The resilience of the Amazon rainforest to natural and anthropogenic stressors is crucial in maintaining biodiversity, modulating regional climate and dampening CO2 increases. However, deforestation and climate change are reducing this
reliance, pushing the Amazon ever closer to the brink of wide-scale dieback.
The Amazon is the world's largest rainforest; accounting for 40% of the remaining global rainforest cover and extending across 5.5 million square kilometres. It is a crucible of biodiversity, home to 25% of all terrestrial biodiversity, 2,500
different tree species and more fish species than any other
river.
The rainforest also acts as a vital sink of carbon, storing between 150-200 billion metric tonnes of carbon. To put that into
context, annual global carbon dioxide emissions are 36 billion metric tonnes. This
means that any wide-scale dieback in the Amazon would necessitate even
more dramatic emission reductions.
Whether the Amazon continues to deliver these key ecosystem services is dependent on its resilience to environmental stressors. These stressors could include natural climate variability, but in reality, it is overwhelmingly
anthropogenically driven climate change and land-use change that has the largest impact on the Amazon.
Resilience describes the ability of an ecosystem to return to its original state following a short-term perturbation, such as a drought, land clearance, or fire. A resilient ecosystem will be able to bounce back to its original steady-state
quickly and can deal with more severe disturbances.
Worryingly, a recent study has highlighted a marked decrease in the resilience of the Amazon since the 2000s. This means
that as the current steady state of the Amazon becomes less stable, the system takes longer to recover following a perturbation. This makes it more vulnerable to further stressors,
especially if the rainforest can fully recover before it is subject to another perturbation (e.g. frequent droughts).
‘A recent study has highlighted a marked decrease in the resilience of the Amazon since the 2000s.’
The authors of the study came to this conclusion by examining changes in vegetation biomass and photosynthesis, computed using satellite-derived vegetation data from the Vegetation Optical Depth Climate Archive (VODCA).
After removing forested areas with human land use, they found 76% of the Amazon was progressively losing resilience from the early 2000s onwards.
This decline is in agreement with other studies that demonstrate a long term decline in the net primary productivity of the Amazon
(how much carbon it takes up), which has reduced by a third
in the last 30 years. During drought events in 2005 and 2010,
dieback was at sufficient levels that the Amazon temporarily became a carbon source rather than a sink.
The researchers suggest that this loss of resilience is a result of expansions in human land use and reductions in mean annual precipitation. As resilience losses are more pronounced in areas closer to human settlements and in regions
characterised by greater reductions in rainfall. The impact of human infrastructure on resilience could be seen up to 150 kilometres away.
The question of resilience is of particular concern for scientists (and us all) because the Amazon is recognised as a potential tipping element of the earth’s climate system.
Meaning if environmental conditions deteriorate sufficiently, a series of positive feedback
mechanisms could rapidly push the Amazon from one stable state to another.
‘If environmental conditions deteriorate sufficiently, a series of positive feedback mechanisms could rapidly push the Amazon from one stable state to another.’
As resilience decreases, it becomes easier for an ecosystem to switch to a new steady state. Hence, trends in resilience can indicate the risk of surpassing this tipping point, even when there is no current widespread dieback. The forest
could be ‘committed’ to significant dieback even if the system appears stable.
Within the Amazon, two positive feedback mechanisms are critical in determining whether a tipping point is reached; fire and deforestation.
Fire and deforestation/forest degradation both decrease forest cover and associated evapotranspiration, which reduces moisture availability and leads to reductions in rainfall. This, in turn, increases the risk of drought (leading to forest
degradation), which then increases fire risk (further reducing forest cover). If forest cover reduces sufficiently, this large scale feedback mechanism may be impossible to stop, regardless of our actions.
Several studies have run simulations that suggest deforestation and anthropogenic warming could push the Amazon past a critical threshold, beyond which, these positive feedback mechanisms would ‘lock-in’ huge forest dieback.
‘Deforestation and anthropogenic warming could push the Amazon past a critical threshold, beyond which, these positive feedback mechanisms would ‘lock-in’ huge forest dieback.’
Given its global importance, there is an urgent need for coordinated global action to safeguard the Amazon rainforest, with a particular focus on empowering and supporting indigenous peoples.
Some of the recent pledges on deforestation and emissions at COP26 are positive, but whether they will be enforced and rolled out fast enough is uncertain. What is known, however, is that a precautionary approach is sorely needed, as once
widespread dieback begins it will likely be too late to stop, regardless of our actions.
Boulton C.A., Lenton T.M. and Boers N. (2022) Pronounced loss of Amazon rainforest resilience since the early 2000s. Nature Climate Change. Volume 12, issue 3, pages 271-278.
Brienen R.J., Phillips O.L., Feldpausch T.R. et al. (2015) Long-term decline of the Amazon carbon sink. Nature. Volume 519, issue 7543, pages 344-348.
Feldpausch T.R., Phillips O.L., Brienen R.J.W. et al (2016) Amazon forest response to repeated droughts. Global Biogeochemical Cycles. Volume 30, issue 7, pages.964-982.
Lenton T.M., Held H., Kriegler E. et al. (2008) Tipping elements in the Earth's climate system. Proceedings of the national Academy of Sciences. Volume 105, issue 6, pages 1786-1793.
Moesinger L., Dorigo W., de Jeu R. et al (2020) The global long-term microwave vegetation optical depth climate archive (VODCA). Earth System Science Data. Volume 12, issue 1, pages 177-196.
Nobre C.A., Sampaio G., Borma L.S. et al. (2016) Land-use and climate change risks in the Amazon and the need of a novel sustainable development paradigm. Proceedings of the National Academy of Sciences. Volume 113,
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