Seed dispersal mechanisms and the vegetation of forest islands in a West African forest-savanna mosaic (Comoe National Park, Ivory Coast)

The transition zone between forest and savanna is typically characterized b y a dynamic patchwork of forest and savanna. We studied the woody plant spe cies composition of 49 forest islands, 18 savanna, and 3 gallery forest plo ts in the Comoe National Park (Ivory Coast), West Africa's largest savanna reserve. TWINSPAN makes a clear distinction in vegetational composition bet ween these three major habitat types but, nevertheless, more than 50% of th e 292 species occur in at least 2 of them. The gallery forest is dominated by Cynometra megalophylla (Caesalpiniaceae), a genus known to dominate humi d forests in other afrotropical regions. Ordination reveals four distinct c ategories of forest islands, (1) humid forests comparable to the gallery fo rest in their species composition, (2) dry disturbed and (3) dry undisturbe d forests and (4) forests formerly inhabited by humans. Disturbed forests h arbor more savanna species but also a distinct group of disturbance-toleran t forest species. Compared to other forest species, in this latter group we found an exceptionally high fraction of animal dispersed species (80% vs. 58%), while wind dispersed species or species lacking long distance seed di spersal mechanisms were correspondingly rare. This pattern occurs in spite of the fact that the frequency of wind dispersed species in general increas es from dense humid forests to open dry forests and savanna. Species lackin g long distance dispersal mechanisms are most abundant among those speciali zed on humid forests. These observations suggest that the species compositi on of forest islands is to some extent determined by the seed dispersal abi lities of the different species.