Two University of Pretoria scientists have contributed to the first-ever global field assessment of the ecological impacts of grazing in drylands.

Professors Peter le Roux, from the Department of Plant and Soil Sciences and Thulani Makhalanyane, DSI/NRF SARChI Chair in the Department of Biochemistry, Genetics and Microbiology, led the South African component of the ground-breaking multidisciplinary study on the effects of grazing in deserts.

Although the effects of climate change have recently become the subject of extensive studies, the precise effects at global scale remain unclear. The new study published in Science, with contributions from the University of Pretoria, reports results from the inaugural global field assessment of the ecological impacts of grazing in drylands. The scientists found that grazing may positively affect ecosystem services, particularly in species-rich rangelands. However, these effects turn negative under a warmer climate.

“Given the large number of people relying on drylands for their livelihoods, this study provides important insights into how grazing and changing climatic conditions could alter the provisioning of ecosystem services like erosion control, carbon storage and soil fertility,” Prof le Roux explained.

The study includes standardised protocols to measure the impact of increasing grazing pressure on the capacity of drylands to deliver several ecosystem services. The team measured soil erosion and fertility, forage/ wood production, climate regulation and the diversity of belowground communities such as soil fungi, protists, invertebrates and bacteria.

“We know that microbiomes are essential regulators of ecosystem services. However, due to the complexities of studying these belowground communities, we lack an understanding of the ecological impacts of grazing on their diversity and function. This work substantially advances our understanding regarding their importance as predictors of ecosystem services in different models,” Prof Makhalanyane said.

Grazing is an important land use that sustains the livelihood of billions of people – it is also tightly linked to many UN Sustainable Development Goals. Grazing is essential in drylands, which cover about 41% of the Earth's land surface, host one in three humans and over 50% of all livestock on Earth.

Despite the importance of grazing for humans and ecosystems, no previous study has attempted to characterise its impacts on the delivery of ecosystem services globally using field data. This seminal study combines efforts from an international team of more than 100 researchers and provides insights and data from a uniquely global survey conducted in 326 drylands in 25 countries from six continents.

“As a team, we worked hard to coordinate sampling to include several sites from Africa. Even though a large number of Africans are directly at risk due to desertification and the effects of grazing, few global studies have included samples from these important locations,” said Prof Fernando Maestre, lead author, Distinguished Researcher at the Universidad de Alicante in Spain and director of the Dryland Ecology and Global Change Laboratory.

Researchers found that the relationships between climate, soil conditions, biodiversity and the ecosystem services measured varied with grazing pressure. The results showed that carbon stocks decreased, and soil erosion increased as the climate became warmer under high grazing pressure. This was not observed under low grazing pressure.

“These results suggest that the response of drylands to ongoing climate change may depend on how we manage them locally,” said Dr Nicolas Gross from the National Research Institute for Agriculture, Food and the Environment (INRAe, France), coauthor of the study.

The impacts of increasing grazing pressure shifted from mostly positive in colder drylands with a lower rainfall seasonality and higher plant species, to harmful in hotter drylands with lower plant diversity and higher rainfall seasonality. The authors also observed that the variety of vascular plants and mammalian herbivores was positively linked to the provision of essential services such as carbon storage, which plays a key role in climate regulation.

The findings of this study are important for enhancing sustainable grazing management as well as  establishing effective management and restoration actions aimed at mitigating the effects of climate change and desertification across global drylands.

This work has been carried out as part of the BIODESERT project, awarded by the European Research Council (ERC) Consolidator Grant programme to Dr Maestre.

“I am very grateful to the ERC for supporting this global survey, as such a high-risk-high-gain project would not have been possible without the generous funding and freedom that comes with an ERC grant,” Dr Maestre said.

“And of course, it would not have been possible without our network of international collaborators, who provided their expertise, resources, and work to survey sites in their respective study areas. The BIODESERT survey also provides a very nice example of the power of global and collaborative research networks to conduct frontier research,” he added.

“In addition to providing a great example of multidisciplinary research, this work is a clear demonstration of UP’s efforts to support research with societal impacts,” said UP Vice-Chancellor and Principal, Prof Tawana Kupe, who congratulated Prof le Roux and Prof Makhalanyane on their contribution to the global study.