Species-rich Forests Better Buffer Climate Extremes
2025-04-15 Biodiversity in forests enhances their capacity to buffer weather extremes brought about by the climate crisis. This is the conclusion of an international team of researchers, which includes scientists from Leuphana University. The project was supported, among others, by the German Research Foundation (DFG).
A walk through the forest on a hot summer’s day brings cooling relief. In winter, meanwhile, temperatures beneath the trees tend to be milder than in the surrounding open landscape. This phenomenon has long been known. “However, until now, we did not know whether tree species diversity also plays a role in this effect,” explains PD Dr Andreas Fichtner from the Institute of Ecology within the School of Sustainability at Leuphana. Together with his colleague, Professor Dr Werner Härdtle, he contributed to an international research project that explored this very question, among others.
The Result: The greater the diversity of tree species in a forest, the stronger the cooling effect. “Forests with a high variety of trees can be up to 4.4 degrees Celsius cooler at midday in summer compared to monocultures,” says Professor Werner Härdtle, an expert in Ecology, Landscape Ecology and Nature Conservation at the Institute of Ecology within the School of Sustainability. Dr Fichtner adds: “In winter, species-rich forests can be up to 1.1 degrees warmer at night.” The study once again underscores the importance of biodiversity - especially in light of the advancing climate crisis.
To draw reliable conclusions, researchers must gather data in settings with comparable environmental conditions. Simply measuring temperatures across different forest types would be insufficient, explains Fichtner: “Soil properties, forest age, water availability, and other factors all play a role.” The solution was provided by the world's largest planted field experiment on tree diversity, located in China - the so-called BEF-China experiment. BEF stands for Biodiversity-Ecosystem Functioning, which examines the relationship between biodiversity and ecosystem functions. In the subtropical climate of China, researchers planted several hundred thousand trees in 2008 across plots consisting of 1, 2, 4, 8, 16, or 24 tree species - ideal conditions for answering the research question. An international group of scientists from Germany, Switzerland, and China conducted their studies between 2015 and 2020, at a time when the trees had already matured. The results have now been published in the journal Ecology Letters.
Global warming is increasing both the frequency and intensity of extreme weather events. Forests can mitigate these extremes, the researchers found. Tree species richness enhanced the cooling effect in summer and improved insulation against winter cold. “This buffering effect of tree diversity was driven by increased canopy density and structural variety in species-rich stands,” the authors note. They further emphasise that safeguarding and cultivation of diverse forests may mitigate negative effects of global warming and climate extremes on below-canopy ecosystem functions and communities.
A more stable forest microclimate benefits ecosystems and the services they provide. Forests are better able to grow and regenerate under such conditions. Soil processes also improve, with more efficient nutrient cycles and enhanced carbon storage - an important contribution to counteracting the greenhouse effect that accelerates climate change.
Researchers from Leuphana University Lüneburg were joined by colleagues from the University of Leipzig, the Technical University of Dresden, and Martin Luther University Halle-Wittenberg. The project was led by scientists from the German Centre for Integrative Biodiversity Research (iDiv).