For decades, researchers have focused on the problem of overgrazing, in which expanding herds of cattle and other livestock degrade grasslands, steppes and desert plains. But a new global study reveals that in large regions of the world, livestock numbers are substantially declining, not growing—a process the authors call destocking.

"We often assume that rangelands are being degraded because we overgraze them, but the data show that it's not the whole story: nearly half of livestock production occurs in areas that have experienced destocking over the past 25 years," said study co-author Osvaldo Sala, an ecologist and professor at Arizona State University.

The findings are important because destocking isn't just the reverse of overgrazing; it poses new ecological and land management challenges. "We need to manage both processes," Sala said. It's not that destocking is automatically positive and that we should just leave it alone."

When livestock numbers drop, for instance, unchecked plant growth can increase wildfire risk. Biodiversity might recover in some areas but decline in others, depending on how ecosystems respond. The researchers published the study in Proceedings of the National Academy of Sciences.

The authors analyzed global changes in livestock numbers from 1999 to 2023 using data from the United Nations' Food and Agriculture Organization. Among their findings:

• Livestock populations have shrunk by about 12% over the past 25 years in regions that held 42% of the world's cattle, buffalo, sheep, and goats in 1999.
• Destocking is especially common in Europe, North America, Australia, and parts of Africa and Asia. The steepest declines are in Eastern Europe, where livestock populations fell by 37%.
• In contrast, livestock numbers are growing quickly in Middle Africa, Central Asia, and South America. In these regions, overall numbers increased by 40% since 1999.

To assess what could be driving the diverging trends, Sala and co-author José Anadón at the Instituto Pirenaico de Ecología looked for links to social, economic, and environmental factors. Changes in international trade did not explain changes in stocking rates and neither did Earth's warming climate, the authors concluded.

"Climate change exists, but it doesn't explain these particular spatial patterns of destocking and increasing stocking rates," Sala said.

Regional economic output emerged as a major factor, along with human population growth. In wealthy regions where livestock numbers are declining, people rely more on feed-based and industrial farming and use more technology. As a result, meat production per animal is 72% higher than in the more resource-limited regions where rangeland herds are expanding.

These less wealthy regions support grazing-based, less productive and subsistence-oriented livestock systems. Human population trends amplify the wealth effect on rangeland grazing, the researchers found: Poorer regions are also the places with the largest human population growth, which is boosting demand for meat.

Why it matters

Livestock grazing takes place on roughly one quarter of the land surface of the planet, making it humanity's most extensive land use. Large-scale decreases in the presence of grazing livestock have broad consequences for planetary health that have been overlooked by conservation scientists and land managers, according to Sala and Anadón, who say the issues remain understudied and incompletely understood. It's not clear, for instance, to what extent destocking might reverse the degradation caused by overgrazing.

Destocking and the resulting decrease in grazing can not only increase wildfire risk in some contexts, Sala said, it can also lead to the elimination of vulnerable plant species by allowing a select few species to dominate.

At the same time, reductions in grazing livestock that promote plant growth could enable ecosystems to capture more atmospheric carbon dioxide, benefiting the global climate.

"This is not just doom and gloom—it's a more realistic, complex picture that suggests both risks and opportunities," Sala said.

Grazing also impacts stream flows; loss of plant cover decreases transpiration by plants and increases runoff.

"Stopping grazing doesn't always mean more water to downstream users; effects are location-specific and need to be studied," Sala said. "Rewilding or introducing different grazers—bison, goats, or other species—may fill functional roles left by cattle, but we need better science to decide what works where."

By focusing so intently on the problem of overgrazing, Sala said researchers and policy makers have overlooked opportunities to manage destocking to achieve societal goals for conservation, carbon storage, and maintaining rural livelihoods.

"These are important issues for land managers, policymakers, and the public," he said. "We need better data, more experiments, and thoughtful policies that recognize regional differences."

Source - https://phys.org