Livestock Impacts To Desert Regions

ABSTRACT: Livestock production occurs in all deserts (except polar deserts). In many desert areas, it is the single most significant human impact. Livestock production includes grazing plants and all associated activities to produce domestic animals. This consists of the dewatering rivers for irrigated forage crops, killing of predators and “pest” species, forage competition between native and domestic animals, soil compaction and erosion, changes in fire regimes, the spread of alien plant species, loss of biodiversity and numerous other ecosystem effects.

INTRODUCTION
Worldwide some 3 billion hectares of land, including deserts, are grazed by domestic livestock, and the majority suffer degradation and loss of biodiversity as a result (Carter et al., 2014).

Deserts are usually defined as arid or semi-arid landscapes, often with high evapotranspiration rates, high rates of solar radiation, and large daily and seasonal temperature range. These factors limit the plant and animal life that can survive in these environments, although there are many remarkable adaptations that species have developed to deal with these extreme conditions.

The Great Basin region of the United States is considered a “cold” desert dominated by sagebrush. Trout Creek Mountains, Oregon. Photo George Wuerthner 

Many people associate the term desert with “hot” temperatures like the Saharan desert in Africa or the Sonoran Desert in Arizona and northern Mexico, which are found where descending air creates dry zones. However, many other deserts are colder, often associated with the rain shadow effect of mountains. Cold deserts like those found in Central Asia (Gobi) or Great Basin in North America will often get snow cover for part of the year. The polar desert in Antarctica is the largest desert area in the world and is almost entirely snow-covered year-round.

No matter where they are found, all desert zones experience periods of acute precipitation shortages, which has significant implications for the human ability to exploit the ecosystem with livestock grazing. Domestic livestock includes grazing animals such as cattle, sheep, goats, horses, donkeys, yaks, camels, and other species.

Humans have traditionally used marginally productive landscapes and steeper mountainous terrain for livestock production, while better-watered landscapes and flatter terrain are reserved for crop production. However, except for irrigated landscapes, most deserts have limited ability to support crop agriculture other than hay or pasture. Consequently, livestock grazing is often the dominant economic use.

Except for the polar deserts, most of the world’s desert areas experience some livestock grazing. Indeed, ungrazed reference points or refugia where livestock grazing has not occurred are difficult to find. (Unless otherwise noted, when I use the term “grazing,” I am referring to cropping by domestic livestock.)

Throughout the world’s deserts, there are many native herbivores. In North American deserts, native herbivores include insects like grasshoppers (Melanoplus spp.), rodents like ground squirrels (Spermophilus spp.), pig-like javelina (Tayassu tajacu) to larger ungulates like mule deer (Odocoileus hemionus) or pronghorn antelope (Antilocapra americana). Herbivores like kangaroos (Macropus) are found in Australian deserts, while Asia and Africa have even larger native herbivores.

Cattle degraded Bureau of Land Management (BLM} lands in eastern Oregon. Photo George Wuerthner

Though there are many native herbivores, it’s important to note that this does not necessarily mean those plant communities are adapted to exotic domestic livestock grazing. Exotic livestock does not utilize the landscape in the same way as native species. And even when a species might be “native” to a particular ecosystem, the tendency to maximize profits and animal production leads to excessive numbers of animals that are above the ability of the landscape to support.

As a generalization, livestock grazing is one of the major human activities responsible for creating or expanding desert areas through “desertification.”

Grasses, shrubs, and scattered trees characterize the vegetation in most deserts outside polar regions. Grasses and shrubs are the dominant forage utilized by domestic herbivores.

ARIDITY IMPOSES LIMITS

Aridity puts limitations on livestock production and tends to exaggerate the ecological impacts of livestock.

First, the lack of precipitation limits plant growth compared to other ecosystems. Regarding primary productivity, desert ecosystems have some of the lowest primary productivity (the rate at which photosynthetic and chemosynthetic autotrophs convert energy to organic substances) on earth. For instance, the United States (U.S.) General Accounting Office (GAO, 1991) concluded that “hot deserts are among the least productive grazing lands in the United States.”

An appraisal conducted in 1984 by the U.S. Bureau of Land Management (BLM) and the U.S. Forest Service found that more than 160 acres of land were sometimes required to support one cow for one month in southern New Mexico, Arizona, southwestern Utah, southeastern California, and most of Nevada (GAO, 1991).

One of the significant characteristics of desert landscapes is variable precipitation. Precipitation has a huge effect on plant growth. Therefore, drought conditions are more likely in desert regions and typically will last longer than in other ecosystems. Since much plant growth depends on the amount and timing of precipitation, prolonged drought can significantly reduce the annual plant biomass production and, thus the forage to support livestock.

