Planning Ecological Security Patterns In A Rapidly Urbanizing Context

Rapid urbanization has caused many eco-environmental problems when it improves our living condition, and put a serious threat to regional sustainability. Hence, how to mitigate these negative effects linking to rapid urbanization has become an urgent task and considerable challenge to maintain social, economic and environmental sustainability. The optimization of regional landscape structure, construction of the ecological security pattern as well as conservation and restoration the necessary regional ecological processes have become an increasing consensus on coping urbanization environmental problems. Yet, the ecological security pattern model is still a conceptual strategy in landscape planning due to lack of practical and feasible spatial planning approaches. Wuhan, as the largest city in the central of China, is undergoing the unprecedented urbanization process with dramatically changing in landscape pattern, ecological processes and environmental condition. Therefore, the researches on the approach to improve our urban landscape configuration will be of important theoretical and realistic significance to combat these eco-environmental problems. In this paper, the historical remote sensing imageries, climate data, basic topographical data, and field investigation data were collected to study the optimum ecological patterns of Wuhan. Hence, the objectives of our study are to focus on the landscape configuration dynamics and its driver-forces, landscape connectivity trends of forests and wetlands, and spatial characteristics of urban heat island (UHI), identify major eco-environmental problems in Wuhan, and develop a set of optimum ecological patterns proposal to eliminate these eco-environmental threatens, and initial to present an feasible landscape approach for urban eco-security pattern planning. The main results are shown as follows:(1) The landscape configuration has significantly changed during1987-2007a. Farmlands and water areas decrease dramatically in their area while built-up areas and forest quickly increase in their size. Such characteristics present a clear trend that the whole landscape configuration was changing from agricultural pattern to urban pattern. Increasing fragmentations were found in forest and water. The Aggregated Index of urban built-up areas increased during the whole research period. Because increasing human activities, the landscape in Wuhan is changing from coarse grain to fine grain, difference of patch area gradually reduced. Urban sprawl, infrastructure development and other human activities have significantly affected the pattern of regional landscape, resulting in continued increase in landscape heterogeneity. Since1991a, the landscape gradually increases the overall degree of dynamic change. The area of various landscape types fluctuated throughout the study period. Grasslands, built-up lands and bare lands have high annual rates of landscape changing but there are some differences in various stages.Agricultural development, urbanization, forest development, and the large precipitation are the main direct drivers of landscape change in1987-1991a. Increasing urban population, agricultural development, and positive eco-construction measures is the main driving force of landscape pattern changes during1991-1996a; The main factors affecting landscape change in1996-2001a, is the accelerated urbanization, the increasing proportion of industrial in GDP, and forestry ecological construction measures. In this period, the landscape changes significantly increased in intensity. Socio-economic development, accelerated urbanization process, and forestry policy with incentives is the main driver of landscape change in the period of2001-2007a. In this period, the landscape changes more intense, urban and rural construction land and forest increased significantly.To alleviate the exacerbated situation of landscape fragmentation in Wuhan, the deciders must consider the benefits of changing stockholder and integrate them into the landscape management policies, and change protection strategy of ecological resources from single patches to whole system to promote regional sustainable development.(2) Based on the generated land-cover data, a cost-distance model was used to estimate and assessed the landscape connectivity trends of Wuhan during the twenty years of1987-2007a. The results shown that, the landscape connectivity among forest patches and that among water patches decreased dramatically in the process of rapid urbanization of Wuhan. Additionally, the landscape areas with high connectivity decreased clearly while the landscape areas with low connectivity increased quickly. This trend indicates that the rapid landscape changes have influenced connectivity of eco-resources. The trend difference in pattern and connectivity of forest indicates that the negative effects on forest connectivity resulted from rapid urbanization have offset the positive effects of afforesting. Therefore, future forest construction projects must change their thinking from a focus on indicators of spatial structure to focus on changes in functional continuity. Trends of water connectivity is similar to the trends of landscape pattern, with the water area decreasing and fragmentation degree increasing, landscape connectivity degree of water continued to decline. In addition, the increasing human activities also influence water connectivity. Therefore, the protection and management of water bodies should not only focus on patch area and patches structure, but also fully take changes in water contrast landscape border into account.(3) The urban land surface temperature (LST) of Wuhan was retrieved using Landsat TM5remote sening imagery and classified into six types according to their temperature value. Based on the LST data, the thermal pattern and thermal environment effect of urban landscape pattern were analyzed. The results shown that that the spatial distribution of thermal environment in Wuhan was uneven, and showed a clear urban-rural gradient distribution. The temperature of downtown significantly higher than outlying areas of the city, UHI areas concentrated on urban central area while the low-temperature landscape mainly appear at outlying areas of the city with significant group distribution characteristics. The patch size of UHI is very small while the patch size of the lowest-and lower-temperature patches is much larger. The Euclidean Nearest-Neighbor Distance (ENN) of the lowest-and highest-temperature landscape is larger than the ENN of the medium-temperature patches.The results also demonstrated that land-cover characteristics significantly affected LST of research area. The average LST of built-up areas is the highest, while the average LST of water is the lowest. The built-up areas share the largest area of highest-temperature