بررسی میزان تاثیر گونه‌های گیاهی تاغ، اشنیان، قره‌داغ و آتریپلکس در طرح‌های بیابان‌زدایی بر کنترل فرسایش بادی

گونه ‌های گیاهی مختلف با داشتن ویژگی‌ های گیاه شناسی خاص خود، در برابر فرسایش بادی تاثیرات مختلفی دارند. در مناطقی که از پوشش گیاهی به‌ منظور کنترل و کاهش فرسایش بادی استفاده می ‌شود، لازم است میزان تاثیر و نقش هر نوع گونه‌ ی گیاهی بر مقدار کنترل فرسایش بادی مشخص شود. در این پژوهش، تاثیر گونه‌ های گیاهی کاشته شده در کانون بحرانی فرسایش بادی منطقه ‌ی نوده پشنگ شهرستان گناباد در برابر فرسایش بادی بررسی و مقایسه شد. برای این منظور، تغییرات ارتفاع سطح خاک در محدوده‌ های تحت پوشش با گونه ‌های haloxylon sp، seidlitzia rosmarinus، nitraria schoberi،atriplex canescens، کشت مخلوط و فاقد پوشش در طول 81 واقعه‌ ی طوفانی طی سال های 1396 و 1397 اندازه‌ گیری شد. این امر با استقرار 18پین فرسایشی در دو تکرار و مساحت 100 مترمربع صورت گرفت. همچنین با تقسیم این وقایع طوفانی به دو گروه وقایع شدید و معمولی، عملکرد هر محدوده در شدت طوفان‌ ها بررسی شد. مقایسه آماری بین محدوده ‌ها نیز با استفاده از آزمون های من ویتنی و کروسکال والیس انجام شد. بر اساس نتایج حاصل، متوسط مقدار فرسایش بادی در محدوده‌ ی فاقد پوشش، 83.6 تن در هکتار بود؛ درحالی‌ که رسوب گذاری در محدوده‌ های با پوشش 6.7 تن در هکتار صورت گرفت که از نظر آماری در سطح یک درصد تفاوت معنی داری داشت. بیشترین تاثیر در کنترل فرسایش بادی، مربوط به محدوده ‌ی تاغ ‌کاری شده بود. بررسی عملکرد محدوده ‌ها نسبت به شدت طوفان‌ ها نشان داد که در وقایع شدید، نقش حفاظتی محدوده ‌ی تاغ بیش از سایر محدوده‌ ها بود و برآیند مقادیر فرسایش و رسوب نیز برابر بود. در وقایع معمولی، بیشترین نقش حفاظتی به محدوده‌ های پوشیده از اشنیان و قره‌ داغ به ترتیب با رسوب ‌گذاری 52 و 37.5 تن در هکتار بازمی‌ گشت. در طوفان ‌های معمولی، گونه ‌های با ارتفاع کمتر و گسترده بر روی زمین ، تاثیر بیشتری بر کنترل فرسایش بادی داشتند؛ درحالی‌ که در طوفان‌ های شدید، گونه‌ های با ارتفاع بلندتر.

Evaluating the effect of plant species of Haloxylon sp, Seidlitzia rosmarinus, Nitraria schoberi, Atriplex canescens used in non-desertification projects on wind erosion control

1 IntroductionThe most suitable method to reduce wind erosion is to create and increase land cover vegetation. Vegetation increases the surface roughness, which reduces wind speed and the sediment carrying capacity. Therefore, the sediments transported by wind are deposited on the ground and in the vicinity of the vegetation. However, each plant species, according to its characteristics, has a special effect on the reduction and control of wind erosion. Selection of compatible and resistant plant species in dry and desert conditions is necessary for this purpose. But, it is necessary to determine the impact of each vegetation type on it. Therefore, in areas where vegetation has been used to control and reduce wind erosion, it is necessary to determine the impact and role of each type of vegetation on the amount and control of wind erosion to identify the most effective type of cover.2 MethodologyIn this research, the effect of plant species that are used in nondesertification projects has been investigated in the critical area of wind erosion in the Nodeh Pashang region of Gonabad county with an area of 94818 hectares. For this purpose, according to the species type, time of planting, area of planting, amount of canopy, species density, and physical and climatic conditions, six homogeneous areas were selected. These six areas were covered by Haloxylon sp, Seidlitzia rosmarinus, Nitraria schoberi, Atriplex canescens, mixed of the species and not covered. The changes in the soil surface profiles were measured by installing 18 erosion pins in two replicates in an area of 100 m2 in each area for 81 dust and sand storm events during the 2018 and 2019 years. Also, the events were divided into two groups of dust storms (severe events) and blowing dust events (ordinary events). In the final, the changes in the soil surface profile were investigated in each area and event type. Also, statistical comparisons were made between areas for each event type.3 Results Discussion Base on the results, the area of Haloxylon sp had the highest percentage of canopy cover (18.4 % ). Also, the mixed speciesarea had the highest plant density. The results confirmed the effect of vegetation in desert areas in reducing wind erosion. The greatest effect on reducing wind erosion was observed in the areas covered with Haloxylon sp, Seidlitzia rosmarinus, mixed of the species, Atriplex canescens, and Nitraria schoberi, respectively. Based on the results, the mean of wind erosion in the uncovered area was 83.6 ton/h; whereas, sedimentation has taken place in the covered areas except for Nitraria schoberi area. This difference was also statistically significant at the level of one percent. In the severe events, the mean wind erosion in areas with vegetation cover was 23.4 ton/h and in the uncovered area was 118 ton/h. In this type of event, the protective role of Haloxylon sp was higher than others, and as a result, erosion and sedimentation values were equal. In the ordinary events, the most protective role was observed in S.rosmarinus and N.schoberi area with 52 and 37.5 ton/h, respectively. Based on the results, increasing the canopy is an effective measure to control and reduce wind erosion.One of the main causes for more impact of the Haloxylon sp on wind erosion can be for more canopy cover area than other species in the studied area. Because the role of wind erosion control is more related to the percentage of vegetation canopy cover. Also, the results of this study showed that species type could be effective in wind erosion control. Based on the results, the protective effect of different species varies with the event intensity. In the severe events, the protective role of Haloxylon sp and mixed of the species was higher than other areas in the studied area; whereas, in the ordinary events, the protective role of Seidlitzia and Nitraria areas was higher than other areas. These results showed the role of species height in reducing wind erosion.4 Conclusions The results showed the best way to control and reduce wind erosion is to create and develop the vegetation in the critical area of wind erosion. The most important reason for this result is to increase the surface roughness due to the vegetation development, which reduces the velocity and sediment carrying capacity of the wind. The results showed that increasing the amount of vegetation canopy increases the control role in wind erosion. However, the control role of plant species in wind erosion is not the same. Therefore, the selection of suitable species to control wind erosion and sediment is required. Among the effective species in controlling wind erosion, the role of Haloxylon sp in controlling wind erosion and soil stabilization has been observed more than other resistant species. Furthermore, the control role of one species in wind erosion is not the same on all events. In ordinary events, shorter and broader species on the land surface have a greater impact on wind erosion control. These species reduce the wind velocity near the ground surface and causing the sedimentation of wind sediment; whereas, taller species will have a greater impact on wind erosion control in severe events.