Environmental filtering is the primary driver of community assembly in forest–grassland mosaics: A case study based on CSR strategies

Aims Ecological strategies can provide information about plant community assembly and its main drivers. Our aim was to reveal the dominant strategies of the vegetation types of forest–grassland mosaics and to deduce the assembly processes responsible for their species composition. Location Hungary. Methods We investigated eight vegetation types of Hungarian forest–steppes. The trade‐off between three key traits related to leaf size and economics was used to calculate Grime's competitive–stress tolerance–ruderal (CSR) value for each species, based on which the mean value for each vegetation type was determined. Detrended correspondence analysis (DCA) ordination was used to reveal the compositional differences among the vegetation types under study. To analyze how ecological strategies correlate with the compositional gradient, we used linear regression between plot ordination scores (the first DCA scores) and each strategy (C, S, and R). Linear mixed‐effect models were used to evaluate the differences between the vegetation types regarding each strategy (C, S, and R). Results Each vegetation type was dominated by the stress‐tolerator strategy, indicating the prominent role of environmental filtering in community assembly. However, ecological strategies differed significantly among the communities. The importance of the stress‐tolerator strategy decreased toward the less harsh end of the gradient (i.e., from grasslands to forests), while the competitor strategy showed a reverse pattern. The ruderal strategy was weakly correlated with the gradient, although its proportion increased toward the harsh end of the gradient. Conclusions With ongoing climate change, an increasing importance of environmental filtering is expected in the assembly of the vegetation types in the studied forest–grassland mosaics. We suggest that CSR strategies offer a useful tool for studying plant‐community assembly rules along environmental gradients. Eight vegetation types (both woody and non‐woody) of forest–grassland mosaics were investigated. Each type was dominated by the stress‐tolerator strategy, indicating the prominent role of environmental filtering in community assembly in the study region. However, the importance of the stress‐tolerator strategy alongside the ruderal strategy decreased from grasslands to forests, while the competitor strategy showed a reverse pattern.