Forest Structure and Health Trends in the Southern Appalachian Montane Spruce-fir and Northern Hardwood Ecosystems of the Black Mountains, North Carolina.

Abstract

Spruce-fir forests of the Southern Appalachians are ice age relics currently existing now in isolated montane islands at elevations above 1400 m. Decline in the spruce-fir ecosystem throughout the region was shown following extensive surveys in high elevation red spruce (Picea rubens Sarg.) and Fraser fir (Abies fraseri (Pursh) Poir.) forests conducted during the 1980?s. Following an observed decline in red spruce crown condition at lower elevations (1500 m) in the Black Mountains of North Carolina during the summer of 2001, it was deemed necessary to conduct a new investigation to characterize trends in forest health in the spruce-fir and adjacent northern hardwood forests.

Beginning in 2002, we undertook a new study in order to gain further information relating to the observed decline by resurveying 28 permanent spruce-fir forest plots installed in 1985 at 1525, 1675, 1830, and 1980 m in the Black Mountains. Simultaneously, we established a new system of 40 permanent plots to survey the northern hardwood forests in 9 areas throughout the Black Mountains between 1220 and 1525 m. Following previous protocols in the spruce-fir forest, and using a similar rubric in the northern hardwood forests, we measured live and dead basal area, live and dead stem density, and assessed tree crown conditions for all overstory species. Insect and disease occurrences were also recorded when found with special attention given to balsam woolly adelgid (Adelges piceae Ratz.) on Fraser fir, hemlock woolly adelgid (Adelges tsugae Annand) on hemlock, beech scale insect (Cryptococcus fagisuga Lindinger) and cankers caused by Nectria coccinea var. faginata (Lohman, Watson and Ayers) on beech, and low crown vigor or defoliation in oaks.

Individual plot assessments in the spruce-fir zone revealed a wide range of response over the 17-year interim and while few results were statistically significant, several profound trends were evident. Results show a large increase in live basal area at 1980 m for Fraser fir with a corresponding large significant (p < 0.10) increase in live stem density of 3237 stems/ha from 1986 to 2003. While not statistically significant, a large rise in dead spruce at 1525 m and a decrease in dead fir at 1980 m were also shown. Data suggests a rapid regeneration of dense and healthy fir is currently underway at the highest altitudes, especially in areas of former severe mortality and overstory collapse. However, the amount of progression towards a climax high-elevation fir forest is highly variable and very patchy. A significant (p < 0.10) decline in crown condition for spruce and fir continues to manifest, especially in mature trees at lower altitudes (1525, 1675, and 1830 m). Causal factors behind the current trend in fir crown decline remain unknown, as balsam woolly adelgid (Adelges piceae Ratz.) was not frequently encountered, suggesting that adelgid populations are currently low. Long term recovery for Fraser fir is uncertain as stems reach adelgid-susceptible age and size classes.

The northern hardwood forests of North Carolina, found up to approximately 1525 m, where they give way to spruce-fir forests, exhibit a unique assemblage of many species endemic to the Southern Appalachians. Common northern hardwood type canopy trees of the Black Mountains include northern red oak (Quercus rubra var. borealis Michaux f.), chestnut oak (Q. prinus L.), red maple (Acer rubrum L.), sugar maple (A. saccharum Marshall), American beech (Fagus grandifolia Ehrh.), and eastern hemlock (Tsuga canadensis (L.) Carr.).

With the exception of red spruce and eastern hemlock, the northern hardwood forest survey found most tree species in an excellent condition. Many feared emerging pathogens and insects were not evident, however it is expected that they may have profound impacts on forests throughout the region. The main value of this study is in the potential for long-term monitoring of these sites and detection of disease onset and incipient mortality before epidemic levels are achieved.