The cumulative impact of livestock is more than “grazing” or “browsing” (see below); rather, these should include the collateral damage from livestock “production” (Wuerthner and Matteson, 2002).

A 1994 U.S. Forest Service report concluded that livestock grazing was the 4th major cause of overall species endangerment and the 2nd major cause of plant endangerment (Belsky et al., 2002).

As the U.S. General Accounting Office (GAO, 1991) concluded in a report to Congress: “Current livestock grazing activity on BLM allotments in hot desert areas risks long-term environmental damage while not generating grazing fee revenues sufficient to provide for adequate management. GAO found evidence of damage occurring on BLM lands and evidence of livestock grazing’s adverse impacts on several wildlife species. Moreover, some damaged lands may take decades to recover–if they recover at all.”

The modern “cowboy” on his ATV herding cattle. Photo George Wuerthner 

Among the well-documented direct impacts of livestock production on desert ecosystems are the destruction of soil crusts, damage to riparian areas, forage competition with native wildlife, the spread of invasive weeds, changes in plant community composition, and losses in carbon storage.

Other aspects of livestock production include disease transmission from livestock to native wildlife, water pollution, the killing of “pests” and predators to protect livestock, the dewatering of rivers for irrigation, and the “capture” of springs and other water sources for livestock (Wuerthner and Matteson, 2002; Fleischer, 1994).

Not all species are negatively impacted by livestock production. For instance, brown-headed cowbirds (Molothrus ater), a nest parasite, increase with more domestic cattle. Sagebrush sparrow (Artemisiospiza nevadensis) likely “benefited” from the shift from grasslands to more shrublands in some cold desert ecosystems (Bock et al., 1993). However, in most cases, the species benefiting are widespread generalists, while those harmed by grazing tend to be rarer or those with special habitat needs.

As Bock et al. (1993) concluded in one research review, “The problem with livestock across much of the West today is not with their presence, but with their ubiquity.”

Those plants and animals, including neotropical migratory birds, intolerant of activities of domestic grazers, have comparatively few places to live.

SOIL CRUSTS

One of the essential negative impacts of domestic livestock, particularly animals herded in tight groups, is the trampling of soil crusts. Soil crust is a critical component of arid to semi-arid ecosystems. Soil crusts are known by many names, including biocrusts, cryptogamic, cryptobiotic, microbiotic, or microphytic crusts. Soil crust consists of cyan bacteria, fungi, lichens, mosses, and green algae and may comprise up to 70% of the plant cover in some communities. Indeed, in many desert ecosystems, there are more species of soil crusts than vascular species.

Biocrust, or soil crust, covers the ground and reduces soil erosion. Photo George Wuerthner 

By covering the soil, biocrusts reduce wind and water erosion and act as a mulch, helping retain soil moisture. In addition, many soil crusts can fix atmospheric nitrogen, so it’s available to other plants. They also affect carbon storage and influence plant germination and growth. Notably, nitrogen is one of the limiting factors in many desert areas. In some desert locations, nitrogen fixation by the soil crust is often one of the essential nitrogen sources (Evans and Belnap, 1999).

Crusts often play a critical role in soil productivity. Nitrogen-fixing cyanobacteria and lichens dominate many biological soil crusts in western North America. Microfungi also weave filaments through the top portions of the soil, holding the soil particles together.

While many desert vascular plants have adaptations to assist germination, such as self-burial mechanisms or rely on rodents for caching seeds, unlike native species, many exotic species like cheatgrass (Bromus tectorum) lack such adaptations and can be inhibited from successful germination by intact soil crust.

By destroying soil crusts, livestock grazing also increases the occurrence of cheatgrass fueled wildfires, one of the significant threats to sagebrush ecosystems and wildlife like sage grouse (Centrocercus minimus).

SOIL COMPACTION AND TRAMPLING

Trampling and compaction of soils are an unavoidable impact on domestic livestock. The destruction of soil crusts, a reduction of water infiltration reduction, and removal of vegetative cover have led to increased soil erosion. A lower infiltration rate means less water will be available for plants, and more surface erosion may occur.

The compaction of soil by livestock hooves reduces water infiltration. Freighter Spring, Idaho. Photo George Wuerthner 

For instance, an experiment in Arizona looked at how vegetation changes have led to increases in interrill areas, decreases in runoff infiltration, and the possibility of greater susceptibility to frost action (Abrahams et al., 1995).

Soil compaction reduces water absorption for plants, making it more difficult for them to spread their roots (Boarman, 2002). A review of grazing impacts on hydrological systems concluded that grazing at any intensity reduced water infiltration (Gifford and Hawkins, 1978).

