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Factors Influencing Reproductive Activity of Juniperus virginiana in the Tennessee Valley

Robert O. Lawton and Paul Cothran
The Journal of the Torrey Botanical Society
Vol. 127, No. 4 (Oct. - Dec., 2000), pp. 271-279
Published by: Torrey Botanical Society
DOI: 10.2307/3088645
Stable URL: http://www.jstor.org/stable/3088645
Page Count: 9
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Factors Influencing Reproductive Activity of Juniperus virginiana in the Tennessee Valley
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Abstract

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 succession 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 (cedar woodlands) on the rocky mountainsides of the adjacent southern Cumberland Plateau only 41% of the J. virginiana > 10 cm dbh were reproductively active, and the male:female sex ratio among those was 2.2:1. Univariate logistic regression models suggest that the likelihood of reproductive activity was (1) lower on the mountainside than in the parkland, (2) increased with tree diameter and with tree height, (3) increased with diameter growth rate, and (4) decreased with increased shading by neighboring trees. Interpretation is complicated because trunk diameter of J. virginiana in these populations was related to tree height, the site, the extent of shading, and to an interaction between site and the extent of shading. Furthermore, trunk diameter growth was greater in the parkland. Stepwise multiple logistic regression suggests three factors affect the relative likelihood of reproductive activity: tree size, the extent of shading, and an interaction between size and site.

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