ارزیابی تاثیر رگه‌های سبز چشم‌اندازها بر تنوع زیستی بوم‌نظام‌های زراعی

اعمال شیوه های مدیریت فشرده بوم‌نظام‌های زراعی، تنوع زیستی را به‌ویژه در حواشی زمین های زراعی به‌شکل نگران‌کننده ای کاهش داده است. هدف این مطالعه، ارزیابی پوشش گیاهی موجود در عناصر زیستگاهی نواری، موسوم به رگه های سبز در یک چشم انداز زراعی در شهرستان گیلانغرب استان کرمانشاه بود. ابتدا نقشه عوارض ساختاری چشم انداز مورد بررسی تهیه شد و سپس انواع حواشی زمین های زراعی به هفت گروه زمین‌های زراعی، راه ها، نهرهای دائمی و غیردائمی، حاشیه‌های هم‌جوار با زیستگاه‌های طبیعی، حاشیه‌های بین دو زمین زراعی و رگه‌های سبز درختی تقسیم گردید. گونه های گیاهی موجود بر مبنای پاسخ به میزان فشردگی استفاده از زمین به دو گروه شامل گونه های متحمل زراعی و گونه های ارزشمند طبیعی طبقه‌بندی شد. فاکتور های مربوط به تنوع در عوارض ساختاری چشم انداز تغییرات در غنای گونه ای گیاهان متحمل زراعی و ارزشمند طبیعی را در مقیاس 2 × 2 مترمربعی توضیح دادند. بیشترین غنای گونه ای کل در زمین های زراعی (43 گونه) و بعد از آن در حاشیه های هم‌جوار با زیستگا ه های طبیعی (37) ثبت شد. بیشترین مقدار شاخص تنوع شانون وینر و بریلیون در گروه گیاهان متحمل زراعی، مربوط به حاشیه های مابین دو زمین زراعی (به‌ترتیب 2.03 و 1.85) و پس از آن حاشیه های هم‌جوار با زیستگاه های طبیعی (1.4 و 1.27) بود؛ و در گروه گیاهان ارزشمند طبیعی، بیشترین مقادیر این شاخص ها برای زمین های زراعی (3.08 و 2.52) و حاشیه های هم‌جوار با زیستگاه های طبیعی (3.08 و 2.52) مورد محاسبه قرار گرفت. نتایج این مطالعه، نقش قابل توجه عناصر نیمه طبیعی موسوم به رگه های سبز چشم‌انداز را در ارتقای غنای گونه های ارزشمند طبیعی، تایید می کند.

Greenveining Elements of the Landscape Structure as the Main Supporter of Biodiversity in Agroecosystems

Introduction Natural and seminatural features including those as patches and marginal elements, construct a network of habitats referred to as green vein elements. In the green veining, the linear elements connect the different parts of the network, while the patches have a role as nodes within the network. These networks potentially place a vast range of biodiversity and play an important role as a refuge for sensitive organisms as well as some habitat specialist species. With regards to crop production and pest management in agricultural fields, pollinators and biological control agents, like predators, are among the most beneficial organisms mostly found in green vein elements. As the biodiversity in agroecosystems is considerably declining, this study was conducted to address the important role of natural and seminatural elements of the landscape in biodiversity conservation.   Materials and Methods The study area was an agricultural landscape located in GilaneGharb County, Kermanshah Province, Iran with a Mediterranean climate. The level of agricultural intensification (AI) was surveyed through interviewing the farmers and considering the indicators such as chemical and organic fertilizers (Kg N/ha/year), pesticide input (utilization frequency of e.g. herbicides, insecticides and fungicides) and the number of tillage operations and mechanical weed control. by providing the geographic map of the area and frequent field observation, seven different types of patches and marginal habitats were identified, including: 1) arable and horticultural fields (Fi); linear elements adjacent to the fields including: 2) within field edges (W.F.E) and 3) noncrop field edges (N.F.E); 4) roads; ditches including 5) permanent ditches (P.D) , 6) nonpermanent ditches (N.P.D) , and 7) woody greenvein (W.Gr) element. 87 sample plots (2 m × 2 m) were recorded in all the elements. Vegetation data from fields were recorded using 18 sample plots; woody green vein 19 sample plots; and other marginal habitats including within field edges, noncrop field edges, permanent ditches, nonpermanent ditches and roads, were sampled by 50 plots. Sampling was done based on systematicrandomized method. Two emergent groups of plant species were introduced regarding their response to land use intensification: Agrotolerant and Naturevalue species.The calculated biodiversity indices were: Jackknife species richness, Shannonwiener, Simpson and Brillion diversity indices, Camargo and SmithWilson Evenness, and finally Sorenson Similarity index using Ecological Methodology software. Results and Discussion The calculated agricultural intensification index (AI) was 49.56; this score was at the range of high intensified agricultural utilization (High AI). Mean observed value of nitrogen input was 211.36 kg/ha, the weighted frequency of tillage operations and pesticide application per hectare was the same as 2.36. Apart from crop species, a total of 87 vascular plants were recorded in the agricultural landscape. The highest species richness was for agricultural fields (43 species), which followed by noncrop field edges (37), woody greenveins (32), within field edges (30), permanent ditches (26), nonpermanent ditches (23) and roads (22). Sorghum halepense (L.) Pers.  (46.56% of the total frequency of individuals existing in the field sample plots) was the most frequent species in the landscape. 21 species were recorded as agrotolerant species. Jackknife species richness was 48.7 in the fields as the most, and 23.8 in the road verges as the minimum. Woody Green veins (W.Gr) had the most number of unique species. The most Shannonwiener and Brillion diversity indices were recorded for agrotolerant and naturevalue species in within field edges (Shannonwiener: 2.03 and Brillion: 1.85) and fields (2.52 and 3.08) respectively. Sorenson similarity index revealed that the elements inhabiting high number of agrotolerant species had a similar spatial condition especially regarding being adjacent to the agricultural fields. Studies reported the outstanding benefits of greenvein elements in promoting plant biodiversity and as a result enhancing diversity of organisms which inhabit in such elements. Conclusion The study indicated the effect of agricultural intensification and types of land use throughout the landscape on biodiversity. Elements with high connectivity to natural or seminatural habitats had the most positive effect on biodiversity of plant spesies. To gain the targets of sustainability in agroecosystems, providing as much as possible natural and seminatural habitats and corridors are suggested.