“No matter how hard we try, the fires are going to keep getting bigger, and the reason is really clear. Climate is really running the show in terms of what burns.” — Park Williams

True, yet there is another driver dictating wildfires in deserts – invasive, non-native grasses. There are grasses that are native to the hot deserts of North America, and they are typically geared toward responding to summer monsoons. Most are perennial bunchgrasses, but there are some annuals as well. However, all respond to summer rain, are green when lighting strikes and so do not offer fuel to “feed” wildfires. Unlike most other plant communities across western North America, desert plants are not adapted to fire, and are more often killed by those fires. Most non-native grasses have a very different strategy. They respond to winter rain, completing their growth and reproduction by early spring. They then turn dry and brittle by summer, becoming perfect tinder for carrying wildfires from Joshua tree to Joshua tree, from creosote bush to creosote bush.

These non-native grasses were thought to have been introduced purposefully by cattle and sheep ranchers, trying to provide forage in an otherwise arid landscape. Initially, at least in the Mojave and Colorado Deserts, those non-native grasses didn’t find the nutrients that they required to take over desert landscapes, the desert soils lacked the rich nitrogen-laden soils that could foster dominance by these grasses. But increasingly these grasses did assert their dominance. Research by UC Riverside’s Dr. Edith Allen and her students demonstrated that these grasses’ current dominance was tied to nitrogen being added to desert soils. The source of that nitrogen was air pollution, smog, blowing east from the Los Angeles basin. Along with climate change, wildfire, now fueled by these invasive annual grasses is putting desert landscapes, especially Joshua tree woodlands, at risk of being changed and lost. Recovery after wildfires is slow at best and due to the heat and hyper aridity born from modern climate change, some desert communities may never recover at all.

At the upper elevation edge of both the Mojave and Colorado Deserts there is a transition zone, an ecotone, where desert species interface with and, at still higher elevations are replaced by, desert chaparral and then pinyon pine woodlands. Here lies an ecological enigma. The desert chaparral plants are adapted to fire. Their seeds often require fires to germinate, and many sprout back from their root crowns days after the wildfire’s embers have cooled down. The spring following a wildfire there is often an explosion of fire-following wildflowers stirred to germinate by the smoke and/or heat of the fire. Yet the desert species do not tolerate fire and neither do the pinyon pines. What is good for the desert chaparral species is disastrous for both pinyon pines and other desert plants. In lieu of wildfire they can all co-occur and thrive. However, when wildfires do occur, only the chaparral species and fire followers are left. Over centuries I imagine a “fluid” ecotone where, in the absence of fire, Joshua trees and junipers and pinyon pines reign, but where and when fires occur chaparral species take over. Some have reported that it could take as long as 700 years for pinyon pines to become reestablished following a fire. Given that chaparral thrives with periodic fire,  and  with the current climate trajectory of being still hotter and drier, it is hard to foresee pinyons and Joshua trees recovering after a fire until that climate trajectory is reversed.

As a result of modern climate change, desert species, both plants and animals, are reproducing and maintaining sustainable and even growing populations at the higher elevation ends of their range. However, at the lower, hotter, and drier ends of their range these populations are waning. That phenomena is resulting in incremental population shifts to higher elevations, including into the aforementioned desert chaparral ecotone. Whether those shifts result in new ecological opportunities and climate refugia, or conflicts with other species and fire regimes for which they are ill adapted, is yet to be determined.

One place to see this transition zone is within the Pioneertown Mountains Preserve, owned and managed by the non-profit Wildlands Conservancy. Soon after the Conservancy acquired this land the 2006 Sawtooth Fire complex was ignited by a lightning strike. Prior to the fire, the preserve included a beautiful example of the pinyon pine – juniper – Joshua tree plant community. In the absence of fire this plant community exists at the upper elevations of the Mojave Desert, the ecotone that transitions from true desert to the higher conifer forests of the San Bernardino Mountains.

On July 9, 2006, the Sawtooth fire changed everything. It burned over 61,000 acres (250 km²), destroyed 50 homes, and one person was killed. The fire was almost certainly fueled by non-native grasses. All the pinyon pines and junipers within the Preserve are gone. Most of the Joshua trees are gone as well, although unlike the pinyons and junipers, some of the Joshua trees survived. What was once a forest is now high elevation (mostly 4,500-5,500 feet) desert chaparral. Dominant species along the six-mile trail now include chamise, big berry manzanita, cupped-leaf ceanothus, birch leaf mountain mahogany, hollyleaf cherry, and desert scrub oak. All were present before the fire, but then were overshadowed by the pinyons and junipers. We saw one true low desert species, a creosote bush, at nearly 5,500 feet – perhaps a regional high elevation record, or if not, nearly so. Gone are pinyon jays and Scott’s orioles. But, the lizards were abundant, especially side-blotched lizards; we saw over 300 lizards, across six different species, the highest lizard density we have found anywhere across the desert and adjacent mountains.

Nature is never constant. Annual seasons, El Niño – La Niña cycles, wildfires, and ice ages all precipitate change. Invasive species and anthropogenic climate change are altering what was a known dynamic to levels that neither we, nor the species being affected, have ever seen before. Those uncharted levels and speeds of change makes predicting outcomes increasingly uncertain. One action we can take is to document these changes, to create a record of how both our effluents and our manipulations of species distributions are impacting the diversity of life.

Nullius in verba

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