ارزیابی روند تغییرات پایداری اکولوژیک فضاهای سبز شهری با استفاده از گرادیان های سیمای سرزمین (مطالعه موردی: شهر سبزوار)

بوم شناسی سیمای سرزمین رویکردی مهم برای مطالعه و بررسی روند تغییرات پایداری اکولوژیک فضاهای سبز در مقیاس شهری می باشد. هدف از این مطالعه کاربرد علم بوم شناسی سیمای سرزمین و ترکیب روش تحلیل گرادیان و متریک های سیمای سرزمین، جهت ارزیابی میزان پایداری فضاهای سبز شهری در شهر سبزوار است. مطالعه از نوع کاربردی و روش تحلیل توصیفی تحلیلی با استفاده از مطالعه همبستگی انجام شده است. بدین منظور فضاهای سبز در محدوده مورد مطالعه با استفاده از عکس هوایی و تصاویر ماهواره ای به روش طبقه بندی نظارت نشده(الگوریتم kmeans) استخراج و تفکیک شدند. تحلیل سنجه های سیمای سرزمین در نرم افزار fragstats انجام شد و نقشه فضایی هر سنجه در فضای سامانه arc gis تهیه گردید و در نهایت، پس از تلفیق نقشه فضایی متریک ها، نقشه پایداری تهیه گردید. برای انجام تحلیل تغییرات پایداری از تحلیل گرادیان با استفاده از دو ترانسکت و پنجره متحرک در دو جهت شمالجنوب و شرق غرب استفاده شد. نتایج حاصل از این تحقیق نشان داد، پایداری در بخش درونی و مرکزی شهر بیشتر است و با حرکت از مرکز به حاشیه از پایداری کاسته می شود. نتایج حاصل از همبستگی متریک ها و پایداری اکولوژیک نشان داد که متریک حاشیه کل(te) با ضریب (0.97) بیشترین میزان همبستگی و متریک ارتباط و پیوستگی(mesh) با ضریب (0.05) کمترین میزان همبستگی با پایداری اکولوژیک را برخوردارند. دلیل تاثیر بیشتر حاشیه به دلیل شکل و فرم فضاهای سبز شهری است که به طور عمده به شکل خطی و مطابق با شبکه معابر توسعه یافته اند. با اینحال فضاهای سبز از کمترین میزان پیوستگی برخوردارند، که این امر لزوم برنامه ریزی و طراحی شبکه های اکولوژیک سبز را افزایش می دهد.

Assessment of the ecological sustainability changes in urban green spaces using landscape Gradient. Case study: Sabzevar urban green space

IntroductionUrbanization has profoundly transformed natural landscapes throughout the world, which inevitably has resulted in various effects on the structure, function, and dynamics of ecological systems at a wide range of scales. For example, land transformations associated with urban expansion can significantly affect biodiversity, energy flows, biogeochemical cycles, and climatic conditions at local to regional scales. With accelerating urbanization throughout the world, therefore, it is becoming increasingly important for largescale ecological research and applications (e.g., natural resource management, land use planning, and biodiversity conservation) to consider these most dramatic land transformations and their ecological consequences. Urban green spaces are fundamental ecological elements in urban structure that formed and transformed in city along time. Green spaces such as parks and sports fields as well as woods and natural meadows, wetlands or other ecosystems, represent a fundamental component of any urban ecosystem. Green urban areas facilitate physical activity and relaxation, and form a refuge from noise. Trees produce oxygen, and help filter out harmful air pollution, including airborne particulate matter. Therefore, sustainable green spaces can provide and enhance the ecological services and urban environment quality. In recent decades, landscape ecology approach has provided a theory and practical framework for assessment of landscape elements spatio patterns. One the most important tools are landscape metric that can quantify the pattern of landscape. In this study, we integrated gradient analysis with landscape pattern metrics to quantitatively characterize the urban green space patterns of Sabzevar urban area, Khorasan Razavi, Iran. We aimed to address several questions: 1) how do different green space types change with distance away from the urban center? 2) How green space sustainability change with distance away from the urban center? 3) What is a relationship between landscape metrics and sustainable properties? The gradient based landscape metrics analysis is now widely used to study the landscape pattern change in respond to urban area.Material and Method Study AreaCity of Sabzevar is one of the cities of Khorasan Razavi province in Iran. It is located in west of Khorasan Razavi in northeast of Iran. The area of this city is 23322 he square kilometer (figure 1). 5500 square kilometer of the total area of Neyshabuor is desert and 3425 square kilometer of this city is heights. It is a part of central plateau climate and it is an arid climate and desert location.Data and MethodFor this study, methodology of research basically involves four steps :(1) to provide a patch layer in vector format (i.e., a polygon layer) was used to measure the composition and configuration of land cover features. It was created based on integrated land use map and calculating and extracting the KMean algorithm. (2) Land cover of study area was classified by land use map and combined with land cover map. Fragstate v.4.2 software was used in order to calculate metrics. (3) Landscape metrics were used in order to study quantitative features of vegetation cover, green spaces changes, relations of landscape structure and ecological sustainability. (4) To analysis relationship between sustainability and landscape metrics, gradient analysis was used form center away in two aspects: northsouth and westeast. Combining gradient analysis with landscape metrics, we attempted to quantify the spatial suitability of urban green spaces.Landscape MetricsTo select and application the landscape metrics, previous studies have introduced landscape metrics according to objectives and methodology of research. Although, a series of landscape metrics, have been developed to characterize the spatial patterns of landscapes and to compare ecological sustainability across the landscapes. However, the number of metrics can be used in evaluating the ecological sustainability, but not all landscape metrics can easily be classified as representing landscape composition or landscape configuration. For example, mean patch size and patch density of a particular patch type reflect both the amount of a patch type present (composition) and its spatial distribution (configuration).ConclusionOur study has demonstrated that the sustainable level and spatial patterns of urban green spaces can be quantified using a combination of landscape metrics and gradient analysis. The results from our study can adequately address the four research questions we defined earlier in Introduction: How does different green space sustainability change with distance away from the urban center? Results showed that green space sustainability decrees with moving from center in two aspects. In landscape levels, semipublic green spaces involved the highest sustainability. Also, Correlation analysis between landscape metrics and sustainability showed TE has the most R2 (0.97) and MESH has the fewest R2 (0.05). Therefore, urban green space developed along the streets and urban networks, which increase the edges of green patches. However, green spaces have the least amount of continuity; it is necessary the ecological approach in planning and design of green ecological networks .The changes in landscape pattern along the transect have important ecological implications, and quantifying the green space gradient, as illustrated in this paper, is an important first step to linking pattern with processes in urban ecological studies.