黄土山丘区植被覆盖变化分析

利用像元二分模型获取研究区植被覆盖度，并对其分级。针对不同等级植被覆盖度建立转移矩阵，研究其数量随时间的变化特征，并利用全局及局部莫兰指数对植被覆盖度的空间集聚状况进行分析，以期为该区植被恢复与保护工作提供依据。结果表明:（1）研究区平均植被覆盖度空间分布整体为中部低两侧高，北部高于南部，整体植被覆盖类型以低覆盖和中低覆盖为主；（2）1991-2010年，研究区裸地、高覆盖类型和中覆盖类型整体占比增加，中覆盖类型涨幅最大；低覆盖类型和中低覆盖类型整体占比减少，低覆盖类型减幅最大；（3）研究区植被覆盖度在1991-2000年退化趋势明显，2000-2010年植被状况转好，退化趋势得到遏制；（4）植被覆盖度的空间聚集情况随着时间的变化逐渐增强，且主要以高值簇和低值簇的形式分布，高值簇和低值簇的空间集聚区域随着时间的变化发生转移；（5）研究区应进一步加强对低植被覆盖区域的恢复力度。

Analysis of Change in Vegetation Cover in Loess Hilly Region

In order to research the quantitative characteristics of mutual transformation, the study of vegetation coverage was based on two pixel models, and the transfer matrix was built based on the different levels of vegetation coverage. The entire and local Moran indices were used to analyze vegetation coverage spatial agglomeration situation in order to provide the bases for the destination of the work for vegetation recovery and protection. The results were as the followings.(1) The average vegetation coverage for the overall spatial distribution was high on the both sides, low in the middle, it was higher in the northern part than that in the southern part, and the types with low coverage and middle-low vegetation coverage were dominant in the whole vegetation cover. (2) In all of the study area, from 1991 to 2010, the proportions of bare land type, the high coverage type and middle cover type to the overall vegetation cover increased, increase of in middle coverage type was the largest; proportions of low coverage type and middle-low coverage type overall reduced, reduction of low coverage type was the largest. (3) The study area of vegetation coverage degraded in 1991-2000, improved in 2000-2010, the degradation trend had been checked. (4) The spatial aggregation of vegetation coverage increased over time, and distributed as the high value cluster and low value cluster. High value cluster and low value cluster agglomeration region shifted over time. (5) The efforts for the recovery of low vegetation coverage type should be strengthened in the whole study area.