A POLICY of suppressing forest fires, coupled with an extreme bout of dry weather, was the kindling that started the huge blazes now raging across western America. But the forests will recover despite the social and economic upheaval. The same cannot be said for deserts and shrubland.
They鈥檝e been quietly burning at an ever-increasing rate since the 1970s. Experts fear that if these blazes continue, the historic desert landscapes of states such as Arizona and Nevada may be lost forever.
While decades without fires have left the forests overgrown with highly flammable fuel, deserts are suffering from the opposite problem. Frequent fires encourage the spread of alien European grasses which are now advancing on great expanses of the western US.
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These grasses fill the open spaces between native bushes, creating a continuous carpet of kindling. Left to their own devices, native flora in regions such as the Mojave Desert in California, the Sonoran Desert in Arizona and open shrublands in the Great Basin of Nevada would need several decades to recover from a fire and regrow enough fuel for another blaze. But the grasses swiftly return, leaving the land ripe for another burn after just a few years, says Matt Brooks, an ecologist with the US Geological Survey in Las Vegas, Nevada. And each fire clears more space for the invaders, creating a vicious cycle that could permanently alter the landscape.
With their sparse vegetation, in the past deserts rarely saw more than one fire per century. But thanks to invasive species such as red brome and cheatgrass, some areas are set alight every few years. Brooks is studying blackbrush, a bush native to Joshua Tree National Park in southern California, which can take up to 75 years to recuperate after a fire. Successive fires could wipe out these natives, he says. 鈥淎t the rate it鈥檚 burning, all of it could be gone in 15 years. And it might not come back.鈥�
The peculiar trees that gave the park its name are better adapted to fire and may recover within a decade, Brooks says. But with the grasses growing back so fast, it鈥檚 possible the fires won鈥檛 wait ten years and the Joshua trees could be lost forever.
And it鈥檚 not just the plants that are in peril. Grass encroaching on bushes will have a knock-on effect on the local fauna. For instance, lack of shade could harm the threatened desert tortoise, says ecologist Todd Esque of the US Geological Survey in Las Vegas. And grasses have overrun the Snake River Birds of Prey Conservation Area in Idaho, where 65 per cent of the native sagebrush has been scorched since the 1970s. Fewer bushes means fewer small mammals for the raptors to eat.
Some scientists are optimistic that the dry conditions that set the stage for the massive forest fires this summer may give the deserts breathing space. After a few years of drought, exotic grasses die off leaving the deserts to recover, says Richard Minnich of the University of California, Riverside. But those same grasses respond quickly to rain, argues Esque, and with another El Nio predicted for this winter, they could soon be back in force, once again inviting fires.