Study of population characteristics and distribution of cheat grass (Bromus tectorum L.) with other grass weeds in wheat fields of Khorramabad

A weed survey was conducted in 2012 to determine the downy brome distribution in 40 irrigated wheat farms of Khoramabad. Factors relating to frequency, species richness, density and relative uniformity and diversity indices and dominance were measured. Also, by using GIS, distribution map for downy brome in this area was drown. Sixteen weed species of poaceae family other than downy brome were also observed. Relative frequency of hirsotum ecotype of downy brome (with8.76%) was higher than tectorum ecotypes (with 4.76%). Winter wild with 19.56% and then wild barley with 13.52 % in mean of 5 sampleshad have the highest relative frequency. Lowest relative frequencies belong to rye brome and bermudagrass with 0.5 %. Among the weedy Johnsongrass and bermudagrass were perennial and other weed species were annual. Furthermore, it was shown that the latitude upon sea leval did not have large effect on density of grasses and cheat grass ecotypes. Shannon-Weiner diversity index in Khorramabad 2.24, Simpson's diversity index 1.04 and Simpson dominance index 0.960 was calculated. Also using GIS techniques distribution map of cheat grass were drawn in these areas. The difference in the indices of species diversity and dominance were associated with the level and type of management practices on farms.