Nine decades of major compositional changes in a Central European beech forest protected area

Lowland forests in Europe went through dramatic changes in the last century. Data accumulated from the nature reserve Buky u Vysokeho Chvojna in the Czech Republic provide a unique opportunity to follow beech forest development using a time series consisting of five points in time from 1926 to 2019. Our goal was to reconstruct changes in plant species richness and plant community composition over this period. Based on the available data, we concluded that vascular plant species richness per plot declined by at least 50%, possibly by 75% since 1951. Compositional dissimilarities between the first survey and subsequent resurveys revealed a directional trajectory of vegetation changes. Treating time as an environmental factor and tree canopy cover as a covariable (and vice versa) in canonical correspondence analysis permutation tests where only the herbaceous layer was used, time turned out to be much more important. Variance partitioning revealed that time explained 28.1% and tree canopy 4.2% of the variation in the species data. The two variables together explained 36.8% of the variance, revealing that the shared effect of these two variables was 4.5%. Ellenberg-type indicator values point to a possible role of increasing nitrogen and decreasing pH. Several other factors potentially responsible for observed vegetation changes are discussed.