AoR 147: Wildfire Depletes Ecosystem Carbon Storage by >50% (Part 1) -- Germino, Maxwell, & Quicke

>> Welcome to the Art of Range, a podcast focused on rangelands and the people who manage them. I'm your host, Tip Hudson, range and livestock specialist with Washington State University Extension. The goal of this podcast is education and conservation through conversation. Find us online at artofrange.com. Welcome to Part 1 of an important two-part episode series on Soil Carbon Change in Response to Fire and Exotic Annual Grass Invasion. My guests today on the show are Matt Germino, Toby Maxwell, and Harry Quicke. Matt is a US Geological Survey rangeland scientist in Boise who will be familiar to longtime listeners. Toby is an ecosystem biochemist, or at least he was when he was still with Boise State University. He's now with USGS. I like that. That's a new word combination for me and I like it. Harry is a scientist. Harry Quicke is a scientist with Environmental Science US, otherwise known as ENVU. And these three recently jointly published a fascinating paper in Communications Earth & Environment titled Annual grass invasions and wildfire deplete ecosystem carbon storage by greater than 50% to resistant base levels. That's a big statement with a couple of provocative concepts such as resistant base levels of carbon, which I had not run across before either. I love that the paper's title is not cagey or evasive or vague. It just lays it out and invites the reader to read more. So, we're here to talk about these significant findings. And at least having read the paper, I think they're significant and the authors believe they're significant which doesn't happen with every study. And they're prepared, I think, to convince listeners that these are findings that matter. So, Matt, Toby and Harry, welcome.

>> Thank you. It's a delight to be back on your show.

>> Yeah, thanks for having us.

>> Yeah, thank you, Tip.

>> Since at least Toby and Harry are new, why don't we spend just a couple of minutes describing what your background is? As I've said before, there are not that many people in the world involved in rangeland science, although I think that's growing and that's encouraging. But I'd love to hear about what your background is and how you came to be doing some significant research in the world of rangelands and soils and carbons. Toby, why don't we start with you?

>> Sure. Yeah. So, my background is originally in chemistry and then biogeochemistry which I took up as a graduate student at University of California, Davis studying forested ecosystems. But like many folks, I found myself drawn to the drylands and connected with Matt Germino after a postdoc. And he was an impactful mentor, helping me to achieve another career goal which was to really dive into management and applied science. And so, I moved from forests to drylands and was able to connect with the US Geological Survey and Matt to help fulfill that desire to get really down into science that was being directly applied and conceived with managers.

>> Yeah, I love that. Harry, where do you live and what's your background?

>> Well, I'm the North American Development Lead for Vegetation Management Solutions. I work for a company called ENVU. Our company is very focused on advancing healthy environments and being a force with nature. I have prior experience managing tree plantations, followed by an academic career and more recently an industrial career. My current focus is on restoration of Western rangelands which led to this collaboration with the USGS and Matt and Toby.

>> This study is intriguing to me because it pulls together several big ideas. And by big, I mean, as everyone knows, big idea with a capital B and a capital I. Exotic annual grass invasions are a big deal in the Western US. Soil carbon is a big deal and is getting more and more attention. How wildfire affects all of those things is a really big deal. And this pulls together a lot of that. Where did the idea for the study come from?

>> Well, we've worked for many years, actually decades, on ecosystem carbon in general because ecosystem carbon is a fundamental component of the structure and function of ecosystems. And by understanding it, we can understand how the whole ecosystem is working. And it literally integrates just about everything we care about in rangeland ecosystems. But the real motivation for us to make such a large investment into answering these questions actually came from Harry, from industry. So, they work a lot with many different types of stakeholders of rangelands. And he was really passionate in promoting the idea that we really need to understand how these widespread impacts of fire and invasives are controlling carbon sequestration because of its societal and policy importance. And so, he actually provided a small amount of funding for us to go after the question and the more data that we acquired and with each little bit of finding that we had, we realized that we were on to a compelling problem. And so, we've gone after it with a much more aggressive, robust effort.

>> Yeah. And from my side, I was involved in a science fellows panel looking at how the company could become more invested in solutions to environmental problems with a focus on carbon. And a lot of the discussion was around agriculture and annual crops where we have, you know, proven systems such as cover crops and no-till. But then, there's also a lot of discussion about, you know, frontier technologies, you know, for example, growing perennial grain crops and so on. And all of that would be a huge technological lift. And we knew at the time that we had these rangelands that were converting to annual grass systems. And so, it became really interesting for us to investigate the topic of how avoiding that conversion to annual grass systems would impact soil carbon. And that led us to this collaboration with Matt and Toby.

