When palm oases catch fire
“The desert tells a different story every time one ventures on it.” — Robert Edison Fulton Jr.
Wildfire in deserts should not happen. Before recent times there would only rarely be enough fuel to carry a fire more than a few meters beyond where perhaps a bolt of lightning struck a Palo Verde or Joshua tree.
Additionally, because fire has not been a regular ecological force in deserts, desert plants have few if any adaptations to survive a fire. As opposed to fires in chaparral, oak woodlands, or many types of forest ecosystems, where plants survive fire and ecosystems can be rejuvenated by periodic burns, desert fires, now fueled by invasive, non-native grasses, leave the desert landscape truly barren. Creosote bushes may take decades or even centuries to recover after extensive wildfire. Fire-following annual plants create spectacular spring shows of color on chaparral slopes for years following a fire. There are no such fire followers in deserts. Second only to climate change, wildfires fueled by those non-native grasses represent one of the greatest threats to Joshua trees.
There is an exception to this maxim of deserts being, or that they should be, a fire-free landscape. Palm oases. Visit almost any desert fan palm oasis and you can see the tell-tale black char on the trunks of still thriving palms. There is no question that desert fan palms easily survive fire. Palm tree species throughout the planet survive and thrive in a world where there are periodic wildfires. It's in their DNA. As monocots, a broad group including grasses, orchids, agaves, yuccas, and palms, the palm trees’ vascular system, the system of moving water and nutrients up and down a stem or trunk, is distributed throughout the palms’ trunk. This contrasts with non-monocot (dicot) trees and shrubs where their vascular system is only on the outer edge of the plants’ trunk or stem, just below the bark. With ample water flowing throughout a palm’s trunk, that water keeps all but the outer edge from being consumed by a fire. The core stays alive.
For dicots, when that outer edge burns the branches and trunks are killed (dicots in fire-prone landscapes often survive by re-sprouting from the unburned root system insulated from the fire by dirt).
Palm oases are centers of high biodiversity. Within their skirts, the still attached dead palm leaves that hug the palm trunks, many creatures find a relatively cool refugia from the intense heat of desert summers. Barn owls, western screech owls, long-eared owls, and great horned owls all roost and nest in palm tree skirts.
Southern yellow bats are, if not restricted to, almost exclusively found in desert fan palms skirts where they can be joined by a handful of other bat species. There are also pack rats, common king snakes, desert spiny lizards, and hooded and Scott’s orioles that all live much of their lives in the skirts of palms trees. A veritable multi-species apartment complex enabling animals of all branches of the “tree of life” to venture into and thrive in deserts. Except when palm oases burn, the palm skirts are turned to ash and then so goes that apartment complex. The mature palm trees survive and eventually form small skirts at the top of the tree, but until new palm trees germinate and grow into adults, palm skirts that reach from the ground to the treetops, forming ground to tree-top ladders that foster that rich biodiversity, are gone.
The relationship of fire in native desert fan palm oases and the other creatures that live in those oases is a paradox. Palms survive fires and, in many cases, produce more flower stalks and fruit following fires. However, the loss of the palm skirts renders the oases far less rich in biodiversity. Lightning strikes during the summer monsoons are certainly one source of those fires, but in the 36 years I have lived here, within the complex of palm oases associated with the preserve centered on Thousand Palms Canyon, Willis Palms has burned twice, portions of Pushwalla Palms have burned twice, Biskra Palms East and part of the grove in the Thousand Palms oasis have each burned once. All were vandal-started fires. The palms mostly survived each fire; the highest cause of palm mortality came from well-meaning, but ultimately futile efforts by fire departments trying to extinguish the fires. However, other palm oasis plants did not fare as well. Honey mesquite, another extremely important wildlife-supporting species does not survive in areas of intense fire. At least in recent history, there has been a clear correlation between the frequency of fires in palm oases to the use, or better said, misuse by recent human visitors.
Going back in time more than a century and beyond, the Cahuilla and Serrano people lived seasonally in and adjacent to palm oases, and according to their oral history, they employed fire to manage the palms. The most compelling reasons given for burning the palms was to stimulate greater fruit production, and perhaps to clear the understory of the oases which would have facilitated the germination and growth of new palms. I imagine that their application of fire would have been “surgical” rather than a general torching of the entire oasis. Killing mesquite living on the edge of the oases would have been counter to their dependency on that species as one of their most important and dependable sources of protein. Burning the very tall palms would also not have been to their benefit since they would have been unable to reach the fruits there not matter how abundant they might be.
Those pre-colonial residents also lived in homes they called a kish, which would have been made in part from palm fronds and so would have been extremely flammable. A less compelling reason given for these people applying fire to the palms was to “control insect pests such as the palm-boring beetles." Since the palm-boring beetle has coexisted with the palms for much longer than any people have lived here, and given that the Cahuilla and Serrano were astute naturalists, it would be challenging to imagine that they would have considered the beetles pests, let alone whether fire would control the beetles. More likely the beetle-control was added by the anthropologists recording the oral histories, adding their European sensibilities about controlling insects be they beneficial, benign, or pests.
People are a part of nature and so some level of burning in palm oases is also a part of nature. That said, the human application of fire will have very different outcomes depending on whether it is “surgical” or broadly misapplied.
Nullius in verba
Go outside, tip your hat to a chuckwalla (and a cactus), think like a mountain, and be safe