基于MODIS数据的中国三种主要土地类型变化的空间特征分析

Spatial-temporal characteristics of three main land-use types in China based on MODIS data

人类活动使得土地利用和植被覆盖发生了巨大变化,直接影响着全球气候。本研究通过从2000—2013年对中国三种主要土地利用类型的NDVI变化特征进行了分析,结果表明:(1)14年来,中国三种主要土地利用类型NDVI平均值均有增强的趋势。(2)三种主要土地利用类型中除耕地中的水田,林地中的有林地和草地中的高覆盖草地增长速率不显著外,其他土地类型增长速率均显著。(3)三种土地利用类型均以改善面积大于退化面积,耕地中改善面积占总耕地的64.21%,退化的区域占18.50%;林地改善的区域占总林地的54.21%,退化的区域占20.13%;草地改善的区域占55.53%,退化的区域占18.23%。三种土地类型均有所改善且改善明显的区域主要集中在甘肃以南,陕西以北和东北部分地区。

Human activities have resulted in considerable change in land use and land cover, which directly influence the global climate system. In this study, spatial and temporal changes were investigated in three land-use types in China from 2000 to 2013, using MODIS data. The three land-use types consisted of woodland, grassland, and farmland. The purpose of this study was to describe the characteristics of vegetation cover change at the national scale using remote sense information. The results showed that： （1） The average of normalized difference vegetation index （NDVI） increased in the three land-use types over the past 14 years. The largest growth rate was found in grassland, whereas the most stable growth rate was in woodland. An increasing tendency in the NDVI in these land covers was mainly attributed to six national key forestry projects in China over the past 14 years, including conservation of natural forests; development of protective forests along the Changjiang River： planning for farmland return to woodland; management of the desertification around the Beijing area; construction of the natural preserve area; and development of forestation with fast-growth tree species. （2） The increases in the NDVI were significant in all sub-classifications of land covers under the three main land-use types, except for paddy fields in farmland, closed-forest land in woodland, and high-coverage grassland in grassland. The most significant growth tendency was found in dry-land in farmland, the four cover types （forested-land, shrub-land, open-forest land, and other forest land） in woodland, and medium- and low-coverage grassland in grassland. （3） The improved area with higher NDVIs was larger than the degraded area in the three different types of land use. Specifically, the improved area and degraded area accounted for 64.21% and 18.50% of the total farmland, respectively. The corresponding values were 54.21 and 20.13%, and 55.53 and 18.23% in woodland and grassland, respectively. The significantly improved areas within all three land types were mainly concentrated south of the Gansu Province and Shaanxi Province, and in parts of northeastern China. The improved areas with higher NDVIs in farmland were mainly located in the northwest region of China, whereas the significantly reduced areas in farmland were found in the urban and high population areas in eastern China. The reduced areas in woodlands were mainly concentrated in the northeastern regions with high population and forested lands along the eastern coast of China. The reduction in forested area was mainly due to urbanization in this region in the past years. However, overall the NDVI increased in this region because of the return of farmland to forest, forestation, and establishment of the natural forest protection area. Our results indicated that the NDVI can be used as a suitable index to describe the spatial and temporal changes in vegetation cover at regional and national levels.