Evaluation of Flora and Distribution of Weeds in Pistachio (Pistacia vera L.) Orchards of Semnan Province

To study the species composition and the weed distribution of pistachio gardens (Pistacia vera L.) in Semnan province, 45 orchards from three cities of the Semnan province were randomly selected and sampled using 1 × 1 m quadrat according to W pattern. Then the weeds species were identified in each quadrate. We calculated some indices including the species frequency, uniformity of distribution, relative frequency and relative uniformity of distribution for each species. In sum, 90 weed species belonging to 23 families were identified of which dicotyledons with 72 species had more diversity than monocotyledons with 16 species. The results showed that in sum 50%, 4.5% and 45% of the weeds were annual, biennial and perennial respectively. Weeds of hoary cress (Cardaria draba), Saltwort (Salsola kali), fat hen (Chenopodium album), bermudagrass (Cynodon dactylon), bindweed (Convolvulus arvensis), Syrian mesquite (Prosopis farcta), Russian knapweed (Acroptilon repens) and Camelthorn (Alhagi camelorum) had the highest abundance respectively. In Damghan city, which has the highest level of pistachio orchards in the province, 12 species with a frequency of more than 60% and a uniformity of more than 20%, are the dominant weeds. The most important weeds in pistachio orchards of Damghan city were Fat hen, bermudagrass, hoary cress, saltwort, Syrian mesquite, bindweed, nut grass (Cyperus rotundus), Russian knapweed and common reed (Phragmites australis), respectively.