Red spruce (Picea rubens) and balsam fir (Abies balsamea) are so similar that" spruce-fir" is often used as if it were a single species. The early monographs ofZon (1914) and Murphy (1917) accurately characterize both species as occupying a similar ecological niche: late-successional, very tolerant of shade, shallow rooted, and widely adapted to a variety of site and stand conditions. These species differ in important ways that influence silvicultural treatment (Fowells 1965). Fir produces abundant seeds, but is so susceptible to various heart-rot fungi that its potentiallife span is limited by the high risk of wind breakage or uprooting. Balsam fir is often cited as the classic example of a species mIed by a pathological rotation, effectively limited to ages 40-70, depending on site quality. Fir is also the preferred host and suffers extensive mortality from defoliation by the spruce budworm (Choristoneura fumiferana). The introduced balsam wooly adelgid (Adelges piceae) also is a serious pest of fir in coastal regions but does not cause serious damage inland. In contrast, red spruce produces seeds infrequently, but is quite resistant to decay and tends to survive budworm defoliation. As a result, red spruce is inherently long-lived, and 300+ year-old trees were not uncommon in virgin forests (Cary 1894a; Oosting and Billings 1951; Leak 1975). Perhaps its most important silvical properties are the abilities to persist as advance regeneration and to respond weH to release after many decades of suppression in very low-light conditions in the understory. Cary (1896) was the first to document the capability of red spmce to respond to release at advancedages, but this remarkable quality was also highlighted by other early foresters (Graves 1899; Hosmer 1902). Subsequent studies (yI estveld 1931; Davis 1989) have found that the ability of spmce to develop slowly in the understory gives this species an initial height advantage that aHows it to compete successfuHy with faster growing fir and hardwoods after release from overstory cover.