Because of climate change, forests are becoming less resilient.

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

Climate change, forests
Climate change, forests

The resilience of forests around the world to disturbances varies, but little is known about how that resilience changes over time.

Giovanni Forzieri of the University of Florence, Italy, and his colleagues used a machine learning algorithm on satellite data of global vegetation from 2000 to 2020 to calculate a resilience metric. The ability of a forest to avoid shifting states, such as becoming savannah, and to withstand perturbations, such as an influx of insect pests, was defined as resilience.

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, according to the researchers. The boreal forests that ring the globe's northern latitudes, on the other hand, experienced an increase in resilience.

According to Forzieri, the difference appears to be due to climate change, which is causing more extreme heat events and water scarcity in the first three climatic regions. While some of these negative effects are felt in boreal forests, they are outweighed by the fertilising effect of higher CO2 levels. The global picture is one of decreasing resilience, which the team describes as a "worrying" trend.

The role of climate change was discovered after using a machine learning model to estimate how different environmental factors, such as temperature and water availability, affected resilience. The degree to which the climate deviated from the norm had the greatest negative impact on resilience.

The findings are consistent with a study published last year that linked tree deaths in Europe to soil drying out, as well as recent warnings that the Amazon rainforest is nearing a tipping point.

According to Forzieri, the findings indicate that new strategies for maintaining forest health will be required. He suggests that one approach to mitigating climate change's impact on forest resilience would be to promote tree species diversity.

The study, according to Tom Crowther of ETH Zurich in Switzerland, who was not involved in the research, provides insights into the increasing vulnerability of biodiversity hotspots in warm, dry regions of the Earth. "As we move into a warmer, drier world, these forest resilience trajectories are likely to erode the ecological integrity of these ecosystems, limiting their capacity to capture carbon," he says.

More data will be required to confirm the findings. "One challenge with satellite data studies is that the period of observation is limited," says Martin Sullivan of Manchester Metropolitan University in the United Kingdom. "While 20 years of data allow for the assessment of changes, it is still a relatively short timeframe for detecting shifts [in resilience]."

Reference: Nature, DOI: 10.1038/s41586-022-04959-9


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