Water run-off experiment tests showed that moderate grazing areas had seven times the runoff compared to lightly grazed areas, and heavily grazed areas had ten times the runoff as lightly grazed areas (Boarman, 2002).

Another effect of soil compaction and erosion are changes in soil temperatures. Grazing by livestock can increase soil temperatures. Hence water evaporation and amplifying the already hot conditions found close to the ground in desert areas. For instance, a significant increase in soil temperature at depths of 2.5, 7.5, and 15 cm was observed in clipped versus unclipped plots (Steiger, 1930).

Trampling by hooves also can affect seeds biomass. For example, a study in the Mojave Desert (U.S.) found a higher number of native seeds in an area protected from livestock grazing and off-road vehicles compared to locations outside of the enclosure, even though there were more seed-eating rodents inside the enclosure as well (Brooks, 1995).

RIPARIAN AREAS

Riparian areas are those lines of water-influenced green vegetation found along waterways. Estimates suggest that riparian areas occupy about 1–2% of the land in many arid landscapes. Yet, despite their relative scarcity, the combination of water, and lush vegetation growth, these thin, green lines are very productive sites and ecologically critical to 60–70% of wildlife in the western United States.

Cows trash riparian area, BLM lands, Ruby Mountains, Nevada. Photo George Wuerthner 

Riparian areas support about a third of all plant species found in the arid West. One study of Arizona’s arid lands concluded that 70% of all threatened and endangered species are riparian obligates (Johnson, 1989).

The highest densities of breeding birds in North America are reported from southwestern riparian woodlands. More than 75% (127 of 166) of southwestern bird species nest primarily in riparian woodlands, and neotropical migrants comprise 60% of the 98 species of land birds (Bock et al., 1993).

Due to the abundance of green vegetation, shade, and water, riparian areas are particularly attractive to domestic livestock. However, their foraging in these areas has multiple impacts (Behnke and Raleigh, 1978; Kauffman and Krueger, 1984; Armour et al., 1991; Poff et al., 2012).

Livestock alter the stream channel leading to more extensive and shallow profiles. These channel modifications, in turn, lead to higher stream temperatures and velocities which can be detrimental to fish, including a three to four-times decline in trout (Salmo) in grazed versus ungrazed stream sections.

Another review study documented that livestock grazing negatively affects water quality and seasonal quantity, stream channel morphology, hydrology, riparian zone soils, instream, streambank vegetation, and aquatic and riparian wildlife (Belsky et al., 1999).

Browsing on streamside shrubs and trees like willow reduces the creek’s shading and habitat for nesting songbirds.

Cattle eliminate streamside vegetation in riparian areas. Photo George Wuerthner 

Soil compaction from livestock (as discussed above) reduces water infiltration and the “sponge” effect of riparian areas. The loss of sponge effects can lead to a reduction in late-season flows.

Removing grass and other streamside vegetation by livestock reduces hiding cover for many species. For instance, sage grouse chicks rely on tall streamside vegetation for feeding and hiding cover (Thompson et al., 2006).

When grass is cropped to golf putting green height (1 cm), many species, from amphibians to reptiles to birds and mammals in riparian areas, are exposed to predators.

FORAGE COMPETITION

As previously stated, productivity in arid climates is generally low; thus, any forage removal by domestic animals can have a disproportionate impact on native species (Willers, 2002). For instance, desert tortoises (Gopherus agassizii) remain in their burrows for extended periods and only emerge to feed when their favorite foods are green and nutritious. Tortoises selectively feed on herbaceous vegetation, the same plants favored by domestic livestock. Avery (1998) in the Mojave Desert demonstrated that tortoise foraging behavior was altered where cattle and tortoises overlapped.

In the absence of livestock, tortoises primarily ate herbaceous perennials (91% of diet), whereas, in the grazed areas, tortoises mainly ate annual grasses (59%), followed by herbaceous perennials (21%). In addition, greater forage removal by livestock affected tortoise reproduction, with fewer eggs laid in drought years where livestock competed with tortoises for food (Tracy, 1996).

Another example can be found in sage grouse. Although the sage grouse, as its name implies, relies on sagebrush (Artemisia spp.) much of the year, the chicks rely on forbs during the first 4–6 weeks of their lives. Grazing by domestic livestock can remove many of these favored plants.

A third example can be found with desert bighorn sheep (Ovis canadensis nelsoni). Domestic sheep and bighorn sheep consume substantially the same foods, and if a herd of domestic sheep moves through wild sheep habitat, they can leave little forage for the bighorns.

