Page 253 - Environment: The Science Behind the Stories

THe SCIeNCe BeHIND THe SToRy

Restoring the species. They sought to return periodic
malpai Borderlands fire to the landscape by conducting
prescribed burns (pp. 338–339) and by
allowing natural fires to run their course
In the high desert of southern Arizona
and New Mexico, scientists and cattle (Figure 1).
ranchers trying to heal the scars left by The group’s research efforts
decades of overgrazing found they had have centered on the Gray Ranch,
to contend with a creature even more burning brush to re-establish grass cover a 121,000-ha (300,000-acre) parcel
damaging than a hungry steer: Smokey in the Malpai borderlands in the heart of the borderlands. At
Bear. McKinney Flats within the Gray Ranch,
Wildfires might seem a natural trampled the soil, and scattered mes- scientists led by Antioch University
enemy of grasslands, but research- quite seed into areas where grasses had researcher Charles Curtin divided
ers in the Malpai Borderlands realized dominated. Ranchers fought wildfires rangeland into four study areas of
that people’s efforts to suppress fire to keep their herds safe, and the federal about 890 ha (2200 acres) each.
had done far more harm. Before large government joined in the firefighting Each area is further divided into four
numbers of settlers and ranchers efforts. “treatments,” or areas with varying land
arrived more than a century ago, this The Malpai’s ranching families management techniques:
semi-arid Western landscape thrived found themselves struggling to make • In Treatment 1, land is burned and
under an ecological cycle common a living. Decades of photos taken by grazed.
to many grasslands. Trees such as ranchers and by University of Arizona • In Treatment 2, land is burned but
mesquite grew near creeks. Hardy botanist Raymond Turner showed not grazed.
grasses such as black grama covered how soil had eroded and how trees • In Treatment 3, land is grazed but
the drier plains. Periodic wildfires, usu- and brush had overgrown the grass. not burned.
ally sparked by lightning, burned back The ranchers knew their cattle were • In Treatment 4, land is neither
shrubs and trees and kept grasslands part of the problem, but they also grazed nor burned.
open. Deer, rabbits, and bighorn sheep suspected that firefighting efforts were
grazed on the grasses but rarely ate to blame. Treatments 1 and 3, which allow
enough to deplete the range. Fed by In 1993, a group of ranchers grazing, also feature small fenced-off
seasonal rains, new grasses sprouted launched an innovative plan. They areas that prevent animals from eat-
without being overeaten or crowded formed the Malpai Borderlands Group, ing grass. These “exclosures” allow
out by larger plants. designating about 325,000 ha (800,000 scientists to make precise side-by-
By the 1990s, however, those acres) of land for protection and study. side comparisons of how grazing
grasslands were increasingly scarce. Ranchers joined government agen- affects grasses. Scientists measure
Ranchers had brought large cattle herds cies, environmentalists, and scientists rainfall in each area and monitor soils
to the area in the late 1800s. The cows to study the region’s ecology, bring for degradation and erosion. Teams
chewed through vast expanses of grass, back grasses, and restore native animal of wildlife and vegetation specialists

Salinization and waterlogging from the soil’s A horizon may pull water containing dis-
are easier to prevent than to correct solved salts up from lower horizons. As the water evapo-
rates at the surface, those salts remain, often turning the
If some water is good for plants and soil, it might seem that soil surface white. Irrigation in arid areas generally has-
more must be better. But we can supply too much water. tens salinization, and irrigation water often contains some
Overirrigated soils saturated with water may experience dissolved salt in the first place, which introduces new salt
waterlogging when the water table rises to the point that water to the soil. Salinization now inhibits production on one-
drowns plant roots, depriving them of access to gases and fifth of all irrigated cropland globally, costing more than $11
essentially suffocating them. billion each year.
A more frequent problem is salinization, the buildup Remedying salinization once it has occurred is expen-
of salts in surface soil layers. In dryland areas where pre- sive and difficult, so preventing it in the first place is bet-
252 cipitation and humidity are low, the evaporation of water ter. The best way to prevent salinization is to avoid planting

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