Woodland with lots of different kinds of trees can do a good job of buffering heatwaves and extreme cold. Now a new study demonstrates that increasing the mix of species can help to mitigate climate extremes.

Florian Schnabel, from the German Centre for Integrative Biodiversity Research in Leipzig, and colleagues measured forest temperatures over a six-year period at the world’s largest tree diversity experiment in Xingangshan, in subtropical China. Their results, published in Ecology Letters, show that species-rich plots provided the greatest cooling effect during summer, with cooling more than 4C greater in an experimental plot with 24 species compared with a single-species plot. Diverse plots also maintained more warmth under the tree canopy on cold nights and during winter.

The reason for this extra temperature buffering is most likely linked to mixed woodland having a greater canopy density (more leaves per sq metre) and higher structural diversity (a mix of small and large trees). These factors reduce the mixing of air and help to insulate the forest environment from temperature extremes. The results add to the growing list of reasons to move away from tree monocultures and to instead preserve and plant diverse forests, to protect both nature and people from climate extremes.