Spatial Patterns of Trees and Structuring Factors in a Trachypogon Savanna of the Orinoco Llanos

Abstract

Tree dispersion was evaluated in a Trachypogon savanna by measuring the distance from individual trees to their nearest conspecific neighbor. The vegetation is a closed bush island savanna with coexistent isolated trees and small patches of semideciduous forest. The isolated trees were in clumps similar to trees growing in savannas and tropical forests. In our study, adults were less clumped compared to juveniles. Environmental and biotic differences related to edaphic heterogeneity, life history, and reproductive strategy could account for the clumped pattern. Different spatial patterns emerged for stems in groves. Thus, uniform spatial distribution was evident in the individuals of the fire resistant species (Curatella americana, Byrsonima crassifolia and Bowdichia virgilioides) and a gap filling species (Casearia decandra). Changes in the demographic components between different age groups provide evidence for density-dependent mortality. A hypothesis mainly based on two scales of disturbance (human impact and gap formation) acting synergetically with a large scale factor (substrate patchiness) is put forward to explain the dynamics of tree invasion and the maintenance of the Trachypogon savanna.