Abstract:

As a transitional zone from closed forest to alpine vegetation, timberline is sensitive to climatic change in two aspects, fluctuation of its boundaries and changes to its structure. Therefore, the demarcation of vegetation limits and clarification of vegetation patterns of alpine timberline is critical to studies on the response of alpine timberline to climatic change.Mt. Wutai, with a summit of 3 058 m a.s.l., is the highest mountain in North China. It is also one of several mountains which reach the climatically controlled alpine timberline in the temperate broadleaved forest zone in China. Former studies were focused on the vegetation classification of meadows, vertical changes of plant species diversity and micro to meso-scale patterns of the meadow near the summit. Vegetation analysis on a large scale is still essential to understand the characteristics of vegetation near the timberline.Vegetation investigation was made at 10 m elevation intervals on the shady slope and 20-25 m on the sunny slope from the upper forest limit to the mountain summit. A total of 280 relevès on the shady slope and 75 on the sunny slope were made. TWINSPAN was used to do vegetation classification of herbaceous communities,and to show the relationship between distribution of plant communities and environmental conditions was shown using DCA. After classification and ordination of herbaceous communities and analyses of distribution of trees and shrubs, vegetation boundaries of alpine timberline were delimited and vegetation characteristics of the upper forest boundary were clarified in this paper. On the shady slope, alpine timberline ranges from 2 810 m to 3 015 m a.s.l. The timberline is dominated by Larix principis_rupprechtii with Picea meyeri and Betula albo-sinensis. The quantity of cones demonstrates that the regeneration ability of Larix principis-rupprechtii is much better than that of Picea meyeri. On the sunny slope, alpine timberline ranges from 2 605 m to 2 790 m a.s.l.. It is dominated by Picea meyeri with some Larix principis-rupprechtii. 4 herbaceous communities, understory herbaceous layer, meadow at forest edge, subalpine scrubby meadow and alpine meadow, were distinguished by TWINSPAN on both slopes. The herbaceous communities change markedly with altitude. Understory herbaceous layer, meadow at forest edge, subalpine scrubby meadow and alpine meadow occur in sequence from upper closed forest to mountain summit on both shady and sunny slopes. DCA results showed that elevation is closely related to the changes of herbaceous communities, implying a key role of climate conditions in the spatial differentiation of herbaceous communities.