zones while water occupied the largest area of the lowest-LST zone Water, beach wetlands and forests influence significantly LST of the neighbor landscape. In most case, there is a clear distance effect and size effect to decrease LST of their neighbor landscape. The effective cooling-distance on built-up area by low-temperature landscape is largest among various land-cover types while the effective distance on vegetation covered areas (i.e. farmlands, forest and grassland).is smaller than others.Additionally, small patches of beach wetlands and forest has relative higher efficiency to decrease surrounding LST. Hence, the cooling effect by several small patches is better than one single large patch. Patch size of cooling landscape could influence the cooling-effects to surrounding landscape in a certain extent, but their impacts are very weak. In order to mitigate urban heat island, several strategies, to improve vegetation coverage of the green space and other landcover types, reduce patch size of built-up areas and bare lands, and establish urban wetlands-forest network and improve urban air duct are proposed(4) Urban greenways are proven strategies to counter ecological fragmentation and improve urban sustainability. However, significant challenges remain when seeking to integrate multiple functions into priority-oriented planning. In this paper, we focus on the city of Wuhan (China) to present an innovative approach for developing multi-functional greenway networks. Based on remote sensing and geographical information systems, this approach applies a least-cost path model, a kernel density analysis and a proxy index to identify and integrate multiple needs into priority greenway networks. Our priorities are bird and small mammal conservation, human recreation and water protection. In the cost settings of the least-cost path model, we include simulated construction costs to realistically identify corridors. This method insures that our results reflect the expenses necessary for the construction of greenways. Our study demonstrates that the kernel density method is an effective tool to illustrate priorities by revealing the potential utilization intensity of corridors. Based on the proposed method, we identify eight potential greenway networks, each highlighting different sets of priorities. We divide these priority greenway networks into three categories of ecological security:ideal greenways, backbone greenways and the comprehensive greenway network. The latter represents the integration of animal conservation, human recreation and water protection objectives. Because priorities can be added, interchanged or weighted according to local specificities, our study offers a methodological framework applicable to developing and developed cities.(5) In order to mitigate UHI, this paper presented a framework for Forest-Wetlands Cooling network (FWC network) planning. The proposed framework was demonstrated by a case of Wuhan. Using the landscape connectivity theory, the presented approach combined source/sink theory, least-cost path model and kernel density estimate to identify the potential cooling network. Urban FWC network is composited of thermal gradient corridor, barrier corridor, low-temperature corridor, green hub and cooling patch.In this paper, the six networks, responding various functions were identified and classified into three environmental-security level of high, medium and low level. The environmental security levels reflect the priorities for their constructions. The comprehensive FWC network represents the lowest needs for eliminate UHI effects and responses the highest priority for construction. The ideal FWC network represents the optimum network to mitigate UHI, and therefore response to the highest environmental security level and lowest priority. Considering the construction cost, main issues of establishing forest-wetlands cooling network are to improve cooling rate of built-up by increase vegetation coverage and to develop cooling corridors.(6) Construction, preservation and connections between forested areas are proven strategies to counter human-induced fragmentation of natural ecosystems in urban areas and improve regional sustainability as a whole. Yet designing forest networks that target multiple species in urban areas remains a challenging task for planners. In this section, we present a modeling framework for multi-species forest network planning in rapidly urbanizing contexts using a case study of Wuhan, a city in Central China. Based on remote sensing and geographical information systems, our approach integrates the species assemblage method, multi-criterion assessment, least-cost path model, kernel density estimates, and priority principle to plan forest networks for regional biodiversity conservation. Focal species assemblages were developed to represent local species with high sensitivity to fragmentation. We include stepping-stone functions in the cost settings of the least-cost path model to realistically identify optimum network for different species assemblages. Our study demonstrates that the kernel density method is an effective tool to illustrate priorities as it reveals potential utilization intensity of corridors. Using the proposed method, we identified seven forest networks accounting for three priority levels of biodiversity conservation within Wuhan:the ideal network, backbone network and comprehensive network. The proposed approach enables planners to readily integrate multi-species demands and develop comprehensive forest networks. This approach may contribute to forest networks planning in rapidly changing areas, especially urban.(7) Assessing functional significance of landscape elements is considered as the important context of conservation planning and the basis of sustainable ecological network. Based on conservation needs of focal species, a potential wetlands network was identified. The centrality method was further employed to assess the functional significance of wetland ecological network in Wuhan. Our results indicated that:the potential wetland network was consisted of29core-habitat patches and56corridors with least travel costs. According to the degree and betweenness, these core-habitat patches and corridors can be categorized into three priority levels, including the highest priority, the medium priority and low priority groups. When the proposed network is implemented, deferent scheduling priorities should be given respectably to various significant levels. Moreover, our simulated results also illustrated the effectiveness of the centrality method. Incorporating focal-assemblage surrogate model, multi-criterion suitability model and least-cost path model, the centrality method is available to rank and identify the key elements in regional ecological network. The future researches are expected to focus on the scale-effects of ecological network.