Effect of permafrost degradation on grassland ecosystem has aroused interests in the scientists due to influence the processes of ecology in the permafrost regions of Qinghai-Tibetan Plateau. To gain insight into the contribution of permafrost degradation to the stability of grassland ecosystem, there is an urgent need to study the properties of grassland ecosystem in the succession stages due to degradation of frozen soil.
A survey of plant vegetation was undertaken during 2003 and 2004 along the Qinghai-Tibetan Highway from Kunlunshan (94°04′ 46 ″E, 35 38′ 51″ N) to the southern Tanggulashan Pass (33°07.120′E,91°52.670′N), to study the properties of grassland ecosystem in the successional stages from marsh meadow, alpine meadow and steppe meadow to desert steppe due to permafrost degradation. Fifty-five spots were selected in the successional community series. Each plots were arranged with three replicates. In each subplot, all plant species present were counted, and coverage, height (50 plants) and frequency were recorded. Biomass was measured by harvesting and drying. The species diversity of the plant communities was calculated using the Shannon-Wiener (diversity) index (H), the Pielou (evenness ) index (J), and richness index (species number) (S). Three soil samplings at 0-20 cm layer were collected to analysis the soil organic matter content. Soil water and temperate were measured.
Accompanying by permafrost degradation, plant species in communities transferred from wet plants in marsh meadow to drought plants in desert steppe, and height and coverage of plant communities decreased, and the richness species index (S) was not significantly different among the successional communities series, whereas evenness index (J) and diversity index (H) were significantly different (P<0.05) , indicating that they first decreased and then increased, peaking in the steppe meadow. In the successional series resulted from permafrost degradation, biomass and carrying capacity generally decreased, however, they were not significantly different between alpine meadow and steppe meadow. Economic value of plants decreased, and weeds in plant communities increased in the sucessional series. Accompanying by the process of frozen soil degradation, soil temperate at 0-20 cm layers increased, however, soil moisture and soil organic matter reduced. These implied that permafrost degradation was disadvantageous to stability of grassland ecosystem in the permafrost regions of Qinghai-Tibet Plateau.