Forests protect animals and plants against warming

The cool freshness of a forst walk on a hot summer day is not just a subjective impression. An international team of researchers have quantified the temperature difference between sites within forests and outside, for the first time across the globe. Measurements occurred at 98 locations spread across five continents, in the tropics, temperate zone and northern boreal forests.

The data show that the maximum temperature in forests is, on average across the globe, 4 degrees lower than outside forests. This knowledge will result in better predictions on the impact of climate warming on forest biodiversity. In Switzerland, the scientists drew on data from the Long-term Forest Ecology Research (LWF) conducted by the WSL. Since the 1990s, the LWF has been collecting detailed data on the environmental impacts of forests on a total of 19 research sites throughout Switzerland.

Temperature difference of 4 degrees

“With their foliage and branches in the canopy, trees create a thermal isolating layer above the forest”, explains Florian Zellweger from the Swiss Federal Research Institution WSL in Birmensdorf. “For this reason, summer maximum temperatures are much lower inside forests than outside. In the winter and at night, this pattern is reversed and forest temperatures are, on average, 1 degree warmer.”

“Our new data show that forest temperatures are on average 4 degrees cooler than outside temperatures when it is warm. Summer heat waves are thus strongly moderated below the tree canopy. Plants and animals inside forests will thus experience the current warming trend to a lower degree than species not living in forests”, says Zellweger. “Since forests cover a quarter of the land surface of the globe and harbour two thirds of all biodiversity, this has important implications for predictions on the impact of climate change.”

Buffer against climate warming

For the first time, the researchers also show that with increasing temperatures, the buffering capacity of maximum temperatures of global forests also increases. The warming of maximum air temperatures within forests is thus probably lower than previously anticipated.

Zellweger: “Even though temperatures outside forests continue to increase, temperatures within forests do not necessarily follow that same trend. The decoupling between temperatures within forests and temperatures outside simply increases. Forests can therefore truly be considered a buffer against climate warming. Accordingly, our findings stress the need to conserve our existing forests and enhance reforestation efforts.