"The wealth of the nation is in its air, water, soil, forests, minerals, rivers, lakes, oceans, scenic beauty, wildlife habitats, and biodiversity ... that's all there is. That's the whole economy. That's where all the economic activity and jobs come from. These biological systems are the sustaining wealth of the world." — Gaylord Nelson

By DR. CAMERON BARROWS

The distribution of animal and plant species across the U.S. are the echoes of past climate changes as much as of today’s climate. Ice-free regions throughout the Pleistocene, warm climates today, plus the occurrence of mountains that capture precious rainfall and offer gradients of temperature and moisture explain much of where there are “hot spots” of species richness today. Those drivers create an uneven distribution of where high concentrations of species occur. Perhaps then it should be no surprise that California has the richest biodiversity of any state within the continental U.S., in fact richer than all the other states combined. That gives California bragging rights, it gives California naturalists an opportunity to see something new nearly almost every time we step outside, and it also gives us a responsibility to ensure that wealth of species is not lost. Within California the distribution of species is also uneven. What would shock most who have not spent time here, California deserts are particularly rich in native reptiles, bees, darkling beetles, annual plants, and shrubs. Richer than the rest of California and far richer than the rest of the country. Bragging rights come with responsibilities.

There are legions of threats impacting the biodiversity of California deserts, and near the top is the interaction of invasive species, a warmer and especially drier climate, and wildfire. The 2023 nearly 100,000-acre York fire, following on the heels of the 2020, 40,000+ acre Cima Dome fire, both within the Mojave National Preserve, underline this concern. To be clear, unlike almost every other California landscape (except tide pools and other wetlands), wildfires naturally would be rare or non-existent in deserts. By the summer months when monsoon-driven lightning strikes are possible, any native annual plants that could otherwise fuel a wildfire would have long-since disarticulated and been blown away with the wind. When lightning strikes a Joshua tree, there would be sparse or no fuels available to carry the fire to other desert plants. That means that throughout the evolution of desert plants there had previously never been a threat of fire, and so the plants never needed to develop adaptations that might allow them to survive being incinerated. In fire prone ecosystems such as chapparal, grasslands, oak woodlands and some conifer forests, plants have developed root burls that survive fires and resprout within weeks of a wildfire. Or they have developed fire resistant seeds, or thick bark protecting the living cambium, all of which allows ecosystems to more rapidly recover after a wildfire. Immediately following a fire there is often a particular set of annual wildflowers that thrive in the burned soils. They are termed “fire-followers” and provide rich resources for pollinators immediately following the wildfire. Desert plants have none of those adaptations, and don’t have any fire followers.

The historical paucity of fires in deserts has changed over the past century. One factor driving that change was the introduction of non-native grasses, particularly members of the genera Bromus and Schismus. The grasses originally came from livestock operations, hoping to provide forage for their cattle and sheep during the dry summer months. Unlike native desert annual plants, these grasses do not disarticulate after they die, and so can remain rooted in place for years. Even dead, theses grasses provide forage for livestock, but they also provide fuel for carrying wildfires. Those desert livestock operations got started during wetter than average years in the early decades of the 20^th century. When more typical dry conditions returned in the 1950s, most (not all) could not sustain enough livestock to be economically feasible and abandoned their desert ranches. Unfortunately, to this day the non-native grasses remain as a legacy of those ranches.

The introduction of non-native grasses was just the first step. The grasses were limited by desert soils short on the nitrogen that they needed for maximum growth and reproduction. That deficit was filled by smog, generated by the millions of cars and trucks plying the freeways of the Los Angeles Basin each day, and container ships bringing in goods from around the world into the Long Beach and Los Angeles ports. The smog, comprised of nitrogen oxides, wafted on the prevailing on-shore winds across the Mojave Desert where the nitrogen compounds fell as a fine dust, or dry acid rain, onto the desert soils. The amount of nitrogen was roughly equivalent to the levels farmers applied to their field to achieve maximum crop yields, thus fertilizing the desert soils and the non-native grasses thrived. The creosote bushes and Joshua trees have little use for the extra nitrogen as they had evolved to thrive in low nitrogen soils. The result was relatively luxuriant grasses filling the spaces between centuries-old Joshua trees and creosote bushes; when dry these grasses became continuous fuels that had not previously existed in the desert. With those fuels in place, the inevitable wildfires happened. Notable fires burned into Joshua Tree National Park in 1995 (Covington Flats fire) and 2006 (Sawtooth fire). The Sawtooth fire eventually consumed 61,700 acres burning Joshua trees along with considerable loss of human properties.

More than 28 years after the fire, the area burned by the Covington Flats fire looks much as it did in 1996, a year after the fire. The Joshua trees and creosote bushes are just not recovering. The Sawtooth fire’s footprint similarly shows little evidence of recovering to what it once was, a Joshua tree - pinyon pine - California juniper biome. The lack of recovery has in part been due to the desert flora’s lack of adaptations to fire, and has not been helped by the extended drought believed to be related to modern climate change. Prospects for recovery from the Cima Dome and York fires are similarly poor. Joshua tree seedlings are particularly sensitive to drought; they simply lack the water storage capacity of the adult plants and so expire by the end of a long, hot, dry summer. Unless they happened to germinate beneath a shrub such as a blackbrush. The shrubs act as nurse plants, shading the seedling Joshua trees from the summer heat and wicking up moisture from deeper soil layers. Wildfires also kill blackbrush and other potential nurse plants.

Contrary to the prevailing dogma, it is not “just a desert.” Joshua trees and creosote bushes are both keystone species within a rich biologically diverse landscape. Joshua trees provide critical structure and food, enabling Scott’s orioles, ash-throated flycatchers, cactus wrens, ladder-backed woodpeckers, red-tailed hawks, and great horned owls to nest across the Mojave Desert. The downed Joshua tree branches provide needed cover and microclimates for desert night lizards and night snakes. Creosote bushes have a long list of bees, beetles, grasshoppers, and more that are only found on creosote. Remove Joshua trees and creosote bushes and the desert rapidly becomes more biologically depauperate.

One ray of hope is that with electric and more fuel-efficient vehicles coming on line every year, smog is diminishing and so should eventually reduce the nitrogen fertilization of our deserts. Less nitrogen should reduce wildfires. Joshua Tree National Park managers are also manually reducing fuels so that when a fire does occur, it should be more limited in extent. Active restoration, planting those keystone species to jumpstart post fire recovery, is also an option. However, such restoration needs to be viewed as a long-term commitment, not a one and done event. Under our current warming and extended drought trend, planted species will require watering and perhaps weeding for many years before they can survive independently.

Nullius in verba 

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

Image below shows smog (aka nitrogen) blowing into the Coachella Valley