Apical control of branch movements and tension wood in black cherry and white ash trees

Abstract

We measured x,y coordinates and growth of 2-year-old branches on ash (Fraxinusamericana L.) and cherry (Prunusserotina Ehrh.) trees through one season of growth. We sectioned the branches at the end of the season and calculated stresses developed by new wood cells through the season. There were three treatments: (1) control, (2) stem girdled above the branch, and (3) stem girdled as in (2), with indolebutyric acid in lanolin added to the girdle (IBA). All branches first moved down, then stopped in controls, reversed to relatively rapid upward movement in treatment 2 and moved slowly upward in IBA treatments. In treatment 2, compared with controls, branches grew more in diameter, particularly on the upper side and at the branch base; stem growth below the branch was reduced; tension wood (TW) formed in ash branches and TW with greater tensile stress than in controls formed in cherry branches. Branches in IBA treatments had diameter growth and TW formation intermediate between control and treatment 2 branches.