Significantly more carbon in the soil of grazed land

A new study by researchers at the University of Iceland at Hólar, the University of Iceland and domestic and international partner institutions has found significantly more carbon in the soil of land that has been continuously grazed than in areas that have been protected from grazing. This runs counter to earlier assumptions that grazing is harmful to both plants and ecosystems. This is the first study conducted in Iceland to investigate how protection grazing affects ecosystem carbon balance. The findings were recently published in the scientific journal Global Change Biology Communications.

“For decades, the prevailing view has been that grazing is harmful to both plants and ecosystems, and excluding livestock from rangeland has been a major conservation focus in Iceland. However, few studies have been conducted in Iceland looking at the effects of grazing on plants and ecosystems,” says Anna Guðrún Þórhallsdóttir, professor of natural resources at the University of Iceland at Hólar and one of the authors of the article.

Without grazing, rangeland disappears and woody vegetation takes over

Anna Guðrún points out that international research over the past two decades has shown that when grazing ceases, rangeland disappears and woody vegetation takes over. Rangeland is a term referring to uncultivated grazing land outside fields and meadows. Around half of the world’s land area is classified as rangeland, and Iceland is home to the most extensive rangelands in Northern Europe. These consist mainly of grassland, heathland and mosaics of the two vegetation types. “Grassland and heathland are habitat types that are maintained through grazing, mowing or burning. Without these factors, shrubs and woody vegetation take over,” says Anna Guðrún.

When rangeland gives way to woody vegetation, the effects on biodiversity are far-reaching, and the many plant and animal species that depend on these habitats decline and disappear. “Today, maintaining rangeland through grazing is one of the main focuses of conservation in Europe,” she says, giving the example of a report by the United Nations Food and Agriculture Organisation in Europe: Europe’s Grasslands: A Different Rangeland Story.

Increasing focus on grasslands in connection with carbon storage

Grasses and herbaceous plants are the defining feature of rangelands. “These have the largest share of their biomass (70–80%) belowground in rhizomes and short-lived fibrous roots. Therefore, most carbon storage occurs below ground, and high soil carbon content is a key characteristic of natural grasslands. For this reason, there is an increasing focus on grassland in discussions about carbon storage,” explains Anna Guðrún. She therefore decided, together with her colleagues in the ExGraze research project, to investigate the effects of grazing cessation on carbon uptake and soil carbon levels in Icelandic grasslands and heathlands. The ExGraze project was funded by Rannis at the beginning of 2021.

In addition to Anna Guðrún, the study was initially conducted by Rene Van Der Wal, professor at the Swedish University of Agricultural Sciences; Richard D. Bardgett, professor at Lancaster University in England; and Björn Þorsteinsson, professor, and Jón Guðmundsson, lecturer, both from the Agricultural University of Iceland. Towards the end of 2021, Christian Klopsch, a doctoral student at UI, joined the team, along with Áslaug Geirsdóttir, professor at the UI Faculty of Earth Sciences, as Christian’s administrative supervisor. Christian is the first author of the article published in Global Change Biology Communications, which formed part of his doctoral thesis, defended in early June this year.

The study compared soil carbon content in areas where grazing had been prevented with areas that had been continuously grazed over time. “A total of 34 grazing exclosure sites were studied in Iceland. These were fenced-off areas within areas that had otherwise been continuously grazed. At all sites, we were able to determine how long grazing had been prevented, based on when the fences were erected. The period ranged from 20 to 83 years. Most of the fences had been installed for forestry purposes. However, on all our sites, immediately adjacent to the fences, there was open land without trees, while on the other side of the fence was land that had been continuously grazed,” Anna Guðrún explains.

The researchers dug three soil profiles, each 60 cm deep, at a distance of 5–15 metres from the fence on both sides, in both grazed and ungrazed land: six profiles on each site. Four soil samples were collected from each profile at different depths for carbon analysis, along with samples to determine soil density. An equal number of samples were collected to measure root biomass.

Grazing animals play an important role in carbon storage

The results showed that significantly more carbon was present in the soil of land that had been continuously grazed. “It is also interesting that the results of the soil carbon measurements correspond entirely with the amount of carbon in roots and plants in these areas. Grazed land has higher carbon uptake, as well as denser and more extensive root systems, and both are reflected in higher soil carbon levels. Since grassland soils generally have a very high carbon content, it is clear that grazing is an important factor for carbon storage in grasslands,” says Anna Guðrún.

She adds that the importance of grazing is also evident in the fact that, when grazing is prevented over long periods, woody plant species become established in grasslands, which then gradually shift into heathland. This was observed at some of the study sites and is consistent with findings from international research. “Heathland has a much lower rate of carbon uptake than grassland, and considerably lower soil carbon levels. Grazing animals therefore play an important role in carbon storage, as grazing not only promotes greater carbon uptake in grasslands but also maintains them and prevents them from shifting into heathland,” Anna Guðrún points out.

The article has attracted international interest

Asked about the significance of the study, Anna Guðrún argues that it deepens our understanding of the importance of grazing for maintaining and sustaining the functioning of grasslands in Arctic regions, as well as its effects on the capacity of these ecosystems to sequester carbon. Recent international studies have reported similar findings regarding the effects of grazing prevention. These include studies on bison grazing in Yellowstone National Park (see, for example, Yellowstone’s free-moving large bison herds provide a glimpse of their past ecosystem function | Science). “Our research findings should carry significant weight in discussions about carbon storage and Iceland’s carbon accounting. Hopefully, they will prompt people to reconsider the effects of grazing on Icelandic ecosystems,” she adds.

The article has attracted considerable interest. Wiley, the publisher of Global Change Biology Communications, selected it from hundreds of articles to be featured it on its news page under the headline Does livestock grazing enhance or hinder soil carbon storage? | John Wiley & Sons, Inc. The environmental website Earth.com also published an in-depth article on the findings.

The article in Global Change Biology Communications is available here.

Other published articles reporting findings from the same study are:

Klopsch, C., Thorhallsdottir, A.G., Bardgett, R.D. et al. Grazing abandonment in Iceland: unearthing the consequences for root biomass and community-level root functional traits. Plant Soil (2026).

Klopsch, C., Thorhallsdottir, A.G., van der Wal, R., Bardgett, R.D., Thorsteinsson, B. and Geirsdottir, A., 2026. Long-term cessation of grazing reduces net carbon uptake in northern grassland and heathland. Agriculture, Ecosystems & Environment, 407,