Study On Urban Forest Landscape Pattern Based On Tree Canopy In Beijing Center Axis Area

Human activity is in an unprecedented breadth and depth influence on urban land use structure and forest landscape pattern.At present,the rapid development of urbanization makes the area of ecological land serious shortage,urban ecosystem is damaged,living environment is deteriorating.When people are seeking the solution,they gradually realize the function of urban forest to improve the ecological environment,and urban forest construction is driven by the demand of increasing tree canopy?Kenney A D,2010?.Urban forest canopy is not the most accurate index to measure of urban forest construction,but also the important goal of the overall planning of forest urban.As a result,reachers carry out the urban forest related research based on canopy cover,and to guide the scientific construction of forest urban in China has important practical valueAs the capital,and an international metropolis,Beijing is the fastest growing regions in the urbanization.This paper choosed the north-south axis as the research area,usd RS and GIS technology,referenced foreign urban forest canopy classification system,through artificial interpretated WorldView satellite imaging in 2013,from the central axis reacher scale,2^th-6^th ring road reacher scale,2^th-6^th ring road in north and south of Beijing reacher scale,and 15plots reacher scale to analyze the characteristics of urban forest landscape pattern.The results showed:?1?The urban construction land had the largest area,followed by the public green space and residential green space.From the city center to suburb,the area of urban construction land proportion gradually declined,public green area ratio increased,agricultural land in suburban areas outside the 5 ring road.This showed that urbanization level decreased with the increase of the ring road,the law of diminishing step by step was the same with the circle spatial development pattern in Beijing city.?2?The tree canopy rate was 21.98%in the central axis.Canopy gap between the different ring road was bigger in north and south region.The tree canopy rate was higher within third ring road,the tree canopy rate gradually declined outer third ring road,north region had higher tree canopy ratio than south region.The 4^th-5^th ring road in north area had the highest tree canopy ratio 30.12%wae due to the existence of the Olympic forest park,the 5^th-6^th ring road in south area had the lowest tree canopy ratio 11.21%wae due to the less public green land area.The public green space provided the largest tree canopy ratio proportion in four types of greenland,followed by residential greenland and road greenland.This showed public greenland and residential greenland were the key factor to determine the change of regional tree canopy ratio.The potential of tree canopy area was 3386.293 hm²,including grassland 2675.783hm²,bare land 710.51hm²,tree canopy ratio could be improved by 15.05%,central axis could achieve the largest canopy rate of 37.03%.Public greenland provided potential tree canopy ratio of 8.96%;Residential greenland provided potential tree canopy ratio of 1.57%;Unit greenland provided potential tree canopy ratio of 1.32%;Road greenland provided potential tree canopy ratio of 0.43%;Unused land provided potential tree canopy ratio of 2.78%.Olympic forest park in the north 4^th-5^th ring road had both higher reality tree canopy ratio and potential tree canopy ratio,this area would become the important ecological zone in the future.The 4^th-6^th ring road in south area had lower reality tree canopy ratio and higher potential tree canopy ratio,this showed that the poor quality of the existing green space,the area of grassland and bareland was large,the suburb in south region was the hotpoint to promote urban tree canopy in the future?3?The central axis had tree canopy patches was 100086,these pathches were divided into five grade according to the size,that was Small-sized patches,Middle-sized patches,Large-sized patches,Super large-sized patches,Extra-sized patches.The number of small-sized patches was 81314,accounting for 81.24%of the total;the number of middle-sized patches was 13915,accounting for 13.90%of the total;The number of large-sized patches was 4248,accounting for 4.24%of the total;The number of super large-sized patches was 525,accounting for 0.52%of the total;The number of extra-sized patches was 84,accounting for0.08%of the total.The distribution features of five grade tree canopy patches in the four scales is very similar,The number of small-sized patches,middle-sized patches and large-sized patches was large,the area was small,and the number of super large-sized patches,extra-sized patches was small,and the area was large.Small-sized patches,middle-sized patches and large-sized patches were concentrated in the central area of the city,the number of super large-sized patches and extra-sized patches were increased in suburb area.This was related to higher degree of urbanization in the central area of the city,urbanization caused the landscape fragmentation and the patch miniaturization.This also related to the second forest belts construction between 5^th-6^th ring road,the forest belt construction contributed to protect the large sized tree canopy patches in suburb area.?4?The formation of landscape heterogeneity was related to natural environment?regional economic development and the difference of social functions.From the central area of city to suburb,the tree canopy patches landscape pattern showed obvious gradient effect,landscape diversity and evenness index increased,the degree of polymerization of landscape and landscape fragmentation decreased,the average area increases gradually.The change of gradient on the one hand reflected the effect of urbanization on urban forest,on the other hand the construction model of urban forest was a“must attack”method under the shortage of land in Beijing.So the size of urban forest patch was smaller and fragmented,It severely restricted ecological environment improvement and ecological service function in the urban centers.