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Volume 88, Issue 9 p. 2259-2269
Article

MORTALITY OF LARGE TREES AND LIANAS FOLLOWING EXPERIMENTAL DROUGHT IN AN AMAZON FOREST

Daniel C. Nepstad

Corresponding Author

Daniel C. Nepstad

Woods Hole Research Center, 149 Woods Hole Road, Falmouth, Massachusetts 02540-1644 USA

Instituto de Pesquisa Ambiental da Amazônia, Avenida Nazaré 669, CEP-66035-170, Belem, Pará, Brazil

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Ingrid Marisa Tohver

Ingrid Marisa Tohver

Instituto de Pesquisa Ambiental da Amazônia, Avenida Nazaré 669, CEP-66035-170, Belem, Pará, Brazil

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David Ray

David Ray

Woods Hole Research Center, 149 Woods Hole Road, Falmouth, Massachusetts 02540-1644 USA

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Paulo Moutinho

Paulo Moutinho

Woods Hole Research Center, 149 Woods Hole Road, Falmouth, Massachusetts 02540-1644 USA

Instituto de Pesquisa Ambiental da Amazônia, Avenida Nazaré 669, CEP-66035-170, Belem, Pará, Brazil

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Georgina Cardinot

Georgina Cardinot

Instituto de Pesquisa Ambiental da Amazônia, Avenida Nazaré 669, CEP-66035-170, Belem, Pará, Brazil

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First published: 01 September 2007
Citations: 471

Corresponding Editor: F. C. Meinzer.

Abstract

Severe drought episodes such as those associated with El Niño Southern Oscillation (ENSO) events influence large areas of tropical forest and may become more frequent in the future. One of the most important forest responses to severe drought is tree mortality, which alters forest structure, composition, carbon content, and flammability, and which varies widely. This study tests the hypothesis that tree mortality increases abruptly during drought episodes when plant-available soil water (PAW) declines below a critical minimum threshold. It also examines the effect of tree size, plant life form (palm, liana, tree) and potential canopy position (understory, midcanopy, overstory) on drought-induced plant mortality. A severe, four-year drought episode was simulated by excluding 60% of incoming throughfall during each wet season using plastic panels installed in the understory of a 1-ha forest treatment plot, while a 1-ha control plot received normal rainfall. After 3.2 years, the treatment resulted in a 38% increase in mortality rates across all stems >2 cm dbh. Mortality rates increased 4.5-fold among large trees (>30 cm dbh) and twofold among medium trees (10–30 cm dbh) in response to the treatment, whereas the smallest stems were less responsive. Recruitment rates did not compensate for the elevated mortality of larger-diameter stems in the treatment plot. Overall, lianas proved more susceptible to drought-induced mortality than trees or palms, and potential overstory tree species were more vulnerable than midcanopy and understory species. Large stems contributed to 90% of the pretreatment live aboveground biomass in both plots. Large-tree mortality resulting from the treatment generated 3.4 times more dead biomass than the control plot. The dramatic mortality response suggests significant, adverse impacts on the global carbon cycle if climatic changes follow current trends.