黄土高原草地生产持续发展研究──Ⅱ．补播沙打旺对退化草地演替的影响

Study on the Sustainable Development of the Grassland Production in Loess Plateau──Ⅱ.Influence of the Declined Grassland Evolution by Reseeding Astragalus adsurgens

沙打旺（Ａｓｔｒａｇａｌｕｓａｄｓｕｒｇｅｎｓ）种群人工草大量进入退化草地百里香（Ｔｈｙｍｕｓｍｏｎｇｏｒｉｃｕｓ）群落后，不仅能有效地改良退化草地，并促进百里香群落在９—１０年较短时间内演替到长芒草（Ｓｔｉｐａｂｕｎｇｅａｎａ）顶极群落，从而为天然草地生产的持续发展打下基础。沙打旺促进这一演替过程的机制，在于它迅速将百里香几乎完全排挤出群落之外，随着它的自然衰退而空出的空间，为长芒草占领创造了条件。沙打旺引起的这一短期人为演替过程，实际是原来百里香群落中种间关系重新调整的过程，各个种群数量变化的结局，取决于它们各自的竞争力。

The varieties of Astragalus adsurgens are introduced into the declined grassland of Thymus mongoricus communities,which can not only impror the declined grassland,but also make the Thymus mongoricus communities evolute into a top community that is Stipa bungeana in 9-10 years.The results can form a good basis for sustainable development of natural grassland.The mechanism of the process is that Astragalus adsurgens can quickly exclude Thymus mongoricus from the communities,and supply enongh space for Stipa bungeana aggtession.The short process of artifical evoloution,in fact,is the adjustment result of the relationship among varieties in communitits.The number change of every variety is determined by its race ablity