Under any of six models of climate change, in 100 years there will be no new trees in Joshua Tree National Park and a significant number of existing trees will be dead, according to a recent Riverside Press-Enterprise story. The climate models, developed by Ken Cole, a biologist and geologist with the U.S. Geological Survey in Flagstaff, Ariz., and plant ecologist Kirsten Ironside of Northern Arizona University, suggest a temperature increase of seven degrees.
Joshua Trees were prolific and widespread 11,000 years ago, Cole told newspaper reporter Janet Zimmerman. Their seeds were carried long distances from Mexico to Nevada in the dung of the Shasta ground sloth. Now, seeds are transported only short distances by rodents.
Climate change is expected to combine with other human impacts to threaten Joshua Trees. Factors mentioned in the Press-Enterprise article include:
- Non-native grass species, such as red brome and cheatgrass, are transported along roads by passing cars.
- The non-native grasses are fertilized by nitrate and ammonium deposited in the soil by car emissions. Edith Allen, a UC Riverside professor of plant ecology, has found that the levels of those chemicals in the park are 15 to 30 times higher than those in an undisturbed ecosystem.
- Dirt patches that separated native plant species are being replaced with a continuous carpet of non-native grass.
- Wildfire is increasing in frequency and intensity as the continuous bed of tinder dry grass carries fire long distances from plant to plant.
A possible bright side: Joshua Trees are taking root in areas to the north, such as Tonapah, Nev., where none existed a century ago because it was too cold.