With the end of June, so ends our lizard surveys on the remaining dune fragments of the Coachella Valley for another year. When the Coachella Valley fringe-toed lizard received federal (threatened) and California State (endangered) protection back in 1980, a planning began process that resulted in the establishment of the Coachella Valley fringe-toed lizard Habitat Conservation Plan in 1986, the first such plan in the nation that attempted to balance species protection and economic growth. That plan then evolved into what we now call the Coachella Valley Multiple Species Habitat Conservation Plan, signed in 2008.

To be clear, back in 1980 the Coachella Valley dunes were already severely fragmented by roadways, freeways, railways, tamarisk rows, and cities. Sand sources and corridors that are critical for delivering sand to the remaining dune fragments were all compromised to one degree or another. The conservation plans did their best to salvage what was left. Principles of conservation biology, such as maintaining connectivity-reducing habitat fragmentation, and ensuring that ecosystem processes (like sand delivery) are intact were impossible to fully incorporate on a landscape that was already sliced and diced as was the Coachella Valley floor. The conservation solution was, and continues to be, an experiment. The hope was that at least some (one or more) of the five remaining dune fragments would be sufficiently robust to be able to sustain a population of fringe-toed lizards. 

As with any experiment you need to collect data to determine success or failure. It took a few years to develop a means to count the lizards that could be applied to all the remaining dune fragments. As I mentioned in my May 29^th dispatch, UCR’s Mark Fisher and Al Muth had already established a research plot to study this species, incorporating an intensive, mark and recapture methodology. Unquestionably the “gold standard” for wildlife surveys, but it requires too much time and effort per plot to be applied across multiple habitat fragments. As I described in that May 29^th dispatch, we opted for many much smaller plots.

Now, 40 years after the lizard was listed for protection by both the federal and State of California governments, each of the dune fragments now under conservation ownership still have what appear to be healthy fringe-toed lizard populations. Forty years in, the experiment is a success, so far. That lizard is tougher than many gave it credit.

One advantage of using many plots to assay the status of the lizards is that we can ask additional questions regarding the habitat quality, from the standpoint of the lizards, across those dune fragments. Even though the lizards are present, additional stressors such as invasive plants, reduced sand transport may be eroding their potential to sustain their populations. The experiment continues at a much finer scale. 

Invasive plants and animals are often touted as one of the primary challenges for protecting native biodiversity worldwide, second only to habitat loss and fragmentation. Places like Hawaii and Florida have been overrun with plants and animals from tropical climates around the world. If you have ever been to Oahu or Maui in Hawaii, almost nothing you see is native, unless you can get to above about 4,000 feet in elevation. The same is true for much of Florida, and there no elevations exist above a couple hundred feet. With as hot and arid as it is here in the desert, one might assume we are free of invasive species since living here without air conditioning and deep well water takes specialized adaptations. Hopeful thinking but woefully wrong. Tamarisk, Russian thistle (tumble weed), Sahara mustard, stink net, and a handful of grasses including fountain grass, buffle grass, Mediterranean split grass, cape needle grass, cheat grass, and red brome lead the list of desert invaders from as far away as the Sahara desert, the middle east, and the Russian steppe. I sometimes encounter folks who argue that these species are here, accept it, and embrace them. These folks will remind me that many of the species we call native actually evolved elsewhere, (creosote bush evolved in southern Argentina, arriving here some 17,000 years ago), so who decides how long a “weed” needs to be here before we can call it native? Isn’t it species-ist to disparage recent invaders? Interesting arguments, but for me the answers are simple. If a recent arrival threatens the existence of established native species, then if we can, we should try to control it. If it is benign, or if it enhances native biodiversity, let it be.

Years ago, when I was the director for the newly establish Coachella Valley Preserve system, I was told by a UCR professor that my number one task was to get rid of Russian thistle. A daunting task, so I did some science to see just what the impact of this weed was. It turned out that at low to moderate densities Russian thistle provides a thorny sanctuary from predators for fringe-toed lizards and for native beetles. At those thistle densities the lizard populations are denser, with higher reproductive success. It also tends to help build sand dunes by capturing sand rather than the sand moving too quickly down wind and leaving the protected lands. We leave Russian thistle alone.

We did the same science with Sahara mustard, but came away with a different answer. The mustard has a very different structure and no thorns, so it doesn’t provide a protective sanctuary. Rather, we found that native wildflowers are reduced when the mustard invades, that no native insects eat the leaves or seeds (we experimentally provided native harvester ants with either just mustard seeds or just native wildflower seeds – those with only mustard seeds quickly perished), and rather than building the dunes, the mustard stabilizes the dunes. Not beneficial, not benign, all negative to the lizards and overall biodiversity.

I have attached hot-off-the-computer summaries for the fringe-toed lizard population densities across the Coachella Valley floor. Two, AD2 & AD4, are active dunes on the Coachella Valley National Wildlife Refuge. Each line represents the lizard density on individual plots within each dune system. MH19-24 is a mesquite dune system at Willow Hole, southeast of Desert Hot Springs, and ESF7-12 represents a series of plots in North Palm Springs, south of the railroad and west of Gene Autry Trail. The way to interpret these graphs is to first understand that average to above average rainfall is good for the lizards (more food, more reproduction) but the effect is measured the following year. So, a wet 2005 resulted in more lizards being counted in 2006. Hatchlings don’t emerge until mid to late summer and into the fall, so are not counted in our spring-early summer surveys, but are counted the following year. Wet years included 2005, 2008-2011, 2017, 2019, and now 2020. Therefore, unless there was something else impacting habitat quality, lizard numbers should show peaks in 2006, 2009-12, 2018, 2020, and next year in 2021.

You can see that the plots on the AD2 dune basically follow that expected pattern, and so do not raise any worries. However, recent declines on the AD4 dune are a real cause for concern. Sahara mustard has recently become dominant on that site, largely due to a misunderstanding on the part of the road crews depositing sand upwind of that dune. They collect sand that becomes a road hazard and truck it to an agreed upon up wind site from the AD4 dune. Unfortunately, they also have put copious amounts of water on the deposited sand, turning it into a cement-like consistency. No new sand has been coming on to the dune, so the mustard has taken over. The large increase in lizards on the ESF7-12 plots is most heartening. That site had been sand-starved until 2017, and since then the lizard population has exploded (in a good way).

Science is so cool.