The role of apical dominance in paradormancy of temperate woody plants: A reappraisal

Paradormancy, also known as summer dormancy, is the temporary dormancy whic h precedes winter or endodormancy in temperate woody plants. Apical dominan ce, the control exerted by the shoot apex over the outgrowth of the lateral buds, is thought to play a primary role in the paradormancy of these curre nt lateral buds which normally do not grow out until the following spring a fter over-wintering. In the present study, to test apical dominance, period ic decapitation and defoliation beginning with early spring flushing and ex tending through the growing season were carried out on eleven tree species (white ash, green ash, red oak, black walnut, pignut hickory, shagbark hick ory, sweetgum, cottonwood, sugar maple, hybrid silver/red maple and white p ine) ranging in age from 6 to 50-60 years. Significant decapitation and def oliation release of current lateral buds into growing branches was found on ly in silver/red hybrid maple and red oak, respectively. In a greenhouse st udy of 1-year-old sugar maple and green ash seedlings, a significant respon se was found only in the latter. The lack of response in most of the older species analyzed indicates that other inhibitory influences may be overridi ng that of apical dominance and suggests that apical dominance does not pla y the primary role in paradormancy in some temperate woody species.