Show notes
In this episode of Where Two Deserts Meet, we sit down with Dr. Cameron Barrows of the University of California – Riverside. With his assistance, we break down what exactly it means for two deserts to meet in Joshua Tree National Park, what that truly looks like out on the landscape, and how it is changing before our eyes. ---TRANSCRIPT:--- Donovan: Where Two Deserts Meet is an official podcast of Joshua Tree National Park. Joshua Tree National Park acknowledges the Serrano, Cahuilla, Mojave, and Chemehuevi people as the original stewards of the land in which the park now sits. We are grateful to have the opportunity to work with the indigenous people in this place, and we pay our respects to the people past, present, and emerging who have been here since time in Memorial. Donovan: Hi, and welcome to Where Two Deserts Meet, a Joshua Tree National Park Official podcasts. My name is Donovan Ian: and I'm Ian. Donovan: And we're both park rangers here at Joshua Tree National Park, Where Two Deserts Meet is a podcast where we investigate topics that often require a bit more detail, and sometimes the help of an expert in the field to gain perspective. Ian: You know, I had a visitor recently asked me about where the line between the two deserts is and Joshua Tree. They were looking for a spot where they could pull off that stand in both places at once kind of thing. But I realized I don't really have a solid answer for them. I usually refer to our park brochure where we have the transition zone labeled or just tell them to look for certain plants that grow in each desert. Donovan: Yeah, that's still a great resource, but we've actually come to understand that it's a lot more complicated. At almost 800,000 acres, slightly bigger than the state of Rhode Island, Joshua Tree National Park is a large, vast open landscape of desert plants, animals, vibrant night skies, and fluctuating climate conditions. Joshua Tree National Park visitation has also skyrocketed to over 3 million visitors in the past few years, pulling in among the top 10 most visited national parks in the country. If you look at a general summary of Joshua Tree National Park in any sort of guide or travel blog, the first few lines usually start with Joshua Tree National Park, a place where two deserts meet, referring to the Mojave and the Colorado Deserts and the transition zone between them. Ian: But wait, what even is a transition zone? If we're going to use that terminology, we should probably define it, right? Donovan: Oh yeah, of course. But it's fairly hard to define. I have always been told that there's usually some good indicator plants that define where those boundary lines occur within the two deserts. Ian: All right, I got this. If I recall correctly, the well-recognized Colorado Desert plants are the Paloverde and the Ironwood, which are often seen down near the south entrance of the park. Whereas in the Mojave, you would look for the famous Joshua Trees, which are usually seen on the north side and especially along Park Boulevard. Donovan: Working in the visitor centers, I have actually seen a lot of confusion with this firsthand, especially visitors who come in through the south entrance of the park expecting to see a Joshua tree, not realizing that they're actually almost an hour south of the nearest Joshua tree. Ian: Yep. That's definitely something a lot of us, park rangers at Joshua Tree, have experienced. Donovan: But I personally think that driving through the transition zone between the Mojave and the Colorado Desert is a huge part of what actually makes Joshua Tree National Park so special. You drive around the corner from any direction, and suddenly new plant life and geological structures appear. For the visitors who are asking about this transition line, how do you usually describe to them where to go? Ian: Well, if I'm at one of the north side visitor centers, I usually tell them to start driving down towards the south end of the park, and they will visibly start to see a shift as they get further and further down. But there isn't really a definite line to look for, mostly because the line is changing. Donovan: Wait, how was it changing? Ian: Well, if you came to the park a few centuries ago, the transition zone might have looked fairly different. It's changing because of more than just one factor, but I know just the expert to talk to about this, Dr. Cameron Barrows of the University of California Riverside's Center for Conservation Biology. Ian: So, we've been driving about an hour now, and we've found ourselves on this beautiful campus. Where are we right now? Donovan: We're actually at the University of California Riverside, but they're extension campus over here in Palm Desert. What's kind of funny though, is when you're driving on the freeway, you wouldn't really know that you're hitting Palm Desert because it's labeled as other desert cities. Ian: Honestly, that's probably one of my favorite signs ever in the history of signs. It really does capture how people feel about the desert. There are a few big cities that everyone knows, like Palm Springs and Joshua Tree, but the other ones are just “other”…“other desert cities.” Cameron: