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.
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