Local disturbance, forest structure and dispersal effects on sapling distribution of light-demanding and shade-tolerant species in a French Guianian forest

The influence of environmental conditions and distance to nearest conspecific adult was determined to explain the distribution of saplings of six tree species in a lowland rain forest of French Guiana. The six focal species were three anemochorous light-demanding non-pioneer species: Dicorynia guianensis, Qualea rosea, Tachigali melinonii, and three zoochorous shade-tolerant species: Bocoa prouacensis, Oxandra asbeckii, Pogonophora schomburgkiana. The study was conducted at the research station of Paracou on forest plots differing in past logging treatments. The description of local environment included a characterization of past disturbance intensity (N = 5 variables), current stand (N = 4) and canopy structure (N = 3). Zero Inflated Poisson models were calibrated for each species to explain sapling numbers according to environmental conditions and distance to the nearest conspecific adult. These models extend generalized multiple regression to the case of discrete data with many zero counts. Model predictions were consistent with species temperaments: as expected, saplings of the light-demanding species were found more in disturbed and open local conditions while more saplings of the shade-tolerant species survived in stable and dense places. Predicted establishment curves of saplings around adults showed contrasting behavior among the species and did not systematically match with a priori expectations. These results are discussed in relation with dispersal syndromes and known establishment patterns in forest regeneration. Both differences in species shade-tolerance in early regeneration stages and dispersal limitation proved to account for sapling distribution in the understorey.