Sex ratios and spatial structure of the dioecious tree Torreya nucifera in Jeju Island, Korea

The sex ratio and spatial structure of different sexes are major components that affect the reproductive success and populationpersistence of dioecious plants. The differential reproductive costs between male and female plants are oftenbelieved to cause a biased sex ratio and spatial segregation of the sexes through slower growth and/or lower female survivorship.In this study, we examined the sex ratio and spatial structure of one population of Torreya nucifera trees inJeju Island, Korea. We also tested the effects of the current tending actions in relation to tree vitality. At the populationlevel, the sex ratio of the 2,861 trees was significantly biased toward males; however, it also showed considerable variationamong different diameter at breast height classes and across habitats according to terrain level (from upper to lower). In1999, before tree management (tending) began, among the ecological traits examined, only climber coverage correlatedwith tree vitality. Intensive tending such as climber removal since 1999 clearly enhanced the vitality of the majority oftrees, but its effects were more conspicuous in medium-sized trees than in small ones, in upper terrain trees than thosein other terrains, and in females than in males. Both male tree domination in small and large trees and tending effects onfemales are likely to reflect the effects of female reproductive costs regarding growth and/or survivorship. Spatial segregationbetween males and females was not observed in T. nucifera. Habitat heterogeneity created by the forest’s rockyground and its implications regarding sex ratios and spatial structure require further studies.