Research On Boundary Definition And Vegetation Quantitative Features Of Wetland-dry Grassland In Siertan, Ningxia

Wetland is a natural complex by the interaction between land and water. As a special ecological system,it has a lot of the important values,such as ecological benefits, economic benefits and social benefits. As a valuable resource in in arid regions in northwest China, wetland also has an immeasurable value in keeping the balance of regional ecology. Therefore, investigations and study on the wetland ecological environment and vegetation growth status can provide important reference to the evaluation of wetland health and protection.Based on the field investigation of Si’er Tan wetland in Ningxia,Yanchi from2009to2013,the location and the width of the ecotone were determined by the method of Moving Split-Windows Technique. Then divided the area into three strips:wetland vegetation zone,ecotone zone,and dryland vegetation zone. The α-diversity,β-diversity, and plant niche of each strips were measured and analyzed to research the relationship between each factor.The results show that,the Moving Split-Windows Technique is applicable to the determination of the ecotone in Si’er Tan wetland,and the appropriate window width is8samples in this area.The distance from ecotone to the core of the wetland is similar in the first three years, and then increase obviously in2012,and decrease in2013,the trend is consistent with the change of the annual precipitation from2008to2012,while the change trend of the ecotone width is not.Between four directions,the distance from ecotone to the core is not the same.the distance in the east line is the biggest, the south line,north line and west line decrease successively.The width of the ecotone in east line is the biggest,while is similar in the other three lines, which indicated that the transition of the ecotone in east line is the most smooth.The analysis of α-diversity of each strip shows that,the richness index and diversity index of ecotone is higher than those of dryland zone,and still higher than those of wetland zone.But the evenness index of ecotone is lower than that of dryland zone,which is different with the trend of the other two indexes.On a whole,the edge effect of the ecotone can be easily reflected. The analysis of3-diversity of each strip shows that,the common species between the ecotone and dryland zone is more than that between the wetland and ecotone.Analysis of species diversity of each direction shows that,the a-diversity is very different from one another,it’s mainly caused by the nonuniform of water and energy,which is caused by the human activities and the fluctuant terrain.Each strip in this area has it’s own dominant species,but high plant niche width doesn’t mean high plant niche overlapping.The correlation analysis between the location and width of the ecotone,the a-diversity,β-diversity, and the annual precipitation shows that,he annual precipitation is the important influence factor to the location and width of the ecotone,as well as to the richness index.The diversity index is significant correlation both with richness index and evenness index,but more higher with the latter.which indicated that the diversity index of this area is affected by evenness index mostly.