Two important indicators with potential to identify Caragana microphylla in xilin gol grassland from temporal MODIS data

Yuan Zhou, Jin Chen, Xue-hong Chen, Xin Cao, Xiao-lin Zhu
State Key Laboratory of Earth Surface Processes and Resource Ecology, Beijing Normal University, Beijing 100875, China.
Abstract: Shrub expansion in arid and semi-arid environment leads to serious issues to earth system regarding net primary production, nutrient cycling, and global carbon balance. Caragana microphylla is a shrub species distributed in Xilin Gol grassland, China, which is expanding into and degrading grassland areas. The current paper proposed two important indicators from Moderate Resolution Imaging Spectroradiometer (MODIS) data that will help potentially distinguish C. microphylla from grass species around it: Difference of Maximum (DM) NDVI/EVI and Difference of Accumulated (DA) NDVI/EVI between wet and dry years. The two indicators were developed based on relative drought resistance of woody vs. grass species. Accuracy assessment was performed using the field survey data collected in Xilin Gol grassland. The results demonstrated that the proposed indicators were effective for identifying C. microphylla, with the overall accuracy of 81.67% and Kappa coefficient of 0.6300. Due to the mixed pixel effect, the performance of the indicators was less desirable when the coverage of C. microphylla was on low levels. In addition, the proposed indicators would be more effective if two years with significant variation in precipitation could be selected. Furthermore, the indicators developed are anticipated to be sensitive to other similar drought resistant shrubs around the world.
Keywords: Shrub expansion; Caragana microphylla identification; Remote sensing; NDVI; EVI.
Published in Ecological Indicators. 2013, 34: 520-527.