Arid Zone Research ›› 2022, Vol. 39 ›› Issue (4): 1155-1165.doi: 10.13866/j.azr.2022.04.16

• Plant Ecology • Previous Articles     Next Articles

Spatio-temporal heterogeneity evaluation of grassland TI-NDVI and NDVImax in northern Xinjiang

JIAO Ayong1(),CHEN Fulong1,YAN Junjie2(),LING Hongbo3,4,SHEN Ruihua1   

  1. 1. College of Water Conservancy & Architectural Engineering, Shihezi University, Shihezi 832003, Xinjiang, China
    2. Institute of Resources and Ecology, Yili Normal University, Yining 835000, Xinjiang, China
    3. Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, Xinjiang, China
    4. University of Chinese Academy of Science, Beijing 100049, China
  • Received:2021-11-20 Revised:2022-02-28 Online:2022-07-15 Published:2022-09-26
  • Contact: Junjie YAN E-mail:943573243@qq.com;yan3550@sina.com

Abstract:

Grassland change is an important component of global change, which has attracted considerable attention. The temporal and spatial heterogeneity of grassland dynamics is the main concern in evaluating grassland dynamics. Northern Xinjiang, which is characterized with diverse grassland types, was selected as the research area. In this study, we calculated the time-integrated normalized vegetation index (TI-NDVI) and annual maximum NDVI (NDVImax) on the basis of the MODIS NDVI data. Using spatial analysis technology of GIS, mathematical statistical methods of coefficient of variation (CV), and Mann-Kendall non-parametric statistics, the dynamic changes of grassland in northern Xinjiang were analyzed from 2000 to 2019, and the comparative advantages of TI-NDVI and NDVImax in expressing the temporal and spatial heterogeneity of grassland were explored. Results indicated that (1) the grasslands in northern Xinjiang, characterized by NDVImax and TI-NDVI, showed evident altitudinal differentiation. In general, the TI-NDVI increased with the increase of NDVImax. However, the areas with the same NDVImax or TI-NDVI showed great differences in TI-NDVI or NDVImax. (2) From 2000 to 2019, the grassland TI-NDVI and NDVImax in the northern Xinjiang showed a significant increasing trend (P<0.01), but the spatial differentiation of the changing trends of TI-NDVI was different from that of NDVImax. 17.55% of the grassland in northern Xinjiang showed opposite changing trends in TI-NDVI and NDVImax. For Altai Mountains and the mountains around Ili Valley, which are characterized with grassland of high coverage, the NDVImax and TI-NDVI showed opposite changing trends. (3) The CV of TI-NDVI was higher than NDVImax in temporal and spatial dimensions in grassland with high coverage in northern Xinjiang. Furthermore, TI-NDVI was more sensitive to the temporal and spatial heterogeneity of high-coverage grassland, which can weaken the influence of saturation defect of NDVI in grassland dynamic evaluation to a certain extent.

Key words: spatio-temporal heterogeneity, TI-NDVI, NDVImax, grassland, northern Xinjiang