An international team of more than 130 scientists, coordinated by INRAE, CNRS and the University of Alicante (Spain), has conducted the first global study to assess the impact of grazing on the world’s arid ecosystems, where 78% of the world’s rangelands are located. Their results, published in Science, show that grazing is beneficial in relatively cold climates and in geographical areas with high animal and plant biodiversity. Conversely, these effects become largely detrimental in warmer regions of the world with low biodiversity. The findings of this study can contribute to the development of more sustainable rangeland management, as well as to the establishment of effective management and restoration actions to mitigate the effects of climate change and desertification.
Grazing by livestock represents the most extensive use of land worldwide. It provides a livelihood for a large proportion of the world’s population, supports important cultural and spiritual activities, and is closely linked to many of the UN’s Sustainable Development Goals. In drylands, grazing is particularly important, as these lands constitute 78% of the world’s rangeland and support more than a billion people who depend directly on livestock as a source of protein and income. However, grazing is also seen as a major factor in land degradation and accelerating desertification worldwide. Despite these issues, no study to date had attempted to characterise the effect of grazing on a global scale. INRAE, CNRS and the University of Alicante (Spain) brought together more than 100 scientists from 26 countries in order to conduct a vast field survey in 326 drylands located on all continents. To this end, they developed standardised protocols to assess the impacts of increasing grazing pressure on the capacity of the world’s ecosystems to provide nine key ecosystem services, including soil fertility and erosion protection, forage/wood production and climate regulation.
Contrasting effects depending on climate and biodiversity
Their results show that the effect of grazing can vary significantly on a global scale and depends directly on climatic, soil and local biodiversity conditions. Thus, grazing is generally beneficial in arid rangeland under relatively cold climates such as the steppes of Mongolia or Patagonia, and in ecosystems with high animal and plant biodiversity such as African savannahs and Mediterranean scrub. In these areas, the diversity of plants and herbivorous mammals – both domestic and wild – promotes the provision of essential services such as fodder production for livestock (quality and quantity), or carbon storage, and soil fertility, while limiting soil erosion. Conversely, the effects of grazing become largely detrimental in warmer, biodiversity-poor arid zones, for example in certain sub-desert areas near the Sahel, in Namibia, Australia or Mexico (on the fringes of the Sonora desert). Overgrazing tends to decrease carbon stocks and soil fertility and increase soil erosion as the climate becomes warmer.
While grazing is generally beneficial in relatively cold climates, this study suggests that grazing could interact with ongoing climate change and reduce the provision of ecosystem services in the world’s hottest drylands, with potentially devastating effects on the future of these ecosystems and their inhabitants [e.g. increased soil degradation and desertification]. In this context, it also highlights the importance of preserving global dryland biodiversity in its entirety (animal and plant), not only to maintain the capacity of dryland ecosystems to provide essential services to humans, but also to mitigate climate change and maintain livestock production in a warmer climate. The response of ecosystems to ongoing climate change – and its mitigation – may largely depend on how rangelands are managed locally as the global climate warms. In short, it is a case of ‘think global, act local.
What is a dryland?
Drylands are defined by climatic zone where the scarcity of rainfall limits vegetation growth (i.e. with an aridity index of less than 0.65). They cover 45% of the earth’s surface and are home to one third of the world’s population. They include sub-humid, semi-arid, arid and hyper-arid ecosystems such as Mediterranean scrub, steppes, savannahs and deserts.