بررسي اثر اجراي طرح‌هاي مرتعداري بر تنوع گونه‌اي گياهان در مراتع شهرستان سميرم استان اصفهان

Investigating Effects of Participatory Range Management Plans on Species Diversity in Semirum-Isfahan Province

به‌ منظور بررسي اثرات اجراي طرح‌هاي مرتعداري بر تنوع، غنا و يكنواختي گياهان در مراتع شهرستان سميرم استان اصفهان شاخص‌هاي غير پارامتريك غناي گونه‌اي، يكنواختي و تنوع گونه‌اي بين دو شيوه مديريت مقايسه و همبستگي بين اين شاخص‌هاي تنوع و خصوصيات پوشش گياهي تعيين گرديد. نتايج نشان داد از ميان شاخص‌هاي مورد بررسي، شاخص‌هاي يكنواختي، در مناطق فاقد طرح به‌طور معني‌داري بيشتر از مناطق داراي طرح بوده‌اند. نتايج آناليز همبستگي نشان داد كه غناي گونه‌اي همبستگي مثبت و يكنواختي همبستگي منفي معني‌دار با پوشش و توليد گياهان چندساله، وضعيت و گرايش مرتع داشته‌اند. در مجموع اجراي طرح‌هاي مرتعداري تأثير زيادي بر افزايش گونه‌هاي گياهي كليماكس و غلبه گياه Bromus tomentellus داشته كه اين امر باعث بهبود وضعيت مرتع و كاهش يكنواختي مناطق داراي طرح مرتعداري شده است. اين رفتار در موازنه بين رقابت گونه‌هاي گياهي و فشار چرا قابل تفسير است و روند توالي جوامع تحت بررسي حالتي را نشان مي‌دهد كه چيرگي بعضي از گونه‌هاي مطلوب، توليد بالا و تنوع كمتر را به‌دنبال دارد.

In order to investigate the effects of range management plans on species diversity, richness and evenness in Semirum rangelands, 52 sites (28 with treated plan and 24 without treated plan) were selected. The non-parametric indices for species richness (Margalof, Menhinick, Jacknife and counting method) and species diversity (Simpson, Camargo, Smith and Wilson and modified Nee) were compared in two management plans. The mean comparisons were made by independent T Student Test and Mann-Witheny U Test, and correlation was determined between diversity indices and vegetation parameters. Based on the results there was no significant difference between the two management systems regarding environmental features, while the implementation of range management plans caused significant reduction of stocking rate. Among the studied indices, evenness of species in sites without treated plan was significantly more than the sites with treated plan. The correlation matrix showed that there was a significant positive correlation between species richness and vegetation cover, production of perennial plans, and the rangeland condition and trend, while evenness showed significant negative correlation with these indices. Generally, implementation of range management plans has considerable effect on increasing climax species, dominance of Bromus tomentellus and it causes improvement of rangeland condition and reduction of evenness. This behavior could be explained by the balance between species competition and grazing pressure. Further, succession process of the studied communities demonstrates domination of some desirable species, high production and less diversity.