Forests are becoming less resilient because of climate change

An analysis of two decades of satellite data shows that forests in arid, tropical and temperate regions are becoming less able to bounce back after events such as drought and logging

By Adam Vaughan

Climate change has been linked with a widespread decline in the ability of many of the world’s forests to bounce back after events such as drought and logging.

Forests around the world differ in their resilience to disturbances, but relatively little is known about how that resilience is changing over time.

To tease out any shifts, Giovanni Forzieri at the University of Florence, Italy, and his colleagues ran a machine learning algorithm on satellite data of global vegetation from 2000 to 2020 to calculate a metric of resilience. Resilience was defined by a forest’s ability to avoid shifting state, such as becoming savannah, and withstand perturbations, such as an influx of insect pests.

The researchers found that more than half of forests in arid, tropical and temperate regions – where the majority of the world’s trees are found – showed a significant decrease in resilience over the two decades. By contrast, the boreal forests ringing the globe’s northern latitudes saw an increase in resilience.

Forzieri says the difference appears to be down to climate change causing more extreme heat events and water shortages in the first three climatic regions. While some of those negative impacts are also felt in the boreal forests, they are outweighed by the fertilising effect of higher carbon dioxide levels there. Overall, the global picture is one of decreasing resilience, which the team says is a “worrying” trajectory.

The role of climate change emerged from using a machine learning model to estimate how much different environment factors – such as temperature and water availability – changed resilience. How much the climate varied from the average had the biggest negative effect on resilience.

The research chimes with a study last year that linked tree deaths in Europe to soils drying out, and recent warnings that the Amazon rainforest is approaching a tipping point.

Forzieri says the findings mean we will need new strategies for how to keep forests healthy. He suggests one approach to mitigate climate change’s impact on forest resilience would be to promote diversity of tree species.

Tom Crowther at ETH Zurich in Switzerland, who wasn’t involved in the research, says the study provides insights into the increasing vulnerability of biodiversity hotspots in warm, dry regions of Earth. “As we move into a warmer, drier world, these trajectories of forest resilience are likely to weaken the ecological integrity of these ecosystems, limiting their capacity to capture carbon,” he says.

Still, more data will be needed to firm up the findings. “A challenge with studies using satellite data is that the period of observation is limited,” says Martin Sullivan at Manchester Metropolitan University in the UK. “While 20 years of data mean changes can start to be assessed, it is still quite a short timeframe for detecting shifts [in resilience].”

Journal reference: Nature, DOI: 10.1038/s41586-022-04959-9

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