خلاصة:
در سیستمهای پیچیده شهری، ساختار اکولوژی نقش زیادی در تاب آوری زیست محیطی دارد. شهر بهشهر به عنوان یک شهر میانی در شمال کشور، به سبب رشد سریع جعیت و گسترش بی‌برنامه فضاهای شهری، دچار تخریب بنیانهای اکولوژیکی سرزمین و به تبع آن مشکلات زیست محیطی فراوانی شده است. بر همین اساس هدف از این مطالعه بررسی روند تغییرات در وسعت و الگوی ساختاری پوشش اراضی شهر بر اساس تبیین ساختار اکولوژی شهری در طی 34 سال اخیر با استفاده از تکنیک سنجش از دور و متریکهای سیمای سرزمین شامل متریکهای Cohesion,MNN,LSI,MSI,MPS,ED,LPI,NP,PLAND,CAاست. طبقه بندی پوشش اراضی شهر با نرم افزار ENVI5. 3و تحلیل سنجه‌های سیمای سرزمین در نرم افزار Fragstats v4. 2. 1، و در نهایت نقشه فضایی سنجه‌ها نیز در فضای نرم افزار Arc GIS انجام شد. نتایج بررسی تغییرات نقشه‌های کاربری اراضی نشان میدهد، لکه‌های ساخته شده در این بازه زمانی به دلیل افزایش جمعیت و تقاضا برای زمین و در نتیجه، رشد شهرنشینی سالهای اخیر به میزان (68 درصد (افز ایش یافته است. اما سایر کاربری‌ها با روند کاهشی مواجه گشته، به طوری که اراضی زراعی (52 درصد) و باغات و فضای سبز (31 درصد) و اراضی بایر نیز، حدود (41) درصد کاهش یافته‌اند. نتایج تحلیل متریکهای سیمای سرزمین نیز نشان میدهد که سیمای سرزمین شهر به مرور زمان، ریز دانه، پیچیده و از نظر هندسی نامنظم تر شده و با کاهش پیوستگی، از هم گسیخته تر گردیده است. در واقع نتایج نشان میدهد که عناصر ساختار اکولوژیکی خصوصا لکه‌های زراعی، باغات و فضای سبز در شهر بهشهر از نظر نحوة ترکیب و توزیع فضایی دارای شرایط مطلوبی نیست و طی دورة زمانی مورد مطالعه از لحاظ وسعت، پیوستگی و ماهیت ترکیب و توزیع لکه‌های اکولوژیکی خصوصا لکه‌های زراعی دچار تخریب شدیدی شده است.
Introduction The trend of urban change and subsequent changes in the ecological structure of Behshahr city during the last 34 years has caused many environmental problems. So that the horizontal expansion of the city to the four directions and consequently the increase of ecological footprint in this city has led to many changes in use, especially from agriculture and gardens within the city limits to residential and commercial, etc., which causes The destruction of the ecological foundations of the urban environment, the reduction of the capacity to absorb pollution and the intensification of pollution, the lack of green spaces compared to the built-up urban spaces, and finally the reduction of environmental resilience in this city. Accordingly, the purpose of this study is to investigate the trend of changes in the extent and structural pattern of urban land cover based on Explanation of urban ecology structure during the last 34 years using remote sensing techniques and landscape metrics. Data and Method The research method in the present study is analytical-descriptive. The data and information required for the research have been collected and processed through library and field studies. In order to identify and create land use maps and with the aim of examining the structural elements of Behshahr city, the images of TM and OLI sensors of Landsat 5 and 8 satellites related to June in two time periods (1986 and 2020) from the US Geological Survey ( USGS) was used. Also for combining bands, processing and classification of satellite images from ENVI 5.3 software, for measuring landscape metrics from Fragstats4.2.1 software, for preparing maps and data of other software, from Arc Gis10.7 software And Arcview3.2 and Excel software has been used to sort the data and prepare the charts. Finally, using appropriate landscape metrics at two levels (class and landscape) including metrics, MNN, LSI, MSI, MPS, ED, LPI, NP, PLAND, CA Cohesion, changes in the ecological structure of Behshahr were evaluated. Results and Discussion In this study, after processing the Landsat satellite images of the studied years (1986 and 2020), land use was classified into four classes: built-up lands, barren and gardens, and green spaces and agricultural lands. According to the results obtained from land use changes, in 1986, lands built have the highest percentage of area, ie 470 hectares (38.5%) among land uses, and respectively agricultural lands, green space and barren in the next ranks. In 2020, the built-up land has grown significantly compared to 1986 and has reached 788 hectares (65%), and other uses, agriculture, green space and wasteland are in the next categories. Also, the analysis of Behshahr Landscape metrics during the last 34 years shows that the metric value of the number of patches (NP) has increased from 599 in 1986 to 863 in 2020. In fact, the decrease in their number indicates fragmentation and The fragmentation of large agricultural spots, green spaces and gardens in the study area is due to the increase in urban construction. This reduces their sustainability and ecological performance. The average patches size (MPS) also shows a decreasing trend and has been reduced from 1.96 in 1986 to 1.43. In general, metric changes in the average patches size indicate an increase in degradation and thus a decrease in ecological resources in the study area. The results of the research also show the fact that the metric value of the average distance of the nearest neighbor (MNN) of Behshahr landscape has increased in the last 34 years and has increased from 79.01 meters in 1986 to 84.69 meters in 2020. This justifies the reduction of connection and continuity of land use patches, especially agricultural lands, gardens and green space. Conclusion In general, one of the obvious results of examining the changes in land use maps of the two periods is as follows: Land use made in this period due to increasing population and demand for land and, consequently, urban growth in recent decades, with the most Area changes have increased and increased by (68%). But other land uses have been declining, so that ecological and green lands, agricultural lands (-52%) and gardens and green spaces (-31%). ) And barren lands have also decreased by about -41%. The analysis of land landscape metrics also clearly shows the effects of human activities and urbanization on the environment, and the results indicate that the landscape of Behshahr city has become more complex, more geometrically complex and geometrically irregular, and with decreasing continuity, It has become more fragmented. In fact, the results of Cohesion, MNN, LSI, MSI, MPS, ED, LPI, NP, PLAND, CA metric analysis show that the studied land uses, especially agricultural lands, gardens and green space in Behshahr in terms of composition and distribution. The space does not have favorable conditions and during the period under study in terms of extent, continuity and nature of the composition and distribution of ecological patches, especially agricultural patches, has undergone a process of severe destruction. So that, changes in the amount of NP (number of patches) and MPS (average patches size) have been indicators of the formation of a downward trend and ultimately the destruction of the system, indicating that reducing the average size of patches, the destruction process in The system shows and in fact a genuine integrated patch has become a number of small patches and has lost its cohesion. Also, the results of the study of land use continuity metrics (MNN and Choesion) show that in the mosaic network of urban ecological patches, especially agricultural lands, gardens and green space, while eliminating a large part of these patches and changing its use. On the one hand, the average distance between similar patches has increased over the last 34 years, and on the other hand, they do not have the necessary area.continuity and integration to provide ecological services to improve the environmental quality of Behshahr.
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