Mixed Forests Weather Compound Climate Extremes Better, Study Finds

Forests that contain a wider variety of tree species are markedly better at withstanding and recovering from simultaneous climate extremes, according to a large-scale new study published in the journal Nature Communications. The research, led by Peking University in Beijing and carried out by an international team of scientists including Dr Hannah White of Anglia Ruskin University in Cambridge, England, analysed data from 88,116 separate forest plots across the United States. Its central conclusion is striking in its simplicity and its scale: when drought and extreme heat arrive together, the damage they inflict on forests is greater than the sum of the individual events, yet species-rich forests consistently suffer smaller losses and bounce back faster than their less diverse counterparts.

The study focused on what climate scientists call compound climate extremes, situations in which two or more extreme events, such as drought and extreme heat, occur at the same time or in close succession. While previous research has typically examined the impacts of individual climate events in isolation, the authors argue that this approach may systematically underestimate the risks posed by climate change, because extremes rarely occur alone in the real world. Between 2001 and 2020, the period covered by the analysis, compound heat and moisture extremes were recorded at least once in every one of the 88,116 forest plots examined, underscoring how widespread these overlapping stresses have already become.

Why should simultaneous extremes be so much more damaging than single events? The study points to amplifying mechanisms that link the atmosphere, the soil and the living tissue of trees. Extreme heat can intensify drought by increasing evapotranspiration, the process by which water is transferred from the land surface to the atmosphere through evaporation and through transpiration from plant leaves. As temperatures climb, trees lose water faster through their stomata, the microscopic pores on their leaves, which deepens the water stress caused by reduced rainfall and drier soils. The combined effect is a physiological squeeze that a forest experiencing either heat or drought alone might survive, but which can push trees beyond their limits when both arrive together.

Heat can also combine with excessive moisture rather than too little of it. When heavy rainfall or waterlogging coincides with high temperatures, soils can become saturated and oxygen-starved, a condition that exacerbates hypoxia in root systems. Roots deprived of oxygen begin to suffer damage, impairing the tree’s ability to take up water and nutrients even after conditions improve. In other words, whether the moisture extreme is a deficit or a surplus, its interaction with heat tends to amplify the harm, producing negative impacts on forest productivity that exceed what either event would cause on its own.

To measure these effects across such a vast area, the researchers combined two complementary sources of information: satellite observations and forest inventory data. The satellite record provided measures of forest productivity, allowing the team to track how much carbon forests captured and how sharply that capture declined during extreme events. The inventory data added ground-based detail about the composition of each plot, including the number and variety of tree species present. This pairing of remote sensing with field surveys allowed the scientists to evaluate two distinct properties of forest ecosystems: resistance, meaning a forest’s ability to withstand a climate extreme while it is happening, and resilience, measured by how effectively the forest recovers its productivity afterwards.

Across all of the plots analysed, the pattern was consistent. When forests were exposed to compound heat and moisture extremes, they generally showed lower resistance and poorer recovery than when they were subjected to individual climate extremes. Productivity fell more steeply during the events, and the return to normal levels of growth was slower and less complete. This finding matters because forests are among the most productive ecosystems on Earth and play a central role in the global carbon cycle, absorbing a substantial share of the carbon dioxide emitted by human activity. If compound extremes erode both the capacity of forests to absorb carbon and their ability to rebound, projections of the future carbon cycle may need to account for these interacting stresses rather than treating them one at a time.

Yet the study also identified a powerful buffer against this damage: biodiversity. Forest plots containing a wider variety of tree species experienced smaller declines in productivity during compound climate extremes and recovered more effectively afterwards. The researchers describe this protective effect as a form of biological insurance, a concept in ecology that captures how diversity spreads risk across a community. Different tree species differ in their rooting depths, water-use strategies, drought tolerances and heat responses. When conditions turn hostile, a diverse forest is more likely to contain species that can keep functioning, sustaining the ecosystem’s overall productivity even as more vulnerable species struggle. In a monoculture or a species-poor stand, by contrast, a single stress can affect nearly every tree at once, leaving the whole system exposed.

Dr Hannah White, Senior Lecturer in Ecology and Conservation at Anglia Ruskin University and a co-author of the study, emphasised the stakes. Forests, she noted, are vital to how the planet functions but are increasingly exposed to more frequent and intense extreme weather events as the climate changes. She explained that much of the research to date has concentrated on individual extremes such as droughts or heatwaves, whereas the new study, drawing on extensive forest survey data and satellite-derived productivity measures, shows that when these extremes occur together the consequences can be substantially more severe, reducing both a forest’s ability to withstand disturbance and its capacity to recover afterwards. Crucially, she added, forests with a greater diversity of tree species consistently performed better under these challenging conditions.

The implications extend well beyond ecology. Because biodiversity appears to govern forest stability under compound extremes, the findings have direct relevance for future carbon cycle projections, which inform climate models and the estimates of carbon sinks used in international climate policy. They also carry practical weight for forest management and restoration. Planting or preserving a mixture of native tree species, rather than relying on single-species stands, could help forests maintain their productivity and their carbon storage through the increasingly volatile decades ahead. In this sense, the study reframes biodiversity not simply as a conservation goal in its own right, but as a functional component of climate resilience, a living hedge against a future in which heat, drought and deluge increasingly arrive hand in hand.

The research, published in Nature Communications under the title Biodiversity buffers forest ecosystems from compound climate extremes, stands as one of the most comprehensive assessments to date of how interacting climate extremes affect forest ecosystems at continental scale. By demonstrating that the whole of a compound event can exceed the sum of its parts, and that tree diversity measurably softens the blow, it offers both a warning and a measure of hope. The warning is that climate risk assessments built on single events may be too optimistic for the world that is emerging. The hope is that one of the most effective defences against that world may already be growing in the world’s forests, in the quiet variety of the trees that stand there.

Subject of Research: The role of tree species diversity in forest resistance and resilience to compound climate extremes

Article Title: Tree diversity protects forests from climate extremes

Article References: Tree diversity protects forests from climate extremes. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: tree diversity, biodiversity, compound climate extremes, drought, extreme heat, forest resilience, forest resistance, carbon cycle, evapotranspiration, Nature Communications, forest productivity, climate change