Crown management and stand density
Determination of optimal stand-density continues to be a difficult problem. A trial cannot be established on every combination of soils, topography, and climate possible across the range of a widely distributed species such as loblolly pine, and continual advancements in nutrition and vegetation management, breeding, and utilization make established trials obsolete. Most of the difficulty in predicting density effects on stand production is that a change in stem size is a secondary response to the tree's environment; the primary morphological response occurs within the crown. Given the ecological relationship between foliage and growing space, and the mechanical relationship between crown size and stem size, crown response to density and cultural treatments should be predictable, which should lead to direct predictions of stem production. Average stem size can be ultimately controlled through management of average crown size. Crown size can be manipulated through a variety of means such as family selection, initial spacing, thinning, fertilization, and vegetation control. Any treatment that affects the mechanical relationship between the crown and stem should produce a change in stem increment. Recording crown development over successive rotations may also provide a means for assessing potential impacts of cultural practices, harvesting, or air chemistry on long-term productivity of the site. Thus, spacing studies that focus on crown development instead of stem increment should increase the efficiency of such studies and make their results applicable over a wider range of site conditions, families, and cultural practices.