Above-Ground Forest Biomass Retrieval and Spatial Distribution Estimation across the Yanhe Basin from Remote Sensing
延河流域阔叶林地上生物量遥感监测及空间分布特征分析

Above-ground biomass of forest is one of the most critical variables for measuring the ecological system productivity of forest. Monitoring forest above-ground biomass provides the basis for exploring the carbon cycle of a forest ecological system. In this regard, forest biomass is of importance to research and applications in forest ecological systems. However, the distribution of forest biomass in the arid-semiarid region based on vegetation index has been far less than clear. Soil erosion is serious across the Loess Plateau, and the environment is incrementally degraded. Studying the forest above-ground biomass over a typical region in the Loess Plateau, the Yanhe basin, would provide valuable reference for reconstruction of vegetation over this region. The authors extracted broadleaf forest information from remote sensing, achieving a classification accuracy of 80.4%. Based on images acquired by Satellite HJ-1 in the growing season in year 2009 and samples collected over the study area, the forest above-ground biomass of the broadleaf forest in the Yanhe basin was estimated by empirical models of remote sensing. We calculated the correlation between five vegetation indices, i.e., Normalized Difference Vegetation Index (NDVI), Ratio Vegetation Index (RVI), Atmospherically Resistant Vegetation Index (ARVI), Modified Soil Adjusted Vegetation Index (MSAVI), and Soil Adjusted Vegetation Index (SAVI) with the above-ground biomass of the forest, indicating that ARVI seems to be the best index reflecting the above-ground biomass. A forest biomass model was subsequently built based on ARVI. The F test examination showed that the above-ground biomass of the forest was correlated significantly with ARVI, suggesting a correlation coefficient of 0.8114. Based on the simulated biomass, the relationships between the biomass and natural-social factors were examined in detail. Factors affecting the spatial distribution of the biomass were extensively discussed. Results showed that in the study basin, the mean biomass of the above-ground broadleaf forest was around 34.45 t/hm2, and the maximum was roughly 209.2 t/hm2. Characteristics of the spatial distribution indicated that the biomass was higher in the south and middle areas whereas lower in the north, east, and west. Climate, terrain, species, and human activities jointly affected the development of the vegetation, among which, water status was a key factor affecting the status of the vegetation. It is also shown that the area of human activities was generally proportional to the location with high biomass. The above-ground biomass of the broadleaf forest in developed regions was found to be generally higher than that in developing regions.