Assessment of the Risk of Amazon Dieback

The Amazon basin is a key component of
the global carbon cycle. The old-growth rainforests in the
basin represent storage of ~ 120 petagrams of carbon (Pg C)
in their biomass. Annually, these tropical forests process
approximately 18 Pg C through respiration and
photosynthesis. This is more than twice the rate of global
anthropogenic fossil fuel emissions. The basin is also the
largest global repository of biodiversity and produces about
20 percent of the world's flow of fresh water into the
oceans. Despite the large carbon dioxide (CO2) efflux from
recent deforestation, the Amazon rainforest ecosystem is
still considered to be a net carbon sinks of 0.8-1.1 Pg C
per year because growth on average exceeds mortality
(Phillips et al. 2008). However, current climate trends and
human-induced deforestation may be transforming forest
structure and behavior (Phillips et al. 2009). Increasing
temperatures may accelerate respiration rates and thus
carbon emissions from soils (Malhi and Grace 2000). High
probabilities for modification in rainfall patterns (Malhi
et al. 2008) and prolonged drought stress may lead to
reductions in biomass density. Resulting changes in
evapo-transpiration and therefore convective precipitation
could further accelerate drought conditions and destabilize
the tropical ecosystem as a whole, causing a reduction in
its biomass carrying capacity or dieback. In turn, changes
in the structure of the Amazon and its associated water
cycle will have implications for the many endemic species it
contains and result in changes at a continental scale.
Clearly, with much at stake, if climate-induced damage
alters the state of the Amazon ecosystem, there is a need to
better understand its risk, process, and dynamics. The
objective of this study is to assist in understanding the
risk, process, and dynamics of potential Amazon dieback and
its implications.