The presence of domestic livestock socially displaces elk and other wildlife. Photo George Wuerthner

Social displacement also influences forage use. Many native species avoid areas where domestic animals are actively grazing. For example, several studies documented that mule deer, pronghorn, and elk (Cervus canadensis) will avoid grazing in the same pastures as domestic animals and are displaced — presumably to less suitable habitat. For instance, in one study in a mountain uplands (so not desert), 94% of the observations of elk Cervus canadensis occurred in pastures unoccupied by livestock (Frisina, 1992).

Another impact of “forage competition” is the loss of hiding cover for small mammals, reptiles, and ground-nesting birds. For instance, sage grouse depend on tall vegetation to hide their nests from predators (DeLong et al., 1995).

INVASIVES AND WEEDS

Invasive plants and animals are either exotics from other countries or native to the region but found in a new location. Among the most problematic invasives in the western US deserts are cheatgrass (Bromus tectorum) and Russian thistle (Salsola tragus), both favored by the disturbance caused by livestock. Other exotics are purposely planted to improve forage for livestock, like crested wheatgrass (Agropyron cristatum). As a result of these factors, livestock facilitate the spread of exotics indirectly or directly.

WATER COMPETITION

Water is typically scarce in desert ecosystems. There are three primary ways that livestock production directly impacts water: (1) direct water consumption and pollution; (2) dewatering of natural water sources like rivers and springs for irrigation to grow hay for supplemental forage; and (3) construction of dams and reservoirs primarily to store water for irrigation.

In many deserts, natural springs and seeps are tapped to provide water for domestic animals, which can reduce the availability of water for native species. In addition, domestic animals often trample the areas around such water sources, leading to soil compaction and a reduction of flows. Ranchers usually pipe water into troughs, making it more difficult for native species to access. Loss of springs and seeps via dewatering has been shown to reduce native snails (Frest Terrance, 2002) and amphibians (Engle, 2002).

The mere presence of domestic animals may socially displace native species. Some native species will wait until domestic animals are absent before they access waterholes. For instance, a study of pronghorns (found that nearly one-half of pronghorn—feral horse interactions resulted in the exclusion of pronghorns from the water).

The production of hay as supplemental forage for livestock is typical in desert areas. Nearly every natural meadow along streams has been converted from natural vegetation of sedges, water birch (Betula nigra), alder (Alnus spp.), and willows (Salix spp.) to nonnative grasses. The losses of native vegetation shrubs have a significant impact on native species. Many songbirds nest and feed in this streamside vegetation.

Many dams and reservoirs built in the western U.S. and other arid regions are constructed primarily for water storage for irrigation. In many instances, that irrigation water is used to grow forage crops for livestock. These dams have many negative impacts on native species—for example, one study documented that riparian forests dominated by cottonwoods (Populus spp.) are declining due to disruptions in natural flood cycles and groundwater levels by dams, groundwater pumping, and water diversions (Beauchamp et al., 2005). Changes in water temperatures and flows due to dam releases also negatively impacted desert-dwelling native fish like humpback chub (Gila cypha) (USFWS, 2017).

Irrigation for livestock forage production (hay) is the primary factor in the dewatering of western rivers. Photo George Wuerthner 

Irrigated hay production for livestock is the primary factor in the dewatering of rivers and streams, compromising aquatic ecosystems.

A review by McAllister et al. (2014) of dams and their associated reservoirs impact freshwater biodiversity by blocking the movement of migratory species up and down rivers, causing destruction or extinction of genetically distinct stocks or species, changing turbidity/sediment levels to which species/ecosystems in the rivers affects species adapted to natural levels. In addition, trapping silt in reservoirs deprives downstream deltas and estuaries of maintenance materials and nutrients that help make them productive ecosystems, filtering out woody debris which provides habitat and sustains a food chain.

Dam management that diminishes or stops regular river flooding of these plains will impact diversity and fisheries—changing the normal seasonal estuarine discharge, which can reduce the supply of entrained nutrients, affecting the food chains that sustain fisheries in inland and estuarine deltas. Modifying water quality and flow patterns downstream.

DISEASE TRANSMISSION TO WILDLIFE

Many wildlife species, especially those closely related to domestic animals, often suffer from diseases transmitted from domestic animals. Chronic Wasting Disease, Bovine Tuberculosis, and brucellosis found in wildlife all have origins in domestic animals. A well-documented relationship exists between population decline in wild bighorn sheep and the spread of pneumonia transmitted from domestic sheep (Schoenecker, 2004).

