With 90-mile-per-hour winds blowing across the UK and Europe this week, new research shows that forests containing a variety of tree species are more likely to survive than monocultures when hit by extreme weather.
Simulations created by the researchers revealed that forests with two or three tree species were on average 35% more resilient to storms than forests with a single species. The type of trees is also important; Forestry plantations often consist of fast-growing tall trees such as conifers, but they are more vulnerable to high winds than slower-growing hardwood species such as oaks.
Extreme weather events such as Storm Isha, which caused deaths, power outages and floods across the UK, are likely to occur more frequently as the climate crisis continues because hot air holds more moisture, fueling storms. Tree destruction during storms is becoming an increasing problem for foresters; In 2021, winter storms destroyed nearly 12,000 hectares (30,000 acres) of forest in Britain.
Principal investigator Dr. from the French National Research Institute for Agriculture, Food and Environment (Inrae). “Monocultures of fast-growing species such as pine, although economically valuable, are more susceptible to storm damage,” said Julien Barrere. “In the context of increasing storm losses across the continent, our study therefore advocates for forest management practices that support diversity and slow-growing tree species,” he said.
The benefits of greater tree diversity were even more pronounced under extreme conditions, such as hot, dry Mediterranean regions and cold parts of northern Scandinavia, according to the paper published Thursday in the journal Functional Ecology.
Researchers created simulations based on data from more than 90,000 real forest sites across Europe to study how they resist and recover from extreme weather events. They say field work is still needed to support the findings. Barrere said: “These are scientific conclusions, not practical recommendations.”
But their simulations support conservationists’ observations in November 2021, when Storm Arwen felled millions of trees and 100-mph winds devastated conifer plantations. Experts at the time said most of the fallen trees were single-species, single-growth conifer plantations that were more vulnerable to storms than native, mixed woodlands.
“The findings are exactly as expected,” said Professor Martin Lukac from the University of Reading, who was not involved in the research. “Trees growing in a mixture not only produce more biomass, but the forests they create are better able to weather the effects of adverse factors, including windstorms.
“We need to plant trees in mixtures, just like the old saying about don’t put all your eggs in one basket. Most natural forests grow in mixtures and are clearly better able to tolerate disturbance than monocultures.
Environmentalists and foresters are working on how to reduce damage when the next storm hits. The National Trust is moving towards more natural tree management. Old oaks, for example, lower their branches as they age to increase their stability, and conservationists hope to leave as many of those branches as possible rather than cutting them down. Storms can also increase forest diversity by increasing the amount of wildlife-rich dead trees and creating more diversity in fields.
“This study seems very timely given the recent weather in the UK,” said Prof John MacKay from the University of Oxford, who was not involved in the research. “It is important to keep in mind that action can be taken now to diversify the structure of forests, but it will take many years, even decades, to provide benefits, given the time it takes for trees to establish and develop,” he said. “It seems crucial to take action in the short term for their future.”
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Previous research has shown that species diversity has other benefits, including greater resistance to drought as well as increased pests and diseases. Kevin Martin, head of tree collections at the Royal Botanic Gardens at Kew in London, says he wants to plant species that can cope with the conditions predicted for the coming decades and beyond.
He said Kew’s research showed “the importance of genetic and species diversity of tree landscapes for urban forests, not only for building climate resilience but also for ensuring resistance to pests and diseases – another growing threat.”
“So it’s vital that we use findings like this and plant the right tree in the right place,” Martin said. “Without this, we run the risk of creating landscapes that will quickly fail.”
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