Forests that contain many different tree species are better equipped to survive harsh weather, according to a major new scientific study. The work suggests biodiversity is not only good for wildlife. It may also be a practical defense against climate change.
The research team examined 88,116 individual forest plots across the United States. That is an unusually large sample. It allowed the scientists to spot patterns that smaller studies would miss. The findings appear in the journal Nature Communications. The project, led by Peking University in Beijing, China, involved researchers from several countries. Among them was Dr. Hannah White of Anglia Ruskin University in the UK.
The focus was on what scientists call “compound climate extremes.” The term describes what happens when two damaging conditions strike at the same time. A heatwave arriving in the middle of a drought is one example.
Most earlier research looked at one type of event on its own. A study might cover heat alone or drought alone. But nature rarely behaves that neatly. Extreme conditions frequently overlap. Studying them separately may therefore paint too comfortable a picture. The true risks of a warming world could be considerably larger than single-event research implies.
To test this, the team combined two very different sources of information. The first was satellite imagery, which reveals how much plant growth is taking place. The second was ground-level forest inventory data, which records exactly which species grow where.
Two qualities were measured. Resistance describes how well a forest holds up while bad conditions are occurring. Resilience describes how quickly it bounces back once the stress has passed.
The results were sobering. Every single one of the 88,116 plots went through at least one combined heat-and-moisture event between 2001 and 2020. No site escaped. When these paired events struck, forests performed worse than when they faced one extreme by itself. They lost more growth at the time. They also took longer to return to normal afterwards.
The damage was greater than simple arithmetic would predict. Two stresses acting together caused more harm than the same two stresses added up separately. The reasons lie in plant biology. Heat deepens a drought because it speeds up evaporation from soil and leaves. Trees lose water faster and run short sooner. Heat can also pair up with too much water rather than too little. Waterlogged ground starves roots of oxygen. Warm conditions make that shortage more dangerous, and root damage follows.
Then came the encouraging part of the story. Plots holding a wider mix of tree species coped noticeably better. Their productivity fell less during compound extremes. Their recovery afterwards was faster and more complete. The pattern showed up consistently across the dataset.
Researchers describe this effect as “biological insurance.” The underlying logic is straightforward. Different species have different strengths and weaknesses. Some shrug off dry spells. Others tolerate soggy soil or high temperatures. In a varied forest, whatever the weather throws at it, some trees will keep functioning. A forest built from a single species has no such backup.
The scientists note that forests rank among the most productive ecosystems on Earth. They influence rainfall, lock away carbon, and shelter enormous numbers of species. They are also facing weather extremes that grow more frequent and more intense as the planet warms.
The findings carry weight for climate modelling. Forests soak up a large share of the carbon dioxide humans release. If diverse forests keep absorbing carbon through extreme years while uniform ones stumble, species mix belongs in future carbon forecasts.
There is a practical lesson for foresters as well. Plantations are often planted with one fast-growing species. This study suggests that variety may be the wiser long-term investment. Diversity appears to buy stability, and stability is becoming valuable.
