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A Negative Fire Feedback in a Transitional Forest of Southeastern Amazônia

Jennifer K. Balch, Yale University, (Presenting)
Daniel C. Nepstad, Woods Hole Research Center,
Paulo M. Brando, University of Florida,
Lisa M. Curran, Yale University,
Osvaldo Portela, Instituto de Pesquisa Ambiental da Amazonia,
Oswaldo de Carvalho Jr., University of Kent,
Paul Lefebvre, Woods Hole Research Center,

Anthropogenic understory fires affect large areas of tropical forest, particularly during severe droughts. Yet, the mechanisms that control tropical forests’ susceptibility to fire remain ambiguous. We tested the widely-accepted hypothesis that Amazon forest fires increase susceptibility to further burning by conducting a 150-ha fire experiment in a closed-canopy forest near the southeastern Amazon forest-savanna boundary. Forest flammability and its possible determinants were measured in adjacent 50-ha forest plots that were burned annually for three consecutive years (B3), once (B1), and not at all (B0). Despite increased vapor pressure deficit and decreased litter moisture, burned area declined 50% during the third burn. Leaf litter production in this forest (4.3 Mg/ha*yr) was only half that of other Amazon forests, and appears to have limited forest flammability. Fine fuel loads fell slightly following the second burn, and fire spread rates doubled and burned area increased five-fold in B3 subplots that received fine fuel additions. Annual tree and liana mortality two years after the initial burn was 5.5% (± 0.5%, SE) in B3, nearly double the background rate, but the lowest fire-induced mortality measured in the Amazon. Dead biomass combustion (± SE) was 44.5 (± 21.2), 23.2 (± 9.1), and 15.3 (± 9.3) Mg/ha during consecutive burns. In this forest, where severe seasonal drought removed microclimate and litter moisture constraints on fire propagation, low litter production inhibited intensity and spread of recurrent fire in a negative feedback, with important implications for its vulnerability to fire-induced replacement by scrub vegetation.

Science Theme:  LC (Land Use and Land Cover Change)

Session:  3C: Land Use and Fire

Presentation Type:  Oral (view presentation (9659 KB))

Abstract ID: 16

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