Growth and development of the thinning canopy in a post-hurricane tropical rain forest in Nicaragua

Abstract

Abstract The effect of catastrophic disturbance on forest structure was studied for 10 years subsequent to the landfall of Hurricane Joan in 1988. Four sites within the damage area and one control site outside of the area were established in the early 1990s and positions and sizes (DBH and crown height) were measured annually. Results of the study are reported in the context of the debate between equilibrium versus non-equilibrium models of tropical forest dynamics. Equilibrium models imply some sort of niche segregation on a species to species basis, whereas non-equilibrium models emphasise chance and history in the development of canopies. In either case, the details of the dynamics of building and thinning after a disturbance are key to resolve the debate. Physical aspects of the developing canopy began with a severely damaged forest with effectively no canopy at all. Two distinct canopies had developed 4 or 5 years after the disturbance; (1) a larger but diffuse canopy made up of the tress that had survived the hurricane standing and had begun resprouting high in their damaged crowns and (2) a ‘thinning canopy’ of very densely packed crowns of small individual trees, resulting from the growth of surviving saplings and seedlings and trees that had sprouted near to the ground. Competitive thinning has begun to occur in this dense lower canopy. Since the disturbance, the increase in number of species has been great, ranging from 134 to 208% over what would be expected in a mature forest. Mortality patterns in the thinning canopy suggest that trees are not dying at random and thus supports a niche-based model of forest regeneration. Qualitative analysis of the thinning canopy also suggests that some species have come to occupy the upper position in the canopy (and are thus likely to be competitive dominants) while other species have come to occupy the lower position (and are thus likely to be competitively suppressed). A qualitative model is proposed illustrating where, during the process of regeneration, various authors have emphasized either a niche (equilibrium) or non-niche (non-equilibrium) model. It is suggested that in the building phase of the post-disturbance forest a non-niche interpretation is most appropriate while in the thinning phase a niche interpretation may be warranted.