Sabina przewalskii community structure in the upper reaches of Minjiang River
岷江上游祁连山圆柏群落结构研究

In this paper,the physiognomy and the structure of Sabina przewalskii community were studied by sample plot method.The results showed that in the life spectrum of the community,hemicryptophyte was dominated,but therophytes also occurred frequently,which presented some features of temperate vegetation.The vertical structure of the community was quite simple,consisting of tree layer,shrub layer and herb layer,and there were no interstratum plants and ground layer.Sabina przewalskii was the only species in the tree layer.In fruticose stratum,the important value of Spiraea alpina was 153.3,ranking the first; while in herb layer,the important value of Carex caespifosa ranked the first,amounting to 36.8.Among the three plot groups on different slopes,spiny-shrubs such as Berberis wilsonae and Caragana erinacea grown on small slope were more than those on bigger slope,so did unpalatable grasses such as Pedicularis axillaries and Artemisia tauguticat,which mainly owed to retrogressive succession caused by frequently grazing.The age and height structures of Sabina przewalskii population indicated a declining trend,and the community would develop retrogressively if disturbances (e.g.,grazing) could not be reduced.The disturbance caused by livestock was more obvious in the plot group on small slope than on bigger slope,and livestock mainly destroyed seedlings and small trees,which made tree population be impossible to regenerate.The coverage of upper layers had a notable impact on the lower layers,and there wasn't any correlation between coverage and diversity index (Shannon-Wiener Index) in each layer.