Low- and moderate-intensity forest wildfires can lessen the severity of future fires, according to new findings on ‘reburns.’
Not all forest fires lead to catastrophic outcomes. Research from the University of California, Davis indicates that low- and moderate-severity wildfires can decrease the intensity of future fires for up to 20 years in specific climates.
The degree to which these second fires, known as reburns, are less severe, and how long this effect lasts, depends on various factors, including climate and forest type. Notably, initial fires continue to reduce future risks even during harsh weather conditions, such as strong winds, high temperatures, and drought, as stated in a study published in the journal Ecological Applications.
The researchers utilized satellite remote sensing technology to analyze over 700 reburns from the last 50 years across the western United States. Their results highlight the beneficial impact of some wildfires on forest resilience, which could guide land managers in focusing their risk reduction strategies amid climate change.
According to lead author Claire Tortorelli, an ecologist at the U.S. Forest Service who conducted the research as a postdoctoral scholar at UC Davis, “We’re in a period of increasing wildfires, which creates challenges for both communities and landscapes. Previous wildfires can influence how future fires behave. Therefore, it’s crucial to grasp the effects past wildfires will have going forward.”
A knowledge gap
Much of the existing research has concentrated on high-severity fires, leaving a gap in understanding about less intense fires that preserve the majority of the tree canopy. Tortorelli and her team aimed to gain insights into the aftermath of these low- and moderate-severity fires.
In addition to analyzing remote sensing data, they assessed the severity of both the initial and follow-up fires while considering factors like weather, forest type, and climate. They modeled the severity of reburns to evaluate the duration and magnitude of the initial fire’s impact on subsequent fuels and risks under varying conditions.
The study found that coastal forests in California and those in the Southwest exhibit longer-lasting effects compared to forests in the Sierra and Cascades.
“It all comes down to the type of vegetation and fuels that regenerate post-fire,” Tortorelli explained. “We still require a deeper understanding of local fuels so that managers can determine how their specific environments will react in future fires or how soon they should return for treatment.”
The reduced fire severity can persist for as long as 20 years in certain ecosystems, though this effect diminishes over time. Subsequent measures, such as prescribed burns or mechanical thinning, can help extend the benefits achieved by the initial fire in terms of reducing fuels and the risk of future fires.
“We can use low-severity fires as a preliminary fuel reduction strategy,” Tortorelli mentioned. “While they won’t carry the entire workload, when combined with management actions, they can significantly aid in the initial phase.”
Widespread effect
The reburn effect can be extensive, even in regions prone to high-severity wildfires, since many of those fires also include patches that burn at low to moderate levels, noted Andrew Latimer, a co-author and professor in the Department of Plant Sciences who co-supervised Tortorelli’s research.
“When you tally up the total area affected, it far surpasses what we’ve been able to treat through mechanical thinning and prescribed burns, making it the most significant form of fuel reduction occurring,” Latimer stated. “This presents an opportunity to maintain forest health.”
Derek Young in the Department of Plant Sciences also co-supervised the research, which received support from the University of California National Lab Fees Research Program.
