QUINN, JAMES A.1* and SCOTT J. MEINERS2. 1Dept.of Ecology, Evolution, and Natural Resources, Rutgers University, New Brunswick, NJ 08901-1582; 2Dept. of Biological Sciences, Eastern Illinois University, Charleston, IL 61920-3099. - Sex ratios, growth rates, and survivorship of red cedar (Juniperus virginiana) on the New Jersey Piedmont from 1963-2000.
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