Study On Urban Forest Landscape Pattern Based On Multiple Data Sources In Guangzhou

As the main element of ecological landscape, urban forest has become the principal part of ecological construction in urban region. The high resolution aerial photo in 2004 and the TM images in 1985, 1995 and 2007, combined with fundamental geographic information(1:10 000)in 2005, were used to explore the landscape pattern of urban forest in Guangzhou on two research scales, including urban and built-up area. On urban scale, the changing extent and tendency of forestland cover type and landscape boundary were analyzed, and the environmental effects of urban forest as well. On built-up area scale, the fundamental data of urban forest was built based on tree-canopy cover derived from the visual interpretation on aerial photo. The scale effects and gradient of landscape pattern characteristics were discussed detailedly, as well as the landscape connectivity and accessibility of neighborhood block units considering the concerned large patches. The results acquired from high resolution imagery provided valuable information for the landscape pattern optimization of urban forest on small scale in Guangzhou. The results showed that:The forestland area of Guangzhou was increased from 1985 to 2007, and stable forestland was the dominant land cover type with the percentage of 35.81%. The proportion of stable forestland increased with the distance away from main roads and the density of roads net, and the stable no-forestland was contrary. The deforestation and afforestation were dominant in the change type in 1995, and the afforestation occurred mostly at the periphery of the stable forestland and non-forestland, while the deforestation dispersed within the boundary of stable types and mainly affected by the urbanized exploiting.The process and intensity of land use can be reflected clearly from the shift and direction of forestland boundary. The analyses were taken based on boundary characters classification and different landscape accessibility zones from the main roads in Guangzhou. Based on the results that both the forestland patch number and the whole lengths of forestland boundary were increased, the trend could be formed that boundary became more complex and landscape became more fragmental. The situation, which the adjacent landscape types of forestland were dominated by cropland, was broken with the increasing of building area and water, the lengths of forest-cropland boundary reduced rapidly and both forest-water and forest-building increased markedly. The decreasing speed of forest-cropland boundary became slow with the increasing distance from the key roads. The most acute zones where the forest-building increased were far away from the key roads gradually, and the forest-water boundaries were mostly distributed in the area which was 1km away from the roads. According to the interaction of landscape types both sides of the boundary, forest-building boundary was a kind of tensed type, and the ecological function would be affected by the increasing. A discussed method based on the analysis of the density of forestland boundary type was tried to maintain the stability of forestland resource in the rapid urbanization areas.Correlative analysis showed that there was a positive correlation between NDVI and the age of forestland, and stable forestland had the highest value of NDVI, while the corresponding value of afforestation recently was the lowest relatively. Although the effect of correlation between NDVI and brightness temperature from the thermal infrared band of TM imagery was unobvious relatively on urban scale, on built-up area scale which affected intensively by human activity, it showed a significant negative correlation. The heat island effect showed clearly in the central city of Guangzhou, and several heat island areas were concentratingrelatively. Tree canopy coverage landscape was analyzed based on the thought framework of function classification and scale system in the central city of Guangzhou. The results showed that the ratio of tree canopy coverage was 19.5%, and the ratio of Tianhe district was the highest (26.5%), while the ratio of Fangcun district was the lowest (6.6%). Ecological beneficial forests were dominant among the type groups of ecological benefits forests, public garden, residential forest stands, production forest stands and special protective forests. The coverage ratio of ecological beneficial forests was 55.4% of the total tree canopy, and secondly the ratio of production forest stands was 19.9%. Mean size of the ecological chunk forest was the largest, while the mean size of roadside trees was the smallest. The coverage ratio of extra large-sized patches larger than 1hm2 was 78.8%, the ratio of small-sized patches (<0.1hm2), medium-sized patches (0.1-0.5hm2) and large-sized patches (0.5-1hm2) was respectively 9.2%, 7.9% and 4.2%. The patch density of small-sized, medium-sized and large-sized patch in Dongshan district is the highest, but the density of extra large-sized patch in Huangpu was the highest, and the density of medium-sized and small-sized patch in Baiyun was the lowest, while the density of large-sized and extra large-sized patch in Fangcun district was the lowest. Extra large-sized patches were dominated by ecological beneficial forests and production forest stands, and residential forest stands were regnant in other sized patches. There were extra large-sized patches distributed mostly in the mountain area, which were located in the north of the central city and the east developing belt in Tianhe and Huangpu districts, and orchard fields in the south of Haizhu district as well. The number of small-sized patches which were planted artificially was the most and the patches of extra large-sized tree canopy coverage existed only in the parks of the old city area. Most of the large-sized patches between 0.5 and 1 hm2 were adjacent to the extra large-sized patches, the pattern might be caused by the fragment of extra large-sized patches in the process of urbanization. Continuous tree canopy is an effective approach for implementing the continuity of ecological progress and pattern. Roadside trees type, being the most at patch numbers and fragmental relatively, has the most potential for forming continuous coverage patch via spatial linkage. The results provided valuable information for related research of urban forest and the landscape pattern optimization at small scale in Guangzhou.The scale effects of classified landscape metrics showed that there were strong positive or negative correlations between grain size and landscape metrics, varying with the landscape composition. Most response curves of landscape metrics with the grain size could be modeled by the CUB, QUA, or INV function explicitly. The probability of changes of sequences of landscape metrics might be higher with the increasing grain size. The results derived from the landscape pattern analysis at core area of the central city in Guangzhou showed that the sub zone of C was more fragmental and some ecological process might be taken place in smaller scale, but the value of LPI (largest patch index) was the biggest among the five sub zones because of the existing large ecological forest. The sub zone of S affected by the large orchards area had the biggest MPS (mean patch size), as well as the standard deviation simutaneously.Several common landscape metrics were employed based on moving windows analysis in Fragstats3.3 software, and the results of scale effects of landscape metrics on grain size and extent were showed in explicit expression. Comparing with quantifying landscape pattern in the entire landscape previously, the explicit expression of partial quantification of landscape pattern could link the pattern and the ecological processes more effectively in smaller scale.The results of landscape connectivity, based on the large patches of the area larger than 0.5 hm2 , showed that the connectivity of core area of the central city in Guangzhou was not so well and the components which were consisted of important patches and other patches were directly related to the thresholds distance of the landscape connectivity. The importance of patches was inspected in different distance thresholds, and the importance values of larger patches for connectivity of tree-canopy cover landscape were more than other sized patches. The large components located in the areas where the important patches existed in the research region. All the patches could be connected each other in the 2km distance thresholds. Respectively, the components sited in the southwest of core area were isolated and could not connect well with others. The blocks were organic composition of urbanized area. Network analyst model in ArcGIS9.2 was used to analyze the accessibility between the blocks and urban forest patches within Outer Ring Highway in Guangzhou, and the service capacity of urban forest patches was examined as well. And then the difference among the blocks was analyzed, combined with tree canopy coverage from the interpretation of aerial photo. The results showed that 73% of the blocks could reach large green patch in 2km walk distance, and about 46% in 1km walk distance but only 18% of blocks could reach large green patch in 0.5km walk distance. Urban forest patches accessibility was the highest in Yuexiu District,while the provision and accessibility were the most inadequate and worst in Fangcun District and Haizhu District. Among blocks that could not reach large green patch in 0.5km walk distance but tree canopy coverage beyond 30%, the percent of institutions block was predominant, while the coverage of 90% of resident blocks was under 10%, and even 64% of those under 5%. The results acquired from Network Analyst model based on block units provided valuable information for the landscape pattern optimization of urban forest on small scale in Guangzhou.