عنوان مقاله [English]
نویسنده [English]چکیده [English]
In recent decades, theories of landscape ecology have offered new perspectives toward planning and landscape design. Development of ecological network concept is one of the findings of this topic. In general, the ecologists and designers use landscape ecology concepts to apply a developed spatial strategy to different urban areas. In order to analyze urban ecological conditions and networks, landscape metrics have been used widely by ecologists. Landscape metric also have been used in order to judge the heterogeneity of urban greenbelts, to construct a sustainable landscape plan, to assess and provide biodiversity conservation planning, to describe landscape patterns for agro-ecosystems and to quantify the changes in forest cover patterns. In addition, the current study also tried to has looked into the urban ecological network of Tabriz city in urban scale in order to provide rehabilitation of urban ecological network of Tabriz city. The city of Tabriz is one of the main industrial cities in Iran with a population of over one and a half million people (Fig. 1). Tabriz with cold winters and temperate summers is located in a valley to the north of the long ridge of the volcanic cone of Sahand.In this study, satellite images of Landsat with ETM instrument of 2002 are used to study the elements of ecologic network. To secure the results, land use maps at the scale of 1:2000 were also used. Meanwhile, in order to perceive and identify the structure of ecological network and its basic components, we essentially elicited the natural and artificial information-based layers such as the hydrological maps, green spaces and transportation network for verifying the natural and artificial patches and corridors. In such a way, we can best examine the ecological network of Tabriz city based on the basic elements of the patch, corridor and matrix. Thus, it is essential to analyze the ecological network through superimposing these layers and studying them based on landscape metrics (McGarigal et al. 2002) which includes MPS (Mean Patch Size), NP (Number of patches) and MNN (Mean Nearest Neighbor). The said metrics having been matched with the selective model (mosaic model) to study the network structures effectively. These metrics are analyzed using Arc GIS. By measuring the Mean Patch Size, large natural patches for conservation were identified. Number of patches indicates the level of fragmentation and the Mean Nearest Neighbor shows the level of isolation and fragmentation of patches. To map these metrics, a combined network of 100-ha hexagonal polygons is used. So the ecological network of the city was zoned and geographical data for each zone was defined. Size of hexagonal polygons was chosen based on the aim of this paper and quality and accuracy of data. Using hexagonal polygons helps optimal coverage of the whole city. With summarizing the features of Tabriz ecologic network, some zones can be identified in the study area. Then the functional approaches will be introduced based on landscape ecological approaches and the purposes assigned for creating ecological networks in urban scale. In this way, the protection and restoration of ecological connection in a system including the core areas, buffer-zones and the biological alternative connections are considered the main objectives of creating ecological networks. Such connection can also be helpful in providing social, cultural and aesthetic functions in urban environments (Bonnin et al. 2007). Some of the important ecological functions of such a network are providing a suitable habitat for the urban wildlife, built corridors to move and transport the species, food and wind and even creating some blocks for some transportation which consequently lead to a protected biodiversity (Ahern 2007). To reach the above mentioned objectives, the following approaches have to be considered: Increasing the consistency in urban ecological network through developing, distributing and promoting the quality of corridors; Maintaining the remnant patches and rehabilitating the spoiled natural patches to develop the balanced distribution in network level; Increasing the artificial green patches to create and maintain their balanced distribution; Increasing the size of patches or building large green patches to make a balanced distribution of large green patches. In general, some solutions can be suggested for each of ecologic zones defined by analysis of study area. In the first zone patches are few and small and the situation is adverse. Density of buildings and population is high in this area. So ecological rehabilitation in this zone is difficult and expensive and it is not possible in short-term. Therefore it is suggested to have a long-term plan for conversion of existing land use to green space. The second zone where patches are smaller and less coherent, conservation of green patches and their integrity is suggested. In the third zone because the patches are small and near each other, conservation value is higher. So conservation of this zone is in a high priority.