Species‐rich plant communities in interior habitats of small forest fragments: The role of seed dispersal and edge effect

Abstract

Questions What are the effects of environmental and dispersal filters on vegetation in small and species‐rich fragments of temperate forests in which species richness increases along the edge–interior gradient? Location Small fragments of thermophilic forests in central Bohemia, Czech Republic. Methods Repeated vegetation surveys and seed rain samplings were conducted in 71 plots located in 17 forest fragments (0.4 to 255 ha) in an agricultural landscape in Central Europe. A subsequent assessment of seed viability was performed via germination in a greenhouse. We evaluated species richness, composition and the similarities between forest vegetation and viable available seeds, accounting for potentially significant environmental conditions. Particularly, we examined the effects of species with different associations to the forest environment in combination with prevalent dispersal strategies. Results Species richness and composition of the herb layer vegetation (including tree and shrub seedlings) in small forest fragments reflected seed distribution and, to a lesser extent, seed viability. Plant species composition showed a nested pattern according to the distance from the forest edge; the species at the edge represented a subset of the species in the forest interior. Forest specialist species with spatially limited dispersal consistently achieved the highest species richness in forest interiors (>200 m from the forest edge), although this differed depending on aspect. Species richness of generalists and open‐land species benefitted from higher light quality and vice versa for forest specialists. Conclusions Small forest fragments maintain species‐rich herb layer communities confined in area‐limited interior habitats. They do this despite being mostly or entirely under the influence of the edge effect and impoverished of forest specialists. Moreover, the species‐rich interiors of the small forest fragments are likely prone to negative changes in species composition induced either by canopy closure or opening in the future.