Gaps promote plant diversity in beech forests (Luzulo-Fagetum), North Vosges, France

Windstorms are major disturbance factors in temperate forests of Western Europe. With climatic changes those events are likely to become more frequent. The study of their impacts on plant communities is essential. Therefore our objective was to evaluate the differences of the plant community after the 1999 windstorm that blew down approximately 968 000 ha across France. This study took place in the North Vosges ( 36 800 ha destroyed). The differences in species diversity, resource requirements and functional plant traits were analysed, with floristic surveys, between undisturbed forest ( 10 plots) and gaps ranging from 250 m(2) and 1.8 ha ( 65 plots). The results showed a higher plant diversity in the gaps. This increase was mainly due to the presence of more light-requiring forest species and more species with high dispersal abilities (anemochorous or long-term persistent seedbank species). On the contrary, species with greater competitive abilities increased their cover and decreased the diversity. The other resource requirements were not modified in the gaps. This short-term study showed that functional traits and their interactions play a major role to determine the species composition in gaps, especially compared to the species requirements for the resources, except light.