GEOPHYSICAL MONOGRAPH SERIES, VOL. 186, PP. 429-449, 2009
The effects of drought on Amazonian rain forests
The functioning of Amazonian rain forest ecosystems during drought has become a scientific focal point because of associated
risks to forest integrity and climate. We review current understanding of drought impacts on Amazon rain forests by summarising
the results from two throughfall exclusion (TFE) experiments in old-growth rain forests at Caxiuanã and Tapajós National Forest
Reserves, and an irrigation experiment in secondary forest, near Castanhal, Brazil. Soil physical properties strongly influenced
drought impacts at each site. Over years 1 to 3 of soil moisture reduction, leaf area index declined by 20–30% at the TFE
sites. Leaf physiology and tree mortality results suggested some species-based differences in drought resistance. Mortality
was initially resistant to drought but increased after 3 years at Tapajós to 9%, followed by a decline. Transpiration and
gross primary production were reduced under TFE at Caxiuanã by 30–40% and 12–13%, respectively, and the maximum fire risk
at Tapajós increased from 0.27 to 0.47. Drought reduced soil CO2 emissions by more than 20% at Caxiuanã and Castanhal but not at Tapajós, where N2O and CH4 emissions declined. Overall, the results indicate short-term resistance to drought with reduced productivity, but that increased
mortality is likely under substantial, multiyear, reductions in rainfall. These data sets from field-scale experimental manipulations
uniquely complement existing observations from Amazonia and will become increasingly powerful if the experiments are extended.
Estimating the long-term (decadal-scale) impacts of continued drought on Amazonian forests will also require integrated models
to couple changes in vegetation, climate, land management, and fire risk.
Citation: Meir, P. et al. (2009), The effects of drought on Amazonian rain forests, in Amazonia and Global Change, Geophys. Monogr. Ser., vol. 186, edited by