Cooling effect of European forests mapped for the first time

(04-10-2021) For the first time, a team of scientists from Ghent University, KU Leuven, and UAntwerp have mapped the temperatures of all European forest tracts.

The results show that the summer temperatures in certain forests can cool down by as much as 10°C compared to the surrounding area.

This cooling function is important in the battle against climate change.

On a hot summer day, forests can feel a lot cooler than the surrounding area, but the exact difference in temperature has been difficult to quantify. An international team of researchers has been measuring the temperature of each European forest. Our faculty was one of the partners involved.

Mini weather stations on the forest floor

Using a dataset of more than 1200 small weather stations across all European forests, the researchers quantified the difference in temperature between the forest understory and the surrounding area.

“This network of sensors on the forest floor is unique as it accurately captures the true temperature under the forest canopy, both for big and small forests,” explains Stef Haesen (KU Leuven), who coordinated the study. “This information is crucial to analyse the impact of climate change on and in forests.”

temperatuurkaart bossen

Forests as thermal insulation

The data show that the maximum summer temperature in forests is on average 2°C lower than in surrounding areas, but the difference can be as high as 10°C. Similarly, minimum temperatures in winter can be 2°C higher, and in some forests even up to 12°C.

“With their foliage and branches in the canopy, trees create a thermal insulating layer above the forest floor. In addition, the transpiration during the photosynthesis process extracts heat from the air, lowering the temperature during summer even more,” explains Professor Koenraad Van Meerbeek (KU Leuven).

“Summer heat waves are thus strongly moderated below the tree canopy, which is increasingly important considering global warming.” 

Effect on climate change on and in forests

"This is a real scientific and technical breakthrough that will undoubtedly improve predictions about the distribution of forest species," Haesen adds. As the new map is very detailed, it reveals differences between and within forests: temperatures vary significantly depending on the local canopy cover, topography or tree species composition.

“If we want to know why certain forests grow in a specific place, we need information from within the forest. With this map, we can manage the forest climate in order to protect forests and their organisms against climate change and increased frequency of extreme weather events,” says Professor Pieter De Frenne from Ghent University.

“This unique database and cooperation puts Flanders at the forefront of microclimate research, a discipline of critical importance considering the climate and biodiversity crisis,” concludes postdoctoral researcher Jonas Lembrechts from UAntwerp.

More information

  • The study “ForestTemp – sub-canopy microclimate temperatures of European forests” is published in Global Change Biology (DOI : 10.1111/gcb.15892).
  • The research was funded by KU Leuven, the European Research Council (ERC) and Fonds Wetenschappelijk Onderzoek (FWO) from the Flemish Government.