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New publication: How more than a century of climate change affected Joshua tree flowering

The following is cross-posted at the Yoder Lab blog.

“Cadillac tourists” viewing Joshua trees bearing fruit. Detail of a digitized page from the Los Angeles Times June 15, 1924 issue, via ProQuest Historical Newspapers.

More than a century ago, in mid-June 1924, the Los Angeles Times devoted a photo spread and several column inches to the second-hand vacation story of some “Cadillac tourists” who saw Joshua trees bearing fruit. It meant, the Times reported, that rain was coming.

M.C. Ellison of Sacramento, who has been touring Southern California in his Cadillac with his family, told the prophecy to J.E. Clark, sales manager for Don Lee. He did not guarantee its accuracy, but admitted that it sounded interesting at least.

“We met an old prospector who was camping among the Joshua-tree forest just beyond the summit of the Cajon [Pass],” Ellison told Clark. “He called our attention to the extremely heavy crop of seeds which the Joshua trees are bearing this year. Almost every tree is loaded with green seed pods.

“‘That means good rains on the desert next season,’ the prospector told us. ‘I have been traveling the Mojave for almost forty-five years now and I have never seen it fail.’”

Joshua trees’ irregular flowering has been a feature of their public image since long before the advent of automobile road-trips. Joshua tree flowers were not observed until some years after the trees were given the formal scientific name Yucca brevifolia in 1871. The same stand of Joshua trees rarely flowers two years in row, and often goes multiple years between big blooms. When the blooms do come, it’s not clear what triggered them. Sometimes Joshua trees flower after a winter of good soaking rains. Sometimes they flower after a run of really dry years. Some people think they need a hard winter frost. Joshua trees will bloom at one site, and a few kilometers away they won’t produce a single bud. Back in 2018, there was a big bloom in Joshua Tree National Park — but only in Joshua Tree National Park — in November, seven or eight months after flowering usually finishes. The LA Times eventually gave up on the idea that the trees forecast the rainfall for the coming year, but newspapers in and around the Mojave Desert continue to report on big bloom years — and years with no flowers to be seen — as a feature of interest for locals and tourists to this day. 

That public interest has given us a way to finally figure out what cues Joshua trees to flower. Making that connection also gives us a new way to study how the trees have experienced climate change trends going back to the early 20th Century, decades before M.C. Ellison and his family left Sacramento to tour the state in their Cadillac. It’s all in a new paper that’s just been published on the website of the journal Ecology Letters, by a team of Joshua Tree Genome Project collaborators. 

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New publication: Conservation challenges and solutions for the Mojave Desert

Burned Joshua trees at the site of the 2020 Cima Dome fire in Mojave National Preserve (Flickr, jby)

The Mojave Desert, home to our favorite woody monocot (Joshua tree), encompasses some of the largest tracts of undeveloped land in the continental United States. That wilderness is under increasing pressure from suburban sprawl as climate change threatens to make its desert landscapes even less hospitable to the thousands of unique native plant and animal species that call it home. At the same time, the Mojave is prime territory for solar and wind energy facilities that can help us slow and stop climate change. A new perspective article in the journal Biological Conservation led by Joshua Tree Genome Project co-PI Chris Smith enumerates the challenges faced by Mojave Desert communities — human and otherwise — and the trade-offs necessary to protect Mojave biodiversity in the 21st Century

With Joshua tree as a recurring case study, we attempt to lay out a general plan for identifying and prioritizing populations of threatened Mojave species that have the best chance of surviving into a climate-changed future. We discuss the challenges of defining species’ current and future geographical distributions, assessing populations’ demographic health, and identifying and quantifying genetic variation that can support adaptation to projected climate change. We also find a lot of opportunity to resolve apparent conflicts between renewable energy development and conservation of Mojave wilderness — with appropriate input from residents and other stakeholders, it should be possible to balance the need to protect the desert’s biological treasures as we build the infrastructure needed to save them from the global threat of climate change.

The full paper is available to read without a subscription via this sharing link through January 20, 2023.

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