“The one process now going on that will take millions of years to correct is the loss of genetic and species diversity by the destruction of natural habitats. This is the folly our descendants are least likely to forgive us.” - E. O. Wilson

The term “habitat” is often misused. Habitats are places where something lives, and so should be defined as that, the place where species x or y occurs. One should not refer to, for instance, a sand dune habitat. Rather sand dunes provide habitat for specific animals and plants. That said, deserts and the species’ habitats that occur there are the Rodney Dangerfield of the natural world: they get no respect. Deserts are typically defined as arid regions (averaging less than 10” or 25 cm of rainfall annually) that support only sparse and widely spaced vegetation or no vegetation at all: any area in which few forms of life can exist because of lack of water. This misconception of deserts being relatively sterile expanses of sand is still there and remains a hurdle, challenging efforts to ensure that these habitats are not destroyed. Whereas the less arid portions of California outside of federal and state parklands have already been largely sliced and diced into cities and farmland, deserts remain a relative frontier, with entrepreneurs increasingly eyeing them for new opportunities. 

Deserts cover one third of California and provide habitat for more than 50% of California’s rich native flora. Of California’s 45 species of native lizards, 78% (35) live in our deserts. One reason for this exceptional biodiversity is that our deserts are not some monolithic, homogenous hot, dry, and sandy expanse. Rather they vary structurally, temporally, spatially, and climatically. This variation is the fodder for species to occupy a myriad of niches. Comparing the desert region encompassing the Coachella Valley to a redwood forest region of northwestern California, (using CalFlora’s What grows here? feature) we find nearly 700 species of annual plants in the desert and adjacent mountains, but less than 440 in the redwoods. However, if we compare perennial, non-woody plants we find the opposite pattern: over 1200 perennial plant species under the redwoods, but less than half that (528) in and around the Coachella Valley. Stability supports more perennials whereas the temporal and spatial variability appears to support more annuals that can endure variable periods of exceptionally hot dry conditions as seeds buried in the sand. 

Back in the 1990s Mark Fisher, Al Muth, and myself were charged with advising on the development of the Coachella Valley Multiple Species Habitat Conservation Plan that was finally approved in 2008. Part of that charge was to define critical habitats that would receive protection under California’s Natural Community Conservation Plan (NCCP) statute. Because the fringe-toed lizard was already identified as endangered under the State’s Endangered Species law, their sand dune habitat would necessarily be included under the NCCP statute. Fringe-toed lizards occupied nearly all the remaining sand dune habitats, however there were other species to consider, and those other species were more restricted as to where across those remaining sand dunes they found suitable habitat. Assuming the remaining sand dunes (5% of the original 100 square miles) all included the same species assemblage allowed for the possibility that economic decisions might result in some dunes and some species not receiving protection. Ultimately, like the indigenous people of the far north with their multiple descriptions and names for various types of snow conditions, we named four different “types” of sand dunes, each providing habitat for the lizard, but additionally each including a distinct array of other species.

Active dunes are the archetype of what most folks envision when thinking of sand dunes. We defined active dunes as areas with deep sands, substantial vertical structure, shifting with every strong gust of wind, and with few perennial plants. Of course, fringe-toed lizards occur there, often in high numbers, but in most years, they would concentrate around active dune edges, avalanche faces, and/or near the sparse plants growing there. Those portions of the active dunes lacking those features do not provide habitat for the fringe toed lizards – except in wetter years. When the winter rains are sufficient to germinate annual plants, the active dunes can be covered with dune primroses. Oenothera deltoides, with their large delicate white blossoms, and another, less showy plant, Dicoria canescens, or bugseed (with just a little imagination their seeds look like small insects). Together these two plants turn the entire active dune into habitat for the lizard as well as a myriad of crickets, ants, and beetles. One of those beetles seems to be an indicator of an active dune – a medium sized darkling beetle, Asbolus laevis, which we have only found on active dunes. However, because sufficient rain is uncommon, the lizard population there fluctuates widely between wet and dry years.

