Application of Graph and Least-Cost Theory to Urban Green Space Network Development and Enhancing Landscape Ecological Connectivity (Case Study: Tabriz City)

Urban areas, including the most sophisticated landscapes and mosaics of natural and artificial elements, are the main attraction of the human population. Population growth and the need to meet human needs are causing ecosystems to become urban areas, resulting in land-use change and fragmentation. Landscape fragmentation is a dynamic, human process that involves changing the type of land cover and dividing a single habitat or ecosystem into discrete parts. Green spaces are recognized as part of the urban landscape and remnants of natural habitats in the city that have numerous social, economic and environmental functions and benefits and play an important role in sustainable development and urban ecology. However, in recent decades, the expansion of cities has caused these spaces to be demolished into smaller parts, which not only endangers the health of ecosystems but also undermines the quality of life of citizens and residents in these areas. Various studies have found the most effective way to deal with the problems of urbanization and ecological cohesion is to reinforce the enduring relationship between man, city, and nature, resulting in the emergence of concepts such as ecological networks. The concept of ecological networks is used as an appropriate approach to improve the ecological values of urban green spaces and is generally developed through the conservation of existing green spaces, the creation of new spatial forms, the restoration, and maintenance of existing connections between green patches, and the construction of new ecological corridors. Tabriz as the largest city in the northwest of the country is the most important center of population attraction in this region of the country and is constantly expanding its physical reach. In recent decades, the city has witnessed many changes in the extent and type of urban land uses, especially in the ecological arena. So many of the city's gardens and landscapes have become over time demolished, fragmented, and reused. In this regard, this research has been designed with the aim of the ecological analysis of the landscape of Tabriz city and presenting solutions to improve its condition.

The city of Tabriz is located in the center of East Azerbaijan Province in northwestern Iran and is the largest city in the region with a total area of 131 square kilometers and a population of over 1.7 million people. In order to achieve the research goals, library studies were carried out and then based on the studies, a conceptual model was developed which included two main steps: First, to evaluate the ecological continuity of the landscape based on the continuity indices and identify the most important urban green spots. Then, design optimal corridors and create an ecological network using graph theories and Least-cost. To evaluate the ecological connectivity of Tabriz, the connectivity indices (Cohesion and IIC) were measured and analyzed using Fragstats4.2 and Conefor2.6 software. Cohesion measures the consistency and consistency of patches in the landscape with Fragstats software. The Integrity Integrity Index (IIC) measures the functional continuity of the landscape using Conefor software based on the concept of graph theory. Also, by analyzing the correlation indices, the most important green spots (core or core spots) of Tabriz city were identified. In the second stage of research, using the most important green spots, using the Linkage Mapper tool, based on graph and minimum cost concepts, the ecological continuity of Tabriz city and continuous network of corridors and ecological spots were improved. This requires three input data (patches or core habitats in vector format, resistance or cost layer, and Euclidean patches text file), obtained by various tools in ArcMap software. By calling all of the Linkage Mapper software input files and applying the appropriate settings, the lowest cost corridors are plotted, passing mainly the areas where the coverage is less resistant.

The results of Cohesion index measurement in Fragstats software, based on the type and nature of land use in the landscape of Tabriz metropolitan area indicate that the lands constructed in Tabriz metropolitan area have the highest correlation with 99/751 and the available ecological spaces (lands). Water, gardens and green spaces are the least correlated among land cover. The analysis of IIC index also shows the most consistency of spots 32, 33 and 34 in landscape of Tabriz city. Finally, by analyzing the results of the correlation indices analysis (IIC and Cohesion) and also using Google images of green spots of higher importance (based on the area of the patch and its location on the landscape) in the city of Tabriz, these were identified. They are located on the outskirts of the city and play an essential role in creating a continuous network of spots and corridors and improving the quality of the environment. To improve the ecological continuity of the landscape, a network of low-cost corridors may be proposed, which usually extend to areas with less land cover, less resistance to displacement and networking. For this purpose, the highest resistance (100 and 80) was made to urban areas and the least resistance (1-50) for green lands (parks, gardens and agricultural lands), vacant land and irrigated lands as the most suitable areas for networking. , Was awarded. Given the weight intervals and cost layers, the corridor network only crosses the points that have the least resistance and connect from one habitat core to another. Finally, communication corridors based on the least cost and graph theory were identified by Linkage Mapper software, which connect the most important green spots in Tabriz metropolis.