Bighorn sheep populations around the West have been dicimated by disease from domestic sheep. Photo George Wuerthner

PREDATOR CONTROL

Another consequence of livestock production is the increased killing of predators to protect domestic animals. Predators like wolves (Canis lupus), cougars (Puma concolor), coyotes (Canis latrans), and bears (Ursus spp.) are known as “top-down” species that shape ecosystems. All of these species have been killed in the name of livestock production. The loss or reduction of these species can have significant ecosystem consequences. For instance, the presence of wolves in Yellowstone National Park is credited with reducing elk browsing on willows and rejuvenating some riparian areas (Ripple and Beschta, 2011).

Predator control has a significant negative influence on native ecosystem loss. Photo George Wuerthner 

Loss of large apex predators creates a release whereby mesopredators like coyote numbers increase. Bobcats (Lynx rufus), gray foxes (Urocyon cinereoargenteus), and Virginia opossums (Didelphis virginiana) were detected more often at sites occupied by pumas. In contrast, coyotes and raccoons (Procyon lotor) were detected less often. The detection probabilities of smaller mesopredators were related to coyotes, a dominant mesopredator (Wang et al., 2015).

PEST CONTROL

Many native species are considered “pests” by livestock operators who seek to reduce or eliminate them from grazing lands. Prairie dogs (Cynomys ludovicianus), gophers (Thomomys spp.), ground squirrels (Spermophilus spp.), and other rodents are often the target of control efforts, sometimes to the point where native species may be endangered (Wuerthner, 1997).

Grasshoppers and other insects are controlled by poison (Shewchuk and Kerr, 1993). The loss of mammal or insects populaitions impacts desert ecosystems since these animals are prey for other species, from fish to birds to mammals.

CARBON STORAGE

Deserts have a low capacity for carbon storage; however, since arid regions cover about 47% of the earth’s land mass, they are thought to make up the world’s third-largest carbon sink on land. Nevertheless, new research suggests that some endorheic desert basins represent a vital carbon sink on the global scale, with a magnitude similar to deep ocean carbon burial (Li et al., 2017).

VEGETATION LOSS

More significant grazing pressure on the Mexican side of the International border provided a good comparison of how different livestock management policies can affect the land. For example, Berelov and Madsen (2011) reported there was far less green vegetation on the heavily grazed Mexican side of the line.

A study of the Mexican-U.S. (Arizona) border found that the more heavily grazed Mexican desert was consistently warmer than the Arizona stations. Sonora (Mexico) stations warm at a statistically significantly faster pace than the stations in Arizona. The stations in Sonora reveal a significant increase in the diurnal temperature range during the summer season (Balling et al., 1998).

Higher temperatures near the surface of the soil can negatively affect insects like native bees and ants, reptiles like snakes, tortoises, and small mammals who move around close to the soil surface.

CLIMATE CHANGE

Although the overall number of domestic animals supported by desert ecosystems is low due to the limited productivity of these sites, domestic livestock have been identified as one of the major contributors to global greenhouse gas emissions (GHG). Their contribution adds insult to the eocystem injuries. While there are no numbers that break out just the domestic animals produced in desert regions, worldwide estimates suggest that all domestic livestock may be contributing as much as 14% of all GHG emissions (Steinfeld, and Food and Agriculture Organization of the United Nations, and Livestock, Environment, and Development (Firm), 2006). A recent estimate put the total global livestock contribution to GHG emissions at 23% (Reisinger and Clark, 2017).

CONCLUSIONS

Livestock production is one of the most significant influences on desert areas where it occurs, often leading to greater desertification and loss of biodiversity. When you consider the overall large landscape footprint and the cumulative effects of livestock production, including the damage to riparian areas, forage competition with native wildlife, disease transfer, soil compaction, alteration of plant communities, predator control, and dewatering of streams and springs for irrigated forage production and troughs, it is easy to understand why some assert it is the greatest threat to our desert ecosystems.

Due to the natural aridity of desert landscapes, the ability to support livestock is limited. If a full accounting of both the economic and ecological costs impacts were done, it would be difficult to justify continued livestock production in arid ecosystems.

THE SOLUTION

Livestock production in aridlands could never be justified if there were an accurate accounting of the true costs of this human activity. Ranchers, in effect, transfer some of their real costs of production on to society or the landscape.

It’s time to admit that livestock grazing in arid lands is a vast ecological and economic mistake. The Voluntary Grazing Permit Retirement proposal is the most practical solution to the continued degradation of public lands. Under the Voluntary Grazing Permit Retirement proposal, ranchers with public land allotments would be paid a fee to terminate grazing privileges and the grazing allotment would be permanently closed to future livestock use.

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