Factors influencing reproductive activity of Juniperus virginiana in the Tennessee Valley

In the dioecious conifer Juniperus virginiana L. reproductive activity and the sex ratio among reproductively active trees are strongly influenced by local circumstances. In managed parkland derived from diverted secondary su ccession on fertile soils in the Tennessee Valley of northern Alabama, 86% of J. virginiana > 10 cm dbh were reproductively active, and the sex ratio in such sites was indistinguishable from 1:1. In mature xeric forests (ceda r woodlands) on the rocky mountainsides of the adjacent southern Cumberland Plateau only 41% of the J. virginiana > 10 cm dbh were reproductively acti ve, and the male:female sex ratio among those was 2.2:1. Univariate logisti c regression models suggest that the likelihood of reproductive activity wa s (1) lower on the mountainside than in the parkland, (2) increased with tr ee diameter and with tree height, (3) increased with diameter growth rate, and (4) decreased with increased shading by neighboring trees. Interpretati on is complicated because trunk diameter of J. virginiana in these populati ons was related to tree height, the site, the extent of shading, and to an interaction between site and the extent of shading. Furthermore, trunk diam eter growth was greater in the parkland. Stepwise multiple logistic regress ion suggests three factors affect the relative likelihood of reproductive a ctivity: tree size, the extent of shading, and an interaction between size and site.