This talk by biologist Allan Savory has been generating some heat:
It’s a long, methodical talk, so for impatient readers, I’ll summarize. Savory’s basic points are that:
- There’s a lot more “desert” in the world than there used to be. Human land management practices have taken viable grassland and turned it into uncovered barren soil.
- The reason grassland desertifies is that the grasses depend on the periodic trampling (and dung and urine) of large herds to stay healthy. By removing the pre-existing herds from the grasslands, we’ve contributed to desertification.
- Among other things, desertification changes the ability of the land to regulate heat, sequester carbon, and break down methane. In other words, it contributes to global warming. (Savory claims this may be a greater contributor to global warming than fossil fuels.)
- We can reverse these effects by gathering livestock in large herds and grazing them in a manner that mimics ancestral movement patterns.
These are pretty extravagant claims, and unsurprisingly, the video has generated some backlash.
The most-cited criticism is, I think, also unfair — at least on the basis of the talk. Chris Clarke writes at KCET that Savory “teaches us to disparage the desert.” Clarke’s primary gripe seems to be with terminology: “desert” might mean grassland ruined by bad land management practices, but it might also mean an ecosystem that’s been desert for thousands of years and would be terribly damaged by an arbitrary addition of vast herds of cattle. He illustrates the point with these photos:
Clearly, says Clarke, the land in the bottom photo is doing something different, and it should not be subjected to Savory’s Put a Cow On It! treatment.
That sounds entirely reasonable to me, but there’s nothing in Savory’s TED talk to indicate that he wants to put livestock on every square inch of desert. A more reasonable interpretation (again — based solely on the video; I don’t know what Savory may have said in other fora) is that he wants to reclaim land that could be productive grassland but has been “desertified” by the removal of large herds. Perhaps Clarke is familiar with some much more ambitious, Dr. Evil-esque plan on Savory’s part to “un-desert” the entire Southwest, but if so, I wish he’d linked to it
A clearer and more dispassionate explanation of why Savory’s ideas may not work some desertified North American grasslands is given here by Ralph Maughan, who is not a scientist but does make some pretty persuasive arguments:
The huge Sahara desert was as dry and bare soiled at the end of the Ice Age as it is today. Twice since the Ice Age, changes in the monsoons (natural climate change) brought rains for a thousand or so years, but then 5 to 7-thousand years ago the rains receded and the desert returned. It changed from desert to grassland and back again apparently without human intervention or the presence or absence of livestock.
Today there is land degradation (desertification) around the edges of this greatest desert and much of it is human caused or aided. The same is true over almost all the planet’s deserts and their degraded margins.
The four deserts of North America are the Mojave, Great Basin, Sonoran, and Chihuahuan. They all have some grasslands within their borders, especially the Great Basin and Chihuahuan Deserts. Savory believes that grasslands are maintained by “proper” grazing — grasses evolved along with grazing animals, and lack of grazing destroys the grasslands.
It’s likely the grasses did evolve with grazers, but Savory also believes the grazers of importance were always large mammals. Further, he believes that sheep, goats, and cattle (the latter a completely human produced animal) acceptably mimic the departed wild grazers. This is not true. Over millions of acres of North America deserts, bison, elk, javelina, and pronghorn never roamed and never grazed the deserts or the patches of grassland within them. These deserts were and are grazed, but by small mammals like rabbits, mice, reptiles such as desert tortoise, and insects. Grasses that evolved being eaten by tortoises and rabbits are not likely to respond well to being eaten in intense, even if short termed, bouts of grazing by the artificially created cow, or Old World animals such as sheep, goats, or horses.
Maughan then goes on to explain that these desert-edge ecosystems are doing a decent job of sequestering carbon, thank you, and running cows on them isn’t going to help.
(UPDATE: Here‘s an Atlantic profile of some ranchers who are trying to put Savory’s ideas into practice. They are working in the Great Plains, where large ungulates did indeed roam and forage, and not in someplace like Arizona or Nevada. This seems like the sensible application to me.)
For a thorough review of a large amount of literature, there’s also this blog post by Pete Sundt. The overall takeaway seems to be that Savory’s ideas could be true, at least under certain circumstances, but that he has so far not pointed to any well-formed scientific evidence that they are.
And this post by a Nature Conservancy prairie expert is also pretty interesting. It doesn’t directly address Savory’s talk, but it does address the claim that trampling per se improves soil health:
[T]he general idea seems to be that mob grazing cattle eat about 60 percent of the standing vegetation and stomp the remaining 40 percent into the soil. Thus, soil organic matter increases and becomes more productive…. I checked with four prominent scientists around the country who study soil nutrient cycling, including soil carbon. When I asked them if the claims from mob grazing advocates made sense, their response was unanimous and strikingly blunt. To quote one of them, “That’s totally bogus”.
In reality, soil organic matter is formed mainly by belowground processes, including root decomposition, root exudates, and mycorrhizal carbon inputs. In prairies, a substantial percentage of plant roots are abandoned to decompose each year and replaced with new roots. Those old roots provide organic matter in abundance, and more importantly, that organic matter becomes a stable part of the soil profile – and is added to and enhanced by the other two processes listed above. My panel of experts said that stomping vegetation into the soil might provide a slight and temporary increase in organic matter near the soil surface, but that it would be unstable and wouldn’t last long.
Perhaps the most illuminating information I’ve found is in the comments section of this blog post from the Washington State University website. Allan Savory himself shows up in the comments, and his performance is fascinating. On the one hand, he seems quite sharp as a scientist, gently mocking experiments that attempted to replicate herd effect with “2 steers rotated through one acre plots.” That’s a totally fair criticism, but at other times Savory seems to abandon altogether any attempt to pin down variables or organize data:
Chad as you wrote on Nov 30th “I have no question that there is strong scientific support for HM.” I assume HM means managing holistically. (we do not use HM or HRM because we learnt that people take that to be yet another management system and there is as I trust you know no management system at all when we use the holistic framework in management. Management systems can only successfully be used where everything is predictable as in inventory control or tracking income and payables in business management)….
It may be that Savory is a thoroughgoing crackpot. (I freely admit that his idea appeals to me because I would like to believe that meat livestock are good for the earth, and perhaps also because I sometimes have pastoral fantasies of keeping some sheep and goats in some quiet patch of the American West, and not because I’ve been able to find hard evidence for it.)
It may also be that he is the kind of useful crackpot (like Freud, say) who brings a good idea into the world and then runs totally amok with it. Time will tell, I guess, whether he’s a mad genius with the germ of a great notion, or just a guy with an unassuming demeanor, a charming accent, and a bunch of well-curated Powerpoint slides.
UPDATE: Forgot to include a link to the blog post that turned me on to Savory’s video in the first place: this explanation, by Michelle Canfield, of why blackberries are not good for erosion control, and how she rescued parts of her farm that had been taken over by blackberries after being left fallow for a number of years. Interesting stuff!