In the wake of the recent controversy in Nevada over rancher Cliven Bundy's illegal grazing of at least 900 cattle on a fragile swath of the Mojave desert, supporters of the rancher have pointed to claims that stocking cattle on desert lands can actually improve the desert and help mitigate the effects of global warming.
The hypothesis that cattle can improve desert lands, referred to by its supporters as "Holistic Management," has long been criticized by wildlife biologists, along with its chief proponent Allan Savory.
Now, a new study by western range ecologist John Carter and four coauthors in the peer-reviewed International Journal of Biodiversity says that the claims made by Holistic Management advocates don't actually pan out in the real world, a charge that's sure to offer opponents of desert grazing abundant rhetorical material to fling at its supporters.
Holistic Management is also variously referred to as also known as Holistic Range Management, the Savory Grazing Method, and other names. The short version of the Holistic Management idea -- which I described in some detail a year ago -- is that arid lands benefit from intense, periodic grazing by large herbivores. The notion is based on promoter Allan Savory's work in his native Africa, which continent indeed has a historic abundance of very large grazers.
Savory and his colleagues contend that arid landscapes like the Mojave Desert are declining because of a lack of big grazers, leading to overgrown and "senescent" bunchgrasses, soils sealed off from precipitation by biological soil crusts, and deprived of vital nutrients due to the lack of giant piles of ungulate dung.
Savory's ideas have a number of passionate adherents, and more passionate objectors. In my piece linked above I give a basic rundown of the factual problems with Holistic Management, and plenty of other observers have weighed in on the topic, some going so far as to accuse Savory of engaging in pseudoscience.
That criticism hasn't been limited to blog posts. An article printed in the journal Rangelands in 2000 poked a couple of hoof-sized holes in Savory's claims, most notably his claim that intense grazing causes increased water percolation in arid land soils due to hooves breaking up soils. It turns out the opposite is true most of the time: compaction by hooves creates a hardpan layer that keeps water from soaking into the soil.
But last week's article in the International Journal of Biodiversity is likely the broadest look to date at Savory and the Holistic Management idea. Surveying peer-reviewed literature on grazing and related topics, the authors found no studies that indicated Holistic Management was environmentally superior to conventional grazing methods.
The authors closely examine four main assumptions behind Holistic Management: the hooves help percolation idea; the notion that western American arid lands evolved in the presence of large grazers; the idea that bunchgrasses "senesce" -- grow old and less productive -- if cattle don't eat them regularly; and the idea that grassland ecosystems and the soils that support them degrade over time if cattle are excluded.
The paper details abundant evidence against each of those claims. There weren't many big grazers in arid lands west of the Rocky Mountains until we brought cattle to the region, and so for at least 12,000 years those desert ecosystems have evolved in the absence of heavy grazing. Bunchgrasses in the deserts do better almost across the board if grazing on them is done only by rabbits and other such small animals. Arid grasslands in the West from which cattle have been excluded routinely offer startling amounts of biological diversity compared to grazed lands nearby. And hoof action in the desert only serves to break up those above-mentioned soil crusts, which protect the desert soil and allow rainwater and snowmelt to seep into the deep soil rather than running off.
The authors also take on Savory's much-lauded claim that if we "restore" deserts by grazing cattle on them, the landscape will become a sink for atmospheric carbon dioxide and thus provide a solution to the climate change problem. Savory has gone so far, as in his TED talk, as to say Holistic Management is "the only way" to address climate change.
The authors of last week's paper ably dismantle that claim. Much of the carbon that's stored in arid land ecosystems is in the form of organic matter in vegetation and soils. Long-term grazing has been shown to deplete the amount of carbon that soils can lock up. Meanwhile, when cattle eat desert vegetation, the carbon those plants have stored gets released to the atmosphere -- much of it by way of flatulence as methane, which is a greenhouse gas 34 times more potent than the carbon dioxide the plants scrubbed from the atmosphere to make the leaves the cattle ate.
All in all, the paper offers a persuasive debunking of the broadest claims of the Holistic Management camp.
Lead author Carter, who manages a grazing restoration project in Idaho, was joined by coauthors conservation biologist Allison Jones of the Wild Utah Project, botanist Mary O'Brien of the Grand Canyon Trust, former U.S. Forest Service lands manager Jonathan Ratner of Western Watersheds Project, and biologist George Wuerthner of the Foundation for Deep Ecology.