关键词: 东灵山, 白桦, 种群结构和动态, 空间分布格局

Abstract:

Aims We studied life history characteristics and spatial distribution of the Betula platyphylla population 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 DBH classes: DBH Ⅰ, DBH<2.5 cm;DBH Ⅱ, 2.5 cm≤ DBH<7.5 cm;DBH Ⅲ, 7.5 cm≤ DBH<12.5 cm, etc. We determined the life table, age structure and survivorship curve of theB. platyphylla population 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 (DBH Ⅴ) 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 that B. 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.

Key words: Dongling Mountain, Betula platyphylla, population structure, population dynamics, spatial distribution