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 (0-1km, 1-3km and greater than 3km) 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 1km 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.