>> Yeah, I love that. It is a number of big questions right now around soil carbon. And maybe the place to jump in here, I'm kind of scanning my notes trying to figure out what's a good starting point. The beginning of our outline says introduction to soil carbon and it's important to rangelands. But I think one of the questions behind that is that there's some skepticism about whether we understand soil carbon changes well enough to build markets around it. Some of us are hopeful that carbon as almost a proxy for ecosystem health could be a way of compensating landowners for the provision of ecosystem goods and services. Ranchers are skeptical of whether that's a viable model, whether it will hold out, you know, whether we're going to push all of this. And then 15 years down the road, you know, we have new scientific discoveries that proves that all of that was a load of hooey and we were off base. So, there's a lot of momentum in different directions, a lot of skepticism about, you know, current efforts with carbon markets. And of course, you know, I feel like one of the main things is that independent of whether or not climate is changing in response to things like soil carbon release or sequestration, I'm prone to believe that soil carbon matters just because soil matters and we want to hang on to it and keep it as healthy as possible. So, there's a lot of pieces there. But you may have your own ideas on why soil carbon is important to rangelands. And maybe I've already said too much about, you know, what my thoughts are. But what are your ideas on why is soil carbon important in rangelands?

>> Well, for me, understanding how carbon flows into the ecosystem and how it's retained is pretty important. So obviously, photosynthesis brings carbon into the ecosystem and understanding how different plant species, particularly ones that are prone to change, is really valuable. So, for example, in cold desert sagebrush landscapes, we're losing our evergreen component. In other words, those species that can do photosynthesis just about year-round, like sagebrush. And also, those are species that are deep-rooted and their photosynthetic activity tends to be more enduring throughout the year, during summer or drought, for example. And so, what happens when we lose them? Well, we're replacing them with shallower rooted species that tend to be more ephemeral. In other words, a much shorter period for photosynthesis each year. We have exotic forbs which can be deeper rooted and they also are changing things. Furthermore, these species all differ in how quickly the carbon in their litter and their detritus will turn over and contribute to soil carbon. So, you know, that's the starting point for me. And carbon sequestration is definitely interesting. And of course, it's of societal value. But to me, soil carbon means so much more. You know, let's start with the point that carbon is incredibly scarce in these landscapes. First of all, it's actually not a huge component of air. Only four parts per thousand of air is carbon. So, very, very small and very, very scarce, right? And soil carbon is typically somewhere between 1 to maybe 4 or 5% at most in rangelands, which also doesn't seem like much. But when you scale that up to think about the vast extent of rangelands, now we're starting to talk important numbers. So, even though carbon might be changing by just a few percentage points like, you know, rangeland soils that have become depleted and carbon might drop from having 2 to 3% percent of their mass as carbon down to like maybe 1% of their mass as carbon. And that might not seem like much. But that change in carbon is incredibly -- can be incredibly profound for things like water infiltration. So, the organic carbon that contributes to soil carbon is super important for allowing pathways for water, for rain to infiltrate into the soil. And then once that water is in soil, soil carbon, especially organic carbon is really important for soil water retention. So, retaining that soil water in the root zone for use during the drier periods that always follow rain events or wet periods. As we know, that's really important. Soil carbon is also really important for inhibiting the formation of physical crusts that inhibit infiltration. So, those hard crusts that you get on many rangeland soils, you know, that the mineralization process is inhibited by organic carbon, for example. So, very important. Also, soil carbon is super important for making nutrients like phosphorus available to plants. So, there's, you know, soil carbon really is important for the -- all these other ecosystem processes that in turn feedback on productivity. Also, soil carbon is probably really important for how herbicides and other tools that we use in restoration function. You know, restoration of native plants obviously is going to be sensitive to soil carbon. But the retention of herbicides, pre-emergent herbicides that are used against annual grasses is probably strongly affected by soil organic carbon in ways that we may not even fully appreciate just yet. So, yes, carbon, soil carbon is important when we talk about sequestration of greenhouse gases into the soil. But there's a much bigger value, I think, to any manager of rangelands in how much carbon is in their soil.

>> I could add a little bit. Excuse me.

>> Go ahead.

>> Yeah. I think one kind of essentially emergent property of all these different co-benefits of carbon that Matt's discussing is, and that our paper gets into, is that carbon is essentially adding resilience to an ecosystem. When we think about restoring an ecosystem or trying to conserve the native plants, that soil water retention can be key, especially late into the summer because of the perennial nature of those plants. And so, the soil water retention we've seen in some studies that aren't yet published, but that that can really improve the success rate of outplantings. And so, there's some connections to these restoration practices that really means that managing for carbon isn't just managing for sequestration and this global outcome which is important, but it's also a key factor in thinking about how to get successful restoration more locally. And I guess I can't speak to carbon markets specifically, but I thought I'd also point out that another exciting part about thinking about drylands and carbon is that their soils are storing at times 10 to 70 times as much carbon as in the above ground biomass. So, this is really why we think about carbon in these ecosystems as being soil-centric in terms of management and understanding. And these soils, even though they hold most of the carbon in the ecosystem, they're also considered to be what we call far from saturation, meaning that there's also a potential for them to gain carbon relative to other ecosystems where the physical and chemical properties may not be conducive to allowing for greater carbon storage. These drylands are considered to have a high potential. So, this definitely, you know, interacts with this topic of climate change and carbon markets, but also the carbon in these systems is providing a really impactful local benefit that can directly affect management outcomes.

