中文摘要：

对比2次不同时间相同地点的植被调查，从植物分布区型、物种重要值、频度和物种多样性等方面入手分析了松嫩平原羊草草甸的时间尺度变化。结果表明。现群落有植物92种。隶属28科71属。与原群落相比减少1科5属18种。分属14个分布区型，其中东北分布区型为后增类型。群落上层以羊草和芦苇占优势，中层和下层分别以虎尾草和蔓委陵菜占优势，在植被划分上属羊草-虎尾草-蔓委陵菜群丛。频度分析则显示目前群落频度分布为A〉B〉C〉D=E→O，暗示群落均匀程度增加。在物种多样性变化上，优势群落羊草群落物种多样性降低，而杂类草和盐生种类群落多样性增加。综上表明，本区植被的变化主要是种类减少，外来成分入侵，优势群落多样性降低，杂类草和盐生种类群落地位上升，群落有可能进一步发生退化。向次生植被演替。而这种退化主要是气候变化及人类不合理活动所致。

英文摘要：

Investigation of the same site at different times revealed the types of temporal change in a Leymus chinensis meadow steppe from the aspects of area type, life form, species frequency and species diversity. There were 92 species belonging to 71 genera in 28 families. One family of 5 genera and 18 species decreased in contrast to the rest of the community. There were 14 area types of which the north area type was new. The analysis of life form spectrum indicated that the community had the characteristics of the typical temperate steppe biological climate. The hemicryptophtes comprised 41 species and made up 37.27% of the community. Compared with the old community the proportion of therophytes increased. The species importance value analysis indicated that the upper layer dominant species was L. chinensis while the middle and lower layer dominant species were Chloris virgata and Potentilla flagellaris. The community belonged to a L. chinensis ＋ C. virgata ＋ P. flagellaris association and the frequency structure was A〉B〉C〉D=E→0, which showed a good evenness. The species diversity of the L. chinensis community was reduced while the others increased. In general,the main vegetation changes were that species number decreased, exotic species invaded, the dominant community species diversity decreased, and the herbaceous species and salt plants became more dominant. The vegetation will further regress and be succeeded by secondary vegetation. Excessive human activities accounted for the vegetation changes.