Effects of human disturbance on species diversity and niche of herbaceous plants along Qiyijiang riparian zone in Ya'an City,Sichuan Province

In order to make a thorough inquiry in effects of human disturbance on herbaceous plant community,an investigation has been conducted along Qingyijiang River riparian zone,Ya'an City,Sichuan Province by using the typical sampling method. The species Richness index D,Shannon-Wienner index H,Simpson index H' and Pielou index Jswwere adopted to make evaluations on the level of species diversity on herbaceous plant community. There are three kinds of sample areas under human disturbances of three different intensities in the investigated zone: flood lands under slight disturbance,mow grasslands under medium disturbance,and abandoned farmlands under severe disturbance. The results showed that sixty-four plant species that belong to 26 families and 53 genera were found in the three kinds of studied areas. Species richness significantly decreased with the increment of disturbance intensity. By analyzing the important values,it was discovered that under disturbances of all levels of intensities,the main bodies of the communities are composed of the species which belong to Compositae,Gramineae,Leguminosae,Polygonaceae and Umbelliferae. However,there was no obvious main edificatory in the communities under disturbances of different levels of intensities,since the important values of each species has no significant difference,indicating the intenses of interspecific competitions. The results indicated that the numbers of the species with niche overlap values above 0. 5 in communities under light disturbances,medium disturbances and severe disturbances respectively accounted for 95. 0%,85. 4% and 74. 2% of the total species numbers. Srensen's similarity coefficient( SS) between communities under disturbances of different levels of intensities were different. Srensen's similarity coefficient( SS) between communities under slight and medium disturbances,medium and severe disturbances,and slight and severe disturbances were 0. 733,0. 719 and 0. 625,respectively. Species richness index D and Shannon-Wiener index H decreased with the increment of the human disturbance intensity,the sequences of them were slight disturbance medium disturbance severe disturbance,and the difference among disturbance intensities were significant. However,there was no significant differences of Simpson index H' and Pielou index Jswamong sample areas.