اثر تراکم‌ پوشش‌گیاهی بر رواناب و هدررفت خاک فرسایش بین‌شیاری در ترانشه‌خاکبرداری جاده‌جنگلی‌ (مطالعه موردی : جنگل کوهمیان- آزادشهر)

نوع مقاله: مقاله پژوهشی

نویسندگان

1 عضو هیات علمی - دانشگاه علوم کشاورزی و منابع طبیعی گرگان

2 دانشگاه علوم کشاورزی و منابع طبیعی گرگان

3 عضو هیات علمی - دانشگاه تهران

4 عضو هیات علمی دانشگاه گنبد

چکیده

چکیده
سابقه و هدف : جاده‌های جنگلی موجب دسترسی آسان به منابع جنگلی شده و بدون وجود آنها نمی‌توان مدیریت مناسب بر عملیات بهره‌برداری ، حمل ونقل، حفاظت و اکوتوریسم اعمال نمود. از سوی دیگر جاده‌های جنگلی یکی از مهمترین منابع اصلی تولید رسوب در مناطق جنگلی به‌شمار می‌روند. امروزه فرسایش خاک و پیامدهای ناشی از آن، یکی از مهم‌ترین چالش های مدیریت جاده‌ها به شمار رفته و به طور جدی منابع آب و خاک را تهدید می کند. بنابراین نیاز است تا فرسایش خاک در جاده‌های جنگلی بررسی و شدت آن به صورت کمی تعیین شود. اندازه‌گیری میزان فرسایش خاک تحت شرایط طبیعی هزینه‌‌بر و زمان‌بر است. در این زمینه باران‌ساز ابزار مناسبی جهت جمع‌آوری اطلاعات رواناب و فرسایش در شرایط طبیعی منطقه به ویژه برای جاده‌های جنگلی است. مطالعات مختلفی عوامل موثر بر فرسایش آبی را در جاده‌های جنگلی مورد تحقیق قرار داده‌اند که نتایج آن‌ها بیان‌گر آن بود که رابطه معناداری بین میزان فرسایش خاک با درصد شیب‌جاده، پوشش‌گیاهی، اقلیم، خصوصیات فیزیکی و شیمیایی خاک‌ها، ترافیک جاده دارد. این پژوهش برای شناخت بهتر نقش پوشش گیاهی در کنترل فرسایش خاک، تولید رواناب و رسوب در ترانشه‌های خاکبرداری جاده‌جنگلی انجام شد.
مواد و روش‌ها: تحقیق حاضر به منظور بررسی تاثیر درصد تراکم پوشش‌گیاهی ترانشه‌خاکبرداریجاده جنگلی بر مقدار رواناب، غلظت رسوب و هدررفت خاک، آستانه ظهور رواناب و ضریب رواناب در طرح جنگلداری کوهمیان آزادشهر انجام شده است. تیمارهای پوشش گیاهی شامل فاقد پوشش گیاهی، کمتر از 25 درصد، 25- 50 درصد، 50-75 درصد و 75- 100 درصد با 4 تکرار در سطح پلات یک متر‌مربعی در قالب طرح کامل تصادفی و با استفاده از یک دستگاه شبیه‌ساز باران با شدت 80 میلی‌متر در ساعت به مدت زمان 15دقیقه با جمع‌آوری رواناب نظیر هر 3 دقیقه یک‌بار انجام گردید.
یافته ها: براساس نتایج به‌دست آمده، متوسط رواناب تولیدی ایجاد شده در پنج سطح فاقد پوشش‌گیاهی، کمتر از 25درصد، 25-50 درصد، 50-75 درصد و 75-100 پوشش گیاهی به ترتیب 7/24، 82/17، 78/12، 23/5 و 64/2 لیتر بر مترمربع، متوسط غلظت رسوب تولیدی به ترتیب66/15، 41/9 و 37/7، 07/5 و 39/2 گرم در لیتر، متوسط هدررفت خاک به ترتیب 93/386، 27/167، 72/93، 57/26 و 86/8 گرم بر مترمربع، آستانه‌شروع رواناب 12، 75، 150، 75/238 و 75/365 ثانیه، ضریب رواناب به ترتیب 8/47، 62/35، 71/25، 58/10 و 27/5 درصد برآورد گردید. نتایج آنالیز واریانس نشان داد که تفاوت معنی‌‌داری در بین مقادیر مختلف مولفه‌های رواناب و هدررفت درصدهای مختلف پوشش‌گیاهی ترانشه‌جاده وجود دارد و نتایج آزمون توکی نیز نشان‌داد که با افزایش پوشش‌گیاهی، میزان رسوب و رواناب به طور معنی‌داری کاهش می‌یابد.
نتیجه‌گیری: اثر پوشش‌گیاهی ترانشه جاده‌جنگلی روی مقدار رواناب، غلظت رسوب، هدررفت خاک، آستانه ظهور رواناب و ضریب‌رواناب کاملا" معنی‌‌دار بوده و به عبارت دیگر، مقدار رواناب و هدررفت خاک با تراکم پوشش‌گیاهی رابطه معکوس و معنی-دار دارد. پوشش‌گیاهی تاثیر و نقش مثبتی در کاهش مولفه‌های رواناب و رسوب ترانشه‌های جاده‌های جنگلی دارد.
واژه های کلیدی: فرسایش‌خاک، ضریب‌رواناب، غلظت رسوب، باران‌ساز‌، شدت بارندگی،