Hello. My name is Dr. Cameron Barrows and I'm an emeritus professor or researcher with University of California Riverside, just recently retired. I've been working in the desert for about 35 years or so. Primarily developing conservation programs for endangered and rare species, but more recently focused on how animals and plants are interacting with their environment and how that environment has been affected by humans and more specifically, climate change. Ian: So, a project that I'm interested in hearing a little more about is one that is titled Managing Species in Transition Zones in the Face of Climate Change in Joshua Tree National Park. Can you tell us a little bit more about this and what spawned this project? Cameron: Sure. Well, what spawned the project was, probably ten, twelve years ago, there was a research publication that indicated that Joshua Trees would be eliminated from the California landscape as a result of climate change. I somewhat jokingly went to the National Park Service and said, “before you change your name to Creosote Bush National Park, maybe we should look at this in a little bit more detail and focus the scale on the park itself.” The park loved the idea, but they wanted us to look at more than just Joshua Trees, but at the entire ecosystem. As we all know, Joshua Tree straddles both the Mojave and the Colorado Deserts. That's the transition zone between the lower hotter dryer Colorado Desert, and the somewhat cooler, somewhat moister Mojave Desert. What we were looking for is a couple of dozen species to see how each of those might respond to climate change over time. But it's affecting us right here where we live, and it's affecting us now. It's not something in the future, it's a current issue. Donovan: Okay. So just to take us back, we've clearly established that there are two deserts within the park, the Colorado and the Mojave. But how exactly do you know which desert you're standing in while you're inside the park and where exactly should you look for that transition zone? Luckily, Dr. Barrows was able to provide us some key signs to look for. Cameron: Well, the Colorado Desert has its own set of species, but there's some overlap. One of the primary species that goes both ways is the creosote bush, and turns out from our analyses, the creosote bush is probably one of the most resilient species to climate change. They don't seem to care all that much. They don't look all that great by the end of summer, but as soon as it rains, they pop right back again. So, that's good news. With regard to that, the Colorado Desert, the lower desert, some of the characteristic species are palm oases. So, the palm Oases within the park are part of the Colorado Desert. Another species that's characteristic of both the Colorado Desert and the Sonoran Desert are ocotillos. As you are transitioning into the Mojave Desert, you start picking up more yuccas, and especially the Joshua Trees. Ultimately at the higher elevations, you're picking up pinions and junipers as well. Donovan: Plants are great indicators to use when identifying what desert you might be standing in. Now, of course, we've already started to establish that these transition zones might not be so clean-cut. Oases are typically found in the Colorado Desert, but can also be found in the lower elevations around the city of Twentynine Palms, which traditionally identifies as the Mojave Desert. This is a great reminder on how nature doesn't always identify with the lines that we draw on maps. Cameron: Well, one of the quotes that I sometimes use is basically that the only thing constant about our earth is change and it's been changing for hundreds of millions and billions of years. On a geologic time scale, if you think about, when the first Native Americans, the indigenous people came to this region, which is anything from 15,000 to 20,000 years ago, somewhere in that range, it was a completely different place. It was much, much wetter, and much, much cooler during that period. There were camels, there were horses, there were… native horses, not introduced horses. There were mastodons and mammoths and giant ground sloths and a very, very different landscape than we see today. Junipers and the pines would've been more extensive. More oaks. Species would've made living in this region much easier for those first inhabitants that came here, but that was at the end of the last glacial, maximum of the Pleistocene. So, whether or not we're still in the Pleistocene or not, we'll have to wait another 20 or 30,000 years to see whether or not we shift back into another glacial period. But currently we're in an interglacial period, which is a drier, warmer period, and so as a result of that dramatic climate change, of course we don't have wild camels. We don't have native wild horses, we don't have mastodons, we don't have any of those mega type species that used to occur here; and what has replaced them with are things that have moved up from the south, from the tropics. Cactus, which they are an iconic species of deserts plants, actually their origin is in the tropics. If you go to Costa Rica or if you go to the islands in the Caribbean, cactus grew all over the