Patterns of development in Abiesbalsamea crowns and effects of megastrobilus production on shoots and buds

Abstract

Measurements and detailed mapping of buds, shoots, and branches of megasporangiate zones of mature Abiesbalsamea (L.) Mill. trees during a period of several years showed that first-order nodal branches were consistently more vigorous than first-order internodal branches of the same age and that lengths of first-order shoots of any 1 year decreased down the crown on nodal branches and, on average, down successive internodes and also down each internode. Similar gradients in bud lengths occurred. Patterns of a similar nature occurred down each branch. Relationships were found between bud lengths and lengths of shoots developed by those buds and between shoot lengths and lengths of terminal buds developed on those shoots. The numbers of buds produced in terminal-bud units showed a curvilinear relationship and numbers of lateral buds produced showed a straight-line relationship with the length of the shoots on which they were initiated. When megastrobili were borne, shoot lengths decreased, hence, numbers of buds produced also decreased, and many more shoots than in non-strobilus-bearing years failed to produce any lateral buds.The nature of the patterns of development which maintain the excurrent crown shape and the periods of development when apical control appears to be operative are discussed.