Dr Adam Pellegrini, Newnham College Lecturer and expert in forest ecosystems and climate change, has shown how extreme fires are reducing forests’ ability to store carbon.
Dr Pellegrini and his colleagues analysed decades’ worth of data on the impact of repeated fires on ecosystems across the world. Their results, published in the journal Nature Ecology and Evolution, show that repeated fires are driving long-term changes to tree communities and reducing their population sizes.
Wildfires are playing an increasingly important role in global carbon emissions. Fire burns five percent of the Earth’s surface every year, releasing carbon dioxide into the atmosphere equivalent to 20% of our annual fossil fuel emissions.
In the past, the majority of carbon released by wildfires was recaptured as ecosystems regenerated. But the more frequent fires of recent years, driven by changes in climate and land use, don’t always allow time for this.
“As fire frequency and intensity increases because of climate change, the structure and functioning of forest ecosystems are going to change in so many ways because of changes in tree composition,” said Dr Pellegrini. “More fire-tolerant tree species are generally slower growing, reducing the productivity of the forest. As climate change causes wildfires to become more intense and droughts more severe, it could hamper the ability of forests to recover – reducing their capacity for carbon storage.”
Savannah ecosystems, and regions with extreme wet or dry seasons were found to be the most sensitive to changes in fire frequency. These effects only emerge over the course of several decades: the effect of a single fire is very different from repeated burning over time. The study found that after 50 years, regions with the most extreme annual fires had 72% lower wood area – a surrogate for biomass – with 63% fewer individual trees than in regions that never burned. Such changes to the tree community can reduce the forest’s long-term ability to store carbon, but may buffer the effect of future fires.
“Planting trees in areas where trees grow rapidly is widely promoted as a way to mitigate climate change. But to be sustainable, plans must consider the possibility of changes in fire frequency and intensity over the longer term,” said Dr Pellegrini. “Our study shows that although wetter regions are better for tree growth, they’re also more vulnerable to fire. That will influence the areas we should manage to try and mitigate climate change.”
Meanwhile, Newnham’s own Global Tree Planting Project, part of our 150th Anniversary celebrations, recognises the importance of urban trees. While our 150 trees will not, of course, counter climate change, each one will play an important role in improving quality of life for those living nearby.
This research was funded by the USDA National Institute of Food and Agriculture, and the Gordon and Betty Moore Foundation.
Pellegrini, A.F.A. et al: ‘Decadal changes in fire frequencies shift tree communities and functional traits.’ Nature Ecology & Evolution, February 2021. DOI: 10.1038/s41559-021-01401-7
Based on an article by Jacqueline Garget