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

Forest susceptibility to fire during a one year El Niño period (1998-99); a case study Western Amazon1,2 Mendoza, E. R. H.; 1,3 Nepstad, D.; 2,3 Brown, I.F.; 3 Solorzano, L.1 Institute of Environmental Research of Amazonia - IPAM;2 Federal University of Acre/Zoobotanical Park UFAC/PZ; 3 Woods Hole Research Center-WHRCUniversidade Federal do Acre-PZ, BR-364 Km 4 Campus Universitário CEP:69900-000 RioBranco – Acre, Brasil;e-mail:elsa_mendoza@uol.com.brAbstractHistorically, forest fires in pre-Colombian Amazonia occurred at intervals of 400 to 700years, and were apparently associated with severe droughts. Forest fires are becomingmore common today through the interacting influences of drought, forest thinningthrough logging, and fires that escape from pasture and agricultural plots. The objectiveof this study was to determine the contribution of several meteorological, fuel, and foreststructural variables to the flammability of a primary forest in southeastern Amazonia(Catuaba Experimental Ranch, Acre State). Two hundred experimental fires wereconducted along 2000 m of transect, accompanied by measurements of air temperatureand humidity, litter height, litter moisture content, leaf area index, canopy openness, andplant-available soil water. Fires were ignited in both a tall, open forest (floresta aberta)and bamboo-dominated forest (floresta de bambu). The area burned by experimental fires(between 1 and 4 minutes following ignition) was correlated most closely with relativesoil humidity, potential available water, and LAI (r 2 = 0.54). Models created from thefield data showed that the probability of fires igniting reached a threshold at relative airhumidity