Drones used to detect drought stress in Swiss forests

During the hot summer of 2023, researchers at WSL used drone footage to investigate how seven native tree species react to drought. Keystone-SDA

Increasing heat and drought are putting forests under pressure. Researchers at the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) have used drones to investigate how native tree species are responding to climate change.

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To strengthen the resilience of forests in the face of climate change, experts need to know how different tree species react to rising temperatures and water shortages, WSL said in a statement on Monday.

Until now, such studies have been expensive and could generally only be carried out on individual trees.

A WSL team has therefore been studying images taken by drones equipped with multispectral cameras capable of recording invisible areas of the light spectrum.

The cameras detect from the air a particular pigment that trees produce to protect their leaves from excessive sunlight during periods of drought.

“This allows us to identify whether a tree is under acute stress even before the damage is visible to the naked eye,” explained WSL geographer Petra D’Odorico in the press release.

+ Swiss forests in race against time

Reactions specific to each species

Using these special cameras, the team repeatedly flew over a forest at the University of Basel’s canopy research site in Hölstein, canton Basel Country, during the heatwave of 2023.

It analysed changes in the crowns of seven native tree species, then compared the aerial data with measurements taken on the trees.

+ Switzerland’s forests of the future

The images made it possible to identify the specific reactions of each species to drought. The researchers observed, for example, that oak trees recover more quickly from a hot day than other species. Conifers, on the other hand, only show signs of water stress after a certain delay, before suddenly dying out.

This method of measurement could in future help to monitor forests on a large scale.

D’Odorico is also studying non-native trees, such as the Lebanese cedar or the Oriental beech, in order to identify species likely to replace native species in regions affected by climate change.

Translated from French by AI/sb

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