“Change is the very nature of Nature. If there's one thing that doesn't change, it is the fact that everything changes.” — Ilchi Lee

"Our dilemma is that we hate change and love it at the same time; what we really want is for things to remain the same but get better." — Sydney J. Harris  

Change happens at different scales. Most of us are comfortable with the changing of the seasons, as long as those changes are similar to what we remember, change we can predict and prepare for. We are much less comfortable with changes outside the realm of our past experiences. Part of our discomfort with change is that nature can be fickle. Nature, responding to anthropogenic inputs at scales never before experienced, is especially fickle. Unprecedented heat waves, hurricanes, flooding and drought, as well as humans moving species around the planet are all bound to have impacts. We know animals and plants and humans do not exist in isolation, rather they are part of complex interacting webs — plants and their pollinators, plants and plant eaters, predators and their prey, carbon nitrogen cycles mediated by tiny microbes hidden in the soil. Change at large enough scales could challenge those web connections, and possibly result in trophic cascades ending in extinctions. We know nature can be robust, but we don’t know how resilient nature can be in the face of the novel insults we throw at natural systems. We don’t know how those insults will impact the web of connections that are the basis of the natural world. That’s the real fear.

One change, or insult, catalyzed by the now global network of human interactions, is the introduction of species into natural landscapes in which they did not evolve or develop webs of interactions. An apparently benign example was our introduction of a plant, common storksbill, sometimes called redstem stork’s-bill, Erodium cicutarium, into the arid lands of western North America. More common on over-grazed, over-burned, or otherwise disturbed ground, it also has encroached into undisturbed landscapes. On those less disturbed, arguably more natural landscapes, common storksbill does not appear to squeeze out the native species, it just seems to occupy open ground side by side with those natives. It turns out the storksbill’s seeds are very nutritious, especially prized by kangaroo rats and pocket mice. There is a native storksbill, Erodium texanum, that can occupy the same ground, but it is relatively uncommon, showing up here in the Colorado Desert only every few years, and then existing side-by-side with its congeneric interloper. So far, no harm, no foul, a benign and perhaps even beneficial coexistence.

A far from benign example is the introduction of Eurasian annual (Bromus and Schismus) and perennial grasses (Cenchrus – fountain and buffel grasses) onto western North America’s arid landscape. Introduced to enhance those lands’ ability to support cattle grazing, the annual grasses sprout early in winter, earlier than native annuals, and so have access to limiting rainwater before the native seeds germinate. One species, Bromus tectorum, has earned the common name of “cheat grass” because it cheats native annual plants’ of their ability to access those early winter rains. Young desert tortoises will eat anything green, even if that means eating the brome grasses. The problem is that the sharp awns on the grass seeds stick in the tortoise’ throats, eventually choking them to death. Introduced perennial grasses simply act as bullies, permanently occupying available open spaces and preventing native annual wildflowers from becoming established, so pollinators are left with nothing (grasses are wind pollinated).

Both the introduced annual and perennial grasses create fuels that carry wildfire. The native annuals complete their life cycles and then disarticulate and leave little or no trace by the time that lightning from summer monsoons can ignite wildfires. In contrast, the non-native grasses provide fuels that are persistent and feed wildfires across a desert landscape that has never experienced wildfire, at least not at a frequency that would allow its plants and animals to evolve adaptations for surviving those fires. Post wildfire desert landscapes are often left without Joshua trees, blackbrush, creosote bushes, brittlebushes, or any bushes, and so cannot support the same levels of biodiversity as an unburned landscape. Nurse plants, shrubs that are critical for protecting seedling Joshua trees through their first decade or two of life are gone. Sounds like a formula for creating negative trophic cascades, and indeed where those fires have burned, that is the result. A possible silver lining is that the density and lushness of the introduced grasses is due to being fertilized and so enhanced by the deposition of nitrogen laden smog wafting eastward into the deserts from Los Angeles. If there is a tidal shift to using EVs, electric vehicles, then that source of nitrogen will disappear.

Climate change represents still another potential for changing and threatening the biodiversity of deserts and our planet. Warm deserts, because they are already near the limits for what we recognize as suitable for supporting life, could be particularly important barometers of change. One of the primary objectives of our community science program is to measure the effects of change due to an increasingly erratic and warmer and, on average, drier climate.  One of the first questions to ask is what then do we measure out of the multitude of plants and animals that call our deserts home. There is no one right or wrong answer. Should we focus on pollinating insects? Yes, except their taxonomy is far from being easy to figure out, even by expert entomologists. Should we focus on birds? Yes, but birds move around a lot to find suitable conditions, and except in and around wetlands, desert birds are often not common. Should we focus on charismatic species? Yes, maybe tortoises, but they spend most of their lives underground and they can live nearly a century.  Successfully breeding and producing surviving young just once during their long lives could be sufficient to sustain a tortoise population.

Detecting change at a population level could take a long time. To detect real change, you need readily detectable species, easy to identify, and common enough to measure real change when it happens. As much as it is engaging to hear about the behavior of a harpy eagle, a snow leopard, or a jaguar, their rarity or the difficulty of conducting effective surveys across many populations living under different conditions makes them poor candidates for doing good population change science. Lizards turn out to be ideal measures of change.

Although at first it may seem counter intuitive, selecting the most detectable, most common, shortest life-span species can be the best candidate for measuring change. They will have the quickest responses to change and their numbers, high or low, provide repeatable, dependable measures of responses to real change. Across the deserts of North America, the best saurian for measuring change is the side-blotched lizard. They typically only live 1-2 years, so they must get large enough to breed and then breed quickly to sustain populations. If conditions are too harsh to support successful breeding, it would only take a year or two at most for the population to crash.

We have 22 trails where we survey for all lizard species, but of course the side-blotched lizards are providing the most informative data sets. Our survey trails include lower elevations in the San Jacinto and Santa Rosa Mountains National Monument, middle elevations in Joshua Tree National Park, and highest elevations on Forest Service, mostly wilderness lands in the San Jacinto Mountains. So far, we have been able to measure incremental side-blotched lizard population density shifts away from the lowest, hottest, and driest elevations, to more moderate conditions at higher elevations. That was expected. The better conditions for survival and breeding are shifting upslope. Still, the populations with the highest densities are within the lower elevation block, it is just that those lizard populations are becoming less dense at the lowest portions of those trails, but sustaining densities at the higher elevations of the same trails. On higher elevation trails, a cooler spring and fall, and a very cold winter may be limiting population growth rates. At all elevations the lizards are showing a high degree of sensitivity to rainfall; more rain results in more food and denser populations. That sensitivity indicates that it is not just increasing temperatures, but rainfall is playing a leading role in determining the trajectory of each population.

As Ilchi Lee said, change is the very nature of nature. Understanding the drivers of change is the realm of science, and well within reach of Community Scientists. Change itself is not to be feared or hated, but knowing the implications of that change on biodiversity, and inevitably on the human condition, will hopefully lead to better future decisions and actions.

Nullius in verba

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