The deserts are the most intact biomes in North America. Their unforgiving landscape has resisted our industrial society's impact, and the invasive species that have thoroughly remade other landscapes are only now beginning to get a toehold in much of the desert.
California's known desert flora includes approximately 2,450 native plant species, nearly 40 percent of CA's native plant diversity on just 28 percent of the landmass of the state. According to Jim André, director of the University of California's Sweeney Granite Mountains Desert Research Center in the Mojave National Preserve, mid-elevation plant diversity in the eastern Mojave Desert rivals that of the ancient redwood forests of Humboldt and Del Norte Counties in California.
Floristic diversity promotes invertebrate diversity, each plant species with its own retinue of pollinators and parasites, borers and grazers -- and the spiders, predatory wasps, scorpions and other invertebrates that prey on them. Entomologists have not even begun to catalog the living library of invertebrate species that live in California's deserts.
Even larger, more conspicuous desert denizens turn out to represent more biodiversity than we may have thought at first. The list of lizard species in the California deserts is subject to regular refinements, with new studies revealing divides between species and subspecies. The best recent example of this is certainly the splitting of the desert tortoise into two species, one on each side of the Colorado River. Lee Lenz of the Santa Barbara Botanic Garden has proposed the Joshua tree be best regarded as two distinct species as well.
What's driving this diversity? The desert's extreme variability.
A new species usually evolves from an old one when a population is prevented from interbreeding with other members of the old species. Without a flow of genes into that isolated population, it will likely diverge significantly from its rootstock species. Eventually that divergence may mean the members of the new population simply cannot interbreed any longer with their relatives, and a new species is born. The preceding explanation is dramatically oversimplified, and you can start bar fights by getting a roomful of biologists drunk and then asking them to define what the word "species" means.
But that simplistic explanation is close enough for our purposes here, in that deserts offer a wealth of opportunities to become reproductively isolated from your kin. Isolated mountain ranges offer "sky islands" of relative moisture in a sea of baking creosote. The valleys between, warm and cozy enough to suit the organisms that like it that way, are likewise separated by impassable walls of relatively cold and dank mountain. Microclimates vary wildly. The north wall of a canyon may be too baked for cacti to do well, while hardy coffee ferns line the rocks of the south wall. Hundreds, perhaps thousands, of wetlands -- from the tiniest seeps to alkali meadows to the marshes along the Colorado River -- hold about 40 percent of the California desert's biodiversity in isolated patches separated by miles of desiccated soil.
Climate and topography, along with a handful of other factors such as soil type, have ensured that the deserts are chock full of divergent populations evolving in their own directions. Climate and topography have also ensured that the distribution of many of those desert species is restricted to small, widely scattered disjunct patches.
Small, isolated populations of organisms can be hard enough to document in a comfortable environment. Put them in a place as resistant to leisurely study as the deserts are, and it's even harder to find them. An astonishing percentage of formal plant species records in the California desert were reported from places within a mile of a paved road. Very few of those observations were made in summer.
Some organisms reveal themselves to the observer only sporadically. I lived in a house in Arlington, Virginia for three years, and it was only in the last two weeks of living there that I realized thousands of 17-year cicadas lived in the yard. In the deserts there are plants that grow and bloom and set seed only in years in which, for instance, sufficient late summer rain soaks the soil. That may happen once in thirty years, and the rest of the time those plant species survive as seeds scattered in the stony soil. If a botanist doesn't happen by that valley when the plants are blooming, their presence remains unknown to science.
And so the deserts are largely unexplored, in a biological sense: much of our deserts' biological diversity is yet to be discovered and described. In the California deserts 25-30 new plant species are discovered every decade, with 150-200 discoveries expected in the next century. According to Jim André as many as 10 percent of the species you see in looking out over a typical Mojave Desert landscape may be undescribed by science. It's a floristic frontier out there.
Though the deserts are indeed largely intact, the pace of disruption -- from urban, industrial, and energy development; destructive recreation; grazing; invasive species colonization; and climate change, among other issues -- is increasing rapidly.
Desert landscapes heal from disruption far more slowly than do other landscapes in less-arid places. Recovery periods can be measured in millennia, if recovery happens at all. Desert biodiversity is thus under increasing threat, with species likely being lost even before science knows they exist.
Current U.S. laws enacted to protect biodiversity, such as the Endangered Species Act and its various state-level analogues, focus on those species in the greatest peril rather than on protecting biodiversity as a whole. These laws are subject to being countermanded by agencies even when they do protect a species, as we have seen in recent Interior Department endorsement of attempts to build industrial solar facilities on the habitat of threatened species. And in order to be protected, a species must make it through a long, arduous listing process. Seeing as the conservative movement has steadily eroded enforcement of the ESA and similar laws since their inception, listing relies largely on litigation or other initiatives by environmental groups.
Despite the deserts' rich biodiversity and biotically intact landscapes, these fragile ecosystems have largely gone unnoticed by environmental organizations when compared to forests, grasslands, coasts and aquatic ecosystems. Despite their richness, their ecological intactness, and their sheer beauty, deserts simply do not have much of a constituency in the non-profit world. Fifteen percent of known California desert plants are listed as rare or endangered, compared to about a third of California plant species statewide. At least forty desert plant species meet criteria for immediate listing.
I refer to the California deserts throughout this commentary, but the situation is similar throughout North America's deserts. We live next door to an ecological wonderland, and we're in danger of losing it -- without even really knowing what we've lost.
Chris Clarke is an environmental writer of two decades standing. Author of Walking With Zeke, he writes from Palm Springs regularly at his acclaimed blog Coyote Crossing and comments on desert issues on KCET weekly. Read his recent posts here.
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