Inbook,
The Effects of Drought on Amazonian Rain Forests
page 429--449. American Geophysical Union, (2009)
DOI: https://doi.org/10.1029/2008GM000718
Abstract
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.
