中文摘要：

雌雄异株植物的雌雄植株在营养和繁殖结构的大小、颜色及寿命,资源获得与分配,与群落其他物种相互作用等方面均存在差异（Delphetal.,1996;2002；Pickering，2000；Gehring et al．，1994）。种群性比是雌雄异株植物的一个重要结构指标，尽管雌树多于雄树（Opler et al．，1978；Alliende et al．，1989），

英文摘要：

Size structure,sex ratios and sex-dependent spatial distribution of dioecious Fraxinus mandshurica were tested in a secondary forest. The results showed that： 1） there were 560 F. mandshurica trees with their DBH greater than 5 cm recorded in a 5. 2 hm2 plot,among which there were 135 male trees,158 female trees and 267 undetermined trees. The sex ratio（male trees /female trees） was 0. 85,which did not significantly differ from 1 ∶ 1（Chi-square test,P = 0. 179） . 2） The average DBH of male trees and female trees was（24. 5 ± 6. 2） cm and（24. 9 ± 7. 9） cm,respectively. The difference in DBH was not significant between male trees and female trees（t-test,P 〉0. 1） . The coefficient of variation in DBH size was identical between male trees and female trees（CVfemale = CVmale = 54%） . The number of undetermined trees tended to decrease with increasing tree size. Almost all trees with their DBH larger than 35 cm were sexed. 3） Saplings（1 cm〈 DBH〈 5 cm） of F. mandshurica showed random distribution,but male and female trees mainly showed clumped distribution in space. 4） No association between saplings and female trees and male trees was detected at 0-50 m scales. A significant attraction between male and female trees at distances of 3-50 m was found under the null hypothesis of type independence. However a significant repellence was observed at very close ranges（1-5 m and 23-28 m） under the random labeling hypothesis. Different interactions were observed between different tree sizes,between male and female trees.