关键词: 雌雄异株, 空间分布, 性比, 水曲柳

Abstract:

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 (CV_female=CV_male=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.

Key words: dioecious trees, spatial distribution, sex ratios, Fraxinus mandshurica