The objective of this research was to investigate sex ratios, growth rates, and survivorship among cohort groups of Juniperus virginiana L. in successional fields on the New Jersey Piedmont. Males and females in six old-fields of different ages were analyzed, starting with the initial data on height and sex expression collected by John Small on labeled recruits from 1963 through 1976. These plants were relocated and censused during the summer and fall of 2000. No changes in sex expression were recorded between 1976 and 2000. The overall sex ratio was exactly 1:1 (332 M, 332 F); only one of the fields showed a significant departure from 1:1. When young, males grew slightly, but significantly, faster in height than females, but relative growth rates dropped by approximately 50% for both males and females once they became reproductive. Female trees were on average 23 cm taller than males at first reproduction. Heights in those males and females surviving to 2000 were not significantly different. There was no effect of an individual's sex on its likelihood of dying, but the plants that became established later, were shorter, and were non-reproductive had an increased risk of mortality. These long-term results strongly support genetically-determined sex ratios and a lack of major differences between males and females in growth rates and survival, which had been suggested by short-term studies elsewhere in the species range.

Key words: dioecy, Juniperus virginiana, New Jersey, sex ratios, successional fields, survivorship