关键词: GlobeLand30, 地形, 耕地低效转化, 空间特征

Abstract: The conversion from cultivated land to another land use type with relatively low benefit has multiple effects on food security and ecological system. To reveal the spatial patterns of this conversion among the first decade of the 21st century in China, in this paper, the conversion from cultivated land to grassland, shrub land and bare land was firstly defined as “low-benefit conversion of cultivated land”. Then, this kind of low-benefit converted land in China from 2000 to 2010 was extracted based on GlobeLand30 and the low-benefit conversion of cultivated land at the patch and county scale was mapped. The proportionality, regional difference and aggregation of spatial distribution were analyzed by multiple approaches and the effects of terrain conditions on low-benefit conversion and the relationship between 2000's original proportion of cultivated land and low-benefit conversion were revealed. The results showed that: 1) The low-benefit conversion rate of cultivated land was only 1.5% for the whole country, but the spatial distribution was very disproportion. At the county scale, more than 70% of the low-benefit conversion occurred in only 16 out of the 2 365 counties and the cultivated land area of these 16 counties accounted for less than 20% of that of the whole country. 2) The regional differentiation of low-benefit conversion showed close relationship with the three terrain ladders in China: regions on the second step particularly in the agro-pastoral transition zones suffered the most serious low-benefit conversion problem of cultivated land; in the Qinghai-Tibet Plateau, counties with very high low-benefit conversion rate and counties with very low rate alternated with one and another; for cultivated land on the third step, the low-benefit conversion rate was very low, but there were still a few high low-benefit conversion clusters in Liaodong Peninsula, Zhejiang and Guangdong coastal areas. 3) For the whole country, the low-benefit conversion rate of cultivated land increases as the altitude increases, and so do regions in which the slope is smaller than 15°, but circumstances when the slope is bigger than 15°are complex. 4) The impact of low-benefit cultivated land conversion on agricultural development depends on local farmland resource endowments. Land use efficiency of the main agricultural areas in China was higher as results showed that low-benefit conversion rate in these areas is low; although in some areas in the Qinghai-Tibet Plateau and the northern Inner Mongolia, the low-benefit conversion rate was very high, the proportion of cultivated land is small, which will not cause large-scale low-benefit conversion of cultivated land. Indeed, counties of which the low-benefit conversion rate and the proportion of cultivated land are both at medium or high levels, should be considered as areas with serious low-benefit conversion problems so as to be paid high attention.

Key words: GlobeLand30, low-benefit conversion of cultivated land, spatial pattern, topography