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Acta Prataculturae Sinica ›› 2020, Vol. 29 ›› Issue (6): 1-13.DOI: 10.11686/cyxb2019427

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Spatio-temporal characteristics of grassland net primary productivity (NPP) in the Tarim River basin

CUI Bo-chao1, ZHENG Jiang-hua1,2, TUERXUN·Hasimu1,2,*, DUAN Su-su1, DU Meng-jie1   

  1. 1. College of Resources & Environment Science, Xinjiang University, Urumqi 830046, China;
    2. Key Laboratory for Oasis Ecology, Xinjiang University, Urumqi 830046, China
  • Received:2019-09-29 Revised:2019-10-28 Online:2020-06-20 Published:2020-06-20

Abstract: We analyzed spatio-temporal changes in grassland net primary productivity (NPP) in the Tarim River basin, based on an improved light use efficiency model (Carnegie-Ames-Stanford approach model, CASA) and moderate resolution imaging spectroradiometer (MODIS) data from 2006 to 2016. To study the temporal pattern, spatial characteristics, spatial stability and the time trend in grassland NPP were used to formulate a simple linear regression model, and derive the coefficient of variation and the Hurst index. The model analyses the temporal variation in grassland NPP in the Tarim River basin from 2006 to 2016. This analysis of the temporal pattern over the 11 years showed that the grassland NPP was variable with 64.1% of the total area, showing increased NPP and for 35.9% of the total area exhibiting falling NPP in the past 11 years. Overall, the grassland NPP of the Tarim basin was 1.31×1011 g C·m-2·yr-1. The main growing season for grassland in the basin is from June to August each year, and NPP during this period accounts for 47.3% of the total annual NPP. A geographic gradient of decreasing grassland NPP from northwest to southeast was observed for these 2006-2016 Tarim River basin data. In the whole basin, the average annual grassland NPP estimated by the CASA model for 2006-2016, was 13.62 g C·m-2·yr-1. The altitudinal change in grassland NPP for the 11 years followed a “decreased-raised-lowered” pattern with increasing altitude, and also some smaller features related to latitude and longitude. The coefficient of variation of grassland NPP over the 11 years ranged from 0.19 to 3.17, in various localities, which indicated the grassland NPP has obvious spatial differentiation. The land area for which the coefficient of variation of grassland NPP is less than 0.5 accounts for 94.6% of the total surveyed land area. Areas of high NPP fluctuation include the Kaikong river basin, the Aksu river basin, the Yarkant river basin, the Hetian river basin, the Tarim River main stream basin, and the Qarqan river basin. The Hurst index of grassland NPP for the 11 years ranged from 0.10 to 0.97 and the mean value was 0.57. This indicates the grassland NPP is expected to maintain the same change-trend in the future. In summary, the patterns of spatio-temporal change in grassland NPP showed that the health status of the grassland ecosystem is improving in the majority of the Tarim River basin, but deteriorating in some local areas.

Key words: net primary productivity, Tarim river basin, grassland, CASA model, spatio-temporal changes