By the late 1980s the composition and structure of forest stands in the southern Appalachian spruce-fir zone were altered by insect infestations to Fraser fir. The response of red spruce, the sole remaining coniferous forest dominant, to this disturbance was followed over twenty years (1983-2003) in an old spruce-fir forest at Mt. Collins, Great Smoky Mountains National Park. Although diameter growth of canopy red spruce (>30 cm dbh) at six plot sites was considerable (mean 10-yr increment 2.1 cm; 1993-2003), red spruce mortality increased sharply (mean 4% yr-1; 1993-2003). Wind-related mortality of canopy red spruce was substantial after the loss of Fraser fir from the canopy circa 1985 (>70% of the dead spruce had broken or uprooted boles; 1983-2003). Wind damage to red spruce was observed at most plot sites, but it was most pronounced on exposed topographic positions, where canopy gap expansion was extensive. The elevated mortality of red spruce at Mt. Collins was not associated with reduced diameter growth. Altered canopy structure has left large red spruce vulnerable to high winds. With the loss of canopy fir and the subsequent increase in mortality of canopy spruce, total live basal area has declined to about half of its pre-disturbance level.
