Vegetable niche dynamic study of the enclosed desertification rangeland in Yanchi County

Through field surveys of 2007, 2009 and 2011, the effect of three different fencing measures on Yanchi arid and semiarid grassland plant niche were studied in this paper by using the Levins niche breadth index and Pianka niche overlap index. The results showed that dominant species of the old enclosure region (E plot) were Salsola ruthenica and Heteropappus altaicus, while dominant position of S. ruthenica increased and that of H. altaicus decreased after fencing. In the new enclosure region (E1 plot), dominant species were Artemisia ordosica, Salsola ruthenica and Ixeris chinensis var. graminifolia. However, dominant position of S. ruthenica decreased and that of I. chinensis var. graminifolia increased obviously. Dominant species were A. ordosica, S. ruthenica and S. alopecuroides in the control area (E2 plot); A. ordosica was the dominant species in the three sampling periods and the niche breadth index of S. alopecuroides steady rised. The niche overlap index amone dominant species of the old enclosure region presented the downward trend through the fencing measure, while the niche overlap index amoge dominant species of the new enclosure region presented the rising trend.