UC Riverside researchers have discovered tiny organisms that not only survive, but thrive in the first year after a fire. The discoveries could help extinguish the flames, which are gaining in size and intensity, and revitalize the landscape.
The Holy Fire burned more than 23,000 acres in Orange and Riverside counties in 2018. In an effort to understand how the fire affected bacteria and fungi over time, UCR mycologist Sydney Glassman led a team of researchers into the burn scar. “When we first entered the fire, I had ash up to my shins. It was a very heavy fire,” Glassman said.
The researchers visited the scar nine times over the next year and compared the burned earth with samples from nearby unburned soil. Their findings, now published in the journal Molecular Ecology, show that the total mass of microbes dropped by 50 to 80% after the fire and did not recover during the first year.
However, some things lived. “Some species increased in abundance, and there were actually really rapid changes in abundance over time in the burned soils,” Glassman said. “There was no change at all in the unburned soils.”
It wasn’t just one type of bacteria or fungus that survived. Rather, it was a parade of microbes that took turns dominating the burned soil in the first year after the fire. “There have been interesting, distinct shifts in microbes over time.” As one species declined, another emerged,” Glassman said.
In the early days, they found microbes with a high tolerance to fire and high heat. Later, fast-growing, spore-rich organisms—capable of exploiting space with little microbial competition—appeared to dominate. Towards the end of the year, organisms capable of consuming charcoal and other high-nitrogen post-fire debris tended to dominate.
Certain microbes called methanotrophs regulate the breakdown of methane, a greenhouse gas. Fabiola Pulido-Chavez, a UCR plant pathology doctoral candidate and first author of the study, noticed that genes involved in methane metabolism doubled in the microbes after the fire.
“This exciting finding suggests that post-fire microbes can ‘eat’ methane for carbon and energy, potentially helping us reduce greenhouse gases,” said Pulido-Chavez.
The researchers are continuing to test whether the fungi and bacteria they found were able to thrive at different points in time due to their unique and diverse properties, or if there is another reason for the shifts they saw in the soil.
“We think that one organism cannot be good at all the skills necessary to thrive in a burn scar,” Glassman said. “If you’re good at heat tolerance, you’re probably not that good at growing fast.”
What the scientists saw in the soil bears some resemblance to the human body’s response to great stress. People are sick and taking antibiotics. The drug destroys the bacteria in a person’s intestines and new organisms begin to appear that were either not there before or were not present in large numbers before.
Eventually, a person’s gut bacteria can return to their pre-infection state, but there is no guarantee.
“We’re also trying to understand what got the land back to where it was before the disturbance, which in this case was a huge fire,” Glassman said. “Much of what we study could be transferred to the human microbiome environment.”
For a century, scientists have known about the ways in which plants can adapt to wildfires and eventually recolonize the burn scar. As this new research shows, fungi and bacteria may have evolved similar coping strategies.
“It’s exciting because we’ve only developed this technology in the last few decades to really understand what microbes are doing in the soil and how they contribute to regeneration,” Glassman said.
What we are now learning about the behavior of microbes after a fire could change older theories about plant behavior because microbes were not included in them. “To me, this is exciting because microbes have been overlooked for a long time, yet they are essential to ecosystem health,” Pulido-Chavez said.
One open question that remains is whether the adaptations that plants and microbes have evolved in response to wildfires will readapt to megafires or recurrent fires. While it may take several decades for a piece of land to burn more than once, it is increasingly common for the same land to burn again in less than 10 years.
In the West in particular, climate change is causing rising temperatures and earlier snowmelt, extending the dry season when forests are most vulnerable to burning. What does an increase in fire size, severity, and frequency do to natural burn recovery?
“Things can recover, but it takes time, and whether or not the country recovers from super-frequent megafires is another story. Can recovery time keep up with megafires? We don’t know that yet,” Glassman said.
