The Yucca brevifolia, better known as the Joshua tree, is looking at an uncertain future as the world continues to warm. New research by a U.S. Geological Survey ecologist shows that the Joshua tree will likely be eliminated from 90 percent of their current range within the next 60 to 90 years.
The study appears in the current edition of the journal Ecological Applications, and was led by ecologist Ken Cole, of the USGS.
“This is one of the most interesting research projects of my career,” said Ken Cole, a USGS ecologist and the study’s lead author. “It incorporated not only state-of-the-art climate models and modern ecology, but also documentary information found in fossils that are more than 20,000 years old.”
The research team used a combination of future climate models, analysis of the climatic tolerance of the Joshua tree, and the fossil record, all in an attempt to project the future distribution of the trees.
What they found does not bode well.
Conclusions from the study show that the Yucca brevifolia could be restricted to the northernmost portion of its current range as early as the end of the 21st century. On top of this, the conclusions show that the ability of the Joshua tree to migrate via seed dispersal to more suitable climates will be severely limited.
Fossil deposits made up of sloth dung and packrat middens along with fossil leaves collected and stored by packrats allowed the scientists to reconstruct how Joshua trees responded to a sudden warming of the climate which took place approximately 12,000 years ago that is in many ways similar to what is likely to take place over the rest of this century.
Their conclusions showed that the ability of Joshua trees to migrate into more comfortable climates via speed dispersal was limited due to the lack of large animals that had, prior to the warming, distributed the seeds over large geographic areas.
Comparatively, the Joshua tree seeds have to rely on seed-catching rodents to disperse the seeds, which cannot travel as far as larger mammals. As a result, Joshua tree migration could be slowed to approximately 6 feet per year, nowhere near enough to keep ahead of a warming climate.