Uncovering the effects of grazing exclusion duration on plant richness and biomass in alpine grasslands using the price equation.

Grazing exclusion is a key strategy for restoring degraded alpine grasslands. However, the mechanisms underlying plant species richness and biomass responses to long-term enclosure, particularly species turnover and biomass redistribution, remain unclear. This study compared plant community composition, diversity, and biomass across alpine grasslands on the Qinghai-Tibet Plateau enclosure for 2, 6, 13, and 18 years and free-grazing sites. The Price equation was used to quantitatively partition the independent contributions of lost, gained, and persisting species to changes in diversity and biomass, revealing how the long-term grazing exclusion affects biodiversity and biomass. After 2 years of enclosure, both diversity and biomass increased simultaneously. The biomass increase was primarily derived from the increased biomass of persisting species, while newly gained species contributed little. After 6 years, biomass reached peak value due to further increases in the biomass of persisting gramineous species. However, the loss of weedy species and reduction in species gains caused a diversity decline. After 13 and 18 years of enclosure, the biomass of persisting species began to decline, leading to a gradual decrease in total biomass. In summary, short-term enclosure should prioritize the recovery and conservation of native species rather than the colonization by new species. During the mid-term, attention should be paid to the potential negative impact of overgrown native gramineous species on overall diversity. Long-term grazing exclusion should be avoided where possible to prevent ecosystem degradation. This study provides a novel paradigm for alpine grassland restoration by disentangling community-level dynamic processes.