Ecology: Tree species diversity enhances forest drought resistance

Tree species diversity could enhance drought resistance in nearly half of global forests, according to an analysis of more than 700,000 forest plots presented in Nature Geoscience. The findings may have implications for current restoration and afforestation policies.

Extreme droughts can strongly reduce the growth — and lead to the death — of forests. Tree species diversity can increase drought resistance, however, this has only been demonstrated regionally and for a small number of forest types. Whether species diversity could stabilize different types of forests around the world in extreme droughts, is currently unknown.

Using global satellite data and evidence for species-richness from over 700,000 forest plots, Tao Wang and colleagues estimate the effect of tree species diversity on the drought response of forests worldwide. Drought resistance was found to be highest in species-rich forests, such as moist tropical broadleaf forests, where the average number of tree species was 65 within a forest plot, and was lowest in species-poor forests, such as xeric woodlands (two or three tree species on average). The authors predict that higher species richness has a positive effect on drought resistance in 44% of global forests, with the greatest effect observed in dry and drought-prone forests, such as xeric woodlands or subtropical dry forests. The team also develop a model that estimates that converting current forest plantations from monocultures to a mixture of four species could increase drought resistance of global plantation forests by 3.2%.

The authors conclude that these findings emphasize the importance of restoring tree species diversity to help forests resist frequent and intense droughts that may occur as a result of global warming.