- Stem growth, stem form development, and the dynamics of crown recession in young red alder (Alnus rubra Bong.) were studied by analyzing annual growth rings of stems and
knots, annual height increments, projected crown areas, and branch diameters. Forty-one
trees were sampled from three plantation spacing studies, representing ages 1 through 12 years and square spacings from 0.94 x 0.94 m to 8.6 x 8.6 m. Data from the spacing studies were used to develop non-linear functions describing height-age and diameter-age relationships, and one-year stem diameter growth rates, in relation to spacing and site index. Linear functions were developed that describe the variation in responses to spacing of stem taper, live crown ratios, projected crown areas, stem diameters at live crown bases, and mean branch diameters. At age 27 years, nine trees were sampled from a thinning study;
naturally established red alder were thinned at age 14 years to square spacings of 4.2 X 4.2 m and 5.8 x 5.8 m, or left unthinned as control. A non-linear function was developed,
describing height-age relationships as affected by thinning intensity. Linear functions were developed that describe the variation in responses to thinning of stem taper, projected crown areas, stem diameters at live crown bases, heights to live crown bases, and mean branch diameters. Stem diameter growth of planted red alder increased faster and culminated earlier at intermediate (3 to 4 m) spacings than at wider spacings. Total diameter growth of trees planted at spacings closer than 3 x 3 m and wider than 6 x 6 m was markedly reduced. The greatest height growth was attained by trees planted at 2, 3, and 4 m spacings; significant long-term height growth reductions occurred in trees planted at the high and low ends of the density spectrum. Planting density strongly affected crown development; trees planted at high densities developed short, narrow crowns, and small branches, while trees planted at
progressively wider spacings had progressively wider and longer crowns, and larger branches. Stem growth patterns were subsequently affected. Trees planted at high densities developed cylindrical form, and widely-spaced trees developed stems with significant taper. Results from the thinning study showed that in response to thinning, crown recession slowed, crown areas expanded, more branch wood was produced, and height growth was reduced. These effects were more pronounced in trees thinned to the widest spacing. Further, stem taper increased significantly after thinning. With increased growing space, allocation of growth to crown expansion appears to occur at the expense of stem height growth; thus, the capacity to produce large crowns has important implications for lumber recoverability and wood quality in red alder.