Strategies for Grazing Exclusion Management Optimization on the Qinghai-Xizang Plateau Based on the Temporal Effect of Ecological Engineering Carbon Sink

Qi Yahui; Wei Da; Wang Xiaodan

doi:10.3969/j.issn.1004-3403.2025.12.008

Abstract：Alpine grasslands on the Tibetan Plateau serve as a critical carrier for the establishment of regional eco-logical security barriers and national ecological civilization hubs,and play a vital role in the global carbon cycle.Over the past two decades,ecological restoration initiatives involving large-scale fencing and grazing exclusion have been implemented across the region to mitigate grassland degradation.However,the spatiotemporal variation patterns and optimization pathways of carbon sink effect resulting from long-term grazing exclusion remain unclear.This study has systematically integrated and analyzed 246 paired cases of grazing exclusion and grazing restoration on the Tibetan Plateau,using multi-scale methods such as field plot observation to elucidate the temporal characteris-tics and regulatory mechanisms of the carbon sink capacity under fencing and grazing exclusion.The results demon-strate that fencing and grazing exclusion have substantially enhanced the carbon sink capacity of alpine grasslands,yielding an average increase of 49%.However,the carbon sink effect exhibits marked non-linear characteristics,peaking approximately five years after implementation of the ecological projects,after which the carbon sink rate gain declines,suggesting the existence of an"optimal carbon sink window".Long-term grazing exclusion results in the excessive accumulation of plant litter,which leads to shading effect and nutrient cycling imbalance,constituting the primary factors behind the decline in carbon sink gain.This finding challenges the traditional notion that"longer duration of ecological restoration projects yields better results"and proposes the existence of a"carbon sink inhibi-tion threshold".Specifically,when litter layer thickness or shading intensity exceeds the ecological carrying capaci-ty,the carbon sink transits from an"incremental"to a"stock"model.The existing ecological project management paradigm urgently requires a shift from a static"long-term grazing exclusion"model to a dynamic and adaptive"pe-riodic rotational grazing"strategy to ensure targeted implementation of ecological projects and sustained enhance-ment of carbon sink capacity on the Tibetan Plateau.