بررسی پایداری و اثرات متقابل خصوصیات فیزیکی - شیمیایی مارن حساس به فرسایش و پوشش گیاهان مرتعی در مناطق خشک و نیمه‌خشک (مطالعه موردی: شهرستان شاهرود)

سازندهای مارنی در اغلب مناطق خشک و نیمه‎خشک به دلیل خصوصیات خاص فیزیکی و شیمیایی، پوشش گیاهی اندکی دارند و استقرار پوشش بر روی آن‎ها با محدودیت‎‎های متعددی روبه‎رو است. جهت درک صحیح وضعیت اکوسیستم‎های مناطق خشک و نیمه‎خشک، شناخت رابطه پویای بین پوشش گیاهی و خاک لازم است. این تحقیق باهدف شناسایی گونه‎های گیاهی استقراریافته و بررسی اثرات متقابل خصوصیات فیزیکی شیمیایی مارن حساس به فرسایش و پوشش گیاهان مرتعی در سازندهای مارنی سه منطقه (جاده طرود، بکران و ری‎آباد) شهرستان شاهرود انجام گرفت. به‌طوری‌که پس از تحدید اراضی مارنی بر روی نقشه‎های توپوگرافی و با استفاده از نقشه‎های زمین‎شناسی، نمونه‎برداری از خاک برای تعیین خصوصیات و اندازه‎گیری تاج پوشش گیاهی انجام شد. میزان فرسایش‎پذیری متوسط در سازندهای مارنی سه منطقه جاده طرود، بکران و ری‎آباد با استفاده از مدل blm صورت گرفت. نتایج به‌دست‌آمده نشان می‎دهد به‌طورکلی وضعیت فرسایش به روش blm در منطقه بکران با بالاترین درصد پوشش گیاهی در طبقه کم و در منطقه جاده طرود و ری‎آباد در طبقه متوسط قرار می‎گیرد. نتایج همبستگی بین شاخص‎های فیزیکوشیمیایی خاک و پوشش گیاهی نشان داد عامل تاج پوشش گیاهی با عوامل خاکی شامل درصد گچ (caso4) و درصد رس به ترتیب در سطح اطمینان 99 درصد و 95 درصد ارتباط داشته و از همدیگر متاثر می‎شوند در ضمن گچ و رس موجود در خاک مارنی شهرستان شاهرود از مهم‌ترین عواملی است که در میزان استقرار پوشش گیاهی نقش بسزایی ایفا می‌کنند. نکته مهم آن است که در هر سه منطقه، گونه فراوان و غالب درمنه دشتی بوده و بدون تردید این‌گونه مرتعی را می‎توان سازگارترین گونه گیاهی در نواحی تحت پوشش سازندهای مارنی در نظر گرفت.

investigating the sustainability and interactive effects of physical-chemical properties of erosion-sensitive marl and rangeland vegetation in arid and semiarid areas (case study: shahrood town)

