GAPS AND FOREST ZONES IN TROPICAL MOIST FOREST IN IVORY-COAST

Regional variation in the characteristics of gaps larger than 10 m2 was determined for three forest sites on different soils, along a climatic and vegetation gradient in the tropical moist forest of Tai National Park, Ivory Coast. The total inventoried area was 71 ha. The three sites were strikingly similar with regard to gap density, gap size distribution, and total gap area. Average gap density was 2.1 gaps ha-1, of which 0.7 gaps ha-1 were estimated to have been created during the last year. Average gap size was 41 m2 (55 m2 for newly formed gaps). Total gap area was on average 0.8 percent of the total inventoried area, versus 0.4 percent for the gaps formed during last year. Mode of gap formation differed considerably between the sites, and reflected site-dependent soil characteristics and floristic and structural composition of the vegetation. In Zagne, the northernmost, driest site, branch fall was the major mode of gap formation (47%), in Tai, the middle site, this was tree snapping (48%), and in Para, the southernmost, wettest site with hardened soil layers, tree uprooting was conspicuous (20%). An apparent paradox was found that at the site with the largest trees (Zagne) relatively many small canopy gaps were created. Branch fall is the preferential mode of senescence of emergent tree species; they slowly drop their branches when they die-off, creating many branch fall gaps. Though modes of gap formation differed between the sites, they resulted in similar gap size distributions. The differences in abiotic and biotic characteristics of the forest zones do not result in a clearly different gap regime. Canopy gaps in the Tai National Park are small, and forest turnover time is long (ca 240 years) compared to other tropical moist forests, resulting in a less dynamic, fine textured forest mosaic consisting of small eco-units.