مجله جنگل ایران

مجله جنگل ایران

A New Method for Development of a Competition Index Using Crown–Diameter Relationship of Naturally Grown Pinus brutia Ten. in Iraq

نوع مقاله : مقاله پژوهشی

نویسندگان
1 بخش جنگلداری، دانشکده مهندسی علوم کشاورزی، دانشگاه دهوک، دهوک، عراق
2 استادیار، بخش جنگلداری، دانشکده مهندسی علوم کشاورزی، دانشگاه دهوک، دهوک، عراق
10.22034/ijf.2026.550576.2078
چکیده
Introduction: Forests cover about 30% of the Earth’s land surface, but in Iraq they are limited, mainly confined to the northern region, totaling around 1.26 million hectares, or 2.9% of the country’s land area. Forests in this region include coniferous and broad-leaved types. Coniferous forests are dominated by pines, which make up approximately 80% of the stand. Calabrian pine (Pinus brutia), native to the Duhok governorate in northern Iraq, covers an area of approximately 50,000 ha in Zawita, Atrush, and Belkaf. This study deals with the regression of crown width on diameter at breast height to be used in the development of a competition index. Crown width is important for forest dynamics, biodiversity, carbon sequestration, and overall ecosystem health.
Materials and Methods: Field data were collected from three distinct locations within Duhok Province, Kurdistan, Iraq. In total, 480 trees were sampled from both open-grown and stand-grown trees. A total of 160 trees were selected from each location (80 open-grown trees, which were free from all competition, and 80 stand-grown trees, where there was inter-tree competition regarding resource access). Of these, 50 trees were used for calibration, while 30 trees were used for validation, resulting in a balanced and robust dataset for analysis. Using Statgraphics Centurion 19 software, separate regressions of Crown Width (CW) against Diameter at Breast Height (DBH) were developed for both tree types. Six groups of allometric regression equations were evaluated using criteria that included the coefficient of determination (R²), bias, mean absolute error (MAE), Ohtomo’s unbiased test, and additional proposed metrics.
Results: Crown width was regressed on diameter at breast height using different types of functions; among them, linear, nonlinear, and logarithmic models with different forms of dependent variables were used. Upon statistical analysis of the developed models, the linear model of the form, Cw = b₁ + b₂ DBH, was selected as the most appropriate one that fit the study data in both tree types across all locations. As a result, there was no major difference between the regression slopes for open-grown trees and those for trees growing within a stand. In addition, this study presented a new method for calculating the competition index.
Conclusion: From the analysis of the samples collected, certain key conclusions can be drawn. First, in all the study sites, the relationships between crown width and diameter at breast height (DBH) did not show any statistically significant differences between open-grown and stand-grown trees. This indicates a relatively low stand density, resulting in minimal competition for resources among stand-grown trees. Second, given the improvement of overall forest structure and productivity, it is advisable that replanting strategies should fill the existing canopy gaps in all sites, since this will make better use of available resources, promote the long-term health of forests, and maintain biodiversity. Lastly, the present study confirmed a strong linear relationship between crown width and DBH for Calabrian pine in Iraq.
کلیدواژه‌ها
موضوعات

عنوان مقاله English

روشی نوین برای ارائۀ شاخص رقابت با استفاده از رابطۀ قطر تاج و قطر برابرسینه در درختان کاج مدیترانه‌ای (Pinus brutia Ten.) طبیعی در عراق

نویسندگان English

Abdulaziz Younis 1
Tariq Salih 2
1 Dept. of Forestry, College of Agricultural Engineering Sciences, University of Duhok, Duhok, Iraq
2 Assistant prof., Dept. of Forestry, College of Agricultural Engineering Sciences, University of Duhok, Duhok, Iraq
چکیده English

