Tracing the signs of local dispersal in the temperate forest understorey using spatially structured vegetation data

Questions: Dispersal is important for the formation of biodiversity patterns. However, studying dispersal is difficult, particularly in established communities. We examined local dispersal processes in the forest herbaceous layer by looking at the abundance of plants in the neighbourhood of the surveyed plots and using dispersal traits and fecundity-related attributes. Location: Thermophilous oakwood in south Moravia, Czech Republic. Methods: We collected plant community and environmental data from 2 m × 2 m plots nested in a 5 m × 5 m square grid, covering 0.36 hectares of temperate forest. We created binomial generalised linear models of species occurrence in the 2 m × 2 m plots, using species frequencies in four adjacent 5 m × 5 m plots (plot neighbourhood) and environmental data, to account for dependence caused by habitat factors. We analysed the relationships between neighbourhood effects and species attributes using linear regression. Results: Approximately one third of species had a stronger association to neighbourhood alone than to local environment factors. For the remaining species, there was a large joint effect of neighbourhood and environment. However, the link between dispersal traits and the neighbourhood effect was weak. The trait analyses showed that plumed appendages were negatively correlated to neighbourhood effects, whereas possession of elongated appendages, high terminal velocity, clonal spread and absence of seed appendages exhibited insignificant positive relationships to the neighbourhood. Conclusions: At the scale of metres, the distributional patterns of forest herbs cannot be solely associated with dispersal. The reasons could be methodological: our data contain a limited set of species with mostly database-derived attributes. However, there may also be ecological mechanisms involved. The spatial distribution of plants could be modified by limited seed production and further reshaped by extinctions during earlier ontogenetic stages.