Mortality and recruitment in a lowland tropical rain forest of French Guiana: effects of soil type and species guild

Abstract

A variety of processes have been identified as playing a key role in maintenance of hyper-rich tropical forest, among which ecological sorting caused by niche partitioning challenges stochastic dispersal processes. However, demographic responses to spatio-temporal resource variation that could result in biased species distributions are still little studied. In this paper we investigate from two censuses, c. 15 y apart, of a 12-ha permanent forest sample in French Guiana, how tree recruitment and mortality rates vary among hydrological soil types known to affect species habitat preferences and among ecological guilds related to species light requirement. The results indicate that both recruitment and mortality vary significantly with respect to these factors. While the mean instantaneous mortality and recruitment rates are estimated to 0.98 and 0.81%, respectively, pioneer species, canopy trees and hydromorphic bottomland soils depart significantly from these values. In particular, the pioneers, regenerating either from the soil seed bank or from post-opening seed rain, show faster dynamics than other species. These two guilds harbour probabilities of mortality elevated by a factor of 1.9 and 3.2, respectively, and probabilities of recruitment elevated by a factor of 4.9 and 3.1, respectively. Conversely, canopy trees show slower dynamics, with probabilities of mortality and recruitment lowered by a mean factor of about 0.5 with respect to other species. We also observe that trees growing in hydromorphic bottomlands prove to have significantly higher mortality and recruitment probabilities, by a factor of about 2 with respect to those growing in terra firme.