Disentangling the effects of traits and environmental factors on species’ successional optima

Recent data and syntheses in central Europe have led to the development of synthetic variables for describing the successional orderings of species. In particular, the “successional optimum” (SO), developed for describing the vegetation in the Czech Republic, reflects the number of years it takes for a species to reach peak abundance after a disturbance. The aim is to combine data on a species’ functional traits and Ellenberg-type indicator values, in order to identify the main plant strategies and environmental factors that predict SO. In this study, linear models with regularization techniques and robust inference methods were used to determine the traits that explain species’ SO, and then an analysis of the explained variance was used to assess the relative explanatory power of each trait. In parallel, the effects of Ellenberg-type indicator values, before and after detrending the SO by traits, were determined. This revealed that five traits had the greatest and most consistent effects: therophytic life form, seed mass, flowering duration, bud bank size and leaf dry matter content. The most important Ellenberg-type indicator values predicting SO were moisture and reaction, as light and nutrient concentrations were associated with these traits. The effects of traits were generally consistent and universal in the different environmental conditions, as the interaction of traits and environment did not change inferences or result in better models. This resulted in a robustly defined strategy that relates species to their successional ordering, highlighting the importance of life forms, competitive abilities, and reproductive strategies in succession.