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Recurrent fire in the Amazonĺs transitional forest: Changes in fuel dynamics and consequences for future fire susceptibility

Jennifer K. Balch, Yale University, School of Forestry and Environmental Studies, (Presenting)
Daniel C. Nepstad, Instituto de Pesquisa Ambiental da Amaz˘nia and Woods Hole Research Center,
Paulo M. Brando, Instituto de Pesquisa Ambiental da Amaz˘nia,
Lisa M. Curran, Yale University, School of Forestry and Environmental Studies,
Oswaldo de Carvalho Jr., Instituto de Pesquisa Ambiental da Amaz˘nia,
Paul Lefebvre, Woods Hole Research Center,

Increasing ignition sources, forest degradation, and a conducive climate in the Amazonĺs transitional forests are resulting in widespread anthropogenic forest fires at a frequency beyond that recorded historically. We have established a once-burned and a twice-burned plot (50-ha each) in intact transitional forest - one of the largest experimental burns in the tropics - to test the effects of repeated fires on fuel combustion, accumulation, and consequent future fire susceptibility. The fires of the initial and second burn, set in August 2004 and September 2005, were low intensity, slow-moving surface fires that rarely crowned. Total downed biomass combustion associated with the first and second burns was comparable; mean biomass consumption was 22.8 Mg/ha (range: 14.3 to 32.3 Mg/ha) and 21.0 Mg/ha (range: 9.9 to 32.1 Mg/ha) for the initial and second burns, respectively. One year after the initial burn accumulation of downed woody and fine fuels replaced surface fuel stocks in all but the 1000-hr fuel size class. Fire-induced changes in stem mortality substantially augment standing fuel stocks, but these fuels may not be available immediately to recurrent fires. These results highlight that available surface fuels do not necessarily immediately increase after an initial fire event. Rather, the rate at which fuels accumulate from fire-induced changes in stem mortality, NPP, regeneration, and grass invasion must be considered for accurately predicting future fire susceptibility.

Science Theme:  CD (Carbon Dynamics)

Session:  3C: Vegetation Structure and Disturbance

Presentation Type:  Oral

Abstract ID: 58

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