Spatio-temporal dynamics analysis of cropland in Northeast China during 1990-2013 based on remote sensing

The Northeast region is one of the most important agricultural production bases in China. To reveal the change rules of cropland in Northeast China, based on Landsat TM/ETM+/OLI images, combining object-based classification and manual interpretation, the information of cropland in 1990, 2000 and 2013 was extracted. Combining the results of classification and other relevant data such as climate, terrain and economy, the characteristics of spatio-temporal pattern and its driving factors in Northeast China were analyzed. The results showed that: combining object-based classification and manual interpretation could access cropland information quickly and accurately, and the classification accuracy was above 93%. The total area of cropland in Northeast China was 41.66 million hectares in 2013, which was 33.51% of total area in Northeast China, including 13.76% of paddy land and 86.24% of dry land. In the 4 provinces, the cropland in Heilongjiang was the most. From 1990 to 2013, the total area of cropland in Northeast China increased by 2.25×104 km2, including 2.21×104 km2 during 1990-2000 and 369.51 km2 during 2000-2013, and the quick change of cropland decreased. The increased cropland was derived mainly from reclaiming wetland of 1.18×104 km2 (49.40%) during 1990-2000 and 4438.62 km2 (67.77%) during 2000-2013. Though the amount was a few, it was an important characteristic that the cropland increased from sea surface reclamation. The decreased cropland was transformed mainly into build-up land and wetland, including 795.89 km2 (39.70%) and 649.27 km2 (32.39%) respectively during 1990-2000 and 2098.85 km2 (32.79%) and 2028.86 km2 (31.70%) respectively during 2000-2013. The cropland occupied by build-up land was mainly distributed around provincial capitals such as Harbin, Changchun and Shenyang and in lower reach of Liaohe River Plain, and the cropland transformed into wetland was mainly distributed in Sanjiang Plain and Songnen Plain. The reclamation from wetland, woodland and grassland receded, and the reclamation from bare land and sea enhanced. The effects of the "Grain for Green Project" were significant. Comparing 1990-2000 and 2000-2013, dry land increased at first and then decreased, and paddy land increased continuously. The increased paddy land was derived mainly from dry land. The proportion of dry land transformed into paddy land and paddy land transformed into dry land was 6:1 during 1990-2000 and 7.7:1 during 2000-2013. Planting pattern change was another important feature. The area-weighted centroid of paddy land generally moved northeastward by 207.41 km, and the area-weighted centroid of dry land changed non-significantly. The cropland across China indicated a significant variation in spatio-temporal characteristics in the past 23 years. The amount of cropland decreased in the south and increased in the north. The barycenter of newly increased cropland moved north. The regions with significant cropland change occupied those conditions which were the annual precipitation from 500 to 700 mm, the mean annual temperature between 2℃ and 4℃, the slope less than 3°, and the elevation less than 200 m. During the 23 years, although climate change impacted the change in cropland, the factors in policy regulation, economic development, scientific and technological progress, population growth, urban sprawl and other human factors played the main roles in the cropland change, which impacted the spatio-temporal characteristics, and policy regulation was the leading factor. The road that the pattern of agricultural development transforms, and the labor productivity and the yield per unit area increase will be the only road to the development of cropland in Northeast China. © 2016, Chinese Society of Agricultural Engineering. All right reserved.