长白山北坡林线灌木草本植物与岳桦的动态关系

Dynamics change of Betula ermanii population related to shrub and grass on treeline of northern slope of Changbai Mountains

以长白山北坡林线为研究区,调查145个样方内岳桦种群的径级结构与林线灌木草本植物的生态重要值。采用常规统计和聚类方法分析岳桦种群与8种常见植物的动态特点,采用典型与单因子相关分析岳桦动态与林线灌木草本的变化关系。结果表明岳桦种群扩张带动林下植物的相继移动,林线上侵不仅是单一乔木的变化,而是森林群落向苔原群落的入侵,从空间上挤占生态位的过程。另外,这种替代中各个成分变化也存在差异,由于各种植物在群落中的地位和竞争力的区别,在替代过程中不同植物变化具有明显的差异性。

It is important to understand the dynamic responses of ecosystems to climate change in the warming. The alpine treeline is regarded as highly sensitive and a potential indicator of climate change, context of global and it has thus become one of the hotspots of global climate change research. Most research on treeline dynamics has been conducted at a population scale, and there have been comparatively few studies of treeline dynamics at a community scale. In this study, treeline dynamics were analyzed at a community scale in the Changbai Mountains by examining the change in relationship between the Betula ermanii community and the tundra community. The treeline of the northern slope of the Changbai Mountains was selected as the study area. The diameter-class structure of the Betula ermanii population and ecologically important values of shrubs and grasses were investigated in 145 quadrats. The age structure of the population was reflected by the diameter-class distribution, and the diameter- class distribution was used to understand the population dynamics of Betula Ermanii. Number of trees, basal area, andaggregation index I were selected to determine the diameter-class distribution characteristics. Because there were many species of shrubs and grasses at the study area, eight common plants （ relative frequency〉O. 05 ） were selected to evaluate treeline change on a community scale. Hierarchical clusters were successively carried out from two to six groups. Three classification methods were adopted in each hierarchical cluster. Finally, the eight common plants were divided into two groups that were subordinate to the forest and tundra community. Conventional statistics including means, standard deviations, skewness, kurtosis, and variation coefficients were used to reveal changes in the dynamics of shrubs and grasses. Canonical correlation analysis between each of the Betula ermanii population variables （shrub, single, andintegration of shrub and single-trunk） and the common plants group-variable were carried out to discover the dynamic responses of the shrubs and grasses to population changes of the three kinds of Betula ermanii. The relationships between nine factors of the Betula ermanii population and the values of 8 ecologically important common plants were evaluated using univariate correlation analyses. The diameter-class structure of Betula ermanii was a reverse-J shape. The population had an expanding trend, leading to an advancing treeline. Forest plants such as Rhododendron chrysanthum and Deyeuxia angustifolia also showed evidence of advance. However, tundra plants, such as Vaccinium uliginosum liar. alpinum, Dryas octopetala Var. asiatica,imum, Carex callitrichos V. Krecz and Carex siderosticha, simultaneously retreated at different speeds in the context of population expansion and treeline shift. The distribution of various forest plants changed at different speeds. The stronger competitive power a kind of plant had, the closer its advance speed to that of Betula ermanii. Likewise, the retrogression speeds of tundra plants were negatively related to competitive power. Also, for a given plant, the closer relationship it had with typical tundra plants, the faster the plant retreated. Therefore, there were obvious differences in the speed of shifts when various forest plants advanced and tundra plants retreated. The population expansion of Betula ermanii drove the shifts of shrubs and grasses, which belonged to the forest community. Treeline shift was not only manifested by tree change, but also by the forest community invading the tundra community. The change differences among various species compositions were very obvious. The difference was particularly obvious during the replacement process of various plants in accordance with their competitive status in the community.