مقدمه: جنگل‌ها حدود 30 درصد از مساحت خشکی‌های زمین را پوشش می‌دهند، اما در عراق مساحت آنها محدود بوده و اغلب در نواحی شمالی کشور متمرکز است؛ چنانکه در مجموع حدود 26/1 میلیون هکتار، معادل 9/2 درصد مساحت کشور را شامل می‌شود. جنگل‌های این منطقه شامل تیپ‌های سوزنی‌برگ و پهن‌برگ هستند. جنگل‌های سوزنی‌برگ اغلب تحت سلطۀ گونه‌های کاج هستند که حدود 80 درصد توده‌ها را تشکیل می‌دهند. کاج مدیترانه‌ای (Pinus brutia) که بومی استان دهوک در شمال عراق است، مساحتی در حدود 50000 هکتار را در مناطق زاویته، اتروش و بیلکیف پوشش می‌دهد. این پژوهش به بررسی رگرسیون عرض تاج با قطر برابرسینه به‌منظور استفاده در توسعۀ یک شاخص رقابت می‌پردازد. عرض تاج برای پویایی جنگل، تنوع زیستی، ترسیب کربن و سلامت کلی اکوسیستم اهمیت دارد.
مواد و روش‌ها: داده‌های میدانی از سه مکان متمایز در استان دهوک، اقلیم کردستان عراق جمع‌آوری شد. در مجموع ۴۸۰ درخت از هر دو گروه درختان رشد‌یافته در فضای باز و درختان رشد‌یافته در توده نمونه‌برداری شدند. از هر مکان ۱۶۰ درخت انتخاب شد (۸۰ درخت رشد‌یافته در فضای باز که عاری از هرگونه رقابت بودند و ۸۰ درخت رشد‌یافته در توده که رقابت بین‌درختی برای دسترسی به منابع وجود داشت). از این تعداد، ۵۰ درخت برای کالیبراسیون و ۳۰ درخت برای اعتبارسنجی استفاده شد که به یک مجموعه ‌دادۀ متوازن و قابل اتکا برای تحلیل انجامید. با استفاده از نرم‌افزار Statgraphics Centurion 19، رگرسیون‌های جداگانه‌ای بین عرض تاج (CW) و قطر برابرسینه (DBH) برای هر دو نوع درخت توسعه داده شد. شش گروه از معادلات رگرسیون آلومتریک با استفاده از معیارهایی شامل ضریب تعیین (R²)، اریبی، میانگین قدر مطلق خطا (MAE)، آزمون بی‌طرفی اوتومو و بقیۀ شاخص‌های پیشنهادی ارزیابی شدند.
نتایج: عرض تاج در برابر قطر برابرسینه با استفاده از انواع مختلف توابع، از جمله مدل‌های خطی، غیرخطی و لگاریتمی با اشکال گوناگون متغیر وابسته، برازش داده شد. براساس تحلیل‌های آماری مدل‌های توسعه‌یافته، مدل خطی به‌صورت
Cw = b₁ + b₂ DBH
به‌عنوان مناسب‌ترین مدل که داده‌های مطالعه را در همۀ مکان‌ها به‌خوبی برازش می‌دهد انتخاب شد. در نتیجه، تفاوت زیادی بین شیب‌های رگرسیون درختان رشد‌یافته در فضای باز و درختان رشد‌یافته در داخل توده مشاهده نشد. افزون‌بر این، در این پژوهش روشی نوین برای محاسبۀ شاخص رقابت ارائه شد.
نتیجه‌گیری: از تجزیه‌وتحلیل نمونه‌های جمع‌آوری‌شده، می‌توان به نتایج مهم زیر دست یافت: نخست، در همۀ سایت‌های بررسی‌شده، رابطۀ بین عرض تاج و قطر برابرسینه (DBH) تفاوت آماری معنی‌داری بین درختان انفرادی و توده‌ای نشان نداد. این امر نشان‌دهندۀ تراکم به‌نسبت کم توده است که به رقابت حداقلی برای منابع در میان درختان توده‌ای منجر می‌شود؛ دوم، با توجه به بهبود ساختار کلی و بهره‌وری جنگل، توصیه می‌شود که راهبرد‌های بازکاشت به پر کردن شکاف‌های موجود در تاج‌پوشش در همۀ سایت‌ها متمرکز شوند، زیرا این کار سبب استفادۀ بهتر از منابع موجود، ارتقای سلامت بلندمدت جنگل‌ها و حفظ تنوع زیستی خواهد شد. در نهایت، پژوهش حاضر رابطۀ خطی قوی بین عرض تاج و قطر برابرسینه را تأیید کرد.

کلیدواژه‌ها English

شاخص رقابت تاج
کاج بروسیا
مدل‌سازی تاج
مدل‌های رگرسیون
معادلات آلومتریک
 
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  • تاریخ دریافت 12 مهر 1404
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