Abstract:

Acer barbinerve(Aceraceae) is one of several understory tree species which occur in temperate forests in the Changbai Mountain region in Northeast China. We studied sex ratios and the spatial distributions of A. barbinerve and their relationships with environmental factors. In 2009, we mapped and sexed all reproductive A. barbinervetrees within a 5.2-ha (260 m×200 m) middle-aged experimental field plot and a 1.0-ha (100 m × 100 m) old-growth plot. In both plots, the sex ratio of reproductive trees was significantly male-biased. A further analysis revealed that the sex ratio was male-biased in small trees (DBH < 2 cm), and turned to a balanced ratio in larger individuals (DBH ≥ 2 cm), suggesting that males may reach maturity at smaller size than females. A univariate O-ring statistical analysis showed that under the complete spatial randomness (CSR) null model, males and females in the middle-aged plot occurred as clumped distributions at 0-88 m scales and 1-13 m scales, respectively. And both genders were distributed randomly in the old-growth plot. Under the heterogeneous Poisson null model, males and females were distributed randomly at 0-100 m scales in the middle-aged plot. The bivariate O-ring statistics indicated that under the random labeling null model, males and females showed spatial repulsion at 1-4 m scales, and then occurred as spatial independence at 4-100 m scales in the middle-aged plot, and both genders showed spatial independence at 0-50 m scales in the old-growth plot. Apparently, both males and females were influenced more by environmental heterogeneity in the middle-aged plot than in the old-growth one. Stand density were found to have a negative relationship with the distribution of females in the middle-aged plot, but it only explained 3.73% of the total variation, and showed litter effect on males. Environmental factors explained even less in the old-growth plot.

Key words: Changbai Mountain, dioecious, sex ratio, maple