The increasing severity and frequency of wildfires pose a significant threat to our ecosystems and the recovery of our burned lands. However, amidst the devastation is a glimmer of hope in the form of microbes. Recent research conducted by scientists at the University of California Riverside (UCR) has discovered the remarkable resilience of these tiny organisms in landscapes affected by wildfires. This discovery has the potential to help revive scorched land after catastrophic wildfires.
In August 2018, the Holy Fire in California consumed 23,136 acres of land around Cleveland National Forest, located near Orange and Riverside counties. The fire allegedly started as an act of arson and quickly spread, fueled by hot temperatures, dry vegetation, and strong winds. After a month, the fire was fully contained, but only after the vast destruction of wilderness and multiple buildings.
When wildfires destroy an area, leaving nothing behind but charred land, the possibility of life emerging from the area seems unlikely. However, some fungi and bacteria have been known to thrive in fire-affected environments. Pyrophilous microbes are specialized bacteria and fungi that thrive in environments following a burn.
In an effort to understand the long-term impact of the fire on bacteria and fungi, a team of researchers led by UCR mycologist Sydney Glassman visited the Holy Fire burn scar several times. By sampling the soil nine times over the course of a year, they investigated bacterial and fungal biomass, richness, and composition using advanced sequencing techniques. They compared the burnt soil to soil samples from nearby unburned areas. These findings have since been published by UCR researchers in the Journal of Molecular Ecology.
According to the study, the wildfire severely impacted the microbial communities. Bacterial biomass decreased by 47%, and bacterial richness went down by 46%. Furthermore, fungal biomass declined by 86%, and fungal richness dropped by 68% (1). Biomass refers to the total amount of bacterial or fungal cells in a sample in order to measure the number of microorganisms in an environment. On the other hand, richness is the density of bacterial species within a sample, representing the variety of taxa present within an ecosystem. These two markers are an important measure of ecosystem health, biodiversity, and stability. The microbial losses did not recover during the first year. Despite these changes, however, the burned soil underwent rapid succession as different microbial communities took turns dominating the post-fire environment.
These microbes, which have adapted to withstand fire, played a crucial role in these dynamics. “Certain species increased in abundance, and in fact, there were really rapid changes in abundance over time in the burned soils” said Glassman, while “There were no changes at all in the unburned soils.”
Initially, the scientists found microbes that could withstand high temperatures. Yet, as time passed, fast-growing organisms with abundant spores began to emerge and take advantage of the available space with limited competition from other microbes. By the end of the year, a shift occurred in the dominant organisms present in the soil. The microbes that thrived on a diet of charcoal and nitrogen-rich debris left by the fire took over. Then, a particular group of microbes called methanotrophs emerged and started consuming methane, a greenhouse gas that contributes to climate change.
Fabiola Pulido-Chavez, a Ph.D. candidate in plant pathology and the study’s lead author, observed that the genes associated with methane metabolism were twice as active following the wildfire. She notes that this discovery indicates that these particular microbes are capable of consuming methane as a source of carbon and energy, which could decrease the levels of greenhouse gasses in the atmosphere.
Further tests are being conducted to determine if the microbes were able to thrive during different periods of time due to their individual characteristics or something entirely separate. The study also revealed the indirect effects of wildfires on microbial succession. The severity of the soil burns and changes in soil moisture were found to influence the post-fire microbial communities. Bacteria typically demonstrated a rapid response to changes in soil moisture, while fungi were less responsive. The research also emphasized the importance of taking more frequent and precise samples over time to accurately understand how bacterial and fungal communities change and develop following a wildfire.
The changes observed in the soil can be compared to how the human body reacts to major stress. When people get sick and take antibiotics, the medicine destroys the bacteria in their gut, which allows new organisms to emerge that were less abundant in the past or not previously there. There is no guarantee that the gut bacteria will completely return to its original state after the infection is gone. To get the land back to its original condition, scientists must understand post-fire microbe behavior, which reacts similarly to the setting of a human microbiome.
Scientists have been studying how plants adapt to wildfires for about a century, gaining valuable knowledge about the mechanisms plants employ in order to recover from fire events. Now, this current research suggests that fungi and bacteria may have similar strategies for dealing with fires.
“This recent progress is truly exciting as it signifies the technological advancements made in the past few decades, enabling us to unravel the intricate workings of soil microbes and their invaluable contributions to the process of regeneration,” Glassman expressed.
Microbe behavior has been overlooked in relation to plants, but as new discoveries continue to unravel, scientists may reconsider their previous ideas about post-fire plant behavior.
Scientists are still trying to determine whether the ability of plants and microbes to cope with wildfires will adjust to the increasing occurrence of recurring fires. In the past, an area of land would experience a burn once every several decades, but now it is becoming more frequent for the same regions to endure multiple burns within the span of fewer than ten years. At this rate, these plants and microbes that were once able to survive fires may face new challenges as the frequency and intensity of wildfires escalate. The interactions between plants and microbes in post-fire environments are crucial for the health and recovery of the affected ecosystem. Climate change is leading to an increased vulnerability to wildfires, particularly in the West. Rising temperatures lead to earlier snow melt and a longer dry season, leading to more intense fire seasons. These more severe fires may leave behind more extensive damage, making it more challenging for ecosystems to recover fully. Understanding the impacts of these changes on burn areas is essential for land conservation strategies.
Although scientists are still determining whether or not land will fully recover after recurring wildfires, these discoveries can help them predict how ecosystems will recover from these increasingly common disturbances in the face of climate change. By understanding the dynamics of microbial succession, scientists can learn more about the recovery process and improve how we manage and restore ecosystems affected by wildfires.
This article was originally published on June 22, 2023.