Wildfire risk increases as trees reclaim eastern U.S. landscape

There are more trees and shrubs in the eastern United States than there were 30 years ago. This growth, driven by processes such as unmanaged forest trees and understory reclamation, is fueling wildfire outbreaks and contributing to changes in fire regimes in the eastern half of the country, according to a new study.

Some parts of the eastern and southeastern United States have seen a 10-fold increase in the frequency of large wildfires over the past 40 years, with the largest increases occurring in Texas and the Appalachian Mountains. However, the association between woody plant growth and large-scale wildfires was missing in the Northeast.

Wildfires occur in woody plants such as trees and shrubs. The eastern United States has seen a 37% increase in tree cover over the past 30 years, according to a new analysis of wildfire and vegetation data. In some regions, high levels of tree cover are directly associated with an increased risk of large wildfires over the same period.

The study “helps narrow down local factors and focus efforts to pre-empt the growing wildfire problem here in the eastern United States,” said the study’s lead author, a landscape ecologist at the University of Florida. said one Victoria Donovan. study.

The study is published in Geophysical Research Letters.

Research shows that growing trees in new locations and growing trees in forests is directly related to increased wildfire risk in the western and central parts of the country. However, whether this is true in the East remains to be investigated.

To test this, Donovan and graduate student Michaela Ivey looked at all the outbreaks that occurred in an area of ​​at least 200 hectares (about 500 soccer fields) in the eastern states between 1991 and 2021. Collected data on wildfires. They then looked at where trees and shrubs were growing in the eastern United States during the same time period. To determine whether tree cover affects wildfire risk, researchers compared the amount of tree cover within a wildfire boundary to the amount that would be expected if wildfires were randomly distributed. We compared.

The analysis found a strong association between wooded forests and the occurrence of large wildfires, but only in some regions of the country. In the eastern temperate forest, which covers nearly half of the United States, each 1% increase in tree cover increased the overall probability of wildfire occurrence in the following year by 3.9%. The association between forest cover and wildfire risk was strongest in eastern Texas and in and around the Appalachians.

However, researchers found no link between wooded forest cover and wildfire risk in some areas of the Northeast and the Mississippi River Valley. The finding “raises all sorts of questions about what other factors are influencing the system,” Ivey said.

In the Northeast, and to some extent the Mississippi River Basin, cooler, wetter conditions could create conditions less likely to cause wildfires. However, many of the Northeastern ecoregions could not be included in the study because there were few wildfires large enough to meet the study’s size requirements. Researchers said wildfires in these areas are likely to remain small because agriculture is fragmented.

Woody vegetation was not consistently linked to increased wildfires across the study area, so climate change, human behavior, or a combination of both may be more important for wildfires than vegetation in some locations. There is a gender. But overall, the study suggests fuel reduction is a good strategy to reduce wildfire risk in the East, Donovan said.

Southern states may need more prescribed fires, researchers warn, as climate change is expected to make the Southeast drier and more prone to wildfires. This study provides a path forward for states and individuals to reduce future wildfire risk.

“Using fuel management to reduce wildfire risk is much more doable than changing climate patterns in the short term,” Donovan said, “but in the long term, “Addressing climate change is likely to be important in reducing fire risk.”