marni formations have little vegetation in most arid and semiarid regions due to special physical and chemical properties. the establishment of coverage on them faced several limitations. to properly understand the state of ecosystems in arid and semiarid regions, it is necessary to understand the dynamic relationship between vegetation and soil. the aim of this study is to identify the established plant species and to investigate the interactive effects of physicalchemical characteristics of erosionsensitive marl and rangeland vegetation in marl formations in three regions (taroud roads, bakran and riabad) of shahroud city; so that after delimiting the marl lands on topographic maps and using geological maps, soil sampling was performed to determine the characteristics and to measure the vegetation canopy. moderate erodibility in marni formations in three areas, taroud roads, bakran and riabad, was done using blm model. the results show that in general, the erosion status by blm method in bakran region with the highest percentage of vegetation is in the lower class and in the area of taroud roads and riabad is in the middle class. the results of correlation between physicochemical indices of soil and vegetation showed that the canopy factor was related to soil factors including gypsum percentage (caso4) and clay percentage at 99% and 95% confidence levels, respectively affecting each other. clay in marl soil of shahroud city is one of the most important factors that play an important role in the establishment of vegetation. the important point is that in all three regions, there is an abundance and predominant species of artemisia plain and, without a doubt, this rangeland species can be considered as the most compatible plant species in the areas covered by marl formations.extended abstract1introductionmarls and their deposits are the most sensitive geological formations to erosion and destruction and a large part of the erodible areas of iran are marl formations. formations with lithology of marl, marlstone, tuff and evaporitic deposits are the formations whose resulting soil is usually unsuitable in terms of physicochemical properties and has low permeability. therefore, the establishment of vegetation in such soils usually face many limitations, as a result, these formations often lack vegetation or have very poor vegetation. in addition, marl formations play a major role in the phenomenon of desertification, which is more intense in their evaporation type. marni formations in shahroud region are sensitive to erosion on the one hand, but on the other hand, due to the high amount of gypsum and salt in them, they cause erosion and transfer of salts downstream of the region. considering the role of vegetation in controlling soil erosion, the present study was conducted to investigate the important properties of marl soils and identify the dominant plant species on these soils as well as the interactive effects of physicochemical characteristics and vegetation of marl zones in shahroud.2materials and methodsto conduct this research, first, data, statistics and research records were collected. then, using a 1: 100000 geological maps of shahroud city, satellite images (to control the boundaries of formations and marl units), a map was prepared. marni units became the province.  in this study, the blm method developed by the us office of land management and it was used to determine the role of vegetation stabilization against erosion. this model presents the erosion status in terms of the sum of the scores of the seven factors in a surface factor scoring table. identification of vegetation in the study area by field visits. according to the number of plots (statistically), the size of the plot (according to the largest canopy of plant species in the plant type), the composition of the vegetation of the region was determined. observation is applied to measure the canopy cover of each plant species as well as bare soil, rocks, pebbles and litter in a randomsystematic method in each type. moreover, 3 samples were prepared from each area from a depth of 20 cm in order to study the physical and chemical properties of marl soils in the habitat of any plant. the total 9 marl soil samples were transferred to the soil and water laboratory of agricultural research and natural resources center of semnan province for analysis. changes in vegetation and physical and chemical properties in shahroud marl analysis were done aby applying variance (anova) in a completely randomized design and comparison of means by duncan multirange test method. the correlation matrix between all physicochemical parameters and vegetation was determined to determine its interactions in the three regions.3 results and discussionthe results of interactions of soil factors (physical and chemical) and vegetation to determine the correlation in marl areas of shahroud city has shown that the canopy factor with soil factor of soil texture components including gypsum percentage (caso4) at 99% confidence level and clay percentage at the 95% confidence level. in general, it can be said that there is a significant relationship between soil physicochemical properties and vegetation percentage in the studied marl areas. considering that the most important factor in reducing soil loss and preventing erosion and stabilization of marl lands is &establishment of compatible vegetation& with them (barkhordari et al., 1400; soleimanpour; et al., 1400 and asgari et al., 1401 ); the findings of this study, which were obtained according to field studies of marl lands and measurement of physicochemical status and vegetation, confirm that in order to protect and stabilize marl lands, it is necessary to undertake the reproduction and establishment of dominant species, plant, herbaceous and wheat perennial, and herbaceous and annual wheat in the study area. considering the existence of this relationship in the three regions of shahroud city, the results of duncan test which show that the percentage of gypsum in taroud road region (region 1) is not significantly different from the other two regions (bakran and reyabad) and plant characteristics (floristic list) and the emphasis on the fact that in addition to the issue of erosion and sediment production, marl lands are mostly low permeability and insufficient moisture for the establishment and growth of plants, it is recommended to establish and propagate zygophyllum eurypterum rangeland species in the areas covered by marl in reyabad region (3), since with the management and establishment of these species, in addition to soil protection, the opportunity to reproduce and preserve these valuable plant species will be provided.4 conclusioncomparing the physicochemical properties of soil and vegetation in marl zones of the three regions of shahroud city shows that the variables of sand, clay, alkalinity, salinity (ec), percentage of gypsum (caso4), percentage of lime (tnv) and sodium adsorption ratio (sar), and vegetation canopy has a significant difference at the level of 5% probability. as we expected from the analysis of variance of soil and vegetation characteristics, the results of duncan method grouping showed that there is no significant difference between the groups in terms of silt percentage, but in terms of lime percentage of regions 1 and 2, there is a significant difference with region 3. it has and in terms of the percentage of gypsum, regions 3 and 1 and regions 1 and 2 are in two separate groups and the difference between them is significant; region 1 is in a common state in terms of this feature. the results of this study also show that the canopy cover in the study area is affected by the presence of soil physicochemical factor including gypsum content (caso4) and clay percentage. the results of the correlation between soil physicochemical indices and vegetation show that soil factor gypsum and clay are among the factors affecting the changes of plant communities in the marl lands of the study area. therefore, it has caused differences in the establishment of vegetation and the type of species.