Reaction to Competition
Red spruce is classified as shade tolerant in the United States and tolerant or very tolerant in Canada. Opinions differ as to whether red spruce is more tolerant than balsam fir, but the relative tolerance may vary with soil fertility and climate (22).
The species' chief competition comes from balsam fir and hardwoods that produce heavy shade, like beech and maple. Competition from aspen, birch, and other thin-crowned species is not so severe. Red spruce prunes itself about as well as most softwoods in dense stands. As much as one-third of the live crown may be pruned artificially without seriously affecting radial growth (5).
A number of studies have demonstrated the ability of red spruce to respond to release after many years of suppression. The vigor of this response does decline somewhat with age, however, and older trees may require about 5 years to recover before showing accelerated growth (7). Reduction of growth to about 2.5 cm (1 in) of diameter in 25 years, for a duration of 100 years, represents about the limit of suppression for red spruce. Many of its associated tree species such as balsam fir and hemlock may outgrow red spruce after release (22).
Red spruce may be grown successfully using even-age silvicultural prescriptions (11,12). Red spruce is very shallow-rooted, however, making it subject to windthrow, a major silvicultural constraint in the management of the species. As a general rule, it is recommended that no more than one-fourth to one-half of the basal area be removed in the partial harvest of a spruce-fir stand, depending on site, to avoid excessive windthrow damage.
Most of the major forest cover types previously listed in which red spruce is a component are considered either climax or subclimax.