>> And most of us would assume that soil carbon is fairly stable. And one of the contrasts that's been drawn in the last 10 years maybe is the difference between rangelands or grasslands and forests where, you know, we see all the time, it's pretty obvious when a forest loses its carbon storage because it goes up in smoke. At least some of it does. And so, there's an obvious loss, but the loss of soil carbon from rangelands is not so obvious. And intuitively, we would feel like it's relatively stable, but maybe that's not quite so much the case as we would like it to be.

>> I think that's the big finding here. The big surprise is that relatively short-term changes in vegetation are affecting the amount of carbon that we would otherwise perceive to be stable in soils. That was kind of a surprising finding which is why we chose the title that we did because it's a real headline.

>> Yeah. Just a quick observation about the paper before we jump into more details. Just an observation about the format of the paper. This paper has the results and the implications and the discussion at the front and then methods at the back. And I don't think I've ever seen that before and I've read quite a few journal articles. Not nearly as many as Matt Germino but quite a few and this was new to me and I found it refreshing. And oddly enough, I think it counters a mental handicap that is an artifact of our digital age that I've written some about before. But some people have called this the age of distraction. And, you know, it's been researched into, reading behavior has even shown that scientists who would stereotypically be thought of as people who are close readers, their eyeball behavior tends to jump all over the page scanning for keywords and just reading phrases rather than submitting themselves to the author and taking in the narrative sequence the way the author intended. But of course, most scientific papers are not written in a human-friendly narrative sequence. They give the background and the materials and methods and then result and conclusions in a fashion that's designed to clearly communicate the scientific methodology and permit the possibility of somebody replicating it. But most readers of a paper have no intention of ever replicating the study. They want to learn about the findings. So, this paper follows a writing style that seems designed to be read and digested. And probably the fact that I'm excited about this and still going on about it proves that I'm a true range nerd. But was that format your idea or is this an innovation that was the journal's and it's common? And maybe it's more broadly common, I've just never run across it before.

>> Yeah. So, this is a great discussion to have. So, we chose a high-impact journal to push these results out to the public because we felt that it was a major discovery. And science and nature and also I think proceedings of the National Academy of Sciences are all journals that are very selective in only publishing the highest impact of findings. And so, they tend to use this format where the methods are pushed to the back of the paper and oftentimes are published in smaller fonts even. And typically, the papers will also have lots of details in the supplemental information. So, the idea is to try to distill the main take-home big findings for easy capture by the reader. So, Communications Earth & Environment is a nature journal. So, you know, the flagship journal is called Nature. And then there's a tier below that where you'll have like Nature Ecology, Nature Climate, Nature Communications. And this is a tier more specialized than that. So, Communications Earth & Environment is a focal journal within the Nature portfolio. So, it uses the very same format as all the other nature journals. And we did choose the journal in part because of that style and their preference for high-impact findings that are simple and easily communicated in this format.

>> Yeah, I really enjoyed it. And maybe my reading has been more confined to rangeland ecology and management than I realized, but it immediately stood out to me and I found it incredibly useful.

>> Well, the important thing here, Tip, is that a lot of the literature in rangelands is actually not coming through journals such as Nature and Science. In my opinion, semi-arid lands and rangelands specifically are fairly less well represented in these highest profile journals. And I think that needs to change. We're doing what we can to change that.

>> Yeah, I appreciate that. Well, what were, in specifics, this study's objectives and results?

