Abstract:The subalpine and alpine meadow vegetation of Wutai Mountain, distributed in altitude from about 2400m a.s.l. through to 3061m a.s.l. at the summit, serves as the largest summer mountainous pasture for cattle grazing around the local area in Northern China. The degradation of meadow with different grades owing to overgrazing in different extents has been observed in both vegetation and soil. Considering some features of vegetation, i.e., the coverage, the aboveground biomass, the ratio of annual to biennial plants in species composition, the species richness and the α-diversity index, five grades of meadow degradation relating to different grazing pressure have been recognized in the area through our earlier studies (see Reference No. 8).
This paper, through a grey correlation analysis at both species and community levels, evaluated the system coupling between the vegetation and the soil along with the degradation process in the subalpine and alpine meadow vegetation of Wutai Mountain. 85 sampling quadrat data, which were collected during the field survey in 2006 with the quadrat sized in 1m×1 m, were involved in the analysis.
The results showed that: (1) The pH-value, the content of total organic matter and the content of total nitrogen in soil varied nonlinearly among different degraded communities. The values of these soil parameters decreased with the grazing intensification on vegetation first, and then rose rapidly until reached their maximum in the extremely degraded meadow communities, where the vegetation were almost totally destroyed by overgrazing and tramping, while the soil was in s great extent mixed with cattle feces; (2) Showing in the grey correlation analysis, both the soil organic matter and total nitrogen contents correlated significantly with vegetation features represented by the aboveground biomass, the plant species diversity and the coverage at the community level; (3) The soil features coupled strongly with the species group consisted mainly of Kobresia pygmaea, K. pusilla, Pottentilla niveaand Festuca rubrain the meadow communities influenced by grazing and the slightly degraded meadow communities, whereas in contrast with another group consisted mainly of Potentilla anserine, P. conferta, Axyris amaranthoides, Polygonum aviculareand Cirsium leoin the extremely degraded communities; (4) The system coupling between vegetation and soil varied on average from the high level with index value at about 0.6-0.8 in the communities before being seriously degraded, to the low level at about 0.4-0.6 in those being extremely degraded, implying that the decrease of the system coupling level between vegetation and soil might therefore be an additive indicator to show the seriousness and extremes of degradation for the subalpine and alpine meadow vegetation.