Colonization front of the understorey palmAstrocaryum sciophilumin a pristine rain forest of French Guiana

Abstract

ABSTRACTAimsAstrocaryum sciophilum(Miq.) Pulle (Arecaceae) is an understorey palm, endemic to north‐eastern South America with a patchy distribution. We tested the hypothesis that the spatial distribution of this palm species is not in equilibrium but is slowly colonizing the forest understorey.LocationInventories and seed dispersal studies were conducted in the undisturbed tropical forest close to the Nouragues research station, French Guiana. Additional data were collected in the entire territory of French Guiana.MethodsWe studied the demography ofA. sciophilumon a 20‐ha plot located at the edge of its distribution. The age of the palms was estimated by postulating an exponentially decreasing abundance by age class. Direct seed dispersal experiments were also conducted, to estimate dispersal parameters. The seeds ofA. sciophilumwere dispersed only by rodents. This information was used to parameterize a forest growth simulator, to study the spatial spread of this species.ResultsWithin the sampling plot, the density ofA. sciophilumdropped sharply from about 500 individuals per hectare to zero. The maturation age was estimated to be 170 ± 70 years, and over 55 years with 95% confidence. Seed‐dispersal experiments yielded an average seed dispersal distance of 11 m and a maximum estimated dispersal distance of 125 m across a generational span of 55 years to maturity. Therefore, the maximal estimated colonization speed is 2.3 m/y.ConclusionsEmpirical results and numerical simulations suggest that the boundary of theA. sciophilumpopulation is a colonization front, and that the range of this species is slowly expanding. The implications of this result in respect of palaeoenvironmental changes in this region are discussed.