Abstract

In temperate rainforests on Chiloé Island in southern Chile (42°S), most canopy trees bear fleshy, avian-dispersed propagules, whereas emergent tree species have dry, wind-borne propagules. In the present study, the following hypothesis was tested: regardless of species, fleshy propagules are deposited in greater numbers in canopy gaps and in forest margins and hence have a more heterogeneous seed shadow than wind-dispersed propagules. To test this hypothesis, the seed rains of these two types of propagules were compared in the following forest habitats: (i) tree-fall gaps (edges and centre); (ii) forest margins with adjacent pastures; and (iii) under closed canopy (forest interior). Seed collectors (30-cm diameter) were placed in two (15 and 100 ha) remnant forest patches (n = 60-100 seed collectors per patch) distributed in the four habitats. Seeds were retrieved monthly from each collector during two reproductive seasons (1996, 1997). In both years, the seed rain was numerically dominated by two species with dry propagules (Laureliopsis philippiana and Nothofagus nitida) and three species with fleshy fruits (Drimys winteri, Amomyrtus luma, and Amomyrtus meli). The seed shadows of the two species with dry, wind-dispersed seeds differed markedly. Seeds of L. philippiana were deposited predominantly in canopy openings, whereas N. nitida seeds fell almost entirely in the forest interior. The fleshy-fruited species, Drimys and Amomyrtus spp., had similar seed deposition patterns in the various habitats studied, but the between-year differences in seed rain were greater in Drimys winteri than in Amomyrtus spp. Although no more than 10% of fleshy-fruited propagules reached the margins of the patch, approximately 7% of these were carried there by birds. Every year, canopy gaps (pooling data from edges and centres) concentrated approximately 60% of the total seed rain of both propagule types in both forest patches. Forest margins received less than 20% of the total seed rain, which was largely dominated by fleshy-fruited species. Seed shadows were a species-specific attribute rather than a trait associated with propagule type and dispersal mode.