The eastern part of the United States is seeing a rise in the number of trees and shrubs compared to thirty years ago. This increase, primarily due to tree growth and the filling in of understory in forests that are not being actively managed, is contributing to more wildfires and altering fire patterns in this region, as highlighted by a recent study.
The eastern U.S. has more trees and shrubs than three decades ago. This growth, driven by processes such as tree and understory infilling in unmanaged forests, is helping fuel wildfires, contributing to changing fire regimes in the eastern half of the country, according to a new study.
Over the last forty years, certain areas in the eastern and southeastern U.S. have seen an increase in large wildfires by as much as ten times, with Texas and the Appalachian region experiencing the most significant rises. However, the Northeast does not show a direct relationship between increases in woody plant growth and large wildfires.
Wildfires are fueled by woody plants like trees and shrubs. Recent analysis of wildfire and vegetation data indicates that there has been a 37% rise in woody cover in the eastern U.S. over the past thirty years. In specific areas, a substantial amount of woody cover directly corresponds with a greater likelihood of large wildfires during the same timeframe.
The research “is helping us narrow in on regional drivers and focus our efforts to preemptively get ahead of the growing wildfire problem here in the eastern U.S.,” said Victoria Donovan, a landscape ecologist from the University of Florida and the lead researcher on the study.
This study was published in Geophysical Research Letters, a well-regarded open-access journal from the AGU that features significant short articles across all fields of Earth and space sciences.
Previous research has established a connection between increased woody cover in new areas or denser forests and a rise in wildfire risk in the western and central U.S. However, it remained unclear whether this also held true for the Eastern regions.
To investigate this, Donovan and graduate student Michaella Ivey gathered data on wildfires that were at least 200 hectares (roughly equivalent to 500 football fields) in size from 1991 to 2021 in eastern states. They then examined the growth of trees and shrubs in those areas over the same period. To understand the impact of woody cover on wildfire risk, the researchers compared the amount of woody cover found within wildfire boundaries to a hypothetical random distribution of wildfires.
The findings revealed a significant correlation between woody cover and large wildfire incidents, though this was limited to certain regions. Throughout the eastern temperate forest, which accounts for nearly half of the United States, each 1% augmentation in woody cover raised the likelihood of a wildfire occurring the following year by 3.9%. The strongest connection between woody cover and wildfire risk was identified in eastern Texas and near the Appalachian Mountains.
Conversely, no relationship was found between woody cover and wildfire risk in the Northeast and various areas of the Mississippi River valley. This observation “raises many questions regarding what other factors might be affecting the wildfire dynamics,” Ivey explained.
Cooler and wetter climates in the Northeast, and to some extent the Mississippi River valley, might foster conditions that are less favorable for wildfires. However, many areas in the Northeast were excluded from analysis due to a scarcity of large wildfires meeting the study’s criteria. Researchers suggested that small wildfires in these regions might be a result of agricultural fragmentation.
Due to the inconsistent link between woody vegetation and wildfire occurrences across the study areas, it is possible that climate change, human activities, or a mix of both have a more significant influence on wildfire risks than vegetation in certain locations. Nevertheless, overall, the study indicates that strategies to reduce fuel loads could effectively lower wildfire risk in the east, according to Donovan.
With climate change expected to make southern states drier and potentially increase wildfire susceptibility, more controlled burns may be needed, as cautioned by the researchers. This research offers a pathway for states and individuals to mitigate future wildfire risks.
“Utilizing fuel management to decrease wildfire risk is far more feasible than altering climate patterns in the short term,” Donovan stated, “although addressing climate change will likely be essential for reducing wildfire risk in the eastern U.S. over the long run.”
