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News Article

Self-amplified forest loss puts the future of Amazonia at risk


Maintaining high structural and functional diversity crucial for conserving the forests

Forest loss may trigger further forest loss as climate change increases the frequency of droughts in Amazonia. A new study found that large parts of the rainforest are at risk of becoming destabilised by the end of the century if dry seasons intensify and forest heterogeneity is not maintained.

The Amazonian hydrological cycle has intensified in the last decades with wet seasons getting wetter and dry seasons drier, which has been partly explained by reduced moisture inflow from the Atlantic. These atmospheric changes impact the vegetation, and the vegetation again impacts the atmosphere. “Reduced rainfall increases the risk of forest dieback, and on the other hand, forest loss can intensify regional droughts. So more droughts can lead to less forest leading to more droughts,” said the first author of the study, Delphine Clara Zemp from the Potsdam Institute for Climate Impact Research.

However, the consequences of the interaction between vegetation and atmosphere – augmented by human-induced logging and forest fires – for the stability of the Amazon basin are unclear. The authors of the recent study set out to investigate whether the combined events might lead to ‘self-amplified’ forest loss, meaning whether forest loss resulting from drought could trigger more forest loss in Amazonia.

The study, published in the journal Nature Communications earlier this month, applied a complex-network approach – a powerful interdisciplinary method for analysing cascading effects. The authors reconstructed moisture recycling networks where nodes represented individual vegetation grid cells within the Amazon basin. The nodes were linked by monthly water fluxes from the source to the sink, or, the change between evapotranspiration and rainfall.

The results showed that the risk of self-amplified forest loss increased nonlinearly as oceanic moisture inflow decreased and dry seasons intensified. However, the results also suggested that the risk of self-amplified forest loss was reduced as forest heterogeneity increased. Therefore, maintaining the structural and functional diversity would be important for conserving the rainforests.

“Under a dry-season halving of rainfall, at least ten percent of the forest might be lost due to effects of self-amplification alone,” the authors explained. “Taking into account the puzzlements of the vegetation-atmosphere feedback, self-amplified forest dieback could amount up to 38 percent of the Amazon basin.” The largest uncertainties arise from the estimated changes in evapotranspiration.

“Projected rainfall changes for the end of the 21st century will not lead to complete Amazon dieback,” reassured co-author Carl Schleussner from a Berlin-based think tank Climate Analytics and PIK. “But our findings suggest that large parts of it are certainly at risk.” The model also demonstrates that droughts would influence those parts of Amazonia that humans have left untouched.

The complex and nonlinear vegetation-rainfall interactions that may cause self-amplified Amazonian forest loss are still poorly represented in vegetation-climate models. The new study addresses the nonlinear relationship clearly, and illustrates the importance of maintaining forest heterogeneity. Nevertheless, since the model did not consider factors like temperature and changes in carbon dioxide concentrations that are central for forest cover regulation, the study is best understood as a sensitivity analysis rather than a demonstration of hydrological system dynamics.

Plenty more information on the topic is available through CABI. For example, searching for DE:("watersheds" OR "water resources") AND forests AND hydrology on the Forest Science database returns 3,705 results. CABI has also recently published a book called Forest Hydrology: Processes, Management and Assessment which can be bought from the CABI bookshop.

 

Reference:

Zemp DC, Schleussner C-F, Barbosa HMJ, Hirota M, Montade V, Sampaio G, Staal A, Wang-Erlandsson L, Rammig A (2017) Self-amplified Amazon forest loss due to vegetation-atmosphere feedbacks. Nature Communications 8: 14681. DOI: 10.1038/ncomms14681

Article details

  • Author(s)
  • Anu Veijalainen
  • Date
  • 16 March 2017
  • Subject(s)
  • Environment