place. Cactus are very happy in hot places, but they're also not too unhappy about being in a wet place. Except for, and this is the caveat, is that where they primarily occur in the tropics is as epiphytes at the tops of trees. So, capturing a fair amount of water as it's falling through the trees, but there's no soil in the trees, so their roots dry out really quickly afterwards. So that adaptation of dealing with both wet and dry, adapted them to living in a desert. Ian: Considering what we know about how desert plants have adapted to these extremely harsh and various environments, we wanted to know how those landscapes are changing in the present. So, we asked Dr. Barrows, what are some factors as to why we are seeing such drastic shifts in desert plants as compared to the past. Cameron: There's two real driving factors: climate change being one of them and the other one really is invasive species. Joshua Trees are in an interesting position in that they are in a pattern of air movement that comes from Los Angeles, and that Los Angeles air continues up to this point. This is one of the potentially good things about people adapting to climate change, if we reduced our impact on our use of cars in trucks and trains and things that burn fossil fuels. That air pattern that's coming from Los Angeles will be cleaner. Right now, it's really dirty. It's filled with nitric oxides of various chemical formulas and those nitrous oxides fall into Joshua Tree as well as much of the Mojave Desert. When they fall, if you were a farmer, you're thinking, how do I increase my crop yields? Well, let's add nitrogen to the soil. Those nitrous oxides are adding nitrogen to the soil. What's wrong is that Joshua Trees don't care about it and neither do bushes or junipers or pinions. They don't respond to that extra nitrogen at all, but what does respond to nitrogen is invasive species. Invasive grasses, invasive mustards, things like that, have moved in. On its face value, it’s really bad, but what makes it much worse is that those species carry fire. Fire has become, in recent decades, a component of the Mojave Desert, which it never used to. There was never enough fuel to allow a fire to move from one Joshua tree in the next Joshua tree or one creosote bush to the next creosote bush. Now those spaces between the trees and shrubs are filled with invasive grasses or invasive mustards, various types, and as a result of that, fires carry across the desert. Some of the listeners might be aware that Cima Dome burned just this past summer, and I think it was a lightning strike, which is a natural event, but it would've hit only one or two Joshua trees and that would've been the end of it, but because of the invasive grasses and other plants, the fire moved in and burned thousands, and thousands of acres, killing most Joshua trees in its path. Donovan: The Cima dome fire that Dr. Barrows is referring to was a fire that burned about 44 thousand acres of Joshua trees in and around the Mojave National Preserve. Around August of 2020, over one million Joshua trees were burned in this fire. I got a chance to follow up with Drew, a Mojave National Preserve botanist, and he said that the dome fire was started by multiple dry lightning strikes. It was the same storm system that started much of the record breaking wildfires that we saw during 2020. Invasive grasses were just one factor that led to the size of this fire. Also, it was during an extended drought period and a heat wave this same week that Death Valley hit 130 degrees fahrenheit for the first time. Winds were strong and erratic contributing to unpredictable fire behavior. The science is clear that invasive grasses can be an issue when it comes to wildfires, but luckily, Dr. Barrow's research can assist with this issue. Cameron: What my science is supposed to do is inform management and help them make decisions. Most of our land managers, whether it's the Park Service or the Bureau of Land Management or local nonprofits, land management is an expensive, under undertaking, and there's not a lot of extra money for that. The science that we do is try to inform the managers as to what the risk is if you don't do anything about this invasive species. And so, what is the impact of that species on the environment? Is it indirect competition with native species? In some cases, that's true. Is it changing the ecosystem so that the native species don't reproduce or they can't exist there anymore? Or is it facilitating fire? Or is it doing none of the above and, and just ignore it because the effort to get rid of it would not be worth the benefit you get from it. Deserts are defined by being dry and for the most part, warm or pretty hot. There are some deserts that are cold deserts, but they are still dry. The main factor that defines a desert is how much rainfall it gets. Temperature impacts that because the warmer it gets, the less of that rainfall actually gets to the plants. It evaporates away. In the Colorado Desert, which is a warmer desert, when we do get rainfall, the rain, a certain percentage of that evaporates and never gets to the plants, never gets to the a…
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