VEGETATION DEVELOPMENT IN CANOPY GAPS IN A TROPICAL RAIN FOREST IN FRENCH GUIANA

Abstract

Canopy gaps in tropical forests are important for regeneration of many species. Rates of gap formation are well studied, but data on rates of canopy gap closure are scarce. In this study I investigate how development of vegetation in recently created canopy gaps in a pristine tropical rain forest varies between three small and three large gaps. The percentage of space occupied by vegetation ("vegetation occupation") was determined at one meter intervals through the expanded gap area (divided in a central and peripheral gap zone), and the first meters of the closed forest adjacent to gaps. Vegetation occupation above each inventory point was determined in three height ranges in different intervals: 0->30 m (5 m intervals); 0-10 m (1 m intervals), and 0-2 m (0.25 m intervals). Inventories were done in October 1991 and November 1993. In the central zone of small gaps, the net change in vegetation occupation was strongest in the 0->30 m range, whereas in the central zone of large gaps, vegetation occupation increased mainly in the lower height ranges (0-2 and 0-10 m). Small gaps seem to fill mainly by means of lateral ingrowth of surrounding trees, and large gaps fill mainly through growth of gap floor regeneration (both advanced regeneration and new recruitment). I estimate that on average, small gaps "disappear" within 5 to 6 years after formation. In large gaps, it may take between 5 to 10 years before a canopy layer has been established which is at least 10 m high.