کلیدواژه‌ها

عنوان مقاله [English]

Effect of vegetation cover percentage on runoff and soil loss of interill erosion in forest road cutslope (Case study: Kohmiyan Forest, Azadshahr).

نویسنده [English]

  • Mohammad Hadi Moayeri 1

چکیده [English]

Background and Objectives: Roads provide access to forest resources for properly management of timber production, transportation, forest protection and ecotourism. Also, forest roads are known as one of the main sources of sediment production in forest watersheds. Globally, soil erosion is one of the most important environmental problems which is threaten soil and water resources. Therefore, it is necessary to investigate on soil erosion of forest roads and determination of its quantity rate. The measurement of soil erosion rates under natural rainfall conditions is costly and time consuming. Data provided by rainfall simulation and static site measurements can be used to predict erosion rates under natural conditions, especially for erosion rates from forest roads. Various studies were investigated the factors affecting water erosion in forest roads and their results had shown a significant correlation among slope percentage, vegetation cover percentage, climate, Physical and chemical soil characteristics, road traffic with the amount of soil erosion. This study, specifically, aimed to assess the effect of vegetation cover on soil erosion, runoff production and sedimentation.
Materials and Methods: This study was done to investigate the effects of vegetation cover of cut-slope forest road on erosion variables such as runoff amount, sediment concentration, soil loss, time to runoff and runoff coefficient in Kohmiyan Forest of Azadshahr. It was conducted five treatments of vegetation cover including 0, <25%, 25-50%, 50-75% and 75-100%, each with four replicates on one square meter plot by rainfall simulation at an intensity of 80 mm/h for 15 min and distance 3 minutes.
Results: The results indicated that the average amount of runoff in five levels of vegetation cover including bare ground, less than 25%, 25-50%, 50-75% and 75-100% were 24.7,17.82, 12.78, 5.23 and 2.64 l/m2, average amount of sediment concentration were 15.66, 9.41, 7.37, 5.07 and 2.39 g/l and average time of runoff were 12.00,75.00, 150.00, 238.75 and 365.75 and runoff coefficient were 47.8, 35.62, 25.71, 10.58 and 5.27 percent, respectively. The results statistically showed significant differences between amount of runoff and soil loss due to vegetation cover of road cut-slope. The results of Tukey test indicated significant differences among mean runoff and sediment of five level and decrease with increased road cut-slope of vegetation cover percentage.
Conclusion: The effect of vegetation cover on the cut-slope road is completely significant on the amount of runoff, sediment concentration, soil loss, time to runoff and runoff coefficient. In other words, the amount of runoff and soil loss has a reverse and significant relationship with vegetation cover percentage. Vegetation cover percentage has had a positive impact and role in the reduction of the amount of runoff and sediment in the forest roads.

Keywords: Soil erosion, Runoff coefficient, Sediment concentration, Rainfall simulator, Rainfall intensity.

کلیدواژه‌ها [English]

  • Runoff
  • soil loss
  • Rainfall simulator
  • Vegetation cover
  • Rainfall intensity
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