Forests with more species cope better with combined heat and drought, a study of 88,116 plots finds

A forest with more tree species copes better with a heatwave and a drought at the same time. That’s the conclusion of a study published in July in Nature Communications, led by Xuetao Qiao of Peking University and now covered by Mongabay.

How it was measured

The team used the US forest inventory programme, which has measured trees and species in plots across the continental country since 1990. It selected 88,116 plots with no recorded human disturbance or fire.

From satellites, it measured “greenness” as a proxy for photosynthesis, comparing it with a normal year during the climate extreme and in the following year.

What it found

• Compound extremes did more damage than the same events occurring separately.
• Heat with drought was worse than heat with excess rain.
• More diverse forests resisted and recovered better from both single and compound extremes.
• Protection was strongest in the most damaging case: heat with drought.

Why diversity might help

Florian Schnabel, a silviculture professor at the University of Freiburg who wasn’t involved in the study, points to two mechanisms: species root at different depths, and each closes its stomata differently under stress. “The single best strategy is diversification,” he says.

The caveats

Diversity doesn’t explain everything. Soil, elevation, tree age and average temperature also play a part, and temperature may matter more.

The data also come from just one country. Diversity effects vary with local conditions, and Schnabel’s experimental plots have shown positive, neutral and negative results. The oldest are only a few decades old: the Sardinilla plot in Panama has just reached 25 years.

To see some of these ecosystems up close, explore the world’s most incredible forests.