Study of structural, successional and spatial patterns in tropical rain forests using TROLL, a spatially explicit forest model

Competition for light, treefall gap formation and recruitment are the critical phenomena in the genesis of tropical rain forests. These aspects are taken into account to build a new spatially explicit forest growth model called TROLL. Competition for light is modelled by calculating exactly the three-dimensional field of photosynthetically active radiation in the forest understorey. Typically, 106 light intensities are computed per hectare at each time step. This light field controls the growth of each tree and establishment/death events. Seed dispersal, dormancy and establishment success as well as a model of treefalls are also included. A special care is paid to the justification and to the validation of each of these modules. The TROLL model is parameterized for a Neotropical rain forest in French Guiana using 12 functional groups of species. Using this model the vertical canopy structure and the tree diametric distribution are investigated. The role of treefalls in maintaining pioneer species is also evidenced. A forest succession scenario is simulated and compared to field data. The model is then used to simulate the recolonization of a previously sterilized area by a rain forest plant community. This scenario is interpreted using information available from palaeorecords over the Holocene period and their validity is discussed. It is suggested that this model could be used to study mosaic-like patterns in rain forests, installation of slowly dispersing species, speciation hypotheses and landscape scale dynamics of rain forests.