The Science of Grazed Ecosystems- what is the problem?

The authors state, “Holistic management (HM) has been proposed as a means of restoring degraded deserts and grasslands and reversing climate change. The fundamental approach of this system is based on frequently rotating livestock herds to mimic native ungulates reacting to predators in order to break up biological soil crusts and trample plants and soils to promote restoration.”

What did the research involve?

The authors address five assumptions of HM with a focus on western N American and semiarid ecosystems. They ask the following questions and review peer-reviewed literature in order to answer them:

• Do Grasses Senesce and Die If Not Grazed by Livestock?
• Does Rest Cause Grassland Deterioration?
• Is Hoof Action Necessary for Grassland Health?
• Can Grazing Livestock Increase Carbon Storage and Reverse Climate Change?
• What Is the Evidence That Holistic Management Does Not Produce the Claimed Effects?
• What about Riparian Areas and Biodiversity?

What were the key findings?

“Grasses, particularly bunchgrasses, have structure that protects growing points from damage, harvests water, and protects the soil at the plant base. Removal of the standing plant material exposes the growing points, leading to loss or replacement by Grazing Crops tolerant species, including invasives.”

“Contrary to the assumption that grasses will senesce and die if not grazed by livestock, studies of numerous relict sites, long-term rested sites, and paired grazed and ungrazed sites have demonstrated that native plant communities, particularly bunchgrasses, are sustained by rest from livestock Grazing Crops.”

“We found no evidence that hoof action as described by Savory occurs in the arid and semiarid grasslands of the western USA which lacked large herds of ungulates such as bison that occurred in the prairies of the USA or the savannahs of Africa. No benefits of hoof action were found.”

“Livestock are a major source of greenhouse gas emissions. Livestock removal of plant biomass and altering of soil properties by trampling and erosion causes loss of carbon storage and nutrients as evidenced by studies in grazed and ungrazed areas.”

“Studies in Africa and the western USA, including the prairies which evolved in the presence of bison, show that HM, like conventional Grazing Crops systems, does not compensate for overstocking of livestock. As in conventional Grazing Crops systems, livestock managed under HM reduce water infiltration into the soil, increase soil erosion, reduce forage production, reduce range condition, reduce soil organic matter and nutrients, and increase soil bulk density. Application of HM cannot sequester much, let alone all the greenhouse gas emissions from human activities because the sequestration capacity of grazed lands ismuch less than annual greenhouse gas emissions.”

“HM does not address riparian areas and biodiversity with its focus on livestock production, although operators could choose these as goals. We have seen no studies of HM impacts on riparian areas and biodiversity.”