 |
| Titel |
Estimating Amazonian rainforest stability and the likelihood for large-scale forest dieback |
| VerfasserIn |
Anja Rammig, Kirsten Thonicke, Tim Jupp, Sebastian Ostberg, Jens Heinke, Wolfgang Lucht, Wolfgang Cramer, Peter Cox |
| Konferenz |
EGU General Assembly 2010
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250044296
|
|
|
|
|
|
| Zusammenfassung |
| Annually, tropical forests process approximately 18 Pg of carbon through respiration and
photosynthesis – more than twice the rate of anthropogenic fossil fuel emissions. Current
climate change may be transforming this carbon sink into a carbon source by changing forest
structure and dynamics. Increasing temperatures and potentially decreasing precipitation
and thus prolonged drought stress may lead to increasing physiological stress and
reduced productivity for trees. Resulting decreases in evapotranspiration and therefore
convective precipitation could further accelerate drought conditions and destabilize the
tropical ecosystem as a whole and lead to an “Amazon forest dieback”. The projected
direction and intensity of climate change vary widely within the region and between
different scenarios from climate models (GCMs). In the scope of a World Bank-funded
study, we assessed the 24 General Circulation Models (GCMs) evaluated in the 4th
Assessment Report of the Intergovernmental Panel on Climate Change (IPCC-AR4) with
respect to their capability to reproduce present-day climate in the Amazon basin
using a Bayesian approach. With this approach, greater weight is assigned to the
models that simulate well the annual cycle of rainfall. We then use the resulting
weightings to create probability density functions (PDFs) for future forest biomass
changes as simulated by the Lund-Potsdam-Jena Dynamic Global Vegetation Model
(LPJmL) to estimate the risk of potential Amazon rainforest dieback. Our results show
contrasting changes in forest biomass throughout five regions of northern South
America: If photosynthetic capacity and water use efficiency is enhanced by CO2,
biomass increases across all five regions. However, if CO2-fertilisation is assumed
to be absent or less important, then substantial dieback occurs in some scenarios
and thus, the risk of forest dieback is considerably higher. Particularly affected are
regions in the central Amazon basin. The range of potential biomass change arising
from the weighting of rainfall patterns is smaller than the uncertainty arising from
CO2-fertilisation effects, which highlights the importance of reducing the uncertainties in the
direct effects of CO2 on tropical ecosystems. Strong biomass changes also imply
changes in forest structure and thus, forest stability. Our results display shifts in forest
composition from closed rainforest to more open forest or even shrubland. Our
probability-based risk analysis could be used to advise regional forest protection. |
|
|
|
|
|
|