TREE SEEDLING PERFORMANCE IN CANOPY GAPS IN A TROPICAL RAIN-FOREST ATNOURAGUES, FRENCH-GUIANA

The effect of natural canopy gaps on the performance cf naturally occu rring tree seedling populations was studied in a tropical rain forest in French Guiana. This was done at two levels of scale. :Firstly, on a 20 m x 250 m forest transect intersecting four canopy gaps, it was in vestigated how patterns of recruitment, growth and survival of seedlin gs of Cecropia obtusa, Dicorynia guianensis and Pourouma bicolor diffe red between canopy gaps and closed forest. Secondly, for one large nat ural canopy gap, performance of seedling cohorts established before (' pre-gap' cohorts) and after ('post-gap' cohorts) gap formation was stu died in relation to environmental heterogeneity. The direct site facto r (DSF) was used as an indicator of light availability in the gap zone . Cecropia specialised in large gaps, and also in specific sites withi n the large gap: seedling performance was increased by light, and by d ead wood. Pourouma mainly germinated under closed forest conditions, w here it can survive for a long period until a canopy gap is formed nea rby. Pourouma seedlings adjusted well to the new gap environment but t hey did not specialise in specific places within the gap. Seedling loc ation of Pourouma seedlings was mainly determined by accidental positi oning before gap formation. Dicorynia was able to germinate both in ga ps and under closed for est conditions. Although the number of gaps st udied in this study was low, the results show that seedling establishm ent, early growth and survival of the three tree species were affected by canopy gaps and by the environmental heterogeneity within a large gap.