>> Sure. So, I can take that. So, the primary objective was actually stemming from another project that we had which looked at what does the literature tell us? What do we already know about how these widespread annual grass invasions are affecting soil carbon or ecosystem carbon? And what we found was that some of the results, if you take that kind of meta-analysis review perspective, some of the results were contradictory to theory and what you might expect. And there was also not a good pairing of studies. Often, the available literature was really measuring carbon as an afterthought, not as a focal point. So, our objective was, after realizing this, we said this is a critical issue. There's up to maybe a million acres a year of land being invaded by these grasses and tens of millions affected by it so far. And we don't know what's happening to the carbon because there's no robust study. So, our objective was to isolate the different key factors affecting soil carbon and to ask the simple question, do exotic annual grasses affect soil carbon? And so, you'll notice if you look into the paper, we had this factorial essentially treatment of wildfire and invasion. And so, wildfire also, as you might expect, affects carbon in these ecosystems. There's a lot of erosion, other things that wildfire is affecting. So, these two disturbances are intertwined. And so, we took a lot of time and energy talking to managers and using satellite data to try and validate site histories and make this comparison looking at how, if we isolate all these other confounding factors, what do we see? What happens when exotic annual grasses invade? And so importantly, that included comparisons not only of the native state of a shrub-steppe, a shrubland, compared to the invaded state, but also looking at invaded shrublands and also perennial grasslands which are often forgotten yet make up a huge part of the mosaic of the sagebrush steppe. So, simply put, our objective was to, with an open mind, ask what is the effect of annual grass invasion on soil carbon in this ecosystem? And I'll also point out that there are some other methodological limitations of previous studies. For example, we took into account the very well-documented microsite heterogeneity. So, all I mean by that is there's very patchy vegetation. It's not kind of wall-to-wall vegetation in this ecosystem. And so, we took into account that variability by sampling in a very directed way. We also made sure to take enough samples. Actually, surprisingly, a lot of research just kind of says, "Well, three or four is a good number." But we used some statistics to estimate the effects and get large enough sample sizes so that we could really be confident in our results. And then just another confounding factor that we were really careful to think about was once you bring the samples back to your lab, there's a million different ways that you could treat that sample. And so going through, really, it's sort of a philosophical thing in a sense to try and decide what is soil carbon. And so, picking out roots very carefully and thinking of roots as a separate carbon pool and really just analyzing the soil. So, overall, we were not only interested in this question of annual grasses, but really wanted to drill down and do our best to address what we saw as shortcomings in past research in that there wasn't a comparison available. I guess the last thing is that any soil scientist will kind of talk your ear off about is bulk density of the soil. And so, if we know -- it's very easy to measure how much carbon is in a small soil sample, but to know how much carbon is across a landscape is much more complex and requires estimating the density of the soil per unit area. And you can imagine it's pretty hard to extract a core of soil from a pit or from a complex ecosystem which is very messy, full of rocks. And so, we spent a long time, I won't talk your ear off about it now, but we spent a long time being sure that our numbers for density which are what the scaling of carbon to the landscape relies on, we spent a long time making sure that those numbers were accurate.

>> In the paper, you also I think do a good job of setting the stage for why this matters. And we've talked around it some. But in the second paragraph, you say that the conversion of diverse deep-rooted perennial plant communities to shallow-rooted annual grasslands is occurring at a rate of 400,000 hectares annually. I think that's nearly a million acres. That's a lot. And it's a lot -- you're saying that's happening per year. I didn't look up the reference for that, but where does that information come from and describe sort of where -- is that happening like on the edges of -- is that because areas are spreading or because there's new cores that are rapidly shifting?

>> I think it's a combination of both. And we got that information from a project led by Kevin Doherty who was at the US Fish and Wildlife Service. And he led a large interagency effort to evaluate the change in these ecosystems over the entire biome. It was called the Sagebrush Conservation Design. And that estimate comes mainly from estimates of vegetation change made through satellite imagery. And so, there's some caveats there. Obviously, the accuracy of estimates of vegetation from remote sensing is something that should be considered, especially when you're looking at range expansion, when, you know, your target exotic animals are invading an area, presumably they are not initially dominant. And so, accuracy of that fringe is probably less than the accuracy of the vegetation estimates where the invaders are already super dominant which is going to be more in the core invaded area. But as cheatgrass and other exotic annuals invade new lands which is unfortunately occurring at higher elevations every year and it's occurring in areas where fire has occurred recently, you know, they're estimating that it's about a million acres per year. And their definition of what constitutes conversion is also important here. And Toby, can you remind me of what that is? I'm trying to remember exactly what it was. I think 15% fractional cover of exotic annuals or of annual herbaceous was the criteria?

>> Yeah. Off the top of my head, I actually don't remember the exact criteria they use so I don't want to mis-specify it. But yeah, in their work, they essentially classify areas of the sagebrush steppe into three tiers of essentially good intact sagebrush steppe, degraded or other. And so, this would have represented their estimation of sagebrush steppe going from that kind of top tier into either the less intact bottom two tiers.

>> Right. The top tier is called core.

>> Yeah. And to your point, once you get to 5% to 15% exotic annual grass, that is more -- that feels and looks like more on the ground than what it sounds like in a number. And that probably -- my guess is that that would represent having crossed some kind of threshold. One of the things that I note to self when I was reading the paper is what are the rates of reversion? And there's been -- I'm aware that there's been tons and tons and tons of research and money spent on this and some of which we've talked about before, Matt. And this is some of the stuff I think that ENVU is working on. But is there any data, and I don't recall seeing it in the paper, on exotic annual grass-dominated ecosystems moving back to sagebrush and perennial bunchgrass? You know, once we've got a situation that's cheatgrass, tumble mustard, rabbit brush and assorted miscellaneous other stuff in there, does that -- is there any data on whether and how much of that's going back in the direction in response probably to active effort?

