Transition Zone
Description
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TRANSCRIPT:
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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 ano
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