As is well known, a walk in the forest can be very refreshing on hot summer days. A study has now made it clear to what extent the composition of the trees plays a role in the cooling effect. As can be seen from the analysis results of satellite data, deciduous trees in European forests lower the temperatures on the surface of the earth much more intensely than conifers during hot periods. The promotion of beech and Co. could thus help to mitigate the effects of climate change, say the researchers.
Some studies have already shown that an increase in the proportion of deciduous trees is good for forests: The species-rich tree communities can provide more ecosystem services and adapt better to climate change than the artificially shaped spruce monocultures that are typical for many areas of Europe. For example, deciduous trees reduce the risk of fire, windthrow and the spread of the bark beetle. In addition, there have already been indications that deciduous trees are of particular importance for the development of the local climate due to their biogeophysical influence on temperature. But so far this effect has not been extensively investigated and quantified, say the researchers working with the Jonas Schwaab Institute for Atmosphere and Climate in Zurich.
Cooling effect confirmed
As part of their study, the researchers took a look from space on the forests of Europe: They used temporally and spatially high-resolution satellite data for thermal radiation, which were generated by the so-called SEVIRI instrument (Spinning Enhanced Visible and InfraRed Imager). The temperatures in the soil area of forests in Europe were derived from them. They linked this information with information about the proportions of deciduous trees in the analyzed areas. From the data they then developed statistical models of how deciduous trees influence temperatures in the area of the earth’s surface.
As the scientists report, their data now systematically illustrate for the first time that deciduous trees reduce surface temperatures significantly more than conifers during periods of extreme heat. The statistical comparison of forests with different degrees of conifer and deciduous trees confirmed this for large parts of Europe. The model shows that an increase in the proportion of deciduous trees from 10 to 80 percent leads to a decrease in maximum daily temperatures during the hottest days of up to 1.8 degrees Celsius in the Atlantic region and up to 1.5 degrees in the continental and Mediterranean areas.
What is the cooling effect based on?
“One of the reasons for the cooling effect is that deciduous trees have a higher albedo than conifers,” explains Jonas Schwaab. “This means that deciduous trees reflect more sunlight and thus less energy is converted into heat on the earth’s surface”. Earlier studies also show that deciduous trees generally evaporate more water than conifers during the growing season. This also creates a cooling effect that contributes to the local climate in tree communities, say the scientists. However, they emphasize that further investigations are now necessary to better understand the details of the causes of the observed cooling effect. “In particular, the properties of different tree species and not just general differences between deciduous and coniferous trees should be taken into account,” emphasizes co-author Edouard Davin from the Swiss Federal Institute of Technology in Zurich.
The results of the current and further studies can feed into the development of measures to adapt to climate change, say the researchers. It may make sense to increase the proportion of deciduous trees in forests, but also in cities, in order to mitigate the effects of global warming. “An increase in the proportion of deciduous forest makes sense, for example, where man-made spruce monocultures dominate that are poorly adapted to the prevailing site conditions,” says co-author Peter Bebi, head of the research group on mountain ecosystems at the WSL Institute for Snow and Avalanche Research in Davos.
Source: Swiss Federal Institute of Technology Zurich, specialist article: Scientific Reports, doi: 10.1038 / s41598-020-71055-1