基于景观可达性的广州市林地边界动态分析

林地边界是景观边界中一种特殊类型，受综合因素的影响而呈现动态变化，其发生位移的位置和方向能清晰地反映出该地段的土地利用过程和强度。通过对广州市1985年、1995年和2007年的土地利用数据进行分析，基于市内主要公路的分布进行景观可达性分区，提取林地边界并根据边界性质进行分类分析,着重研究了林地边界的动态变化特征。结果表明，研究时段内广州市林地面积相对稳定，而林地斑块数量和林地边界总长度持续增加，林地呈现出边界复杂化和景观破碎化的趋势。广州市林地的邻接景观以耕地为绝对优势的局面因建设用地和水域的增加而打破，表现为林地与耕地邻接边界长度迅速减少，而林地与水域、林地与建设用地邻接边界显著增加。从1985年到2007年，林地与耕地邻接边界的减少速度随着与主要公路距离的增加而变缓；林地与建设用地邻接边界增速最快的区域逐渐远离主要公路；林地与水域邻接边界更多分布于主要公路1km以外的区域，且随着时间推移逐渐靠近主干道路。

Forestland boundary dynamics based on an landscape accessibility analysis in Guangzhou, China

Much progress has been made in understanding landscape boundary or edge effects the concept was put forward by the wildlife ecologist, Leopold, in 1933. Boundary is similar to semipermeable membrane, regulating the flows of energy, mass and organism among environment patches or landscape units. As a special type of landscape boundary, forestland boundaries change with both physical and anthropogenic disturbances. The location and direction of forestland boundary changes can reflect the process and intensity of regional land use changes. Land use maps of three periods that were derived from TM images in 1985, 1997 and 2007 were employed to explore the dynamic characteristics of forestland boundaries in Guangzhou City. The analyses were conducted based on boundary characters classification and different landscape accessibility zones from the main roads. First, according to the first level land use classification that included 8 land types, forest, cropland, building area, water body, grassland and unused land, the linear features of boundary on three periods of land use maps were obtained by using the overlay tool of ArcGIS9.2. Then, the land cover features were classified according to adjacent landscape and named forest-cropland, forest-water body and forest-construction respectively, and then the boundary length were statistically analyzed by Excel. Second, main roads including national highways, provincial highways and expressways were selected and the distances from roads were used to divide landscape zones, and three zones were obtained according to the distances (0-1000 m, 1001-3000 m and greater than 3000 m) from the roads. The results suggested that boundaries became more complex and the landscape became more fragmented when both the forestland patch number and the total lengths of forestland boundary increased. We found that croplands are no longer the dominant landscape surrounding the forestlands due to increased area for urban construction and waterbody. We found rapid decreases in length of forest-cropland boundary and increased boundaries of forest-water and forest-urban building. From 1985 to 2007, the forest-cropland boundary decreased and the rate is declining with the increasing distance from the main roads. The most acute zones where the forest-building increased moved away from the main roads gradually, and most forest-water boundaries were distributed in areas 1-km away from the roads and moved to main roads over time. The detailed characters of the urbanization and land use pattern of Guangzhou could be reflected through the dynamic changes of three kinds of boundaries including forest-cropland, forest-construction and forest-waterbody. The extent of built-up area of the central city expanded outward continually and some new towns such as Huadu district, Zengcheng district and Cenghua city have enlarged quickly, and the trend that other construction land including industrial and mining has encroaching upon ecological land such as forest, cropland and waterbody was observed evidently and the range has went beyond the area adjacent to the main roads, and the amount of forest-construction boundary increased in the area that far away from the main roads. The landscape boundary length was described in this analysis, and the width also was an inherent character and analyzing of boundary width was a valuable aspect. Building more wider boundary and coming into being buffer belt were helpful to maintain the stability of forest.