بررسی خطر بادافتادگی درختان کاج الدار در پارک جنگلی سرخه حصار

نوع مقاله : مقاله کامل علمی پژوهشی

نویسندگان

1 دانشیار ، دانشکده منابع طبیعی و کویرشناسی، گروه محیط زیست، دانشگاه یزد، یزد، ایران،

2 دانش‌آموخته‌ کارشناسی‌ارشد ، جنگلداری، گروه محیط زیست، دانشگاه یزد، یزد، ایران

چکیده

چکیده
سابقه و هدف: بررسی و مطالعه ضریب قدکشیدگی و نسبت تاج درختان در پارک‌های جنگلی به‌منظور تعیین پایداری توده‌ها در برابر باد ازجمله موارد مهم در مدیریت این عرصه‌ها است. مهم‌ترین علّت نیز حضور گسترده خانواده‌ها و وسایل نقلیه در این مناطق است که در صورت افتادن درختان ممکن است خسارات جبران‌ناپذیری به بار آورد. ازاین‌رو این پژوهش باهدف بررسی حساسیت درختان سرپای کاج تهران در بخش‌های مختلف پارک جنگلی سرخه‌حصار، نسبت به بادافتادگی انجام شده است. همچنین تلاش شده است تا مناسب بودن قطر برابر سینه به‌عنوان متغیّری که اندازه‌گیری آن ساده و کم‌هزینه است، برای پیش‌بینی نسبت تاج و ضریب قدکشیدگی به‌عنوان دو شاخص مهم در تعیین حساسیت درختان به بادافتادگی، مورد ارزیابی قرار گیرد.

مواد و روش‌ها: پس از بازدید میدانی، تعداد 14 قطعه جنگل‌کاری انتخاب شد به‌نحوی‌که پراکنش مناسبی در سرتاسر پارک داشته باشند. درمجموع 151 اصله درخت به‌صورت تصادفی انتخاب و قطر در ارتفاع برابر سینه، ارتفاع کل، ارتفاع تنه، ارتفاع تاج، نسبت تاج و ضریب قدکشیدگی اندازه‌گیری و محاسبه شد. از آزمون t مستقل برای بررسی اختلافات در دو روش کاشت شامل ردیف‌های کنار جاده و لکه‌های جنگلی استفاده شد. تحلیل رگرسیون نیز برای مدل‌سازی رابطه قطر برابر سینه-ضریب قدکشیدگی و همچنین قطر برابر سینه-نسبت تاج انجام شد.

یافته‌ها: بر اساس نتایج، میانگین سطح مقطع درختان اندازه‌گیری شده 034/0 متر مربع و میانگین حجم آن‌ها 208/0 متر مکعب بود. با توجه به تنوع فواصل کاشت، سطح مقطع توده‌های کاج به ترتیب 45/9 تا 4/54 متر مربع در هکتار و حجم توده‌ها 8/57 تا 8/332 متر مکعب در هکتار محاسبه شد. نتایج نشان داد ضریب قدکشیدگی به‌طور متوسط 29/57 درصد بوده و ازنظر این شاخص 7/0 درصد درختان در وضعیت ناپایدار قرار داشتند. متوسط نسبت تاج نیز 557/0 بوده و ازنظر این شاخص، 6/2 درصد درختان در وضعیت بسیار ناپایدار قرار داشتند. اختلاف معنی‌داری بین لکه‌های جنگلی و ردیف‌های کنار خیابان ازنظر طول تاج، نسبت تاج، ارتفاع تنه و ضریب قدکشیدگی وجود داشت. مدل خطی برازش معنی‌داری بر داده‌های قطر برابر سینه-ضریب قدکشیدگی و همچنین قطر برابر سینه-نسبت تاج داشته، درصد خطا به ترتیب 13 و 7/11 درصد و مقدار ضریب تبیین 28/0 و 17/0 بود.

