Abstract: The investigation on the species and composition characteristics of Carex lasiocarpa and Calamagrostis angustifolia communities distributed mostly in Sanjiang Plain showed that C.lasiocarpa and C.pseudocuraica were the dominant species,with the total important value 56.4%.C.angustifolia was the dominant species of C.angustifolia community,with the important value 50.8%.Species diversity analysis suggested that there were some fluctuations in Simpson (D),ShannonWiener (H) indices,and Pielou evenness (J) of the two communities.In these two communities,significant positive correlation was observed between H and J,significant negative correlation existed between H and D,but no significant correlation was found between H and D.The H,D,J and S of C.lasiocarpa community were higher than those of C.angustifolia community,but the difference was no significant.The similarity index of the two communities was 46.5%,indicating that there was a definite relation between them.

Key words: Weed community, Tillage method, Herbicide, Cornfield, Diversity