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Acta Prataculturae Sinica ›› 2016, Vol. 25 ›› Issue (8): 14-26.DOI: 10.11686/cyxb2015455

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Monitoring of grassland herbage accumulation by remote sensing using MODIS daily surface reflectance data in the Qingnan Region

YANG Shu-Xia1, ZHANG Wen-Juan2, FENG Qi-Sheng1, MENG Bao-Ping1, GAO Jin-Long1, LIANG Tian-Gang1, *   

  1. 1.State Key Laboratory of Grassland Agro-ecosystems, College of Pastoral Agriculture Science and Technology, Lanzhou University, Lanzhou 730020, China;
    2.Qinghai Province Grasslands Station, Xining 810000, China
  • Received:2015-09-23 Revised:2015-11-23 Online:2016-08-20 Published:2016-08-20

Abstract:

Monitoring of grassland herbage accumulation using remote sensing technology has a potentially important role in understanding seasonal changes in grasslands and optimizing animal husbandry and grazing management. In this study above ground biomass (AGB) and its spatial distribution was recorded using in-situ measurements during the growing seasons from 2010 to 2013 in southern Qinghai province, and regression models using in-situ AGB data and the corresponding daily surface reflectance product of Terra MODIS were established. The spatial analysis method was used to calculate four vegetation indices (NDVImax, EVImax, NDVImean and EVImean) using MOD09GA data, and the accuracy of the inversion models was then analyzed, and the spatial distribution of the NDVI mean values in the previous 10 years characterized. With the algorithms optimized in this way, we estimated the aboveground grassland biomass and its spatial distribution for the previous 10 growing seasons. It was found that the aboveground biomass gradually increases from northwest to southeast, and different grassland types have characteristic biomass differences. The biomass of mountain meadow was highest among the grassland types included in this 10 year study, and reached 1280 kg DW/ha in 2010. The biomass of alpine meadow, warm steppe, warm desert and marsh ranged between 244.9 kg DW/ha and 902.4 kg DW/ha, The biomass values of alpine meadow grassland, alpine desert, and alpine desert grassland were much lower, and were below 65 kg DW/ha. The elevation had a marked effect on biomass, with grassland biomass decreasing with increasing elevation above 3500 m. At elevations between 3500 and 4000 meters, peak biomass was 1358.8 kg DW/ha; between 4000 and 4500 meters, the biomass was below 920 kg DW/ha, and between 4500 and 5000 meters the biomass averaged approximately 574.2 kg DW/ha. Above 5000 meters elevation, the biomass averaged approximately 94.4 kg DW/ha. The trend of NDVI mean values in last 10 years indicates that most regions in the Three River Headwater region (The Yellow River, The Yangtze River, and The Mekong River), which span different administrative areas, can be categorized as showing ‘mild improvement’ or ‘improvement’. Overall, the trend in grassland vegetation status is positive.