Most dry rangelands under danger due to increased grazing demand

Results from the first-ever global field assessment of the ecological effects of grazing in drylands are reported in a new study that was just published in Science. The worldwide research team discovered that grazing can have beneficial benefits on ecosystem services, especially in rangelands with a variety of species, but that these effects change from positive to negative in warmer climates.

The life of billions of people depends on grazing, which is a vital land use that is closely related to numerous UN Sustainable Development Goals. Grazing is crucial in drylands, which account for 41 per cent of the Earth's land surface, one in three people who live there, and more than 50 per cent of all livestock on the globe.

Despite grazing's significance for both people and ecosystems, no prior study had, yet, made an effort to define its effects on the provision of ecosystem services at the global level using field data. In order to do this, a multidisciplinary team of more than 100 experts from around the world under the direction of Dr Fernando T. Maestre (University of Alicante, Spain) performed a first-of-its-kind worldwide survey in 326 drylands spread across 25 nations and six continents.

"We used standardized protocols to assess the impacts of increasing grazing pressure on the capacity of drylands to deliver nine essential ecosystem services, including soil fertility and erosion, forage/wood production and climate regulation. Doing so allowed us to characterize how the impacts of grazing depend on local climatic, soil and local biodiversity conditions, and to gain additional insights on the role of biodiversity on the provision of ecosystem services essential to sustain human livelihoods", says Dr Maestre, director of the Dryland Ecology and Global Change Laboratory (Alicante, Spain).

Researchers discovered that the correlations between grazing pressure and the ecosystem services measured and the biodiversity, soil quality, and climate differed. "In warmer drylands, the consequences of increased grazing pressure on ecosystem services were primarily negative. According to Dr Alice Nunes, a coauthor of the study and a researcher at the Centre for Ecology, Evolution and Environmental Changes (cE3c) at the Faculty of Sciences at the University of Lisbon (Ciencias ULisboa), "These results highlight the importance of managing grazing locally to cope with ongoing climate change in drylands, a particularly important issue in oak woodlands that we studied in Portugal and were part of this work.

Increased grazing pressure had primarily good effects in cooler drylands with lower seasonality in rainfall and higher species richness of plants, but detrimental effects in hotter drylands with lower plant diversity and higher seasonality in rainfall. "When it comes to grazing on drylands, there is no one size fits all solution. It is crucial to take into account local conditions when managing cattle and wild herbivores because any effects of grazing, especially overgrazing, will differ around the globe, according to Dr David Eldridge, a coauthor of the study from the University of New South Wales in Australia.

Regardless of grazing pressure, the authors discovered beneficial correlations between plant species richness and the provision of numerous ecosystem services such as soil carbon storage, erosion control, and both quality and quantity of feed. The PhD candidate Melanie Kobel from cE3c at Ciencias ULisboa and coauthor of the study says, "Our results highlight the importance of conserving and restoring diverse plant communities to prevent land degradation, ensure delivery of essential ecosystem services for humans, and mitigate climate change in grazed drylands."

The results of this study have significant implications for establishing management and restoration initiatives that effectively mitigate the effects of ongoing climate change and desertification across the world's drylands, as well as for achieving more sustainable management of grazing.