中文摘要：

在长白山次生杨桦林及次生针阔混交林中各建立1块5.2hm2固定样地,于2006—2008年的4—10月观察繁殖器官（花、种子）,据此判断样地内雌雄异株树种山杨和水曲柳成熟植株的性别,研究雌雄异株树种山杨和水曲柳性比与种群密度及林分密度间的关系,并利用随机区块抽样技术,建立种群性比与取样面积、种群密度和林分密度之间的关系,通过GLM模型检验种群性比的密度依赖性。结果表明：雌雄异株树种山杨和水曲柳雌雄植株数均随着取样面积的增大而呈线性增加;山杨和水曲柳种群性比具有显著的密度依赖性（P〈0.001）,种群性比随着林分密度的增大而减小;次生杨桦林样地中,繁殖植株密度及种群密度与山杨种群性比呈显著负相关,与水曲柳种群性比呈显著正相关,次生针阔混交林样地中,繁殖植株密度和种群密度与山杨性比呈显著正相关,与水曲柳种群性比呈显著负相关。可见,不同林型内山杨和水曲柳种群性比对繁殖植株密度及种群密度反应不同。

英文摘要：

A 5. 2 hm2-plot was respectively established in a secondary Populus davidiana-Betula platyphylla forest and secondary conifer and broadleaved mixed forest in Changbai Mountains. The gender of all reproductive individuals of Fraxinus mandshurica and Populus davidiana in the plots were determined by observing reproductive organs （flowers and / or seeds） through binoculars within the study plots from April to October in 2006,2007 and 2008. The relationships between sex ratios （male to females） and population density and local stand density were studied for the dioecious tree species,Fraxinus mandshurica and Populus davidiana. The relationships between sex ratio and sample area,population density and stand density were studied using random-quadrat method. The density-dependent sex ratio was tested by GLM model. The results showed that,the numbers of males and females increased as increasing sample areas for the dioecious tree species,F. mandshurica and P. davidiana. Sex ratios exhibited significant density-dependent for the two dioecious species （P 0. 001）. Sex ratios decreased with increasing local stand density for F. mandshurica and P. davidiana. Sex ratios showed different responses to density of reproductive individuals and population density in different forest types. The sex ratios of P. davidiana decreased as increasing stem density of reproductive individuals and population density,and those of F. mandshurica increased as increasing stem density of reproductive individuals and population density in secondary P. davidiana-B. platyphylla forests. But contrary results were found in secondary conifer and broadleaved mixed forest. Thus,we concluded that density-dependent sex ratios depended on the species group of studied tree populations in the forests. The response of sex ratios for P. davidiana and F. mandshurica to density of reproductive individuals and population density was different in different forest types.