Leaf ‘scorching’ likely to increase due to global warming

Researchers warn against misinterpreting brown leaves in the forest Keystone-SDA

Climate models may overestimate the resilience of forests, if they fail to distinguish controlled leaf senescence from damage caused by heat and drought, say Swiss scientists.

Researchers at the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) have issued a warning about this in a commentary published in the specialist journal Nature Climate Change. What looks similar from a distance can have very different consequences for the tree, the WSL said on Thursday.

In the case of controlled leaf senescence, the tree sheds its leaves in an orderly manner, reabsorbing valuable nutrients in the process. In contrast, when leaves are ‘scorched’ by heat and drought, the leaf tissue is irreversibly damaged. The tree then loses nutrients before it can store them.

The difference is significant

From space, both processes appear similar: the forest turns increasingly brown. Biologically, however, the difference is significant. If heat damage is interpreted as controlled leaf senescence, the resilience of forests to climate extremes could be overestimated.

According to the WSL, the summer heatwave of 2018 demonstrated just how deceptive first impressions can be. At that time, beech trees in the Schaffhausen area already had brown crowns by mid-August. The following year, many of them failed to sprout properly – an indication that they had in fact been damaged.

With global warming, such cases are likely to become more frequent. The researchers are therefore calling for controlled experiments to determine more precisely the thresholds between adapted leaf ageing and irreversible damage.

Translated from German/sub-editing gw