In the Burning Desert

Palm Springs caught a break this past weekend; winds that had been buffeting the area for several days died down Sunday night, allowing the local fire department to put out a seven-acre brushfire in Chino Canyon before it spread. The fire, along the road to the Palm Springs Aerial Tramway, could easily have spread to wildlands to the north or west of the city. A moderately wet winter has meant exuberant growth of both native and exotic plants, adding to the fuel load of the surrounding wildlands: an unlucky gust of wind could have sent embers up onto the steep desert slopes of Mount San Jacinto. But the winds were light, and firefighters were able to douse the blaze within about an hour. Bullet dodged.

According to a report released by the National Interagency Fire Center (NIFC) last week, Southern California likely isn't facing a catastrophic wildfire season in the first half of 2011 -- certainly reassuring news for those of us eyeing the millions of acres in Texas that have burned so far this year. But what's true for the coast and mountains may not be true for the state's deserts.

The NIFC's 2011 National Seasonal Assessment Workshop for the Western States, Alaska and Hawaii, compiled by a regional network of fire, weather, and climate specialists, identified a swath of the Southwest from Arizona to Kansas as facing above-average risk of wildfire until July -- bad news for fire-weary Texans -- but their forecast for California is more ambivalent:

In other words, the wet winter we just got done enjoying has moistened the forests and chaparral, and most of the state isn't expected to burn down until late summer at the earliest.

In California's deserts, though, that wet winter may have increased the threat of fire rather than damping it.

Since the 1980s or so we've learned that fire is a natural part of many Western landscapes, and that suppressing it can cause more injury to the ecosystem than letting it burn. But that's not true of the desert. For most of the last 12,000 years or so, wildfire has been a stranger to most of the deserts of the southwest. Wildfire requires a continuous supply of burnable fuel to spread, but the deserts didn't offer that supply until quite recently, at least not in the lower elevations. Extreme aridity meant plants had to compete for every drop of water; the traditional desert landscape below about 5,000 feet was generally characterized by widely dispersed shrubs and small trees separated by expanses of stony soil. There have always been occasional fires in the desert's higher-altitude conifer forests. Below that altitude, however, an individual lightning-struck mesquite or yucca might burn to the ground, but the fire wouldn't spread.

That changed with the advent of a few species of invasive exotic plants that thrived in the arid desert landscapes.

There's red brome, for instance; a grass native to the Mediterranean basin, was among the earliest of the problem species to arrive: it was established in California by 1848, and had spread throughout the Mojave Desert by 1950. Red brome's close relative cheatgrass was here not long after, and now forms nearly solid stands throughout the Great Basin Desert.

Buffelgrass, which has marched through the Arizona Upland section of the Sonoran Desert like a conquering army, is expected to do much the same before long in California's low desert. It is closely related to, and closely resembles, the ornamental fountain grass that has escaped cultivation and now dots southern California's mountainsides.

Sahara mustard might be the scariest of the invaders. Thought to have been introduced into the deserts as an undetected hitchhiker in date palm seedlings planted around Coachella, Sahara mustard can grow profusely even in years too dry for red brome and buffelgrass.

A wet desert winter promotes the growth of these exotic plants, and they take advantage of every drop of moisture, filling what had been more or less unvegetated expanses of stony soil between native shrubs and cacti. Where trees struck by summer lightning or careless-tossed cigarettes once burned to the ground, then smouldered and went out once the fuel was gone, the flames now leap into a near-uninterrupted carpet of dry fuel and race on to the next tree or shrub.

Since wildfire is a relative newcomer to the desert, native plants haven't had any reason to evolve adaptations to wildfire. When a swath of desert burns, those native plants often have a hard time re-establishing themselves. The exotic grasses and mustard have no such problems: they spring back readily after destructive fires, freed from competition with the natives. A few big fires and the landscape changes utterly.

After the wet winter of 2004-2005, a series of summer monsoon storms swept across the deserts. One lightning strike after another touched off fires in California, Nevada and Arizona. More than a million acres of formerly fire-proof desert burned in the months of June and July. Much of that land now bears a thick carpet of invasive plant matter.

On Mount San Jacinto just uphill from the site of the Chino Canyon fire of this weekend, red brome grows in abundance. It gave the once-russet slopes above Palm Springs an odd greenish cast from January through April. It's turning yellow right now. A stray spark from a cigarette, a lightning strike, or an overheated muffler could send fire racing up the incredibly steep slope. It may not happen this year, but it will happen, some hot June or July after a wet winter, with fire season in the rest of California still months away.