پایش تغییرات پوشش گیاهی منطقۀ حفاظت‏شدۀ جنگلی هلن و دلایل آن براساس تحلیل دو‏زمانه NDVI

نوع مقاله: مقاله پژوهشی

نویسندگان

1 استادیار دانشکدۀ منابع طبیعی و علوم زمین، دانشگاه شهرکرد

2 کارشناس ارشد جنگلداری، دانشکدۀ منابع طبیعی و علوم زمین، دانشگاه شهرکرد‌

چکیده

این مطالعه با هدف کاربرد تحلیل دو‏زمانۀ شاخص NDVI، استخراج‌شده از تصاویر چند‏طیفی سنجندۀ TM ماهوارۀ لندست 5 در پایش تغییرات پوشش گیاهی منطقۀ حفاظت‏شدۀ جنگلی هلن در استان چهارمحال و بختیاری و دلایل آن انجام شده است. به این منظور ابتدا بخش‌های جنگلی با تراکم متوسط و کم از نقشۀ کاربری منطقه جداسازی شدند. سپس عملیات پیش‏پردازش شامل تصحیحات رادیومتری بر روی تصاویر سنجندۀ TM مربوط به سال‏های 1990 و 2009 از منطقه انجام شد. برای بررسی وضعیت شاخص NDVI، اطلاعات باند‏های چهارم و دوم از هر دو تصویر، استخراج و سپس میزان تغییر تراکم پوشش گیاهی با استفاده از این شاخص‏ محاسبه شد. نتایج نشان داد که میزان تراکم پوشش گیاهی از سال 1990 تا 2009 در 4/12‌درصد از کل منطقه افزایش داشته است که 5/7‌درصد در بخش جنگلی با تراکم متوسط و 9/4‌درصد در بخش جنگلی با تراکم کم بوده است. همچنین در 63/0‌درصد از کل منطقه تراکم پوشش گیاهی کاهش یافته است که 17/0‌درصد مربوط به بخش جنگلی با تراکم متوسط و 46/0‌درصد مربوط به بخش جنگلی با تراکم کم بوده است. با در نظر گرفتن میانگین دمای بلند‏مدت و بارندگی زمستانه در این دو مقطع زمانی، افزایش تراکم پوشش گیاهی را می‏توان علاوه بر افزایش میانگین بارندگی زمستانه و دمای بلند‏مدت سالانه، مدیون تغییر عنوان آن به منطقۀ حفاظت‏شده و جلوگیری از بهره‌برداری و تخریب این بوم‌سازگان خصوصاً در بخش کوهستانی و مرتفع دانست. همچنین کاهش تراکم پوشش گیاهی در بخش‏های کم‏ارتفاع مشکلی است که نباید نادیده گرفته شود.

کلیدواژه‌ها


عنوان مقاله [English]

Monitoring of Vegetation Cover change in Helen Forested Protected Area and its Causes based on Bi-temporal Analysis of NDVI

نویسندگان [English]

  • Ali Jafari 1
  • Zahra Arman 2
1 Assistant professor, Shahrekord University, Faculty of Naural Resources
2 MSc graduate of forestry, Shahrekord University, Faculty of Naural Resources
چکیده [English]

This paper aims to detect occurred changes in vegetation cover of forested Helen protected area using extracted NDVIs from Bi-temporal multispectral images of Landsat TM. To do so, at first forest areas with low and moderate density cover were identified and separated on land use map. Then preprocessing applications including radiometric corrections were done on both 1990 and 2009 images. Also for calculating NDVIs, data on 4th (near-infrared) and 2nd (red) bands were extracted from both images. Finally, changes in vegetation cover from 1990 to 2009 were calculated using NDVI of the study area. Results show that density has increased in 12.4% of the study area including 7.5% in moderate and 4.9% in low density areas. Moreover, in 0.63% of the total area vegetation density was decreased 0.17% out of which belongs to forested area with moderate density and 0.46% to low dense. Taking into account precipitation and temperature trends during this period, these results might be related to increasing long term annual temperature and winter seasonal precipitation, respectively. Also, considering this area as a protected area from 1992 and implementing more protective affairs can be related to these outcomes.

کلیدواژه‌ها [English]

  • Helen Protected Area, NDVI
  • Landsat TM images
  • Ecological Monitoring, climatic condition
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