بررسی تغییرات گستره جنگل های مانگرو با استفاده از RS و GIS (بررسی موردی: مانگروهای استان هرمزگان)

نوع مقاله : مقاله پژوهشی

نویسندگان

گروه علوم جنگل، دانشکده منابع طبیعی و علوم زمین، دانشگاه شهرکرد، شهرکرد، ایران

چکیده

سابقه و هدف:
اکوسیستم‌های مختلف ساحلی، به ویژه مانگروها، تقریبا به‌صورت دائمی و همزمان، در معرض تنش‌ها وآشفتگی‌های چندگانه محیطی (ژئولوژیک، فیزیکی، شیمیایی و بیولوژیک) قرار می‌گیرند و از نظر ویژگی‌های‌شان در طول زمان و مکان، متنوع هستند. نتیجه مستقیم وقوع این تنش‌ها و آشفتگی‌ها، کاهش وسعت و سلامتی مانگروها و به دنبال آن تشدید گرمایش جهانی و سایر تغییرات اقلیمی، کاهش کیفیت آب‌های ساحلی، کاهش تنوع زیستی و تخریب زیستگاه‌های ساحلی است. با توجه به این پیامدهای نامطلوب ناشی از کاهش وسعت مانگروها، اولویت‌بندی اقدامات مدیریتی و فراهم آوردن زیرساخت‌های مطلوب برای جلوگیری یا کاهش گستره این اکوسیستم‌ها ضروری است. دست‌یابی به این هدف در گرو آگاهی و اطلاعات کافی و دقیق درباره روند تغییرات ایجاد‌شده در مانگروها در طول زمان است که می‌تواند نقش مهمی در کارایی و موفقیت برنامه‌های احیا و توسعه آنها داشته باشد. بنابراین هدف این پژوهش بررسی تغییرات ایجاد‌شده در گستره مانگروهای استان هرمزگان در یک دوره زمانی 30 ساله است.
مواد و روش‌ها:
در این پژوهش برای بررسی تغییرات گستره مانگروها در طول زمان، از تصاویر ماهواره لندست مربوط به مقاطع زمانی 1986، 2000 و 2016 استفاده شد. پیش‌پردازش‌های لازم بر روی تصاویر با استفاده از نرم‌افزار Idrisi انجام گرفت و پس از استخراج نقشه‌های پوشش گیاهی مانگرو در مقاطع زمانی ذکر‌شده، تغییرات گستره مانگروهای زون‌های رویشگاهی خمیر، قشم، تیاب، سیریک و جاسک در نرم‌افزار ArcGIS تجزیه و تحلیل‌ شد و مقادیر متوسط تغییرات وسعت رویشگاه‌ها در دو دوره زمانی قبل و بعد از سال 2000 و نیز تمام دوره 30 ساله محاسبه و بررسی شد.
نتایج و بحث:
نتایج این پژوهش نشان داد که در میان زون‌های رویشگاهی مورد بررسی (خمیر، قشم، تیاب، سیریک و جاسک)، زون رویشگاهی خمیر بیشترین مقدار متوسط کاهش وسعت (64/4- هکتار در سال) و زون رویشگاهی سیریک بیشترین مقدار متوسط افزایش وسعت (5/23 هکتار در سال) را در دوره 30 ساله داشتند. نتایج همچنین نشان داد که در دوره زمانی 2000 تا 2016، زون‌های رویشگاهی سیریک و قشم به ترتیب بیشترین مقدار متوسط افزایش و کاهش وسعت را در میان زون‌های مورد بررسی داشتند (به ترتیب با مقادیر متوسط تغییرات وسعت برابر با 47/32 و 38/21- هکتار در سال). تجزیه‌و‌تحلیل تغییرات وسعت مانگروها در رویشگاه‌های مختلف نشان داد که به رغم کاهش وسعت کلیه رویشگاه‌های مانگرو استان هرمزگان در دوره زمانی پس از سال 2000، رویشگاه سیریک دارای افزایش قابل‌توجه وسعت در این دوره زمانی نسبت به دوره پیش از سال 2000 بود که دلیل آن جنگل‌کاری با گونه‌های حرا و چندل در پهنه‌های گلی این رویشگاه در سال‌های اخیر بوده است.
نتیجه‌گیری:
نتایج بررسی تغییرات گستره مانگروهای استان هرمزگان نشان داد که روند تغییرات گستره مانگروهای استان هرمزگان در طول دوره 30 ساله از سواحل خلیج فارس به دریای عمان به‌صورت افزایشی بوده است که نشان‌دهنده تاثیر عوامل مختلف محیطی بر نحوه تغییرات وسعت مانگروهای استان در طی زمان است. در نهایت می‌توان گفت نتایج حاصل از این پژوهش می‌تواند با فراهم آوردن اطلاعات به‌روز و دقیق در زمینه تغییرات وسعت رویشگاهی استان هرمزگان به برنامه‌ریزی‌های اثربخش برای انجام اقدامات حفاظتی و احیای مانگروهای استان کمک قابل‌توجهی کند.

