Alien grasses are finding new homes in Arizona

 

By the end of June, some 20 wildfires had reduced large patches of Arizona’s desert scrublands to ash. The blazes eventually burned over 200,000 acres and killed many huge and venerable saguaros, along with smaller cacti, trees and shrubs.

"Invasive" grasses carried these fires, those species from somewhere else that are increasingly blamed for environmental degradation. They are safe to dislike and deplore, since we feel no moral duty to protect them. They have no advocates, no constituency.

But the presence of flammable grasses from Africa and Asia is not simply nature’s way of telling us something’s wrong. Our modern fire problem may stem from poor grazing practices dating back to the 1880s.

Until the mid-19th century, Arizona was home to significant expanses of desert grasslands, mostly at elevations between 1,500 and 3,500 feet. These grasslands, superficially similar to shortgrass prairie, carried the fires that limited scrub. But unlike the prairies, they could not tolerate heavy grazing, and territorial-era entrepreneurs stocked far too many cattle. That bubble burst by the 1880s, and south-central Arizona became a boneyard.

Stripped of vegetation and bereft of their topsoil, Arizona’s desert grasslands were then "invaded." The cactus and shrubs of Arizona’s "real" desert fanned out to occupy this new territory.

Today, some of those same areas are becoming fire-prone again as a new suite of grasses redefines the region. Whether the plants evolved in Africa or Eurasia, all come from climates comparable to the Arizona deserts.

Some, like buffelgrass and Lehmann’s lovegrass, were planted for range improvement and have subsequently spread. Others arrived in hay, feed and seed, and in the guts and hair and even between the toes of imported livestock. The arrivals of many went unmarked, at first.

Red brome, the lowland counterpart of high plains "cheatgrass," now appears along wash edges and almost anywhere else where water and silt briefly accumulate. It loves to burn. Another species, Mediterranean grass, can be found practically everywhere in the desert. Nobody is really sure when or where it first moved in; it can grow in thousands of plants per square yard, and every dust devil and monsoon wind redistributes its countless seeds.

Many exotic grasses travel along the same corridors we do. In the 1980s and 1990s, buffelgrass, grown widely for livestock forage in parts of Mexico and now common in the Tucson area, worked its way up through Phoenix, and then north and west along interstate and other highways. It is ideally suited to roadsides watered by runoff from rain.

Even Border Patrol vehicles appear to be spreading exotic plants down Pima County’s back roads. These plants exploit every mode of travel. Debris from mowing Bermuda grass lawns sloshes down storm drains to desert washes and rivers, where it can resprout from fragments during the next pulse of runoff.

The presence of exotic grasses in the desert is just one outcome of the ways Arizonans have lived for the past century and a half. They reflect processes begun on a vast scale before Arizona even became a state, and practically everything we do here now contributes further to changes whose details we can’t predict.

There is simply no way that a commercialized society moving as many people and as much stuff as quickly and as often — and over as vast an area as we do — can avoid carrying other lives along with us. These immigrants don’t try to stow away. They don’t sneak in. They just get caught up in the gradients of the season.

The bad news is that some of the desert we knew, or at least sort of knew from postcards, magazines, television and highway scenery, is going away. Mourn if you will. All the governor’s task forces or hoe-wielding environmentalists will not be able to reassemble the old desert. Few experts would even be able to describe what’s missing. For now, intensive weeding maintains a few small museum pieces.

The good news is that plants can still live here. Many unwitting but ecologically qualified pioneers have arrived, entrained in our currents of commerce. By now, some "exotic" grasses in this region have already experienced a hundred generations of evolutionary selection, and may fundamentally differ from their old-world progenitors.

In other words, the aliens are quickly becoming the new natives, and some could already be unique species. Appreciate them, if you can, for what they are — the children of unlikely survivors adapting to a changing region. We reflexively declare that they don’t belong here. On the other hand, the individuals under scrutiny have never been anywhere else.

Matt Chew is a contributor to Writers on the Range, a service of High Country News (hcn.org). He lives in Phoenix where he studies the history of ecology at Arizona State University.