高精度遥感影像下农牧交错带小流域景观特征的粒度效应

在GIS和RS技术支持下，以农牧交错带六道沟小流域2010年的WV-1高精度遥感影像为基础，编制了小流域景观类型图，选取经典景观指数，在类型和整体景观的水平上，探讨了农牧交错带小流域景观格局指数随粒度变化的基本规律，并分析了各景观格局指数间的相关性。结果表明：在1-50 m粒度范围内，农牧交错带六道沟小流域景观格局指数的“临界粒度”现象明显，总体而言，在0.5 m分辨率下六道沟小流域的景观格局指数的“临界粒度”为10 m，适宜计算的粒度范围为5-10 m，所以在利用高精度影像对小流域景观进行预测、对比和评价等研究时，需注意粒度的影响并进行一定的粒度转换。农牧交错带小流域景观形态具有分形特征，各类景观斑块的分维数对粒度变化的响应不同，分维数随粒度的增大呈非线性下降趋势，表明景观类型边界趋于简单化。相关性分析一方面定量反映了所选景观指数受粒度变化影响的相关性程度，另一方面可为后续农牧交错带小流域因“退耕还林（草）”工程引起的景观格局变化研究提供参考。

Effects of higher resolution image and spatial grain size on landscape pattern in a small watershed of the farming-pastoral zone

Effects of spatial grain size on landscape pattern, especially the study of critical grain size, has been developed during the last two decades to describe and quantify complex landscape patterns and to link landscape patterns and ecological processes. Scale is an important issue in both landscape ecology and remote sensing. Scale in landscape ecology involves both grain size and extent. However, past studies mainly used low spatial resolution images. Thus, it is necessary to identify the scale characteristics and appropriate grain extent of farming-pastoral zone in higher resolution images. A high resolution image of a small watershed with areas of farming-pastoral zone was interpreted to create maps of landscape pattern. In the GIS and RS environment, the vector drawings were transformed into shutter drawings according to different spatial grain sizes. The landscape pattern was then converted to ArcGrid formats with grain sizes of 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 m using ArcGIS Spatial Analyst. Landscape indexes were chosen and the relations between spatial grain size and these landscape indexes were determined by correlation analysis. Landscape indexes were examined at the class-level including five Area/Perimeter/Density indexes, seven Shape indexes and eight Contag indexes; and landscape indexes were also chosen at the landscape-level including four Area/Perimeter/Density indexes, four Shape indexes, three Contag indexes and four Diversity indexes. The results showed that the scale effects of selected landscape indexes were different in the farming-pastoral zone. The scale effects were apparent at both the class and the landscape levels. Critical grain sizes of landscape indexes of the farming-pastoral zone were evident, such as the grain size of 10 m for the PD, IJI and FARC-MN indexes in the watershed. An appropriate grain extent (5-10 m) was identified for calculating the landscape indexes of the farming-pastoral zone for the high resolution image. For these reasons, the scaling conversion should be taken into account in order to provide reference for studies such as forecasting landscape changes, comparison analyses and evaluations of the land use types based on landscape metrics. The various landscape type patches in the small watershed had a fractal character and the fractal dimensions of landscapes responded to scaling differently, such that fractal dimensions decreased nonlinearly with increasing grain size. Moreover, it indicated that at the border of landscape types there was a tendency towards simplification. This study should provide useful information about farming-pastoral zone effects on landscape mechanisms and the importance of scaling to these areas in high resolution image spatial models in future research.