کلیدواژه‌ها

عنوان مقاله [English]

Mapping area changes of mangroves using RS and GIS (Case study: mangroves of Hormozgan province)

نویسندگان [English]

  • Davood Mafi Gholami
  • Masoumeh Baharlouii
  • Beytollah Mahmoudii
Department of Forest Science. Faculty of Natural Resources and Earth Sciences, Shahrekord University, Shahrekord, Iran
چکیده [English]

Introduction:
Different coastal ecosystems, especially mangroves, are exposed permanently and almost simultaneously to multiple environmental stresses and disturbances (geological, physical, chemical and biological) which are varied in terms of their characteristics over time and space. The direct result of these stresses and disturbances is the reduction in area and health of mangroves and the subsequent exacerbation of global warming and other consequences of climate change, reduced coastal water quality, loss of biodiversity and degradation of coastal habitats. Considering the adverse consequences arising from the reduction in mangrove forest area, prioritizing management actions and providing appropriate infrastructure is essential to prevent a decrease in the extent of these ecosystems. Achieving this goal depends on having accurate and sufficient information and knowledge about the process of changes in the extent of mangrove forest habitats over time which can play an important role in the efficiency and success of rehabilitation programmes and the development of these ecosystems. Hence, the aim of this study was to investigate the long-term changes occurred in areas of mangrove forest of Hormozgan Province.
Materials and methods:
In this study, Landsat images from 1986, 2000, and 2016 were used to study changes in the extent of mangroves over time. The necessary pre-processing was doneconducted on images using Idrisi software. After extraction of the mangrove vegetation maps in the aforementioned years, changes in mangroves of the Khamir, Qeshm, Tiab, Sirik and Jask habitats were analyzed in ArcGIS software and the average values of areas of mangroves were calculated for two periods, namely pre- and post- 2000, and during a 30-year period.
Results and discussion:
The accuracy assessment of the classified images showed that the overall accuracy was equal to 92%.  The results also showed that among the zones investigated (Khamir, Ghesh, Tiab, Sirik and Jask), Khamir habitat zone had the highest average annual value of area reduction (equal to -4.64 h/yr) and Sirik habitat zone had the highest average annual value of area expansion (equal to 23.5 h/yr) during the 30-year period. The results also showed that during period of 2000-2016, Sirik and Qeshm zones had the highest average value of expansion and reduction in area, respectively (equal to 32.47 and -21.38 h/yr, respectively). Analysis of mangrove area changes in different habitats showed that, despite the reduction in the extent of all mangroves in the period after 2000, the mangroves of Sirik habitat had significant increase in area in this period compared to the period before 2000 which was due to forestation with Avicenna and Rhizophora in the mud flats of this habitat in recent years.
Conclusions:
The results of the study of changes in the areas of mangroves of Hormozgan Province showed that the trend of change the in area covered by the mangroves of Hormozgan Province over a 30-year period has been increasing from the coasts of the Persian Gulf to the Oman Sea; this indicates the impact of various environmental factors affecting the changes in the extent of the mangroves of the province. Finally it can be said that the results of this study, by providing up-to-date and accurate information about areas changes of mangrove habitat in Hormozgan Province, can help significantly to the planning of effective actions to protection and restoration of these habitats.

کلیدواژه‌ها [English]

  • Coastal ecosystems
  • Satellite images
  • Extent changes

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