Amazonian forest functional composition and resilience to sellective logging: an enquiry using permanent sample plot data and computer simulation models

Abstract

This study set out to explore the hypothesis that previously undisturbed Amazonian terra firme (non-flooded) tropical forests show a gradient in resilience to selective logging as a function of tree species functional composition and in particular a positive relation with the presence of a specific ecological guild regarded as intermediate in the process of ecological succession known as the light hardwoods (LHW‟s). Field data came from the Manaus and Tapajos regions in Brazil and the Puerto Maldonado region in Peru. In response to drought stress induced canopy opening which is the natural disturbance analogue to selective logging, there was a significantly better performance in terms of turnover (diameter growth, mortality and recruitment) of the LHW‟s relative to climax species. Inresponse to selective logging trees growing within logging gaps showed a similar growth performance gradient 3 years after logging when species ecological guild was not taken under account.In series simulation experiments where conducted to determine actual stand levelcompositional and biomass responses to logging. Forest dynamics models in the SYMFORframework were used to conduct simulations of the most common logging practices. Results indicated that functional composition deviation from undisturbed forest showed a positive relation with resilience with LHW‟s proportions but only up to a certain threshold. Above this their proportion was positively related with deviation from primary forest conditions and therefore negatively related to resilience. A similar pattern was observed for stand basal area with intermediate sites showing the greatest resilience. For sites with low and medium proportions the opposite pattern was observed with sites of highest proportions showing the second greatest resilience followed by sites with lowest. This study indicates that there is a positive correlation between proportions of LHW trees in a forest stand and resilience to selective logging as currently practiced in the Brazilian Amazon but only up to a certain compositional threshold in functional composition.