A thin layer found in the top few centimeters of soil plays a big role in its ecology.
Biocrust is built, maintained and inhabited by a bunch of different organisms — including lichen, moss and algae. If you’ve been around it, it’s very likely you didn’t even notice it.
But for Keven Griffen, a Ph.D. student at Northern Arizona University, it could be a key to soil health — and to an extent, the health of the surrounding environment.
Griffen studies soil ecology and also works with the Desert and Intermountain Restoration Team, or DIRT Lab. She joined The Show to talk more about all of this
Full conversation
MARK BRODIE: Keven, ecologically, what does biocrust do? What purpose does it serve?
KEVEN GRIFFEN: It does a lot of things. I think the main, sort of, functional trait that it's identified with tends to be soil aggregation, so literally like holding the soil surface together. That's actually one of the things that it's defined by, is this tendency to sort of aggregate soil particles together.
And that's really important, especially in places like the Sonoran Desert where we have pathogens that dwell in the soil. So things like Valley fever, you don't want, airborne for everyone to breathe in. And so, biocrusts are really important in holding those particles together and keeping them in place.
But they also do a lot of other things in the desert, in particular, they're really involved in nitrogen and carbon cycling, so bringing nutrients into the soil. They actually have a really complicated relationship with plant growth, but they can be suppressive of invasive weed growth, and that's something that we look at a lot. And then they can regulate things like hydrology and where the water goes and how it soaks into the soil, so they do a lot for us despite being so small.
MARK BRODIE: When you talk about sort of being a soil aggregator, is it the kind of thing that they could potentially help keep dust on the ground and from being kicked up into the air? Is that a function that a biocrust can serve?
GRIFFEN: Yeah, definitely. And that's actually one of the main reasons that we tend to look at them is because they can be so important for helping not keep your soil from blowing away.
BRODIE: Yeah, I would imagine for a lot of reasons that would be a fairly important thing. You think about dust storms coming through. You think about even erosion in an area after a wildfire, things like that. Having soil that can be kept together and not just sort of loose out there in many ways would be very important.
GRIFFEN: Yeah, and that's one of the things that we study a lot is sort of the role of these organisms, especially in disturbed areas, so soils that have been sort of scraped up by bulldozers or you mentioned fire, that's something that we work on quite a bit, is how can we encourage these biocrusts and particularly mosses in a lot of areas to grow back post fire and help us just keep that soil in place?
BRODIE: I'm curious about sort of this, what seems to me to be kind of a dichotomy in the sense that these bio crusts can be fairly productive and fairly strong on the soil, but if you step on one, that's it. Right?
GRIFFEN: Yeah, I actually think this is one of the coolest things about biocrusts. They are incredibly hardy in so many ways. So we actually think that biocrusts were probably one of the first types of communities to colonize the earth's terrestrial surface.
They're super resistant to UV radiation. They can fully desiccate in a lot of cases and dry out, and then when they get a little bit of water, they'll come back just as they were before. In a lot of cases, they're just incredibly tolerant of harsh conditions, and that's why we tend to find them in areas like deserts, but also in areas like glacial retreat zones. And in Antarctica, we have biocrusts. So they're really, really hardy.
But then at the same time, they have this fragility and vulnerability to things like you mentioned, like physical disturbance. So if you step on them, it takes a really long time for them to grow back depending on where they are and especially things like fires, bulldozing — all of these things that tend to happen where you have lots of humans. They're not necessarily adapted to deal with that.
And so, that duality of their strength, but at the same time their fragility, I find really fascinating and also, like, a little bit relatable, which I think is why I like to study them so much.
BRODIE: Sure. You mentioned how long it can take to rebuild them if they are disturbed or destroyed. Is there anything that can be done to speed them up? Because it seems as though in many cases having more of them would be beneficial.
GRIFFEN: Yeah, so it's a really good question, and the science of biocrust restoration is really very new. For a long time, the thought was, “Once they're gone, they're gone, we can't cultivate them.” And luckily we've actually found that that's not true. You can grow biocrusts. I mean, you can't grow them from nothing. You need, we usually call it inoculum.
So you take biocrusts from an area that's going to be disturbed in some way. So a lot of times that's like a trailhead expansion or construction that's going to happen. And you can go in and rescue that biocrust, like harvest it with a little trowel. You can pass it through a sieve, and then you can literally in some cases just take that sieved biocrust and sprinkle it on the soil surface of somewhere you want to restore it, and it will grow back.
And then you can do other things like take some of that inoculum into a greenhouse or a raised bed, and if you irrigate it and give it shade, you can get it to grow.
So those are things that our lab works on in particular. But there are other labs — even in Arizona, like there's a fabulous lab at ASU that does a lot of cyanobacterial culture and they can even do things like taking hyperlocal samples of a cyanobacterial community in the soil and grow it out on location and isolate just that strain and put that back on the soil surface.
So it's actually a growing field and a really exciting field because it turns out you can make more biocrust and you can restore it to areas that previously we thought were kind of unrestorable.
BRODIE: Are there downsides to having more biocrust?
GRIFFEN: I don't know that I would necessarily say there are downsides. I would say there are dangers, in the way that there are dangers anytime you're moving organisms around. We do know that there can be pathogens in biocrusts.
So there's something called cyanoraptor, which sounds very ominous, but it's a patch that, it's actually like a predatory, I think bacteria, but I could be wrong about that. But it sort of attacks the cyanobacteria and causes these plaques on the soil. So you don't want to be moving that around.
There are soil fungi that can be deleterious in some situations, so I think we just want to be really careful with only really moving biocrust that's local, that we've looked at really closely, to make sure we're not transplanting these more carnivorous strains.
But I don't know that there's necessarily a downside. I think there are probably locations where you're not going to get success, but I think in most cases where you do get success, it can be beneficial for the ecosystem in a pretty big way.
BRODIE: So what in your mind then would be like the best case scenario here? Is this the kind of thing where, in a perfect world, the entire Sonoran Desert — at least the areas where there isn't development or something else on the ground — would be covered in biocrust? Is it more of a strategic targeting of where it would be most beneficial? What do you think is the ideal outcome here?
GRIFFEN: Well, I think from a restoration perspective, you kind of have to target the areas that are most in need of restoration and where you think you're going to have the highest chance of success. So when we look at where can we put biocrust back where it's going to have the biggest impact, I think the first question we have to ask ourselves is, “Was there biocrust here in the first place?” And that can be a really hard question to answer.
So, I think we want to put it in places where we feel we have a pretty good chance of success and where we feel it can have a beneficial impact. But, I think it's also one of those things where putting biocrust on the ground alone is not going to fix everything if we don't also sort of stop the source of the degradation.
You're never gonna fix everything just by reintroducing biocrust, but I think it's a really great way to sort of catalyze broader ecosystem recovery if we can also address those other sources of degradation.