Stabilized sand fields often surround active dunes, but lack their vertical relief, being rather flat with shallow sand hummocks behind relatively dense perennial, woody shrubs such as creosote and saltbush. Stabilized sand fields exist peripheral to the main sand corridors and consist of small sand hummocks mixed with finer clay deposits from rare flood events. Not stable in the sense of permanent structures, but the sand volume is much less, and the perennial shrubs give this habitat the impression of being relatively resilient to change. Except where there might be a larger accumulation of windblown (aeolian) sand, fringe-toed lizards are rare in this habitat. However, this is the primary habitat for flat-tailed horned lizards here in the Coachella Valley. When those winter rains are timed exactly right, stabilized sand fields become a riot of spectacular wildflowers, including purple mats of sand verbena, Abronia villosa, yellow desert sunflowers, Geraea canescens, white spectacle pods, Dithyrea californica, and bluish lupines, of various species. Unfortunately, when the rains come too early, stabilized sand fields can also become choked with a nonnative invasive plant, Sahara mustard, Brassica tournefortii which does not provide habitat for any native species.

Mesquite Dunes and Hummocks share some of the characters with active dunes such as a deep sand accumulation, but rather than lacking much perennial shrub cover, they have dense patches of honey mesquite referred to as a bosque. These bosques form where there is sufficient near-surface groundwater to support the germination and growth of mesquite, typically along earthquake faults. As the mesquite mature, they can capture wind-blown sand. As that sand accumulates the mesquite grow just high enough to stay above the sand surface, giving the impression that the mesquite is growing atop the dune, whereas it is the dune growing beneath the mesquite. Some Mesquite dunes can grow to 30-40’ or more in height. Here the mesquite are the foundation of the food web. Since the mesquite are tied to groundwater, not annual rainfall, the fringe-toed lizard population there shows little change between years. Rainfall, or the lack of rainfall, has little influence on resources that sustain the arthropods the lizards eat, as long as the mesquite continue to thrive. Unfortunately, portions of the mesquite bosques are dying, and a lowering groundwater is a possible cause. Here Coachella Valley round-tailed ground squirrels, cottontails, and jackrabbits are found in the highest densities we see anywhere in the region.

Ephemeral sand fields are the fourth dune community we named. Confined to the western, windiest portions of the Coachella Valley, ephemeral sand fields were so named because the wind energy moving sand through this habitat exceeds the sand supply. New sand arrives episodically as the result of uncommon flood events eroding sand from the San Bernardino Mountains. If no new sand has been added for several years, the wind carries the existing sand downwind leaving exposed rocks and gravel. Good for some species such as desert horned lizards and zebra-tailed lizards, but not for the fringe-toed lizards. Despite the high wind energy there is high shrub cover, primarily indigo bush and creosote; more stable hummocks of sand form in the leeward shadow of the shrubs and can sustain fringe-toed lizard populations, albeit at lower densities, between flood-born sand infusions. Those shrubs, especially the indigo bush, but also California croton and sandpaper plant, have palatable flowers and here, more so that on any other dune system, the fringe-toed lizards’ diet is vegetarian, approaching the diets of desert iguanas which are also abundant in this habitat. Ephemeral sand fields provide habitat for the lizards and provide habitat for the endangered Coachella Valley milkvetch. Higher numbers of milkvetch occur here than anywhere else in the Coachella Valley.

Differences in wind, shrub cover and sand delivery rates have resulted in a rich tapestry of habitats for diverse plant and animal communities. Although there are not a lot of studies for comparison, taken as a whole, there are more species darkling beetles inhabiting the Coachella Valley dunes than any other place reported so far; anywhere. Some of those species are found only here, some are more widespread, but this is not a sterile, monotonous landscape. 

Nullius in verba 
Go outside, tip your hat to a chuckwalla (and a cactus), think like a mountain, and be safe.