Phenology, seed dispersal and difficulties in natural recruitment of the canopy tree Pachira quinata (Malvaceae)

Maria Clara Castellanos,Pablo R Stevenson

doi:10.15517/rbt.v0i0.3150

Abstract

Life history and recruitment information of tropical trees in natural populations is scarce even for important commercial species. This study focused on a widely exploited Neotropical canopy species, Pachira quinata (Malvaceae), at the southernmost, wettest limit of its natural distribution, in the Colombian Amazonia. We studied phenological patterns, seed production and natural densities; assessed the importance of seed dispersal and density-dependent effects on recruitment, using field experiments. At this seasonal forest P. quinata was overrepresented by large adult trees and had very low recruitment caused by the combination of low fruit production, high seed predation and very high seedling mortality under continuous canopies mostly due to damping off pathogens. There was no evidence of negative distance or density effects on recruitment, but a clear requirement of canopy gaps for seedling survival and growth, where pathogen incidence was drastically reduced. In spite of the strong dependence on light for survival of seedlings, seeds germinated readily in the dark. At the study site, the population of P. quinata appeared to be declining, likely because recruitment depended on the rare combination of large gap formation with the presence of reproductive trees nearby. The recruitment biology of this species makes it very vulnerable to any type of logging in natural populations.

Highlights

Many tropical timber tree species get a high share of damage, because in addition to the destruction of their habitats due to deforestation, they are selectively logged in areas where their native forests are still standing (Nepstad et al 1999, Asner et al 2005)
Our results contribute to the knowledge of early recruitment of tropical canopy trees and potential density-dependence effects, and highlight the sharp contrast between the low recruitment of this species in native forests compared to the ease with which it is cultivated for timber
Our results picture a population of P. quinata represented mostly by adult trees and with very low recruitment

Summary

Introduction

Many tropical timber tree species get a high share of damage, because in addition to the destruction of their habitats due to deforestation, they are selectively logged in areas where their native forests are still standing (Nepstad et al 1999, Asner et al 2005). Because target species are usually large and long-lived trees, they are likely to play important ecological roles in the forest and their overexploitation could have additional negative consequences to other plant and animal species. In spite of their commercial and ecological importance, it is surprising how little is known about the life history and requirements for recruitment of many timber species in their natural habitats, even if they are widely logged or cultivated (Guariguata & Pinard 1998, Schulze et al 2008b). Our results contribute to the knowledge of early recruitment of tropical canopy trees and potential density-dependence effects, and highlight the sharp contrast between the low recruitment of this species in native forests compared to the ease with which it is cultivated for timber

Methods

Results

Conclusion