白桦(Betula platyphylla)群落是北京东灵山地区主要的群落类型之一。该文从生命表特征、年龄结构、 存活曲线以及种群和不同龄期个体群空间分布格局4个方面，研究了北京东灵山地区白桦种群的生活史动态特征与空间分布规律。研究结果表明：北京东灵山地区白桦种群在其生长过 程中，当胸径达到20 cm左右时（即第Ⅴ龄级时），由于种内不同个体间为争夺空间与阳光， 将遭遇一次死亡高峰，随后将进入一个平稳的生长期，最后在第Ⅵ龄级之后，死亡率再次逐渐升高；北京东灵山地区白桦种群属于衰退型种群；白桦种群的存活曲线基本接近Ⅰ型（曲线凸型），虽幼苗存活率较低，但整体上白桦种群对环境具有较强的适应能力；在种间竞争较小的情况下，白桦种群呈聚集分布，而种间竞争激烈时种群分布趋于随机；生物因素和环境因素是影响白桦种群空间分布格局的两个主要原因，表现在不同的环境条件下，白桦种群不同年龄级的个体群呈现出集群分布或随机分布，处于不同发育阶段的个体群，其空间分布格局是随时间变化的。
Aims We studied life history characteristics and spatial distribution of the Betula platyphyllapopulation in Dongling Mountain to explain: 1) population growth characteristics, and 2) how can biological and environmental factors affect population distribution and dynamics?
Methods B. platyphylla is distributed mainly on the eastern slope of Dongling Mountain peak, Nangou and Goushicao in Longmen National Forest Park. We sampled trees in 41 quadrats (10 m×10 m), and, in each quadrat, we chose 2 grids (5 m×5 m) for shrubs and 4 grids (1 m×1 m) for grasses. The diameter at breast height (DBH) of each tree was recorded, and we divided them into nine DBHclasses: DBH Ⅰ, DBH＜2.5 cm; DBH Ⅱ, 2.5 cm≤DBH＜7.5 cm; DBH Ⅲ, 7.5cm≤DBH＜12.5 cm, etc. We determined the life table, age structure and survivorship curve of theB. platyphyllapopulation to analyze population structure and dynamics. We divided trees into three groups based on the nine classes of DBH in order to analyze spatial patterns for different age classes: young trees, DBH Ⅰ-Ⅱ; adult trees, DBH Ⅲ-Ⅴ; and old trees, DBH Ⅶ-Ⅸ.
Important findings There is a peak of mortality at a DBH of about 20 cm (DBHⅤ) caused by intraspecific competition for space and light resource. The population is in a stable growth period at DBH Ⅵ, after which mortality increases gradually. The age structure of the population indicates a declining population, suggesting thatB. platyphylla is replaced by other species in succession. The survivorship curve of B. platyphylla population generally matches a Deevey Type Ⅰ, although seedlings are rare and have a low survival rate due to high crown density. The spatial distribution patterns of the population differ among plots and growth periods. The distribution pattern tends to be clumped on the eastern slope of Dongling Mountain peak where interspecific competition is not intense, but tends to be random in Nangou and Goushicao where interspecific competition is intense. The spatial distribution in different growth periods is clumped or random. Clustering is more pronounced for adult trees than old trees as a result of biological and environmental factors. Populations tend to clump when interspecific competition is not severe in a wet, cold, sunny habitat in Dongling Mountain. Intraspecific competition also affects the clustering intensity of different growth periods.