Water deficiency, extreme wind could push southern Amazon past point of no return

A new study reveals more than 70% of trees dying at the edge of the world’s largest rainforest suffered significant climate-related damage years earlier. 

Researchers at the University of Leeds, University of Oxford, and State University of Mato Grosso (UNEMAT) in Brazil have investigated around 5,000 tree deaths in 19 areas of remaining forest at the southern tip of the Amazon. The driest, hottest, and most fragmented region in the rainforest, which has experienced severe droughts in recent years, the vast majority of trees included in the work were found to have suffered crown breakage before they began to die. 

Official figures suggest around 70% of all trees dying in these areas show signs of severe crown damage and breakages, a common impact of climate extremes, specifically wind and low rainfall. This is significantly higher than the rate in other parts of the rainforest. 

The investigation, published in the Journal of Ecology, is the first to evaluate large-scale the causes of tree mortality in the southern Amazon, and those responsible believe this confirms that flora in this region is under ‘exceptional stress’ as a result of this climate-driven damage, making it difficult for them to recover and survive. 

‘Crown breakage hugely increases the risk of tree death. Once broken, the risk of death is much higher, especially when a large part of the tree canopy is broken,’ said Dr Simone Matias Reis, of UNEMAT, lead author of the study. ‘The growth of broken trees is also affected, as these trees lose capacity to photosynthesize and so take-up less carbon, which in turn increases the risk of death.’

The impact of climactic water deficits – low rainfall – on trees in these areas is of particular concern to the researchers. All current modelling predicts more prolonged and intense seasonality for the Amazon in the coming years, which means longer periods of low precipitation and therefore more crown damage.  

Professor Ben Hur Marimon from UNEMAT, study co-author, said: ‘The cumulative effects of tree breakage may be one of the most important components of the Amazon tipping point, beyond which the forest can no longer recover.’

In related news, wildfires are predicted to increase by 50% by the end of the century, with elevated risk in regions previously completely or mostly unaffected by such events.

Image credit: 蔡 嘉宇