Tracking climate change through the Joshua tree

Measuring a young Joshua tree on Section 33, a 624-acre wildlife linkage corridor acquired by Mojave Desert Land Trust in 2013 (Photo: Brandy Dyess)

It’s 10am and the sun already feels strong. Seventh and eighth graders pile out of vans and start applying sunscreen. They’ve driven 150 miles from Grauer School near San Diego to become citizen scientists for the day.

“I see you’re all wearing the right shoes,” observes Adam Henne, outreach and volunteer coordinator at Mojave Desert Land Trust. In a safety briefing he warns the group about the cholla cactus and reminds everyone to hydrate. “One more thing you’ll need to watch out for: snakes. A good rule is never to put your hands or feet where you can’t see them.”

The students are on Section 33, an MDLT-managed wildlife linkage property in the town of Joshua Tree. It’s one of 28 locations in a climate change data collection project run by Joshua Tree National Park, UC Riverside and the Great Basin Institute. Their subject: whether climate change is affecting the Joshua tree (Yucca brevifolia).

The partnership is looking at a model developed by UC Riverside ecologist Dr. Cameron Barrows of the evolution of plant species in the national park and surrounding area. His model predicts the park’s Joshua tree population would be reduced by 90% under a further 3-degree planetary warming, with the plant only surviving in some pockets at a higher elevation.

“We’re really looking for on-the-ground data to either substantiate or refute the model,” explains Nick Graver, a vegetation monitoring technician from the Great Basin Institute who works out of the national park. “ Do we see evidence of this on the ground? Do we see evidence of less reproduction in the hotter areas? Having these demographic sweeps is a huge piece of understanding, building that evidence.”

Nick is leading the school group’s climate science excursion together with Dr. Lynn Sweet, a plant ecologist at UC Riverside. As part of today’s demographic sweep, the students are identifying parent Joshua trees and new sprouts, and recording their GPS, measurements and health.

Dr Lynn Sweet advises the students how to measure a young Joshua tree nestled inside a Mormon tea plant (Photo: Brandy Dyess)

“Great job!” says Lynn, as one of the students spies a Joshua tree sprout hidden within a Mormon tea (Ephedra) plant that is functioning as a “nurse plant”.

The MDLT property is one of the project’s few observation plots outside the national park.

“Looking across elevation gradients, we really like to have the stuff outside the park because plants don’t recognize the political boundaries that we have,” says Nick. “It helps us get a better picture of what is going on inside and outside the park. We have completed all the Joshua tree surveys in the park last year and so we are really excited to get this one done here as that’s our last Joshua tree plot.”

The project does vegetation surveys, looking at the entire plant community as well as the lizard population in each plot, and will return to each one over the coming years to track changes.

Dedicated crews of local volunteers support as citizen scientists, doing the monitoring once or twice a week. Some drive all the way from Los Angeles to take part. High school and college groups have been involved since 2016.

MDLT volunteer Tom Rottman looks on as students inspect an adult Joshua tree for size and health (Photo: Brandy Dyess)

“From the start this was meant to be a citizen science project because we can’t possibly get all the work done,” says Lynn.

“We did a study a couple years ago looking at the difference between the data that professional biologists took in terms of the lizard survey on a plot and what the citizen scientists took on the same plot. Better species richness and more lizards were found by basically using more volunteers. More eyes on the ground are able to see more species and more lizards.”

For Nick, the citizen science project has been a “huge step forward” in the amount of data collected. “It really strengthens our science and our understanding of the park. We’ve started making management decisions based on the research we’re doing.”

The research was propelled by a USGS study published in 2011 modeling the response of Joshua trees to expected levels of climate warming. The authors suggested Joshua trees will go extinct over much of their current range by the end of the century.

Section 33 looking towards Joshua Tree National Park (Photo: Drew Reese)

A follow-up study by UC Riverside’s Center for Conservation Biology in 2012 concurred that Joshua trees will be negatively impacted by climate change, but predicted that there will be places within and surrounding the national park that will provide buffers against extinction — places referred to as “climate refugia”.

The importance of this current, citizen science-fueled research is that it helps assess the existence and extent of these refugia, providing a focus for future conservation.

As a widely recognizable symbol, the Joshua tree can be useful in helping the public understand how climate change affects the Mojave Desert.

“The Joshua Tree is a valuable part of the ecosystem,” says Nick. “It provides a lot of services for lizards, birds and other things. It’s also something people care a lot about. It’s really easy for people to think, well ‘what does Joshua Tree National Park look like without Joshua Trees?’ That’s a really hard question.”

To join the citizen science team vegetation demographic sweeps, contact [email protected] and to help with lizard surveys in the plots contact [email protected]