اثر آتش بر برخی ویژگی های شیمیایی خاک جنگل در نزدیک تنه و مرز تاج بلوط ایرانی (.Quercus Brantii Lindl)

آتش می تواند طیف گسترده ای از خصوصیات فیزیکی، شیمیایی، کانی شناسی و زیستی خاک را بسته به شدت خود تغییر دهد. هدف از انجام این پژوهش، بررسی و مقایسه اثر آتش بر ویژگی های شیمیایی خاک جنگلی در موقعیت های متفاوت در زیر گونه درخت بلوط ایرانی (برودار) (.quercus brantii lindl) در شهرستان مریوان بود. برای انجام این تحقیق، دامنه ای که در مرداد ماه سال 1396 آتش سوزی رخ داده بود، انتخاب شد. سپس ترانسکتی بر روی خطوط تراز به طول 250 متر پیاده شد و در فواصل 30 متری نزدیک ترین درخت برودار انتخاب شد و در نهایت دو نمونه خاک در عمق 50 سانتی متری و در دو فاصله نزدیک تنه (50 سانتی متری) و مرز تاج برداشت شد. در مجاورت این دامنه؛ منطقه شاهد انتخاب و به همین ترتیب عمل شد. در نهایت 32 نمونه خاک سوخته و نسوخته، برداشت و پس از انتقال به آزمایشگاه برخی ویژگی های شیمیایی شامل کربن، نیتروژن، فسفر، کلسیم، منیزیم، پتاسیم تبادلی، ph و ec اندازه گیری شد. نتایج نشان داد که با افزایش فاصله از تنه درخت، مقدار کربن و نیتروژن خاک افزایش یافت. فسفر، کلسیم، منیزیم و پتاسیم با حرکت به سمت مرز تاج درختان کاهش معنی داری داشتند. ph و هدایت الکتریکی نیز با افزایش فاصله از تنه درختان کاهش معنی داری داشتند. به طور کلی می توان گفت با حرکت از موقعیت نزدیک تنه به طرف مرز تاج خصوصیات خاک سوخته متفاوت بوده است که به دلیل تفاوت در مقدار مواد قابل اشتعال تجمع یافته، احتمالا شدت آتش کمتر شده و در نتیجه اثرات متفاوتی بر خاک گذاشته است.

Effect of Wildfire on some Chemical Properties of Forest Soil Near Base Trunk and Crown Border of Persian Oak (Quercus brantii Lindl.(.

Introduction: Fires are natural processes in many ecosystems, constituting a natural, even vital, component of forests. Fire can change the soil properties depending on its severity. In semiarid regions, the effects of fire are more vigorous in comparison with other regions. In these regions, forests restoration is much more difficult especially in the summer when temperatures reach maximum levels and cause fires that reduce soil nutrients by burning organic matters and vegetation. Since the frequency of fire events in Zagros oak forests have been increasing in recent years, therefore, in this study, the chemical properties of soil investigated immediately after fire. Most wildfires in these forests are surface fires with lowtomoderate severity due to low forest density, great distances between trees and few forest floor plants.;Materials and Methods: The study area is located in Kurdistan Province, western Iran, around Marivan that has been burned in July 2017. One transect was installed on the contour line with 250 m length on the burnt slope. Eight Persian oak trees were selected at 30 meters interval. Two soil samples were collected in each tree from depth of 05 cm. The two positions of soil samples including: the first one was 50 cm far from the base trunk and the second one was on the edge of tree crown border. In the control area, eight Persian oak were selected in the adjacent area of burned area with same topographic and plant conditions and soil samples were collected same as burned area. Finally, soil organic carbon (SOC), Total nitrogen (TN), available phosphorus, potassium, calcium, magnesium, pH, and EC were analyzed.;Results and Discussion: The results of this study showed that fire has a significant effect on soil properties, so that organic carbon reduced and amount of available phosphorus, calcium, magnesium and potassium of soil increased in burned soil. Organic carbon decreased significantly (P lt;0.01) in the burned soil in comparison to control treatment near tree trunk while it did not have any significant difference in the border of tree crown. The lowest Organic carbon was 6.19% in burned soil near tree trunk and the highest 9.15% in unburned soil in the border of tree crown. Total nitrogen did not show any significant difference between all treatments. Phosphorus increased significantly after the fire in the burned soil by comparison with control in the both positions. The increase of available P in soil after fire can be due to added ash as the fire partially and completely combusted plant debris in the soil. The highest phosphorus was 130.08 mg/kg in the burned soil near tree trunk and the lowest was 65.67 mg/kg in soil of control area in the border of tree crown. Cations including Ca, Mg and K were significantly higher near tree trunks in burned soil compared with control area, while only Ca and Mg of soil showed significant differences in the border crown position. The pH of burned soil was 7.62 and 7.05 near tree trunk and border of tree crown, respectively, and it was 7.15 and 6.89 near tree trunk and border of tree crown, respectively, in control area. The EC of burned soil was 1.70 mS/cm and 0.66 mS/cm near tree trunk and border of tree crown, respectively and it was 0.44 mS/cm and 0.54 mS/cm near tree trunk and border of tree crown, respectively in control area. Oneway ANOVA showed that two positions of soil samples had significant effect on all soil parameters except nitrogen. In the Zagros oak forests, there are a lot of flammable materials inside stands, which can lead to low and medium intensity fire .According to the results of this study, the amount of organic carbon of burned soil near tree trunk was less than the crown border because of high accumulation of flammable materials and high fire intensity. ;Conclusion: In general, it can be concluded that wildfire causes significant changes in chemical properties of forest soils. Changes in the chemical properties of soil between burned soil and control area differed with movement from tree trunk to border of tree crown, so that the amounts of phosphorus, potassium, magnesium, calcium, acidity and electrical conductivity were reduced and the amount of carbon increased. Hence, it seems that properties of soil burned has diffiered by moving from the tree trunk to the border of crown trees probabley because of the differences in the amount of accumulated litter, consequently has an effect on the characteristics of the soil in different postions.