The shallow root system, thin bark, and flammable needles of red spruce make trees of all ages very susceptible to fire damage (11). The acreage of red spruce originally present in the southern Appalachians has been reduced to a fraction of what it once was by fire and clearcutting (22). Many former spruce sites are occupied by inferior tree species, blackberries, and ferns after 20 years (47).
The most important insect enemy of red spruce is the spruce budworm, Choristoneura fumiferana. Although red spruce is much less vulnerable to damage than balsam fir or white spruce, largely due to later bud flushing in the spring (3), much damage and mortality occur in stands containing large quantities of mature balsam fir. Blum and McLean (4) suggest that factors such as stand age, species composition, density, and vigor contribute to the vulnerability of spruce-fir stands to budworm damage and suggest steps to alleviate damage. Additional, detailed information may also be found in Sanders, et al. (42) for spruce-fir stands in the Northeast, the Lake States, and Canada.
The eastern spruce beetle, Dendroctonus rufipennis, damages mature trees of red spruce. Two species of sawflies, the European spruce sawfly, Diprion hercyniae, and the native yellowheaded spruce sawfly, Pikonema alaskensis, have severely defoliated red spruce in localized areas (22). The eastern spruce gall adelgid, Adelges abietis, can be a serious pest on spruce when abundant. The pine leaf adelgid, Pineus pinifoliae, forms unsightly but relatively harmless conelike galls on red and black spruce (Picea mariana), which are alternate hosts (46).
Red spruce has few diseases. Needle cast caused by Lirula macrospora may result in severe defoliation of the lower crown and a subsequent reduction of growth. Phellinus pini and Phaeolus schweinitzii, the most destructive of red spruce wood-rotting fungi, are usually confined to overmature or damaged trees. Climacocystis borealis causes butt rot in overmature trees (22). Trees are occasionally attacked by Armillaria mellea and Inonotus tomentosa.
All along the eastern Appalachian mountain chain, from the New England states to Georgia, growth has declined in high-elevation red spruce since the 1960's (25). In recent years, this decline has been accompanied by increased mortality and crown damage in high-elevation red spruce. Apparently, no significant natural biotic or abiotic causal agents have been identified, although it has been hypothesized that interaction among naturally occurring insect and disease factors and anthropogenic air pollutants, or air pollutants acting alone, are at the root of the problem. Sulphur dioxide (S02), nitrogen oxides (NOx), and volatile organic compounds are the pollutants of primary concern; secondary pollutants such as ozone and nitric and sulfuric acids are also believed to be important factors (29).
Growth decline and mortality in low-elevation red spruce in northern New England, while increasing in some areas, appear to be within the normal ranges for trees and forests of various ages, compositions, and density. However, some foliar symptoms have been detected in both red spruce and white pine, particularly from ozone exposure.
Red spruce is occasionally infected with eastern dwarf mistletoe, Arceuthobium pusillum, a parasite causing growth reduction, tree mortality, and degradation of wood quality (24).
Mice and voles have been found to consume and store significant amounts of spruce seeds in preference to those of balsam fir, suggesting one reason for the low ratio of spruce to fir seedlings commonly found in naturally regenerated stands (1,23). Wildlife damage to the terminal buds of young spruce, presumably by birds, also has been noted (2). Some injury and mortality are also caused occasionally by porcupines, bears, deer, and yellow-bellied sapsuckers (11). Red squirrels clip twigs and terminals and eat reproductive and vegetative buds (41).