They did not expect such a slaughter. And yet, researchers from the Smithsonian Environmental Research Center, the University of Oxford and the National Research Institute for Sustainable Development (IRD) are categorical: tree mortality in several Australian rainforests has doubled. over the past decades. Their work, based on the monitoring of more than 8,300 trees on 24 sites and nearly half a century, has just been published in the journal Nature. And they could have serious consequences for our future.
Several studies had already alerted us to the worrying state of certain tropical forests, which constitute the green lung of the planet. This is intended to be more precise thanks to modeling and Australian databases running over nearly 50 years. “When we compare the 70s and 80s with the last three decades, we realize that the annual rate of tree mortality has doubled, from 1 to 2%. This may seem low in absolute value, but this phenomenon concerns large areas. This is also a major trend that potentially leads to a halving of the life expectancy of trees and therefore of the carbon storage time in the trunks. This is a very important result. which has very serious implications when thinking about the role of forests in mitigating climate change,” says forest biologist and ecologist David Bauman, one of the study’s lead authors.
“Climate change is involved”
More work will be needed to say that what is happening in Australia is most likely happening elsewhere. However, the average climatic conditions of Australian forests seem fairly representative of a large proportion of tropical rainforests found in other regions of the planet. Moreover, the increase in mortality measured there closely follows the increase in temperature. This generates significant stress by forcing the plants to sweat. “This mechanism undoubtedly plays a large part in this increase in mortality. Of course, it is possible that other phenomena come into play. But the overall result seems clear: climate change is involved” explains David Bauman.
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If this theory is confirmed, tropical rainforests could soon become sources of carbon. “This would mean that future temperature forecasts could be underestimated by current models. The challenge of limiting warming to well below 2 degrees would become more urgent and difficult, giving even more weight to the warning messages contained in the latest IPCC report”, continues the expert.
Should we then reforest massively? Pay attention to received ideas. “Planting trees takes a lot of time and requires a lot of money and energy for a high failure rate. In some regions it must be part of the toolbox used to mitigate climate change. But given the urgency of the situation, it is better to focus our efforts on preserving existing forests and, of course, on reducing our greenhouse gas emissions, says David Bauman.
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Especially since other indicators turn red. This Wednesday, May 18, the UN reported that four key markers of climate change broke new records in 2021: greenhouse gas concentrations, sea level rise, temperature and acidification of oceans. This report is “a lamentable litany of humanity’s failure to combat climate change”, denounced the head of the United Nations, Antonio Guterres.
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