>> Well, the problem with restoration and starting to recover these highly degraded areas that are dominated by invasive annual grasses is that it's extremely difficult to replant, reseed into those areas. So, some of it is done but it's only done on really quite small areas at this point relative to what we're losing every year. Part of that difficulty is because these are arid systems and, you know, rainfall is not reliable. And so, it's -- you know, you may or may not get anything surviving after a replanting effort. So, there's been a big initiative that started with the Western Governors' Association and picked up by the NRCS and Fish and Wildlife, you know, as to how we actually target this massive problem of invasive annual grass dominance in the west, western rangeland. And they came to the conclusion that the starting point, what seemed to be the obvious starting point which was taking the worst areas and trying to recover them was not a very effective approach. So, the approach they came up with was something which is now called protect the core which means that we need to stop the transition of these deep-rooted perennial systems from that transition to a stable state dominated by annual grasses. So, we need to protect what we have rather than trying to come back from a devastated state.

>> Mm-hmm. Right. Avoiding the conversion in the first place is critical.

>> Yeah. The loss of intact perennial systems exceeds the rate at which they are recovered.

>> Right.

>> And often --

>> Not a long shot.

>> Yeah. And often, the recovery is not to the mixed woody herbaceous state. It tends to more commonly be towards the seeded perennial grassland state.

>> Mm-hmm. Well, having said that, I appreciated the way the paper jumped straight to the results. I've been beating around the sage bush here. What did you find in the study?

>> So, key finding is just in the title to the paper which was that we found burning, so a wildfire or invasion to both reduce soil carbon stocks by about 50%. And interestingly, if you have a site that is burned and also invaded, there's no synergistic effect. So also, the loss, if you have both disturbances was 50%. So, number one, 50% loss of carbon with 20 to 50 years of invasion, carbon that takes thousands of years to build is to us a stunning result. And also that they don't interact to create a larger loss was a very curious result. So, that is the second half of the title which led us to speculate on the reduction of carbon to what we call the resistant base level. And that gets us into a little bit more of some muddy details. If you look into the plots, we see that a lot of that carbon was lost from deep soils, which is surprising because we usually think of the top soil, the first say 10 centimeters, as the most biologically active component of the soil. There's a lot of -- you know, the annual roots are there. There's a lot of growth and microbial activity. More frequently, that part of the soil is moist. So, finding that these deeper soils were actually the ones suffering these losses was really interesting, especially --

>> How deep is it?

>> Sorry, yeah.

>> Deep to us is, in this case, we segmented it into different depth fractions and we're looking at between 60- and 100-centimeters depth.

>> Wow.

>> So, for soil scientists, a lot of the times, you go out and you take the zero to 10 centimeters soil. Again, there's a lot of research showing that's the most biologically active, most likely to change in response to some kind of management or disturbance. Makes sense. Closer to the source of the disturbance, maybe it will change more. But we suspected, you know, one of our curiosities here was, you know, well, if we're changing from a deep tap-rooted perennial system to a shallow-rooted annual system, there must be some difference that would also occur at depth. We didn't know going into this that we would find any because soils tend to be slow to change. But yeah, to our surprise, that was where the largest changes were occurring. So, there's an implication here. We didn't actually separate carbon into its multiple fractions. So, there's a key thing here which is that we measured total soil carbon. Commonly, people will split carbon into organic versus inorganic carbon. Organic being, you know, essentially decomposed leaves and roots, microbial biomass. And inorganic being actually mineral carbon comes in the form of calcium carbonates most commonly. And in these deserts, there's often a deep -- in deep soils, you see an accumulation of these carbonates. And so, while we didn't separate them, although that's, you know, for next steps in this research, we will be doing that. So, while we didn't separate the two organic and inorganic fractions, the loss of deep soil carbon is especially interesting because it implicates a loss of soil inorganic carbon which is presumed to be even more stable and resistant to change than organic carbon. So, as all research tends to, this leads to more questions.

>> It opens more questions.

>> Yeah.

>> Well, I'm impressed. I'm not a soils person. I don't know nearly as much about soils as I ought to and would like to. But I have made a few pathetic attempts to dig a soil pit. And it's -- for one thing, it's not easy to get down to 60 centimeters to 100 centimeters in most rangeland soils, especially in places with shallow basalt bedrock. But even in places where you do have soil, it doesn't feel like there's much going on down there.

>> But there is.

>> That's fascinating.

