Print PageA variety of abiotic and biotic factors are hypothesized to affect the maintenance of tropical forest diversity, and understanding these is the topic of continued study. Due to anthropogenic pressures which reduce the integrity of these forests, it is now imperative that factors influencing the recovery of diversity after disturbance be understood as well. This study addresses the maintenance and recovery of tropical forest diversity post-fire in the southern Amazon, a region which is highly threatened by agriculture and associated fires. The forest forms the transition between cerrado (savanna) and the Amazonian rainforest and is therefore predicted to be vulnerable increasing temperature and drought associated with climate change. Within the context of an experimental burn we examined the regeneration of this forest, hypothesizing that fire, nutrient additions, and herbivorous insects would have interacting effects on the diversity of regeneration. Specifically, nutrient additions might lessen the negative effect of fire on diversity, and insects may increase diversity, particularly in burned areas with nutrient additions. Insect exclosure plots were constructed in burned and unburned forest with and without the addition of nitrogen and phosphorus, and all new regeneration was marked and measured over six months, spanning the transition from the wet to dry season.
Results/Conclusions
Regeneration growth, abundance, and diversity were impacted in complex ways by the treatments. Growth was greatest in burned plots and plots with nitrogen, but it was limited by the addition of nitrogen and phosphorus together. Burned plots with the addition of nitrogen and phosphorus together had the lowest seedling abundance, and unburned plots without herbivores had the highest abundance of regeneration. Herbivores reduced rare species diversity (based on the Shannon-Wiener index) but increased species evenness in burned plots (Simpson’s index). The species composition differed between burned and unburned plots, and there was a greater abundance of resprouting species in the burned area. Overall, diversity is negatively affected by fire, and the application of fertilizers does not appear to assist forest recovery. Herbivores increased species evenness, increasing diversity, as the Janzen-Connell hypothesis would predict, and this effect was particularly strong in burned plots. This study provides an important evaluation of the recovery of diversity after fire in a threatened tropical forest.
