Monitoring forage harvesting area in semi-arid pasture based on Landsat TM images

Abstract: Mowing grass for livestock utilization is one of the most traditional way of using natural grassland in the semi-arid pastoral areas. Managing cuttings in pasture not only warrant material for grassland livestock husbandry and but also can sustain the grassland as the ecological barrier of Chinese inland ecosystems. The natural grassland in those regions plays an important role in livestock rearing, wind break, sand stabilization, soil and water conservation, air purification, climate regulation and so on. However, the information about the spatial distribution, the productivity fluctuation and degradation status of harvesting forages in natural pastures in China is limited, which seriously threatens forage grassland reserves and emergency relief in China. As such, a systematic study on forage harvesting in natural pasture is necessary and important. In this study, the resource inventory of forage harvesting pasture in semi-arid pastoral areas of north China was carried out in order to understand the status of forage harvesting pastures for their spatial distribution and resource profiles. After a field investigation conducted in 2013 and 2014 (the investigation time was at the end of July to the beginning of September) in areas including Inner Mongolia Autonomous Region, Heilongjiang, Jilin and Hebei province, we recorded the location each survey area, grassland types, dominant species, the height, density, coverage of the natural grassland, and consulted the mowing time of forage harvesting pasture in the local grass court. In addition, the Landsat TM5 remotely sensed images which spatial resolution was 30 meters and has seven spectral channels, were used as the data source (a total of 256 images) after being geometrically corrected, projection transformation, format conversion and false color composite of band 4, 3 and 2. First, the indoor pre judgment was used to the images to determine the field survey area. Then establishment of interpretation was processed by combining the spectral features of TM images and the field survey points. Finally, we used information compound method in visual interpretation to achieve the area of pasture under forage harvesting in semi-arid pastoral areas in north China. Then classification accuracy evaluation was carried out. The results showed that the area of forage harvesting pasture in the semi-arid regions was 8.0035 million hm2 which accounted for 2.85% of the grassland area in the northern China, with an average of interpretation accuracy of 76.78% and the average of the Kappa coefficient of 0.54. Among them, the largest area of forage harvesting pasture appeared in Inner Mongolia, reached 6.8804 million hm2, followed by Heilongjiang Province of 0.6703 million hm2, Jilin Province of 0.2477 million hm2 and Hebei Province of 0.2050 million hm2. The forage harvesting pasture area of Hulunber meadow steppe, Horqin sandy grassland and Xilingol typical steppe were 1.8089 million hm2, 0.9644 million hm2 and 3.9540 million hm2 respectively. Temperate steppe, temperate meadow steppe and lowland meadow were the main vegetation types harvested from those pastures, and a little distribution in the mountain meadow and temperate desert steppe. The results made up for the deficiency for the area of the domestic forage harvesting pasture data and provided data for analysis of forage harvesting pasture changes in the semi-arid pastoral areas of China.