Trends and variation in vegetation greenness related to geographic controls in middle and eastern Inner Mongolia,China |
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| Authors: | Jinwei Dong Fulu Tao Geli Zhang |
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| Institution: | (1) Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, 100101, China;(2) Graduate University of Chinese Academy of Sciences, Beijing, 100039, China;(3) Key Laboratory of Resources Remote Sensing and Digital Agriculture, Ministry of Agriculture, Beijing, 100081, China; |
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| Abstract: | Extensive studies have investigated the relationships between climate change and vegetation dynamics. However, the geographic
controls on vegetation dynamics are rarely studied. In this study, the geographic controls on the trends and variation of
vegetation greenness in middle and eastern Inner Mongolia, China (mid-eastern Inner Mongolia) were investigated. The SPOT
VEGETATION 10-day period synthesis archive of normalized difference vegetation index (NDVI) from 1999 to 2007 was used for
this study. First, the maximum value compositing (MVC) method was applied to derive monthly maximum NDVI (MNDVI), and then
yearly mean NDVI (YMNDVI) was calculated by averaging the MNDVIs. The greenness rate of change (GRC) and the coefficient of
variation (CV) were used to monitor the trends and variation in YMNDVI at each raster grid for different vegetation types,
which were determined from a land use dataset at a scale of 1:100,000, interpreted from Landsat TM images in 2000. The possible
effects of geographic factors including elevation, slope and aspect on GRC and CV for three main vegetation types (cropland,
forest and steppe) were analyzed. The results indicate that the average NDVI values during the 9-year study period for steppe,
forest and cropland were 0.26, 0.41 and 0.32, respectively; while the GRC was 0.008, 0.042 and 0.033 per decade, respectively;
and CVs were 10.2, 4.8 and 7.1%, respectively. Cropland and steppe shared a similar trend in NDVI variation, with both decreasing
initially and then increasing over the study period. The forest YMNDVI increased throughout the study period. The GRCs of
the forest also increased, although GRCs for cropland and steppe decreased with increasing elevation. The GRCs of cropland
and steppe increased with increasing slope, but the forest GRCs were not as closely related to slope. All three vegetation
types exhibited the same effects in that the GRC was larger on north-facing (shady) slopes than south-facing slopes due to
differences in water conditions. The CVs of the three vegetation types showed different features to the GRC. The CVs for all
three vegetation types were not affected by aspect. The CVs for forest and cropland showed minor effects with changes in elevation
and slope, but the CV for steppe decreased with increasing slope, and increased with increasing elevations to 1,200 m, before
decreasing at higher elevations. Our findings suggest that the role of geographic factors in controlling GRC should also be
considered alongside climate factors. |
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