A recent international study including researchers from the University of Fribourg, has revealed that the diversity of tree species in forests plays a crucial role in regulating extreme temperatures. The study is based on the BEF-China project, which is the world’s largest experimental facility on tree diversity and is located in southern China. Hundreds of thousands of trees have been planted in plots containing between one and 24 different species, enabling the impact of diversity on the forest microclimate to be analysed over six years.
The study’s main findings are:
- Mitigation of heat peaks. Forests composed of 24 species have demonstrated a cooling capacity of up to 4.4°C compared to monocultures during periods of high summer heat.
- Insulation against the cold. Diverse forests also retain heat better during cold nights and in winter, providing increased protection against low temperatures.
- The role of forest structure. Higher foliage density and greater structural diversity improve forests’ ability to stabilise the microclimate by reducing air exchange with the outside.
These results suggest that promoting species diversity can strengthen forests’ resilience to climate extremes. This has important implications for reforestation initiatives and urban forest design, particularly in Europe, where heat waves are becoming more frequent.