EFFECT OF MICROHABITAT ON SEED FATE AND SEEDLING PERFORMANCE IN 2 RODENT-DISPERSED TREE SPECIES IN RAIN-FOREST IN FRENCH-GUIANA

1 The establishment probabilities, short-term survival, growth rates a nd biomass allocation patterns of seedlings in two large-seeded tree s pecies, Carapa procera (Meliaceae) and Vouacapoua americana (Caesalpin iaceae), were studied in contrasting microhabitats at Paracou, French Guiana. 2 Seeds (100 per habitat per species) were buried to simulate rodent caches into gap and understorey microhabitats (n = 20 of each) surrounding mature parent trees. The experiment was replicated in Cal apa procera (in early March and May) to investigate the effect of temp oral variation in seed dispersal on the establishment process. 3 Survi ving seeds and sprouting seedlings were repeatedly censused during 2 y ears after establishment, and the causes of mortality determined. Grow th and biomass parameters were calculated for surviving seedlings afte r 2.5 years. 4 A greater proportion of seeds and germinating seedlings were dug up but less seedlings suffered from damping-off in C. procer a than in V. americana. For both species, short-term survival of seedl ings was lower in the understorey where predation by mammals and dampi ng-off occured more frequently than in gaps, 5 Damping off killed more Carapa procera n seedlings when buried in March than in May, whereas mammal predation caused more deaths in May planted seeds. 6 Although s urvival and growth were enhanced in gaps for both species, seeds and s eedlings were much more intolerant to the understorey microhabitat in Carapa procera (almost 100% mortality in shaded habitat) than in Vouac apoua americana. 7 Seedling biomass allocation was consistent with pre vious data for large-seeded species but differed markedly between the two study species.