>> Yeah. There's a lot going on down there. So, carbon is, you know, let's talk a little bit about the carbon cycle. So, carbon enters the soil via one of two paths. Mostly, it's entering through photosynthesis and organic matter or organic substances that might be extruded from roots. And carbon can also enter through purely physical paths where you have silicate minerals which can actually absorb CO2 directly. It's actually -- that pathway is probably very small compared to the biological pathway. But then what happens, that carbon could be cast away in mineral forms eventually, like either organic or inorganic forms. And the inorganic forms can be solubilized and moved around or even out of the soil profile with meteoric waters. Meteoric waters is just a fancy word for rain that's passing into the soil profile. In most rangelands, there's rarely enough annual precipitation to push water out the bottom of the soil profile. But where soils are shallow, and especially on steeper slopes, a lot of times, you can get what we might call subterranean flow. That rainwater can percolate, infiltrate into the soil, pick up some of the dissolved inorganic carbon, hit like a layer of what we might call caliche, like an impermeable layer, or it might hit like the bottom of the soil profile, the top of the bedrock. And it might move along there. And it might, in some cases, might eventually find its way into flowing waters or aquifers. The carbon can also be respired in the same way that humans respire CO2, so don't soil microbes. And so, that's another important path. So, those are useful things to think about when we try to envision, what does all this look like? When you dig that soil pit and you're looking at soil texture, that's the first thing you notice. How hard is it to get the shovel into the ground? And if it's really hard, you've got an impermeable surface. You might even have like a -- if it's a loam soil, you might have a physical crust. If it's sandy, there's a lot more air and there's a lot more vertical movement of water both in and out of that soil profile. Anyways, you keep digging, you're passing through those darker surface carbon-rich layers and you're getting into the less fertile, deeper horizons. And eventually, Tip, you're saying, yeah, sometimes it's hard to get below 60 centimeters. A lot of times, it's hard to get below 30 centimeters. And oftentimes, the actual soil depth might be 2 meters which is, you know, close to 6 feet. But it might be difficult to get the shovel below the 30- or 60-centimeter horizon where you have those impermeable caliche layers. Well, what is caliche? Caliche is formed from carbonates, carbonates. And so, what does that mean? It means that carbon has been sequestered into that layer. And that layer is now inhibiting both the flow of water, probably also nutrients, and definitely is restrictive to roots in some way. So, all of that matters. And here's the thing. When you start thinking about all these things and you think about like, well, how do we create a sampling design to estimate carbon stocks and changes in carbon stocks that could be induced by wildfire invasives? Now, the problems, the science gets nuanced.

>> Yes. One quick question before you get into the sample design and I do think that that's interesting and worth talking about. So, what's the mechanism for the pretty significant soil carbon loss with both fire and with conversion to exotic annual grass? Is it that there's more exchange going on than we would have thought previously below ground and that once you no longer have active roots at that depth, that there's no more biological mechanism for new -- there's no more organics being extruded from the roots? Or is there some other mechanism that's going on?

>> Well, we'd like everybody to first appreciate that we are measuring the net balance of carbon in these soils. And the net balance, just like your bank account, is always going to be a product of inputs minus outputs. So, I think your audience is very familiar with shrub steppe and sagebrush steppe landscapes and they can appreciate that when you go from a diverse, mixed woody herbaceous community to an annual grassland, well, you've greatly changed the inputs. There's just simply less photosynthetic activity occurring every year with the conversion to exotic annual. So, your inputs surely have changed. The outputs, you still have respiration. But Toby, what are other outputs that we've thought of? I've just hinted at a few of them, but what do you think?

>> Yeah. So, two key ones that are actually abiotic that deserve much more attention. First, one of the classic ways, if you go to the field and you're a good soil scientist, you've got some acid in your soil testing kit and you can drop a drop of acids. And these carbonates are just like a volcano that you'd make as a kid with your baking soda and your vinegar. Well, that is actually a change in pH that could be a result of some of the ways that the different plants are affecting the soil chemistry and hydrology. Could be a way to essentially liberate some of that CO2 back to the atmosphere. Another key thing here is changes in hydrology. So, effect of changing from a perennial to an annual system is the season of transpiration and growth is going to change. And there's also some changes that have been documented in the literature based on where their roots are, a number of other things that could mean there's a difference in the way that water is flowing through the soil and the depths that it's reaching. So, to be fair to this study and to also, again, say there's more questions than answers, it's possible that some of that carbonate, that inorganic mineral carbon could be washed to deeper layers and the fate at that point is uncertain. Could it be in an aquifer? Could it actually be stored or could it be running off into shallow streams and exposed and released to the atmosphere? So, there's some interesting, also, abiotic pathways that probably at the end of the day, because of how difficult it is to study deep soils, we need to start modeling to understand what could be occurring to determine the fate of that carbon.

