Removing sheep and other livestock from highland grasslands could weaken long-term soil carbon stocks, new research questions the need to remove grazing animals from land to meet climate change goals.
The study, led by the University of Manchester, suggests that while livestock removal may increase short-lived carbon held in plants and dead vegetation, it may also reduce more stable forms of soil carbon, which are essential for long-term climate mitigation.
Researchers found that complete removal of herbivores is associated with a loss of mineral-associated organic carbon (MAOC), a type of carbon bound to soil minerals that can remain trapped for decades or centuries.
Grasslands contain about a third of the world’s above-ground carbon, most of which is stored underground. As governments pursue net-zero targets, removing livestock from historically grazed grasslands is increasingly being promoted as a scalable climate change solution.
However, the study warns that looking at total carbon levels alone can be misleading about how safely that carbon is stored.
The findings, published in the Proceedings of the National Academy of Sciences (PNAS), show that carbon durability is just as important as carbon content when assessing land use change.
“Ungrazed grasslands tend to accumulate more unprotected carbon in plants and leaf litter, which is associated with lower levels of soil carbon protected by minerals, which are the most resistant forms to decomposition due to warming,” said lead author Dr. Honghong Chou.
“Although high grazing intensity can have negative effects on soil carbon, our results show that completely excluding grazers does not necessarily lead to increased long-term soil carbon stocks.”
For farmers and land managers, the findings suggest that the complete removal of livestock from upland grasslands does not necessarily yield the expected climate benefits.
This study shows that low-intensity grazing can play a role in maintaining stable soil carbon, highlighting that it’s not whether it’s grazed, but how the land is managed that matters.
An international team of researchers analyzed 12 upland grasslands spanning an 800km north-south gradient from Dartmoor in the UK to Glensough in Scotland.
At each site, we compared grasslands that had not been grazed for more than 10 years to neighboring areas that had been grazed for the same period.
Ungrazed grasslands generally accumulate faster-cycling carbon in plant biomass and surface litter. However, they usually contain low levels of MAOC in the soil.
Decreases in long-lived soil carbon were associated with vegetation changes associated with the removal of grazing sheep.
Grass-dominated landscapes often gave way to dwarf shrubs such as heather. These shrubs form relationships with specialized fungi known as ericoid mycorrhizae, which slow the decomposition of litter.
This process increases short-lived carbon on the ground, but also accelerates the breakdown of older, more stable soil carbon as nutrients are released to support plant growth. When the soil becomes wet, the minerals that normally protect MAOC can be further weakened.
“When we view herbivore removal as a universally beneficial strategy for carbon mitigation, the continuity of carbon durability within ecosystems is often overlooked,” said Dr. Shanshi Liu of the Yale Center for Natural Carbon Capture, who co-led the study.
“As slowly cycling carbon decreases, grassland carbon stocks may become more vulnerable to future climate change.”
Researchers say their findings are particularly relevant as the UK and other countries develop land-use frameworks, environmental plans and carbon markets aimed at meeting net-zero commitments.
Professor Richard Burgett, Head of Ecology at Lancaster University, who initiated the study, said: “Our results suggest that maintaining low-intensity grazing on large areas of upland grassland in the UK is important to protect the most stable forms of soil carbon.”
The authors stress that this study does not advocate overgrazing, but rather more balanced grassland management that considers both carbon storage and carbon residue.
They say future climate strategies need to recognize that long-term outcomes depend not only on how much carbon grasslands store, but also on how much is safely held under different grazing systems.
