Colorado researchers examine how soil rebuilds itself after wildfires
There’s a big, oven-sized box sitting in a lab at the Colorado School of Mines. John Spear, a professor of environmental microbiology, opens the door and puts in an ash sample from a Colorado fire before starting it up. It sounds like a plane engine, but this machine has a very different function.
“This is a scanning electron microscope,” Spear explained. “And we can see things that are very small. This microscope will magnify things 10,000 times, and we don't know what we're going to see until we put it in there.”
He’s on the hunt for microbes, tiny living things invisible to the naked eye that exist all around us and include bacteria, fungi and viruses. They're crucial to cycling nutrients to make healthy soil, allowing plants to grow — and regrow. But wildfires can burn up to 96% of them, as Colorado State University researchers have shown. This microscope allows Spear to see what cells are left.
“When you look at an image like this, you're just trying to diagnose what's in front of your eyes,” he said, looking at the ash sample magnified on his computer. “It looks like moon sand. [But] this is a whole mix of mineral, microbes, ash – stuff that came from the fire itself. And all this right here is what's making a new kind of soil.”
A window into this "new kind of soil" is increasingly important as wildfire seasons in the West stretch longer. Fires are burning hotter and covering more ground – about 7 million acres so far this year, according to data from the National Interagency Fire Center.
“When fire burns the soil, it's taking a native ecosystem and really drastically altering it,” Spear said. “It's a major disturbance.”
Spear’s team wants to understand how soil copes. By analyzing microbial survival and activity deep in the soil, he hopes to gain insights into the ways in which soil in charred ground restores itself.
“So the goal is, can we predict the outcome of a fire before it happens?” he said. “Can we predict how fast a soil will become a soil again after this drastic disturbance?”
His team started their tests back in 2016. Since then, they’ve looked at three fires in Colorado: the 416 Fire, the Decker Fire and the Marshall Fire. Their initial research was published back in June in Applied and Environmental Microbiology.
Spear said this research can help preserve soil quality as climate change bakes the Mountain West.
“Fire is with us,” Spear said. “We need to understand how that affects our whole ecosystem around us because that's going to affect our water quality, the way we can grow food and the way we can live, recreate, and be near a forest.”
Searching for microbes
To analyze the soil, Spear's team needs to collect it first. They visit burn scars about a week after a fire cools.
“We'll go in there literally with a spatula that we sterilize and we'll scoop out the soil and we'll put it in tubes and we freeze it in the field, and then we bring back and extract DNA out of it,” Spear said.
The DNA analysis is Carmen Villaruel’s job. She’s a graduate student at the Colorado School of Mines who runs tests on the soil. She starts by putting the tubes into a bead beater.
“I've already put the ash and soil in [the tubes], but they have these really tiny silica beads in them,” Villaruel explained. “We can put the soil in with a little bit of lysis solution and then agitate it. So it (the bead beater) just shakes it around to create a lot of different shearing forces to break apart different cells.”
The next step is to put the tubes in a centrifuge to separate the solid aspects of the solution from the liquid.
“So that split allows us to separate out the beads and the soil chunks and remnants,” Villaruel said. “And our DNA will be suspended in the liquid now.”
For her, this research is personal. She grew up in California and lived with the impacts of wildfires.
“I want to be involved in figuring out how we can remediate these areas after this," Villaruel said. "How are communities going to recover, especially as these fires are moving more into this wildland urban interface?”
Helping forests rebound
The research is still in the preliminary stages, but Spear has been surprised by how quickly microbes rebound, even after fires rob the soil of many nutrients.
“Even at medium and high severity, the microbes are back and working within days,” Spear said.
They're breaking down burned soil and rebuilding it. With this information, Spear’s team can use a process called statistical learning to predict how the soil will recover over time.
“Statistical learning will help you predict that X number of microbes will give you this kind of response, and the microbes can actually help you predict the chemistry of the soil, too,” Spear said. “You're really thinking about what is the carbon doing, what is the nitrogen doing in the soil.”
Michael Wilkins is another researcher who studies how wildfires affect the soil microbiome. He's an associate professor of soil and crop sciences at Colorado State University, and his work looks at what exactly the microbes are doing in the soil.
“We can look at the molecules that the microbes are producing, and that gives us an indication of which ones are actually active versus which ones are sitting there not doing anything,” Wilkins said. “We can basically reconstruct these genomes of like hundreds of different microbes and work out how they might be interacting and what processes they're carrying out.”
So far, he’s found that some of the microbes are able to grow back after fire in part because they produce spores that make them more heat resistant.
“After the fire, these little spores, they can reanimate, and the bacteria can come back from those spores structures,” Wilkins said. “So that was a key strategy that many of the microbes use to survive in these conditions.”
Trees and other plants are often seeded with different microorganisms to promote growth, and Wilkins said this research can help pinpoint which microbes are best to help landscapes affected by wildfire recover.
“If we're planting trees in these severely burned ecosystems, we could amend them with microbes that could really enhance the growth of the trees and the ability of those seedlings to survive,” Wilkins said.
But there's a lot more to forests' resilience in the face of megafires than soil microbes.
Chuck Rhoades is a biogeochemist based at the U.S. Forest Service's Rocky Mountain Research Station. His work focuses on how the whole ecosystem builds itself back and if it builds back to what would be expected in a less-disturbed forest.
“It isn't necessarily just whether or not the soil is working; it's whether the plants make it back into the site,” Rhoades said.
The ecosystem would recover and forests would regenerate on their own when the fire season was shorter and less severe, Rhoades said, but now climate change is affecting the kinds of plants these areas can support.
“Places that were formerly forest may not be forest in the future,” Rhoades said. “These severe fire seasons may send vegetation in directions that may not look like it did before, and it may take a really long time.”
When trees don't have a chance to grow back, one effect is that harmful nutrients can more easily slip through burned soil, contaminating water and increasing the chances of algae blooms.
“You can think of the trees as being sort of a filter or a sponge that keep nutrients and retain them in upland areas in the forest itself,” Rhoades said. “If we're seeing severe wildfires in those areas and those areas are not revegetating, then we should be expecting that we may have downstream consequences.”
These fires — and their impacts — aren’t going away. But Spear said his microbial research can help us adapt.
“We used to have a fire season in Colorado. Now we have yearly fire. It's fire season all of the time,” Spear said. “If we can better understand how to manage fire and manage the rebuilding process of that by understanding soil, to me, that is priceless.”
This story was produced by the Mountain West News Bureau, a collaboration between Wyoming Public Media, Nevada Public Radio, Boise State Public Radio in Idaho, KUNR in Nevada, the O'Connor Center for the Rocky Mountain West in Montana, KUNC in Colorado, KUNM in New Mexico, with support from affiliate stations across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting.