Spatial Pattern Analysis of Individuals in Different Age-classes of Betula platyphylla in Huoshan Mountain of Shanxi Province
山西霍山白桦种群不同龄级立木的点格局分析

Betula platyphylla is a pioneer plant and is distributed intensively in Huoshan mountain.One 50 m×50 m quadrat was established in Qiliyu from which we recorded the DBH of each individual and the spatial points of all individuals were mapped.The data were analyzed by point pattern analysis.All individuals were divided into four DBH classes： DBH Ⅰ（DBH≤7 cm）;DBH Ⅱ（7 cm〈DBH≤14 cm）;DBH Ⅲ（14 cm〈DBH≤21 cm）;DBH Ⅳ（DBH〉21 cm）.The results of this study showed：（1） The densities of four age-classes varied in the order： age-class Ⅱ〉age-class Ⅲ〉age-class Ⅰ〉age-class Ⅳ.The middle age-classes Ⅱ and Ⅲ had many more individuals than age-classes Ⅰ and Ⅳ,which indicated that the population was currently in decline.（2） The individuals of all age-classes focused on clumping distribution in space,except the age-class Ⅰ.The feature of clumping distribution became more significant with increasing age.（3） The relationships between individuals in different age-classes were significantly correlated with each other on a small scale,but became non-significant with increasing scale,except for age-classes Ⅰ and Ⅱ,age-classes Ⅱ and Ⅲ,and age-classes Ⅱ and Ⅳ.