若尔盖西部草甸的基本类型、特点及近几十年来的变化

2000年8月对若尔盖西部草地的调查，确定了该地18个草丛类型（不包括典型的沼泽植被）。经群丛间Pearson最大相关系数配合生境作图，将该地区的草地群丛分成3大类，即沼生草地，中生性草甸和旱生性草地。各群丛的SW指数，物种丰富度，地上生物量，裸地面积按照生境序列作图，显示中性草甸具有最高的物种丰富度和地上生物量。群丛C和J分别是沼生和旱生植被与中生性草甸之间的拐点式过渡类型，其物种丰富度明显比周期的群丛低，生境转换关键种分别为鹅绒委陵菜和垂穗披碱草。在草地物种组成上，杂类草占81．3％，莎草类仅占6．8％；群丛建群种方面，杂类草占61％，莎草类占28％；在次优势种方面，杂类草和禾草所占比重都有所增加。草原成分出现在丛中生至旱生的群丛中，在有些群丛中甚至成为次优势种。沼泽消退，黄河河道附近沙化以及过牧的阳坡山地生长带刺的旱生化植被，说明当地正经历着干旱化的过程，原因不仅有自然的还有人为的，特别是草地的过度使用。最后对当地草场的管理及发展提出了一些建议。图3表2参20

BASIC TYPES AND CHARACTERS OF THE WESTERN ZOIGE MEADOWS AND THEIR CHANGES IN RECENT DECADES

The basic types of the western Zoige meadows were investigated in August 2000 and 18 types of grassland associations were identified in this area, not including typical swamp vegetation. The Pearson correlation index of associations was calculated with software SPSS 10.0. The associations ranged from sandy, dry to aquatic habitats according to their habitat requirements and results of Pearson correlation index. The associations could be classified into 3 groups: swamp vegetation, meadow and xerosere communities. The study on Shannon-Wiener index, species richness, aboveground biomass and bare land coverage revealed that the meadows in moderate habitat had the highest productivity, species richness and less bare land coverage. Associations C and J were inflexion communities between meadow and extreme habitat vegetation. Species richness in inflexion communities was distinctly lower than that of the surrounded communities. Their key species in habitat transformation were Potentilla anserina and Elymus nutans. Species composition of this region showed that forbs consisted of about 81.3%, while sedges only about 6.8% of the total species. As for the dominants in communities, forbs accounted for only 61%, while sedges about 28%. Forbs and grasses with subdominant status were all increased. Prairie species established in meadows and xeric communities. In some cases, they even became subdominant species. Meadow changes in recent decades suggested that the habitat became drier along with the shrinkage of swamps, establishment of many prairie plant species and desertion along the Yellow River. Reasons for the degradation of meadows and suggestions for sustainable development of this area were also discussed in this paper. Fig 3, Tab 2, Ref 20