Research in height growth has been carried on in the east by Kienholz, Cook and Baldwin; in th emiddle west by Rees and Friesner; and in Montana by Kirkwood.

Kienholz showed from his observations on red oak, white ash, red maple, gray birch, white or paper birch, yellow birch, tulip poplar, large-toothed aspen, trembling or quaking aspen, red pine, and European larch that these species fall into two groups according to seasonal length growth.