The dynamics of age structures on Agropyron michnoi and Leymus chinensis in community with two dominant species populations

In this study, the method of unit sampling was adopted for two years to investigate and analyze the age structure of clonal tillers and seedlings of Agropyron michnoi and Leymus chinensis in the secondary succession process of Hulunbeier sandy vegetation in north China. The results indicate that in single and mixed communities, tillers of A. michnoi were composed of 3 or 4 age classes respectively, and those of L. chinensis were composed of 2 age classes. Seedlings of A. michnoi were all composed of 4 age classes, while those of L. chinensis were composed of 2 or 3 age classes, respectively. The tillers number of A. michnoi and L. chinensis in single community reduced by 10.8 and 29.7%, respectively in 2010 when compared with those in 2009; while in mixed community, the tillers number of A. michnoi reduced by 8.9%, but that of L. chinensis increased by 15.9%. In single community, the seedlings numbers of A. michnoi and L. chinensis, respectively reduced by 26.3 and 31.2%, while in mixed community, the seedlings number of A. michnoi reduced to 22.0%, but that of L. chinensis increased by 7.1%. The number ratio of various age classes of A. michnoi and L. chinensis seedlings in 2009 was basically the same as that of tillers in 2010. Both in single and mixed communities, the A. michnoi population tended to change from growing type to stable type or declining type, while L. chinensis population always remained increasing with slight reduction. The general tendency was obviously shown specially in mixed community. L. chinensis could be considered as the dominant species, while A. michnoi lost its dominant status and made the companion species in the community.Key words: Tillers, seedlings, clone, age structures, single community, mixed community.