退耕前后20年延安市土地利用变化及驱动因素分析

Analysis of land-use change and driving factors in two decades before and after returning farmland to forest in Yan’an City

利用1980-2020年7期土地利用类型遥感数据和1981-2020年降水、温度、人口、GDP等数据,采用数理统计、转移矩阵等方法,分析延安市退耕还林前后国土空间格局变化及其对气候变化的响应。结果表明,退耕还林前受干旱和人口增加双重影响,延安市出现毁草种地现象,耕地面积增加了327.24 km^(2)。退耕还林后,耕地减少了2421.84 km^(2),减少时段主要集中在2000-2010年,占耕地减少面积的94.1%,耕地主要转换为林草地。延安市林地面积增加了923.43 km2,以其他林地变化最为明显,占林地增加面积的65.9%,其次是灌木林,增加面积占比为25.2%。退耕还林后延安市草地面积增加了1362.02 km^(2),高、中覆盖草地分别增加338.63、1186.41 km^(2),低覆盖草地基本不变。2000年以后,延安市降水量增加、温度偏高,特别是延安市北部年降水量达520 mm以上,是林地和中高覆盖草地形成的主要原因。土地利用变化主要集中在延安市北部,2020年北部低覆盖草地面积占延安市北部国土面积的17.1%,但生态还是很脆弱,加之气候持续变暖且不确定性增加,严重制约着延安市北部生态恢复,需要政策支持和持续关注。

Using 7 periods of remote sensing data of land use types from 1980 to 2020 and the data of precipitation,temperature,pop⁃ulation and GDP from 1981 to 2020,the changes of the spatial pattern of national land and its response to climate change before and af⁃ter the reforestation of Yan’an City were analyzed by using mathematical statistics and transfer matrix.The results showed that before the grain for green,under the dual influence of drought and population increase,grass seed land was destroyed and the area of cultivat⁃ed land had increased by 327.24 km^(2) in Yan’an City.And after the grain for green,the cultivated land decreased by 2421.84 km^(2).The decrease period was mainly concentrated from 2000 to 2010,accounting for 94.1% of the reduction area of the cultivated land.The cultivated land was mainly converted into forest and grass land.The area of forest land in Yan’an increased by 923.43 km2,with the most obvious change in other forest land,accounting for 65.9% of the increasing area of forest land,followed by shrubland,the in⁃creasing area accounting for 25.2%.The area of grassland in Yan’an City increased by 1362.02 km2 after the grain for green,with 338.63,1186.41 km^(2) of high and medium cover grassland respectively,while low cover grassland remained basically unchanged.Af⁃ter 2000,the increase in precipitation and high temperature in Yan’an City,especially in the northern part of Yan’an City,where an⁃nual precipitation reached 520 mm or more,were the main reasons for the formation of woodland and medium and high cover grass⁃land.Land use changes were mainly concentrated in the northern part of Yan’an City,and the area of low-cover grassland in the north⁃ern part accounted for 17.1% of the land area of the northern counties and urban areas in 2020,but the ecology was still fragile,and the continued warming and increasing uncertainty of climate seriously restricted the ecological recovery in the northern part of Yan’an City,which needed policy support and continuous attention.