Initial period of sexual maturity determines the greater growth rate of male over female in the dioecious tree Juniperus communis subsp. communis

Dioecious species are a very interesting object of study because of predicted differences between male and female individuals. Most dioecious species have a higher reproductive effort in female individuals in comparison with males. The object of this study was common juniper (Juniperus communis subsp. communis), dioecious shrubs or small trees. This study examined differences in radial growth rate between male and female individuals and the effect of climatic factors on tree-ring width in this species. Wood samples were taken from 30 trees (15 females and 15 males) and subjected to the standard procedure of dendrochronological dating. Females had lower growth rates than males after the age of 17 years. The greatest differences between genders in growth rate were observed between 17 and 25 years. After 26 years, male tree-rings were still wider, but the differences were much smaller. The differentiation of tree-ring width between males and females probably started when the female trees reached sexual maturity and started to produce seed cones. Differences between sexes in tree-ring width were noticed also in their reaction to climatic conditions. When compared to males, female individuals tended to be more sensitive to low temperature and low precipitation. This sensitivity of dioecious species could be one reason for their greater susceptibility to extinction in times of progressive climatic changes.