>> So, to summarize, cheatgrass strongly changes the hydrology of the soils. And it simply does not use -- cheatgrass and other exotic annuals do not use all of the precipitation that arrives at a site every year, especially compared to a native intact system. And what this means is that you tend to get an accumulation of deeper soil water and a greater propensity to push the inorganic carbon out of the soil profile. Now, another thing is that cheatgrass is very shallow rooted. It actually can form fairly dense, fibrous mats of roots within the top few centimeters of the soil. And so, you know, there have been cases where we have measured an enrichment of organic carbon. Other papers have found this too. Other studies have found this. Owing to cheatgrass's concentration in that upper few centimeters of the soil. Now, one of the key things here that we've tried to emphasize is that the effect of cheatgrass is not simply its direct effect, its immediate biological effect. The indirect effects are super important. Both the hydrology, but also its promotion of wildfire. So, the more wildfire you're having with cheatgrass and every time you have a wildfire, you're volatilizing, you're combusting off the above-ground biomass. More importantly, Tip, some of your audience might remember our past discussions about post-fire erosion. And in particular, wind erosion. Wind erosion is really prevalent after wildfires on rangelands. Rangelands tend to be -- they're obviously a little bit drier. A lot of times, they are flatter landscapes than let's say forests. And wind erosion can sweep off like the top 1 to sometimes 5 or more inches of soil where the greatest concentrations of carbon reside, especially when the site has become dominated before the fire by cheatgrass. So, post-fire wind erosion losses of carbon, we've documented that in my research in previous years and it is a very substantial number. Where does that carbon go? When the sediment is blowing around in the air, there's probably lots of like maceration and processes that are occurring that are leading to the movement of that carbon into forms that will never return back to the earth's surface. But there's also a substantial redistribution, that carbon maybe getting blown into distant mountains and landing on snow or something like that. That's been documented.

>> I've also seen situations where that wind erosion is enough wind that it's moving significant sand and the sand saws off some of the perennial plants that were trying to come back after fire.

>> Absolutely, yup.

>> I have a question. I'm not sure if this is the place for it or not. I do want to talk about the methodology because I think that's interesting. If you have a core sagebrush perennial bunchgrass ecosystem and it burns and the combination of factors means that it does not convert to exotic annual grass, does that -- I think what I'm hearing and I can't remember whether I read it, does that also results in significant silo carbon loss?

>> In the timeframe of our study, so let's take a step back here and think about different soil types. So, grasslands, especially in the Midwest, oftentimes have mollisol soils which can be really dark. I'm thinking of Iowa grasslands right now. And that darkness is an indicator of the high-carbon content in them. But in the context of our study, we did expect, and frankly, we do expect in the long run that soils underneath dense stands of perennials will probably in the long run be important for carbon sequestration. But in the 25, what was it, 20 to 25 years from fire or invasion to when our measurements occurred, in that timeframe, we weren't detecting evidence that carbon has been increasing. Now, mind you, our study was not designed to look at the trajectories. And we have a separate follow-on study that is, you know, especially designed to answer these questions of restoration benefits. And obviously, one of those is going to include -- one of those restoration techniques is going to be seeding of perennial grasses. But in the mid to short-term temporal scope of our study, it's true that the fire alone without invasion was resulting in an appreciable loss of carbon.

>> Yeah.

>> That kind of surprised us. It was a surprise finding.

>> Well, meanwhile, back in the soil pit, how in the world do you measure these things?

>> Super carefully. Toby, how do we start?

>> Sure. I guess -- I think this is a great time to start with a shout-out which is to an amazing field crew. We have some very dedicated and passionate technicians. You know, I was lucky enough to dig many soil pits, but to have help on all of them. And so, but yeah, once you, you know, get to a site, that's actually getting to a site is a huge part of it because of trying to validate the history of management, ecology and disturbance at the area. But once you get there, we're careful to randomly place a transect through the core of a vegetation type. And we dig soil pits that span the different soil plant microsites that are present in an area. So, that means, you know, we know from a lot of past research that there's a lot of very spatially specific biogeochemistry and movement of carbon underneath the canopy of an individual shrub. And you get, you know, a few inches out from the drip line of where that shrub's canopy is and you have a whole different biological and chemical scenario. And so, we are careful to stratify our sites into the relevant microsites, as we call them, the soil plant microsites. Dig a soil pit which means trying to be very careful about digging a pit, but not disturbing the area that we would eventually sample. And then going in and from very specific depths using a very thin-walled cylinder to push it as gently as possible into the soil, extract a sample so that we're not only sampling the soil but also its volume. So again, a little while ago, I was talking about the density. And that part of it is really the key because you get the density wrong and understanding the scaling of it to the landscape is all thrown off. So, essentially, we get down in there and you have a lot of heads 1 meter underground, really trying to as carefully as possible extract these thin -- we kind of sharpen the edges of these steel cylinders and sample from within each of these depth ranges so we can represent the whole soil. Yeah. And then, we do that repeatedly. So, in this case, in many of these sites, we sampled three pits or essentially three microsites so three pits and then replicated that five times across a transect. And also, we're careful to take a lot of accompanying data to understand the plant community so that we could, between different regions that the study was done in, so we could kind of compare, you know, was this site in this region much more dense in one microsite versus the other, for example. And so, the above-ground complexity was also taken into account so that we could standardize our results.

