Upland sheep grazing linked to more stable soil carbon, researchers say

Removing sheep and other livestock from upland grasslands could weaken long-term soil carbon storage, according to new research that questions calls to take grazing animals off land to meet climate targets.

The study, led by the University of Manchester, suggests that while removing livestock can increase short-lived carbon held in plants and dead vegetation, it may also reduce more stable forms of soil carbon that are crucial for long-term climate mitigation.

Researchers found that total grazer removal was associated with losses of mineral-associated organic carbon (MAOC), a form of carbon bound to soil minerals that can remain locked away for decades or centuries.

Grasslands hold around a third of the world’s terrestrial carbon, most of it stored below ground. As governments pursue net-zero targets, removing livestock from historically grazed grasslands has increasingly been promoted as a scalable climate solution.

However, the study warns that looking only at total carbon levels may give a misleading picture of how securely that carbon is stored.

The findings, published in Proceedings of the National Academy of Sciences (PNAS), show that carbon durability is as important as carbon quantity when assessing land-use change.

“While ungrazed grasslands tend to accumulate more unprotected carbon in plants and litter, they are associated with lower levels of soil carbon protected by minerals, which is the form most resistant to warming-induced decomposition,” said Dr Luhong Zhou, lead author.

“Although high grazing intensity can negatively affect soil carbon, our results show that total grazer exclusion does not necessarily lead to greater long-term soil carbon storage.”

For farmers and land managers, the findings suggest that blanket removal of livestock from upland grasslands may not always deliver the climate benefits expected.

The research indicates that low-intensity grazing can play a role in maintaining stable soil carbon, highlighting the importance of how land is managed rather than whether it is grazed at all.

The international research team analysed 12 upland grassland sites across an 800-kilometre south–north gradient in the UK, from Dartmoor to Glensaugh in Scotland.

At each site, they compared grasslands that had been ungrazed for more than ten years with neighbouring areas that continued to be grazed over the same period.

Ungrazed grasslands generally accumulated more fast-cycling carbon in plant biomass and surface litter. However, they typically contained lower levels of MAOC in the soil.

The decline in long-lived soil carbon was linked to changes in vegetation following the removal of grazing sheep.

Grass-dominated landscapes often shifted towards dwarf shrubs such as heather. These shrubs form relationships with specialised fungi known as ericoid mycorrhiza, which slow litter breakdown.

While this process increases short-lived carbon at the surface, it can also stimulate the breakdown of older, more stable soil carbon as nutrients are released to support plant growth. Wetter soils may further weaken the minerals that normally protect MAOC.

“Viewing grazer removal as a universally beneficial strategy for carbon mitigation often overlooks the continuum of carbon durability within ecosystems,” said Dr Shangshi Liu from the Yale Center for Natural Carbon Capture, who co-led the study.

“When slow-cycling carbon declines, grassland carbon stocks may become more vulnerable to future climate change.”

The researchers say the findings are particularly relevant as the UK and other countries develop land-use frameworks, environmental schemes and carbon markets aimed at meeting net-zero commitments.

Professor Richard Bardgett, chair of ecology at Lancaster University, who initiated the study, said: “Our results suggest that maintaining low-intensity grazing in upland grasslands, which cover large areas in the United Kingdom, is important for protecting the most stable forms of soil carbon.”

The authors stress that the study does not argue for overgrazing, but instead supports more balanced grassland management that considers both carbon storage and carbon persistence.

They say future climate strategies will need to recognise that long-term outcomes depend not just on how much carbon grasslands store, but on how securely it is held under different grazing systems.