Forest fragmentation is a prevalent phenomenon worldwide and has important consequences for the functioning and ecology of tropical forests. In the Amazon specifically, previous analyses have shown compellingly that forest fragmentation can drastically reduce aboveground tree biomass within 4 years of edge creation. However, uncertainties remain regarding long-term biomass dynamics after fragmentation. Here we ask: What are the long-term effects of forest fragmentation on aboveground tree biomass in Amazonian forests? Our study site is the Biological Dynamics of Forest Fragments Project (BDFFP), a long-term and large-scale forest fragmentation experiment located in the Brazilian Amazon. We use long-term tree monitoring data from sixty-nine permanent plots located within nine experimental forest fragments, ranging in size from 1ha to 100ha. This includes consecutive diameter at breast height (DBH) measurements, taken between 1980 and 2009, and species identifications for all trees (DBH ≥ 10cm) located within these plots. Tree DBH measurements are converted to biomass estimates using an allometric model derived in nearby Amazonian forests.
Results/Conclusions
Our results corroborate previous findings of a drastic decrease in biomass 2-4 years after experimental fragmentation at the BDFFP, with a drop to 84% of pre-fragmentation biomass. In the long-term, we also find evidence of at least a partial recovery of aboveground tree biomass following the fragmentation disturbance. Preliminary results indicate that biomass in BDFFP edge plots regained pre-disturbance levels starting 10-15 years after fragmentation. However, ongoing analyses are being conducted to account for post-fragmentation changes in tree community composition. Previous work shows that pioneer and early-successional species increase in density following fragmentation. Because these species have lower wood density than the old-growth species they replace, our current results may overestimate biomass recovery. Taxon-specific allometric models for biomass estimation will be needed to accurately quantify long-term biomass stocks at this site. The BDFFP is an experimental landscape which does not experience many of the pressures encountered in other fragmented forests of the region, including logging and fire events. As such, the BDFFP is a “best-case” scenario and biomass recovery at the site may not be representative of the state of other fragmented forests in the region and in tropical forests worldwide.