藏北高原高寒草甸植被生产力对冷暖季放牧的响应

Response of Plant Production to Cold-season and Warm-season Grazing in Alpine Grasslands of the Northern Tibetan Plateau

为了更好地预测放牧活动对青藏高原高寒草地生态系统时空格局变化的影响。2008年7月在藏北3个高寒草地生态系统进行了围栏与自由放牧对比试验,包括1个高寒草原化草甸冷季放牧样地(ASMWP)、1个高寒草原化草甸暖季放牧样地(ASMSP)和1个高寒草甸暖季放牧样地(AMSP)。本研究通过观测2012~2015年生长季的归一化植被指数(NDVI)、绿波段归一化植被指数(GNDVI)、土壤调节植被指数(SAVI)、地上生物量(AGB)和总初级生产力(GPP),探讨了暖季放牧和冷季放牧对高寒草地植被生产的影响差异以及不同类型高寒草地植被生产对放牧的响应差异。结果表明:冷季放牧使ASMWP的2012~2015年平均的NDVI显著下降22.27%,SAVI显著下降23.50%,AGB显著下降17.28%,GPP显著下降22.48%,而暖季放牧对ASMSP和AMSP的2012~2015年平均的NDVI、SAVI、AGB和GPP则都没有显著影响。放牧使ASMSP样地2012~2015年平均的GNDVI下降15.33%(p=0.091),而对ASMWP和AMSP样地的2012~2015年平均GNDVI无显著影响。因此,放牧对植被指数、地上生物量和总初级生产力的影响与放牧季节和草地类型有关。

To better predict the impact of grazing activities on changes in the spatial and temporal patterns of alpine grassland ecosystems on the Tibetan Plateau.A grazing experiment was conducted in an Alpine Steppe Meadow Site for Cold-season Pasture(ASMWP),an Alpine Steppe Meadow Site for Warm-season Pasture(ASMSP),and an Alpine Meadow Site for Warm-season Pasture(AMSP)on the Tibetan Plateau in July 2008.The Normalized Difference Vegetation Index(NDVI),green NDVI(GNDVI),Soil-Adjusted Vegetation Index(SAVI),Aboveground Biomass(AGB)and Gross Primary Production(GPP)were obtained during growing seasons in 2012~2015 to compare the responses of plant production to grazing between warm-season grazing and cold-season grazing,and between different types of grasslands.Grazing significantly decreased the NDVI by 22.27%,SAVI by 23.50%,AGB by 17.28%and GPP by 22.48%at the ASMWP site,but did not significantly change the NDVI,SAVI,AGB and GPP at the ASMSP and AMSP sites across all the four growing seasons in 2012~2015.Grazing marginally significantly(p=0.091)reduced the GNDVI by 15.33%at the ASMSP site rather than the ASMWP and AMSP sites.Therefore,the effects of grazing on vegetation index,aboveground biomass and gross primary production varied with grazing seasons and grassland types.