Monday, April 8, 2013

Joshua Trees Blooming Across the Southwest: Is it a problem or just a good year?

During my travels a few weeks back, I noticed a lot of Joshua trees were blooming along Highway 138. We stopped and snapped a few close-ups without giving it much thought. I knew they bloom off and on in different parts of the Mojave Desert. It has come to my attention, via the Press-Enterprise of Riverside, that the Joshua trees are actually blooming everywhere in the Mojave this year. It's unusual, with millions of the trees producing flowers.
According to the article, biologists are not in agreement about what this means. Some seem to think that the bloom is evidence of plentiful soil-water conditions because of extensive late summer-early fall rainstorms.  Others point to two years of overall severe drought, and average temperatures that are 2-3 degrees above average. The trees are reproducing because of stress, a sort of last gasp to produce seed before dying.
Being a geologist, I can't speak to the precise reason for the once-in-a-lifetime bloom, but geologists have provided some perspective about the prospect for the species' survival. Global warming is in fact leading to higher temperatures across the southwest, and the trees must propagate at higher elevations to survive as a species. This has become difficult over the last few thousand years, because there are no longer any grazing animals that can consume the fruits and spread the seed via their droppings.
The last far-ranging animal that did so was the Shasta ground sloth (Nothrotheriops shastensi) , which went extinct across the southwest more than 12,000 years ago. Without the animals to spread the seeds, they can only fall to the ground underneath the parent tree. There are some fears that the Joshua tree will disappear from its namesake National Park in a few generations.
And that would be a real shame. They are beautiful trees.
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