تعداد مناسب نمونه برای برآورد تاج‌بارش تک‌‌درختان بلوط ایرانی (Quercus brantii) در جنگل‌های زاگرس

نوع مقاله: علمی- پژوهشی

نویسندگان

1 دانشجوی دکتری، دانشکده منابع طبیعی و علوم دریایی دانشگاه تربیت مدرس، نور، ایران

2 دانشیار، گروه جنگلداری و اقتصاد جنگل، دانشکده منابع طبیعی دانشگاه تهران، کرج، ایران

3 استادیار، گروه جنگلداری و علوم جنگل، دانشکده منابع طبیعی و علوم دریایی دانشگاه تربیت مدرس، نور، ایران

چکیده

تغییرات مکانی تاج‌بارش به‌دلیل ساختار ناهمگن تاج‌پوشش و الگوهای متغیر بارندگی بسیار زیاد است. مطالعات موجود در زمینه تعیین تعداد نمونه مناسب برای برآورد این متغیر بسیار ناچیز است. هدف این پژوهش، تخمین تعداد جمع‌آوری‌کننده‌های موردنیاز برای برآورد میانگین تجمعی تاج‌بارش پنج تک‌درخت بلوط ایرانی (Quercus brantii) با درصد خطای معین در جنگل‌های زاگرس نزدیک شهر ایلام است. در جنگلی در نزدیکی شهر ایلام به مدت 14 ماه و در طول دوره رویش، اندازه‌گیری تاج‌بارش توسط 16 عدد جمع‌آوری‌کننده در هشت جهت زیر تاج‌پوشش هر تک‌درخت انجام شد و میزان بارندگی نیز توسط شش عدد جمع‌آوری‌کننده‌ باران مشخص شد. در این دوره، 23 مورد بارندگی با مجموع عمق 257/4 میلی‌متر اندازه‌گیری شد که به‌طور متوسط 68/9 درصد آن به‌صورت تاج‌بارش از تاج‌پوشش عبور و به کف جنگل رسید. میانگین تعداد جمع‌آوری‌کننده‌های لازم با درصد خطای پنج، 10 و 15 درصد از میانگین تجمعی تاج‌بارش و با حدود اعتماد 95 درصد به‌ترتیب 70 (41 تا 138 عدد)، 18 (10 تا 35 عدد) و 8 (5 تا 15 عدد) عدد تخمین زده شد. بنابر نتایج این مطالعه، تعداد 16 عدد جمع‌آوری‌کننده مورداستفاده برای اندازه‌گیری میانگین تجمعی تاج‌بارش با خطای 15 درصد کافی است و برای تخمین آن با درصد خطای کمتر باید تعداد جمع‌آوری‌کننده‌ها افزایش یابد.

کلیدواژه‌ها


عنوان مقاله [English]

The optimum samples size to estimate throughfall for individual Brant`s oaks (Quercus brantii) in Zagros forests

نویسندگان [English]

  • Omid Fathizadeh 1
  • Pedram Atarod 2
  • Hormoz Sohrabi 3
1 Ph. D. Student, Department of Forestry and Forest Sciences, Faculty of Natural Resources and Marine ‎Sciences, Tarbiat Modares University, Noor, I.R. Iran.‎
2 Associate Prof., Department of Forestry and Forest Economics, Faculty of Natural Resources, ‎University of Tehran, Karaj, I.R. Iran
3 Assistant Prof., Department of Forestry and Forest Sciences, Faculty of Natural Resources and Marine Sciences, ‎Tarbiat Modares University, Noor, I.R. Iran.‎
چکیده [English]

Throughfall (TF) has a large spatial variability due to the heterogeneous canopy structure and variable rainfall patterns. In this study, the aim was to estimate the optimum number of collectors needed to obtain a mean cumulative TF value within certain error limits for five individual Brant’s oak trees (Quercus brantii) in the Zagros forests of Ilam in western Iran. Sixteen TF manual gauges were placed beneath the five selected tree canopies in eight geographic directions and the gross rainfall (GR) was measured by the mean of six homemade gauges for a period of 14 months in leaf-on condition. During this period, 23 rainfall events with cumulative depth of 257.4 mm were collected, of which an average TF rate of 68.9% reached the forest floor. An average of 70 (range between 41-138), 18 (range between 10-35), and 8 (range between 5-15) gauges would be required to estimate mean cumulative TF to within ±5, ±10, and ±15% percent errors at the 95% confidence level, respectively. Based on the results of this study, 16 gauges are sufficient to estimate mean cumulative TF with an error of 15% and a confidence interval of 95%. However, the number of gauges should be increased if a lower error rate for the mean cumulative TF estimations is required.

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