干旱和放牧对内蒙古草地总初级生产力的影响及其演变特征OA

Grassland degradation is one of the main ecological issues in Inner Mongolia.To combat this issue,Inner Mongolia has launched a series of grassland protection policies centered around grazing management since the early 2000s.However,how these policies regulate grazing activities to influence the response of grassland gross primary productivity(GPP)to drought and its spatiotemporal characteristics remains unclear.This study systematically evaluated the synergistic effects and impact pathways of grazing policy transformation and drought stress on the GPP of meadow steppe,typical steppe,and desert steppe in Inner Mongolia from 1992 to 2018.The results showed that:(1)From 1992 to 2018,the GPP of grassland in Inner Mongolia exhibited an overall insignificant declining trend(56.54％),while the GPP of desert steppe showed an increasing trend(53.56％).The Standardized Precipitation Evapotranspiration Index(SPEI)exhibited an overall declining trend(95.54％),with the most severe drought conditions occurring during the first phase of grazing policy implementation(2000-2010),where most SPEI values were lower than-0.5.Grazing intensity generally declined(95.88％),but during the free grazing period(1992-1999),it showed an increasing trend(54.97％).(2)From the free grazing period(1992-1999)to the second phase of grazing policy implementation(2011-2018),the importance of SPEI first increased and then decreased,while the importance of grazing intensity first decreased and then increased.GPP and SPEI were generally positively correlated(89.01％),but their correlation varied across different grassland types and periods.(3)Both grazing intensity and SPEI had significant direct impacts on grassland GPP.As policy implementation progressed,the direct impact of SPEI gradually weakened,while the influence of grazing intensity shifted from negative to positive.The study results confirm,to some extent,the positive role of grazing policy transformation in restoring grassland ecosystems.