Spectrum and vertical distribution of diaspore dispersal modes in a seasonal forest in Southern Brazil

Diaspore dispersal is presumed to have great fitness for plants, which could be enhanced by different dispersal modes. Our aim was to generate a dispersal spectrum and to seek for analyze relative ecological importance of tree-species dispersal modes in a seasonal forest in Santa Maria, Rio Grande do Sul, Brazil (approximately 53º54'W and 29º38'S) and, with these data, to investigate the relationship between vertical structure of the forest and dispersal strategies. The tree survey included all individuals with perimeter at breast height > 15 cm, in 100 sample units (10×10 m). We classified dispersal modes by diaspores and potential dispersers in the field, and when necessary through specialized bibliography. Fifty-eight tree species from 26 families were sampled. Of these species, 74% are zoochoric, 24% anemochoric and only Gymnanthes concolor Spreng. is autochoric. By analyzing the proportion of dispersal strategies based on relative density, we found that 80% of the trees are zoochoric, 12% anemochoric and 8% autochoric. In the study area, we found significant differences in vertical distribution patterns of species grouped by dispersal strategies. Zoochory occurred in all vertical strata while autochory was limited to the understorey. Anemochory occurred mainly in species with emergent trees.

dispersal modes; dispersal spectrum; vertical structure; seed dispersal; zoochory