The effects of grazing and fencing on grassland productivity and diversity in alpine grassland ecosystem in the Tibetan highland

Abstract

Anthropogenic activities, such as grazing and fencing, have been known to alter the productivity and biodiversity of grassland ecosystems, potentially affecting their functioning. However, the impact of these activities on aboveground biomass (AGB) and plant diversity in alpine grasslands at different altitudes, as well as how they may be affected by soil nutrients and environmental climate, is not well understood. To address this knowledge gap, a study was conducted in the Lhasa Valley of Tibet. In 2013, twelve metal fences were set up at mountainous transects, and field surveys were conducted at twelve paired sites in early August 2021. The results of the study showed that AGB was slightly higher in fenced sites compared to grazed sites at altitudes from 4000 to 5100 m, but decreased with altitude at a slower rate in grazed sites. Plant diversity indices exhibited a unimodal pattern with increasing altitude, with no significant differences between fenced and grazed sites. Soil nutrients and environmental climate were found to be positively correlated with plant diversity indices and AGB at both fenced and grazed sites. Multiple linear regression models revealed that AGB and the Shannon index were largely influenced by soil nutrients (AP and AN) rather than by growing season soil temperature at fenced sites, while AGB and the Shannon index were more impacted by growing season soil temperature than by soil nutrients at grazed sites. These findings provide important insights into the impacts of grazing and fencing on above-ground biomass and plant diversity in mountainous environments.