نتیجه‌گیری: درمجموع، درختان کاج الدار در پارک ملی سرخه‌حصار در وضعیت پایداری قرار داشته و درصد کمی از آن‌ها نیازمند بررسی بیومکانیکی بافت‌های چوب به‌منظور تعیین حداکثر سرعت باد قابل تحمل و تعیین اقدامات احتیاطی مانند هرس هستند. همچنین متغیر قطر برابر سینه در جنگل‌کاری‌های متنوع انجام شده ازنظر تراکم، به‌تنهایی برای پیش‌بینی ضریب قدکشیدگی و نسبت تاج کافی نیست و علاوه بر آن لازم است اندازه‌گیری ارتفاع کل و ارتفاع تاج به‌منظور محاسبه و پیش‌بینی شاخص‌های پایداری انجام شود. با توجه تأثیر مساحت و شکل لکه‌های درختکاری در بروز و شدت بادافتادگی، لازم است شکل لکه‌ها به صورت قطره اشکی که رأس آن به سمت بادهای غالب منطقه باشد در نظر گرفته شود تا خطر بادافتادگی در مکان‌های پرتردد به حداقل برسد.

کلیدواژه‌ها


عنوان مقاله [English]

Assessing the risk of windthrow for Eldar pine trees in Sorkhe-Hesar forest park

نویسندگان [English]

  • Bahman Kiani 1
  • Ramtin Madadi 2
1 Yazd University
2 YazdUniversity
چکیده [English]

Abstract
Background and objectives: Study of slenderness coefficient and crown ratio of trees in forest parks to determine the stability of the stands against the wind is one of the important issues in the park management. The most important reason is the intensive presence of families and vehicles in these areas, which can cause irreparable damage if trees fall. Therefore, this study was conducted to investigate the sensitivity of Eldar pine trees in different parts of Sorkheh Hesar Forest Park to wind throw. Attempts have also been made to evaluate the suitability of diameter at breast height, as a variable that is simple and inexpensive to measure, to predict the crown ratio and slenderness coefficient as two important indicators for determining the susceptibility of trees to wind throw.

Materials and methods: After a field survey, 14 patches were selected for sampling so that sampling sites were well distributed throughout the park. A total of 151 trees were randomly selected and their diameter at breast height, total height, trunk height, slenderness index and canopy ratio were calculated. Independent t-test was used to examine differences between tree lines and patches. Regression analysis was also performed to model the relationship between diameter-slenderness index as well as diameter-crown ratio.

Results: Based on the results, the average basal area of the measured trees was 0.034 m2 and their average volume was 0.208 m3. Considering the variety of planting spaces, basal area and volume of pine stands were calculated 9.45-54.4 m2. ha-1 and 57.8-332.8 m3. ha-1 respectively. The results showed that the average slenderness index was 57.29% and that 0.7% of the trees were in unstable conditions. The average crown ratio was 0.557 and based on this index, 2.6% of trees were unstable. There was a significant difference between the forest patches and the tree lines along the streets in terms of crown length, canopy ratio, trunk height, and slenderness index. The linear model had a significant fitting to the data of diameter-slenderness index as well as diameter-crown ratio, with error percentage of 13 and 11.7% and coefficient of determination of 0.28 and 0.17, respectively.

Conclusion: In general, pine trees in Sorkheh Hesar National Park are in a stable condition and a small percentage of them need biomechanical study of wood tissues in order to determine the maximum tolerable wind speed and take precautions such as pruning. Also, diameter at the breast height in various plantings in terms of density, alone is not enough to predict the slenderness coefficient and the crown ratio of the trees. It is necessary to measure the total height and crown height of the trees to determine the slenderness coefficient and crown ratio. Due to the effect of the area and shape of tree patches in the incidence and severity of wind throw, it is necessary to consider the shape of the spots as a teardrop that is directed towards the prevailing winds in the region to minimize the risk of falling in busy places.

کلیدواژه‌ها [English]

  • Crown ratio
  • Park management
  • Tree plantation
  • Slenderness coefficient
  • Stability
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