Episode 105: How does soil recover after a wildfire?

John Spear: 

Soils are complex, and how they recover from a drastic event like wildfire is equally as complex, but also surprisingly resilient. It is amazing how much change there is from burn day zero to one year later. You see this macroscopically when you have green plants and small trees, but the soil is really showing that change quickly, and how we rely on that resiliency to regrow a burn zone, that’s a huge thing for me.  

I’m John Spear, I’m a professor of civil and environmental engineering here at the Colorado School of Mines. 

The Conveyor: 

You’re listening to The Conveyor, the podcast that brings you the latest research, new discoveries and world–changing ideas from Colorado School of Mines. 

The Conveyor: 

One of your current projects is studying the microbiomes in geochemistry across burn sites. How did you get started on this research? 

John Spear: 

So we got into this work because of a graduate student who’s working with me, Alex Honeyman. Alex’s father, Bruce Honeyman, was one of my PhD co-advisors, and they lost their house in the Fourmile Canyon Fire in 2010. So Alex has a passion for fire. He’s also a red card wild land firefighter, which means he can go out and fight wildfires in different places, and he had this idea to start thinking about how soils redevelop or reclaim or reform after a wildfire. He got a national science foundation graduate research fellowship funded to do this work, and we got into this work about four years ago. It’s a really fun thing to think about, because there’s not a lot known about it.   

John Spear: 

When we see a fire, we think about forests, we think about the bunnies and the deer and the elk and everything that’s on that. We don’t think about water quality subsequent to the burn and how ash might affect water quality that we depend on living here in the state drinking water, of course. So all these things are connected, but not a lot is known about how soil reforms after a wildfire. So I like to put it in the context of, I need you to think about your body. So your body is composed of many organs, and I would argue that every one of those organs is important. One of the most important ones of course, is the largest organ in your body, which is your skin, and skin is critical for maintaining you. It’s your interface with the world at every level, temperature, pain, pressure, feel, all of that. And the earth has a skin too. Every terrestrial surface on Earth has soil, and forever for human history, we have treated that soil poorly, and burn severity is a critical thing—it affects us.  

John Spear: 

You can have a superficial first degree burn on your skin—that’s a sunburn. You can have a second–degree partial thickness burn, which gets into the lower layers of your skin, and that’s going to blister up and ooze. You don’t really want that. And you can have the worst, which would be a full thickness third–degree burn, where it’s going to take a lot of time, pressure, think about how you’re going to heal that portion of your body that has burned. So wildfire is the exact same thing. You can have a superficial low–severity burn, you can have a moderate–severity burn and you can have a high–severity burn. Why I put this in the context of your body is if you can think about those three different burn stages, if you want to get that soil to come back, it’s not too hard to come back from a superficial burn, a low–severity burn. If it’s a full burn and the ash layer is a foot deep, the topsoil is supposedly ruined, and I use that word ruined cautiously, because you could say, is it ruined or how can it rebuild and reclaim and come back? 

The Conveyor: 

I like that analogy. Each type of burn has its specific need and way to heal.  

John Spear: 

This is 100 percent correct. 

The Conveyor: 

So what does the research exactly look like when studying microbiome recovery?  

John Spear: 

So what we like to do is we like to look at a control soil that’s near the burn site, and we’d like to understand what’s in that soil. And to do that, we ask the classic scientific questions of who, what, when, where, why and how? We ask those questions by obtaining a soil sample, and we’ll extract the DNA and RNA out of the soil. The DNA and RNA are coming from microbes that live in the soil—it’s amazing how much life there is in a typical healthy soil. There are about a billion cells in a gram of soil, and that’s the stuff that makes the soil smell good. It’s the biology of the soil that makes it thrive, and we want to understand how that’s thriving. 

John Spear: 

So we’ll extract DNA and RNA, and we’re trying to determine what kinds of organisms are living in that healthy soil. So that’s great to do on a control site, on the edge of a burn, then we’ll ask the same questions and do the exact same methods going up into the burn, and then we’re looking at what’s on top of the ash, what’s in the middle of the ash, what’s below the ash, and we’re thinking about who’s there, what are they doing, how are they doing it? We can ask those questions and come back the following year and ask the same question at the same sites and start seeing variants and difference. 

The Conveyor: 

How do you collect the soil? What sort of technologies? I know you’re not going out there with a spoon. 

John Spear: 

I laugh because I could say that we’re not going out there with a spoon, but in fact, we are. What we’ll do is we go out there with a shovel, and we’ll flame sterilize the shovel. So we don’t want to sample what’s on the shovel from whatever I just picked up with the shovel prior. So you can sterilize the shovel, you can scoop at the soil, you can dig down into the ash layers and then you go in there with a little spatula or a little spoon. You flame sterilize that and you go in there and you’re aseptically collecting something so that it’s sterile up until the point of collection. Is it sterile in the environment? No, but we’re trying to understand the environment at the point of collection without introducing other DNA or RNA into that sample. So we’ll sample that, put it into a sterile tube and then we’ll bring it back to the lab where we’ll do DNA, RNA extraction, geochemical characterization. So yes, the spoon is a very effective scientific collection device, and it works great. 

The Conveyor: 

As you gain a better understanding of soil recovery, how is this research going to impact say firefighters in the future?  

John Spear: 

So I think what’s going to be great about this work and what’s coming out from it already is that firefighters are going to start understanding that skin layer of the earth in a new level where they’re going to understand how that thing that’s growing a forest and feeding elk is alive, and it’s alive that extends down into the subsurface. It’s important for firefighters to understand that, because I think they can fight a fire better if they’re starting to think about, oh man, my arm’s on fire versus, oh man, my head’s on fire. 

John Spear: 

So if you put it into that body context again, you can start thinking about what’s the most effective way to fight that fire, and when you think about how the body or the forest is going to recover from that fire, gives you a new perspective on how you’re going to fight that fire. That happens with the firefighter on the ground, trying to think about I’m going to let that log burn and I’m not going to let that one burn. That’s a decision that can be made, at the square–foot scale by the person on the ground, and I think this information for how a soil microbiome recovers is really going to help the firefighter on the ground. 

The Conveyor: 

Okay, so it can bring a greater training and awareness on an almost tactical level? 

John Spear: 

Exactly and you can think about it, so a doctor that’s going to do surgery on your body has a whole lot of knowledge and tactical knowledge. A firefighter is doing the same thing—they’re going to have a whole other level of knowledge to understand how can I fight that fire in a more effective way? How can I perform a better surgery on this patient? I think there’s going to be a great power to that. We’re going to have not only new technology, but new knowledge that’s going to allow us to fight fires in new ways, and that on–the–ground control and understanding is going to help that. 

The Conveyor: 

Thanks for listening to The Conveyor, to learn more about civil and environmental engineering here at the Colorado School of Mines and our graduate program, visit mines.edu/ceegrad, and join us back here for our next episode.