Livestock grazing aggravates climate change impacts
As climate change advances, public lands across the American West represent a tremendous potential for sequestration of carbon, protection of precious fresh water supplies, and preservation of intact habitat for imperiled species. And yet continued fossil fuel development, timber extraction, and commercial livestock production on these lands negate this potential, and have resulted in the alarming reality that US public lands are actually net emitters of greenhouse gases, rather than the greenhouse gas (GHG) sinks they would be with proper management.
Globally, the United Nations Food and Agriculture Organization estimates that livestock production contributes at least 14.5 percent of global greenhouse gas emissions, with most from cattle production. The majority of these emissions are from enteric methane (CH4) produced in the digestive systems of cattle—and emitted, yes, as cow belches--and nitrous oxide (N2O) from fertilization of pastures. Significant GHGs also result indirectly from cattle production via the decomposition of manure, the production and processing of feed—including the intrusion of pasture and feed crops into forests—and from the transportation of cattle and their products.
While intuitively, raising cattle on grasslands rather than in feedlots seems both more humane and less carbon-intensive, a number of studies have found that grass-fed cows emit far more methane than feedlot-raised cows. Grass-fed cows take longer to mature, allowing them a longer period of time in which to emit methane; this effect is exacerbated for cattle reared on arid western lands where forage quality and quantity are limited.
While some studies have found these increased emissions are partially mitigated by the ability of grazed pastures to store carbon, this carbon-storage potential is only realized through active management—frequent herding, range riding, and pasture rotation that are not the norm across many public land grazing allotments, and least of all on the large, sparsely vegetated allotments typical of public lands in the arid intermountain west.
Any reference to the carbon sequestration benefits of grazing also raises the question of against what baseline these benefits are measured: for while grazed pastures may do a better job of sequestering carbon than a suburban subdivision or shopping mall, these are outcomes from which at least in the foreseeable future, our public lands are protected. But in comparison to the forests, pinyon-juniper woodlands, and native bunchgrass and cryptogamic soil ecosystems they displace, grazed rangelands generally represent a very poor carbon storage deal indeed.
And this is in large part due to the extensive degradation of soils, vegetation, and native ecological conditions that occurs when large numbers of non-native ungulates are introduced into a system that did not evolve in their presence. Soils hold on to carbon in the form of living and dead roots in the top few centimeters of soil, and aerial parts of vegetation that remain in the absence of significant disturbance. With sustained livestock grazing, however, accelerated erosion results in the loss of organic matter-rich topsoil and the consequent conversion of sequestered carbon into gaseous greenhouse emissions.
Other impacts of grazing on the ability of soils to sequester carbon are well-documented. The loss of organic matter and nutrients due to removal of vegetation by ungulates, as well as diminished permeability caused by hoof compaction, result in nutrient-poor, dry soils that are less productive and less supportive of native vegetation. As climate change advances, warmer temperatures, diminished precipitation and enhanced wildfires throughout much of the intermountain west will exacerbate these effects, leading to positive feedback loops with the potential to devastate native ecological communities. These effects, combined with the massive dewatering of streams and destruction of riparian corridors that result from grazing—which amount to the wholesale destruction of habitat essential to a majority of the arid west's biodiversity—mean that ecosystems have very little leeway to adapt as climate conditions change.
As climate change begins to stretch most ecosystems past the point at which normal processes can no longer function, responsible management includes minimizing stressors on already impacted lands. Grazing by domestic cattle and sheep has no place on western public lands whose wildlife habitat, water storage and filtration, and other ecosystem services will become ever more critical to the survival of wild and human communities.