W. Henry McNab

Forest disturbance in hurricane-related downbursts in the Appalachian mountains of North Carolina

Abstract We characterized five 0.2–1.1 ha gaps created by downbursts during Hurricane Opal in xeric oak forest at the Bent Creek Experimental Forest, Asheville, NC. Direction of windthrow was nonrandom in four of the five gaps, but differed among gaps suggesting that each was caused by an independent downburst. Windthrows reduced tree density by 19–39% and basal area (BA) by 30–53% within gaps. Most windthrows were uprooted (17–38% of all trees) versus broken below 1.8 m height (0–3%). Most species were uprooted in proportion to their abundance regardless of canopy position. Red oaks (Quercus coccinea, Quercus rubra and Quercus velutina) were disproportionately uprooted, while Nyssa sylvatica and Acer rubrum were resistant to uprooting. As a group, Quercus lost 27–47% of individuals and 41–50% of BA. Q. coccinea lost ≥44% of trees and >55% of BA in sites where it occurred. Only minor shifts in canopy species dominance were evident. For several species, significantly more large-diameter individuals uprooted than their smaller counterparts. No relationship between dbh and number uprooted was detected for the red oaks, however. Canopy position appeared to have little bearing on this relationship. Uprooting disturbed 1.6–4.3% of the ground area and displaced 130–587 m3 of root–soil–rock masses (rootmasses) per gap. We suggest that episodic, high-intensity wind is not uncommon, and has a substantial influence on forest structure, species composition, regeneration and microtopography of the southern Appalachian mountains at variable scales.

Probability of occurrence and habitat features for oriental bittersweet in an oak forest in the southern Appalachian mountains, USA

Abstract Oriental bittersweet (Celastrus orbiculatus), an introduced vine from southeast Asia, has become a serious threat to native forests in the eastern United States. It is typical of many exotic species in that quantitative ecological relationships are unavailable for assessment or management. We devised a rapid survey technique useful for hazard rating and modeled the probability of occurrence of oriental bittersweet in relation to environment, competition, and disturbance in stands of deciduous hardwoods in mountainous terrain. Oriental bittersweet was present on 39% of the study area, which has been managed by the selection system of silviculture and was recently disturbed by hurricane-force winds. Bittersweet was significantly associated with (1) topographic variables indicative of mesic environments, (2) density of midstory arborescent vegetation, (3) overstory canopy gaps, (4) past silvicultural harvests, (5) overstory canopy composition, and (5) scarification of the forest floor. Search distance from plot center to the first individual of bittersweet was significantly less (P=0.04) on mesic than xeric sites. We developed a logistic regression model with five significant (P

An unconventional approach to ecosystem unit classification in western North Carolina, USA

We used an unconventional combination of data transformation and multivariate analyses to reduce subjectivity in identification of ecosystem units in a mountainous region of western North Carolina, USA. Vegetative cover and environmental variables were measured on 79 stratified, randomly located, 0.1 ha sample plots in a 4000 ha watershed. Binary transformation of percent cover followed by direct and indirect ordination indicated the 185 inventoried species were associated primarily with soil A-horizon thickness, soil base saturation, and aspect. Redundant cluster analyses, consisting of divisive and agglomerative methods for multivariate classification of core plots, followed by selective discriminant analysis of remaining non-core plots, indicated that the continuum of vegetation and environment could be grouped into five ecosystem units. Approximately 20 herbaceous, shrubs, and tree species and several soil and topographic variables were highly significant discriminators of ecosystem units. We also demonstrated that redundant cluster analysis may be used to subdivide ecosystem units into subunits of uniform understory composition and associated environment. Validation and refinement of classification units, linkage with faunal biological components, and arrangement into landscape areas suitable for resource management is needed before field application.

Classification of Local- and Landscape-Scale Ecological Types in the Southern Appalachian Mountains

Five local ecological types based on vegetative communities and two landscape types based on groups of communities, were identified by integrating landform, soil, and vegetation components using multivariate techniques. Elevation and several topographic and soil variables were highly correlated with types of both scales. Landscape ecological types based only on landform and soil variables without vegetation did not correspond with types developed using vegetation. Models developed from these relationships could allow classification and mapping of extensive areas using geographic information systems.