چکیده درمنه دشتی (Artemisia sieberi Besser) از تیره Asteraceae گونه ای دارویی در فلور ایران بوده که اسانس آن در درمان بیماری های انگلی و عفونی کاربرد دارد. طی سالیان اخیر، بخش هایی از رویشگاه های درمنه، توسط عوامل انسانی تخریب شده است. این تحقیق با هدف بررسی نیازهای آت اکولوژی و برآورد تراکم درمنه در سال 1396 در منطقه روداب سبزوار انجام گرفت. ابتدا محدوده درمنه زار بر روی عکس های ماهواره ای، تعیین و اطلاعات بوم شناختی آن، شامل (توپوگرافی، اقلیم، خاک، زمین شناسی و فنولوژی) جمع آوری گردید. در مرحله ی بعد، تراکم درمنه در مراتع تخریب شده با استفاده از مدل شبکه عصبی مورد آزمون قرار گرفت. بدین منظور 70 نمونه تصادفی خاک متشکل از متغیرهای مستقل (بافت، EC،SAR ، pH،N ،P ،K ، کاتیون ها، ماده آلی و درصد آهک) و نیز تراکم درمنه (متغیر وابسته) برای ساخت مدل استفاده گردید. نتایج نشان دادند که درمنه دشتی، ارتفاعات 1400 تا 1800 متر، شیب های صفر تا 12%، بارندگی 160 تا 200 میلی‌متر و خاک های لومی تا لومی ماسه ای آهک دار با شوری کم را ترجیح می‎‎دهد. فعّالیت رویشی درمنه از اواخر اسفند شروع شده و تا اوایل آذر بذرها می رسند. همچنین نتایج پیش بینی مدل نشان داد، کمترین تراکم درمنه با 11/0 در مترمربع مربوط به اراضی می باشد که 40 سال تحت تنش شخم قرار داشته اند و بیشترین تراکم درمنه با 4/0 در مترمربع مربوط به اراضی است که دو سال از تخریب آنها می گذرد.مدل رگرسیون (R2) نشان داد که متغیرهای مستقل، 95% در تعیین تراکم درمنه نفش دارند. تفاصيل المقالة

Environmental factors have major impact on the distribution and yield of plant species. For this purpose, the responses of Khorasanian sainfoin (Onobrychis chorassanica Bunge.) were evaluated with regard to some environmental factors in habitats of Khorasan Razavi province in 2018- 2020. Generalized Additive Model (GAM) was used to investigate the response of this species to soil and topographic factors. The results indicated that O. chorassanica exhibited a substantial response to some environmental factors in its habitat. The response pattern of this species includes the gradient of soil, Total Neutralizing Value (TNV) as well as soil clay percent, followed by the monotonic increase model. Therefore, with the increase in the values of these factors, its vegetation cover percent increased. In contrast, the response of this species along with the gradient of soil sand percent followed the monotonic decrease model and with enhancement of the factor amount, the presence of O. chorassanica decreased. Soil studies have revealed that this species is mainly distributed on loamy to sandy loam soils. The response pattern of O. chorassanica along with the gradient of Organic Carbon content (OC%) and soil litter percent complied with unimodal model and its optimal growth levels for these factors were 0.4% and 30%, respectively. The geographical response of this plant also displayed that the vegetation cover percent of the studied species increased in the western and north aspects and is rarely apparent in the southern and southeastern aspects. Investigation of O. chorassanica response on gradient of topographic and soil factors provided valuable information for determining ecological needs of this species, which can be considered in vegetation management and range improvement operations in similar areas. تفاصيل المقالة

Environmental factors have huge impact on yield and distribution of plant species. For this purpose, the response of Dorema ammoniacum (Apiaceae( canopy cover to some environmental factors was investigated in its natural habitat in south of Sabzevar, Iran in 2018-2020. Generalized Additive Model (GAM) was used to investigate the response of this species to soil and topography factors. The results showed that the edaphic and physiographic factors of the habitat had significant effects on the canopy size of D. ammoniacum. Environmental factors such as sand, litter, organic matter, lime, pH, N, P, K and altitude followed a monotonic increase model in response of canopy size. So, by increasing these factors, the canopy size of D. ammoniacum increased. In contrast, the response of canopy cover of this species to the gradient of clay, slope, EC, and SAR was a monotonic decrease model so that by increasing of these factors, the canopy percentage of D. ammoniacum was decreased. Results of the soil study showed that the plant is principally distributed on sandy loam and loamy sand soils. The reaction pattern of D. ammoniacum canopy cover in confronting with the gradient of silt, bare soil, and stone and gravel followed unimodal and the optimal level for them was 1%, 30% and 1%, respectively. Generally, investigation of D. ammoniacum canopy reaction to gradient of some environmental factors gave profitable data for characterizing the ecological demands of this plant. In other words, awareness of the impact of environmental factors on D. ammoniacum canopy cover can give range managers good information to recognize arable lands for cultivating this important species and recovering its destroyed habitats. تفاصيل المقالة