Forest disturbance spectrum of the Amazon
Tropical forests play an important role in global carbon cycle by storing and potentially sequestering a large amount of carbon and are currently considered for climate mitigation policies associated with REDD (Reduced Emission from Deforestation and Degradation). However, recent studies show that there is a large uncertainty on both the stock and dynamics of these forests associated with patterns of tree mortality from natural disturbances. Based on a forest census network of approximately 150 forests plots, Amazon forests constitute a ~0.6 Pg C y-1 sink. The size of this sink has been questioned because frequent large disturbances would invalidate the interpretation of the sparse plot network. We characterize the spectrum of forest disturbance across the entire Amazon basin based on previously published data and we assess the implications of this spectrum on the tropical old-growth forest carbon sink. We use records of biomass changes from a spatially distributed forest census network in the Amazon supplemented by two large forest plot surveys in the Eastern Amazon (53 ha and 114 ha) and an analysis of multiple satellite images to map, detect and estimate the severity of large wind disturbances (blow-downs). We found two disjoint disturbance regimes – small-scale tree-fall gaps within the range of 0.01-0.1ha and rare larger-scale disturbances caused by severe winds predominantly in the western Amazon. Small disturbances (0.01-0.1 ha) are responsible for above-ground biomass losses of about 2.5 Pg C y-1 over the entire Amazon region, but large-scale disturbances for only 0.01 Pg C y-1 because they are extremely rare. Results of a simple stochastic forest simulator based on growth statistics from the forest census and the basin-wide disturbance spectrum indicate that rare larges disturbances do not change the estimates of the positive growth rate trends of old-growth forests previously reported.
NASA Terrestrial Ecology Science Team Meeting
Espírito-Santo FDB, Gloor M, Keller M, Malhi Y, Saatchi S, Palace M, Frolking S, Phillips O. 2013. Forest disturbance spectrum of the Amazon, NASA Terrestrial Ecology Science Team Meeting, La Jolla, CA, April 30 – May 2, 2013.