Final Report Supplement - Joint Fire Science Program

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Amazon drought and its implications for forest flammability and tree growth: A basin-wide analysis
Type Journal Article
Author Daniel Nepstad
Author Paul Lefebvre
Author Urbano Lopes da Silva
Author Javier Tomasella
Author Peter Schlesinger
Author Luiz Solorzano
Author Paulo Moutinho
Author David Ray
Author Jose Guerreira Benito
Abstract Severe drought in moist tropical forests provokes large carbon emissions by increasing forest flammability and
tree mortality, and by suppressing tree growth. The frequency and severity of drought in the tropics may
increase through stronger El Niño Southern Oscillation (ENSO) episodes, global warming, and rainfall inhibition
by land use change. However, little is known about the spatial and temporal patterns of drought in moist tropical
forests, and the complex relationships between patterns of drought and forest fire regimes, tree mortality, and
productivity. We present a simple geographic information system soil water balance model, called RisQue
(Risco de Queimada – Fire Risk) for the Amazon basin that we use to conduct an analysis of these patterns for
1996–2001. RisQue features a map of maximum plant-available soil water (PAWmax) developed using 1565
soil texture profiles and empirical relationships between soil texture and critical soil water parameters. PAW is
depleted by monthly evapotranspiration (ET) fields estimated using the Penman–Monteith equation and
satellite-derived radiation inputs and recharged by monthly rain fields estimated from 266 meteorological
stations. Modeled PAW to 10 m depth (PAW10 m) was similar to field measurements made in two Amazon
forests. During the severe drought of 2001, PAW10 m fell to below 25% of PAWmax in 31% of the region's
forests and fell below 50% PAWmax in half of the forests. Field measurements and experimental forest fires
indicate that soil moisture depletion below 25% PAWmax corresponds to a reduction in leaf area index of
approximately 25%, increasing forest flammability. Hence, approximately one-third of Amazon forests became
susceptible to fire during the 2001 ENSO period. Field measurements also suggest that the ENSO drought of
2001 reduced carbon storage by approximately 0.2 Pg relative to years without severe soil moisture deficits.
RisQue is sensitive to spin-up time, rooting depth, and errors in ET estimates. Improvements in our ability to
accurately model soil moisture content of Amazon forests will depend upon better understanding of forest
rooting depths, which can extend to beyond 15 m. RisQue provides a tool for early detection of forest fire risk.
Publication Global Change Biology
Volume 10
Issue 5
Pages 704-717
Date May 2004
Journal Abbr Glob. Change Biol.
DOI 10.1111/j.1529-8817.2003.00772.x
ISSN 1354-1013
Short Title Amazon drought and its implications for forest flammability and tree growth
URL http://www.blackwell-synergy.com/links/doi/10.1111%2Fj.1529-8817.2003.00772.x
Extra Keywords: evapotranspiration; fire; hydrology; NPP; rainforest; soil moisture; tropical; water balance.
Date Added Saturday, August 27, 2011 10:34:48 PM
Modified Saturday, August 27, 2011 10:37:30 PM
American forests : A history of resiliency and recovery
Type Book
Author Douglas W. MacCleery
Abstract no abstract
Series Forest History Society’s Issues Series
Edition 1st edition
38 of 626 9/1/2011 11:40 AM