Ecosystems the size of Amazon can collapse within decades
11 March 2020 | Adaptation
Even large ecosystems the size of the Amazon rainforest can collapse in a few decades, according to a study that shows bigger biomes break up relatively faster than small ones.
The research reveals that once a tipping point has been passed, breakdowns do not occur gradually like an unravelling thread, but rapidly like a stack of Jenga bricks after a keystone piece has been dislodged.
The authors of the study, published on Tuesday in the Nature Communications journal, said the results should warn policymakers they had less time than they realised to deal with the multiple climate and biodiversity crises facing the world.
To examine the relationship between an ecosystem’s size and the speed of its collapse, the authors looked at 42 previous cases of “regime shift”. This is the term used to describe a change from one state to another – for example, the collapse of fisheries in Newfoundland, the death of vegetation in the Sahel, desertification of agricultural lands in Niger, bleaching of coral reefs in Jamaica, and the eutrophication of Lake Erhai in China.
They found that bigger and more complex biomes were initially more resilient than small, biologically simpler systems. However, once the former hit a tipping point, they collapse relatively faster because failures repeat throughout their modular structure. As a result, the bigger the ecosystem, the harder it is likely to fall.
Based on their statistical analysis, the authors estimate an ecosystem the size of the Amazon (approximately 5.5m km2) could collapse in approximately 50 years once a tipping point had been reached. For a system the size of the Caribbean coral reefs (about 20,000 km2), collapse could occur in 15 years once triggered.
The paper concludes: “We must prepare for regime shifts in any natural system to occur over the ‘human’ timescales of years and decades, rather than multigenerational timescales of centuries and millennia.
“Humanity now needs to prepare for changes in ecosystems that are faster than we previously envisaged through our traditional linear view of the world, including across Earth’s largest and most iconic ecosystems, and the social-ecological systems that they support.”
The paper says this could be the case in Australia where the recent Australian bushfires followed protracted periods of drought and may indicate a shift to a drier ecosystem.
Scientists were already aware that systems tended to decline much faster than they grew but the new study quantifies and explains this trend.
“What is new is that we are showing this is part of a wider story. The larger the system, the greater the fragility and the proportionately quicker collapses,” John Dearing, professor in physical geography at the University of Southampton and lead author of the study, said.
“What we are saying is don’t be taken in by the longevity of these systems just because they may have been around for thousands, if not millions, of years – they will collapse much more rapidly than we think.”
Dearing said he was concerned that one of the possible implications of the study was that complete destruction of the Amazon could occur within his grandchildren’s lifetimes.
“This is a paper that is satisfying from a scientific point of view, but worrying from a personal point of view. You’d rather not come up with such a set of results,” he said.
A separate study last week warned the Amazon could shift within the next decade into a source of carbon emissions rather than a sink, because of damage caused by loggers, farmers and global heating.
Experts said the new findings should be a spur to action.
“I think the combination of theory, modelling and observations is especially persuasive in this paper, and should alert us to risks from human activities that perturb the large and apparently stable ecosystems upon which we depend,” said Georgina Mace, professor of biodiversity and ecosystems at University College London, who was not involved in the studies.
“There are effective actions that we can take now, such as protecting the existing forest, managing it to maintain diversity, and reducing the direct pressures from logging, burning, clearance and climate change.”
These views were echoed by Ima Vieira, an ecologist at Museu Emílio Goeldi in Belém, Brazil. “This is a very important paper. For Brazil to avoid the ecosystem collapse modelled in this study, we need to strengthen governance associated to imposing heavy fines on companies with dirty supply chains, divestment strategies targeting key violators and enforcement of existing laws related to environmental crimes. And we have to be quick.”
However, the methodology was not universally accepted. Erika Berenguer, a senior research associate at the University of Oxford and Lancaster University, said the regime shifts paper relied too much on data from lakes and oceans to be useful as an indicator of what would happen to rainforests.
“While there is no doubt the Amazon is at great risk and that a tipping point is likely, such inflated claims do not help either science or policy making,” she said.
The authors said their study was not a forecast about a specific region but a guide to the speed at which change could occur.
Source: The Guardian