A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

PREDICTING EDGE-DRIVEN CARBON EMISSIONS FROM FRAGMENTATIONOF AMAZONIAN FORESTSSusan G. W. Laurance 1 , Henrique E. M. Nascimento 1 , William F. Laurance 2,1 ,Sammya D’Angelo 1 and Ana Andrade 11 Biological Dynamics of Forest Fragments Project, National Institute for AmazonianResearch (INPA), C.P. 478, Manaus, AM 69011-970, Brazil2 Smithsonian Tropical Research Institute, Apartado 2072, Balboa, Republic ofPanamáEdge effects in fragmented landscapes alter aboveground biomass in Amazonianforests, with potentially important implications for carbon storage and greenhousegas emissions. We studied edge-related biomass dynamics in 50 1-ha plots infragmented and continuous Amazonian forests by integrating long-term data onmortality, damage, growth, recruitment, and floristic composition of large (>10 cmdbh) trees with measurements of nearly all other live and dead plant materialabove the soil surface. Carbon flux to the atmosphere was estimated bydetermining the mean loss of aboveground biomass near forest edges from largetreemortality and damage and from increases in the density of light-woodedpioneer species, subtracting observed increases in necromass and understorybiomass, and then determining the fraction of decomposing necromass that islikely to be emitted as carbon emissions.For 29 plots that were located within 300 m of edges, live biomass of large treesdeclined by an average of 22.7 (+31.8) Mg ha -1 during the first 10-19 years afterfragmentation. These same plots averaged 1.7 and 10.1 Mg ha -1 more understorybiomass and necromass, respectively, than did plots further from edges. Thesevalues suggest a net biomass decline of 10.9 Mg ha -1 within 300 m of edges.Assuming that 50% of biomass is carbon and that at least 75% of decompositionalloss results from wood respiration (principally from fungal and microbialdecomposers) that directly produces C emissions, this implies a net flux of at least4.1 Mg C ha -1 to the atmosphere within 300 m of forest edges. The remainingbiomass (about 1.4 Mg C ha -1 ) would be exported to soils and streams in the formof wood particles and leachates, and a significant fraction of this is likely to bequickly respired to the atmosphere. The overall C emissions are thus predicted tobe on the order of 4-5 Mg ha -1 within 300 m of forest edges.Because tree mortality is elevated within roughly 300 m of edges, our findingssuggest that an average of 12-15 Mg C are released for every 100 m of forest edgethat is created. Given that many tens of thousands of kilometers of forest edgehave been created in Amazonia, the carbon emissions from edge effects could beconsiderable.