>> So, Toby's response there could be summarized into two key steps. And as hard as the soil sampling was, I mean, we're talking, you know, digging a huge number of pits and sampling the soil with seemingly surgical precision in order to not compress the soils so that we could actually know the bulk density. Again, that is critical. It's easy to determine the percent of soil mass that's carbon. OK? So, we have a gas chromatograph and a really fancy laboratory here where we do that. But it's super difficult to get an accurate measurement of bulk density, the mass per volume of the soil. And you must know bulk density accurately in order to convert your measurement of percent carbon to the grams or pounds of carbon per unit area. In other words, what we call the carbon stock. And most people are interested in that carbon stock because that's what matters. That is the unit for knowing carbon sequestration, not percent carbon but mass of carbon per unit area, right? So, that's the critical thing. So yes, all of that is super hard. But Tip, we spent about as much time planning our sampling out with like an incredibly exhaustive, detailed search for sites. And so, what was the problem? What was the challenge? The challenge here is that there are so many confounding factors associated with cheatgrass and other exotic annuals and their impact on carbon. So, just think about it. If you were to predict where cheatgrass would be on a landscape, most of your audience would first say, "Well, where do we have fire? Where do we have certain soil types? Where have we had certain land use practices that might have resulted in cheatgrass invasion?" And all of those factors are confounding issues that could easily affect the carbon that we measure. And if we didn't control for those variables, then we could erroneously attribute the changes in carbon to cheatgrass when in fact, it might have just simply been, "Well, the grazing was different." So, what does that mean? It means that we had to double down with some super detailed assessments on what had happened on these sites. So, it caused us to filter through thousands of different possible site locations and distill down to the three eco-regions and the particular sites within them and to formally account for fire effects because they are inextricable. And if you want to know, you know, they're inextricably linked to annual grasses.

>> Yeah. If I dropped myself in a random location, drop out of a helicopter with a parachute onto a piece of rangeland, the random point at which you fall would have a dozen or two dozen soil types within a mile radius. And they all behave somewhat differently. And my observations of cheatgrass, at least in the Columbia Basin, the Intermountain West, are certainly confounded, meaning that I feel like I really can't attach cheatgrass presence or prevalence to any particular factor. You find them in rocky roadsides that haven't had any disturbance since the road cut went in. You find them in places that have never had any disturbance including grazing at all. You find them in places where you have a variety of soil types, a history of grazing, history of no grazing, you name it. It feels like it's fairly ubiquitous and obviously opportunistic. So, I can't even imagine what it would look like to say, "Well, we're going to sample the Intermountain West."

>> Yeah. It's hard. And actually, we have done that. We've expanded this analysis. This paper actually is what we call Phase 1 of our project. So, we focused on the Northern Basin & Range, the Idaho batholith, and the Snake River ecoregions. So, an ecoregion is a large area that is distinctive in terms of its soils, maybe subtle uniqueness in vegetation, and also climate. And sagebrush steppe and cheatgrass occur over many different types of ecoregions. But our first cut here was to go after three ecoregions. And here, we've reported the findings. But now, we've added, Toby and Harry, is it five more ecoregions? I should know this.

>> Mm-hmm.

>> So, we've greatly expanded the work across all of these different areas. And you're right, it is challenging. You do see cheatgrass in all of these areas but the closer and closer you look at it, you do start to see patterning. And, you know, for anybody that's ever sunk a shovel in the soil in many locations, you begin to appreciate that we're not dealing with a sea of sagebrush or a sea of cheatgrass. We're dealing with landscapes that have actually a remarkable amount of diversity in them. And a lot of that diversity is cryptic. And so, it takes a really skilled eye to appreciate the underlying diversity. And it's also pretty challenging to attribute, you know, the vulnerability or the resilience of these landscapes to the different aspects of the cryptic diversity. It's both a challenging issue with our semi-arid rangelands, but it's also a great career opportunity. And I can jest and say it's also job security. It's going to take more than a few lifetimes to figure all this out.

>> Thank you for joining us for Part 1 of this important two-part series. Please make sure to subscribe to the podcast and join us next time for Part 2 of this discussion with our guests, Matt Germino, Toby Maxwell, and Harry Quicke. Thank you for listening to the Art of Range podcast. Links to websites or documents mentioned in each episode are available at artofrange.com. And be sure to subscribe to the show through Apple Podcasts, Podbean, Spotify, Stitcher, or your favorite podcasting app so that each new episode will automatically show up in your podcast feed. Just search for Art of Range. If you are not a social media addict, don't start now. If you are, please like or otherwise follow The Art of Range on Facebook, LinkedIn and X, formerly Twitter. We value listener feedback. If you have questions or comments for us to address in a future episode or just want to let me know you're listening, send an email to showatartofrange.com. For more direct communication from me, sign up for a regular email from the podcast on the homepage at artofrange.com. This podcast is produced by CAHNRS Communications in the College of Agricultural, Human and Natural Resource Sciences at Washington State University. The project is supported by the University of Arizona and funded by sponsors. If you're interested in being a sponsor, send an email to showatartofrange.com.

>> The views, thoughts, and opinions expressed by guests of this podcast are their own and does not imply Washington State University's endorsement.