Branch angle in red maple trees

The vertical branch angle 10 cm from the base of 17 branches on 6-year-old red maple (Acerrubrum L.) trees increased as leaves grew out and decreased when leaves abscised, with a net increase in angle. The angle 20 cm from the base of 222 branches on five 32-year-old trees did not increase with increasing branch age. Angles of young branches varied more than 37° within each year class. Angle was significantly related to branch diameter in two of five trees. Leaf weight on the branch was significantly related to branch angle in only one of five trees. Variable amounts of tension wood formed in all branches on the young trees and in 26 of 28 branches sampled from the old trees; 22 of the 45 branches examined had tension wood on both the upper and lower side of the pith. Despite the tendency to increase the angle by bending from leaf weight, long-term increases in angle were (i) obscured by variability in angle within each age class and (ii) apparently counteracted by tension wood maintaining branches at their equilibrium position.