Growth rates, survivorship, and sex ratios of Juniperus virginiana on the New Jersey Piedmont from 1963 to 2000

Abstract

QUINN, J. A. (Department of Ecology, Evolution, and Natural Resources, Rutgers University, New Brunswick, NJ 08901-1582) and S. J. Meiners (Department of Biological Sciences, Eastern Illinois University, Charleston, IL 61920-3099). Growth rates, survivorship, and sex ratios of Juniperus virginiana on the New Jersey Piedmont from 1963 to 2000. J. Torrey Bot. Soc. 131: 187-194. 2004.-Studies of the growth, survival, and sex ratios of dioecious species have been predominantly short-term. This research investigated growth rates, survivorship, and sex ratios among cohorts of Juniperus virginiana L. from 1963 through 2000. Males (M) and females (F) in six old-fields of different ages on the New Jersey Piedmont 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 almost 1:1 (333 M, 332 F); only one of the fields showed a significant departure from 1:1. 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 (and older) 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 plants that became established later were shorter, often non-reproductive, and 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 single-year studies elsewhere in the species' range.