Abrupt increases in Amazonian tree mortality due to drought-fire interactions

Interactions between climate and land-use change may drive widespread degradation of Amazonian forests. High-intensity fires associated with extreme weather events could accelerate this degradation by abruptly increasing tree mortality, but this process remains poorly understood. Here we present, to...

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Published in:Proceedings of the National Academy of Sciences - PNAS Vol. 111; no. 17; p. 6347
Main Authors: Brando, Paulo Monteiro, Balch, Jennifer K, Nepstad, Daniel C, Morton, Douglas C, Putz, Francis E, Coe, Michael T, Silvério, Divino, Macedo, Marcia N, Davidson, Eric A, Nóbrega, Caroline C, Alencar, Ane, Soares-Filho, Britaldo S
Format: Journal Article
Language:English
Published: United States 29.04.2014
Subjects:
Biomass
Brazil
Climate
Droughts
Fires
Humidity
Temperature
Time Factors
Trees - physiology
Vapor Pressure
Water
Brazil
fireline intensity
stable states
MODIS
forest dieback
fire mapping
ISSN:1091-6490, 1091-6490
Online Access:Get more information
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Summary:Interactions between climate and land-use change may drive widespread degradation of Amazonian forests. High-intensity fires associated with extreme weather events could accelerate this degradation by abruptly increasing tree mortality, but this process remains poorly understood. Here we present, to our knowledge, the first field-based evidence of a tipping point in Amazon forests due to altered fire regimes. Based on results of a large-scale, long-term experiment with annual and triennial burn regimes (B1yr and B3yr, respectively) in the Amazon, we found abrupt increases in fire-induced tree mortality (226 and 462%) during a severe drought event, when fuel loads and air temperatures were substantially higher and relative humidity was lower than long-term averages. This threshold mortality response had a cascading effect, causing sharp declines in canopy cover (23 and 31%) and aboveground live biomass (12 and 30%) and favoring widespread invasion by flammable grasses across the forest edge area (80 and 63%), where fires were most intense (e.g., 220 and 820 kW ⋅ m(-1)). During the droughts of 2007 and 2010, regional forest fires burned 12 and 5% of southeastern Amazon forests, respectively, compared with <1% in nondrought years. These results show that a few extreme drought events, coupled with forest fragmentation and anthropogenic ignition sources, are already causing widespread fire-induced tree mortality and forest degradation across southeastern Amazon forests. Future projections of vegetation responses to climate change across drier portions of the Amazon require more than simulation of global climate forcing alone and must also include interactions of extreme weather events, fire, and land-use change.
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ISSN:1091-6490
1091-6490
DOI:10.1073/pnas.1305499111