonomic homogenization is occurring across Central European forests.