Study shows how moderate grazing boosts grassland productivity

LANZHOU — Chinese scientists have recently proposed a key scientific mechanism in explaining how moderate grazing enhances productivity in alpine grasslands, according to Lanzhou University. This study provides a new perspective in explaining how moderate grazing can improve community productivity and offers a key scientific basis for the sustainable management of alpine grasslands, the university said.

The study was conducted by researchers from Lanzhou University in Northwest China's Gansu province, Nanjing University in Jiangsu province and the Chinese Academy of Sciences' Northwest Institute of Plateau Biology in Qinghai province — with their findings published in the journal Oikos.

"Throughout the long history of human grazing, it has been well known that moderate grazing can enhance grassland sustainability by promoting biodiversity and productivity. However, understanding of its scientific mechanism was insufficient," said He Jinsheng, a professor at Lanzhou University and leader of the study.

To explore this key scientific issue in grassland management, the research team established a large-scale grazing experiment based at the national field scientific observation and research station of the alpine grassland ecosystem in Haibei Tibetan autonomous prefecture in Qinghai.

Researchers found that expansion of the functional trait space of grassland plant communities is one of the key mechanisms by which moderate grazing promotes the productivity of alpine grasslands.

Functional trait space is an overall multidimensional framework, where each dimension represents a different functional trait — such as plant height, leaf size, and leaf nitrogen and phosphorus content. "It can be understood as a 'coordinate system', in which plants can be positioned according to their traits," He said. "The volume of the species making up this community represents the potential of this community in resource utilization."

In an alpine meadow, scientists conducted a yak grazing experiment via four methods — grazing exclusion and light, moderate and heavy grazing. The team measured 13 functional traits across 22 commonly occurring plant species.

Grazing increased biomass production by 16.7 to 28 percent — with low and moderate grazing significantly expanding the functional trait space, the study revealed.

Such expansion showed a strong positive correlation with biomass production, primarily mediated by increased variation in leaf traits, which are associated with enhanced photosynthetic efficiency.

This study confirmed, for the first time in alpine grasslands, that the expansion of functional trait space is the core mechanism for promoting grassland productivity through moderate grazing, He said.

"This finding not only proposes a new perspective in explaining that moderate grazing can improve community productivity — but also provides a key scientific basis for the sustainable management of alpine grasslands," He said.