Current stand structure and composition, biomass levels and distributions, stand level foliage surface area (LAI) estimations, and mortality and growth patterns were determined using consistent sampling methodology for a network of 142 (20 m x 20 m) permanent plots at three southern Appalachian spruce-fir sites (Mt. Rogers National Recreation Area (NRA) of Virginia, the Black Mountains of North Carolina, and the Great Smoky Mountains of Tennessee and North Carolina). Baseline conditions were documented to accommodate future efforts to determine actual phenomena of forest decline in a highly disturbed ecosystem. Information on structure, composition, and growth and mortality trends were combined to develop a model to predict forest change for the next two decades.
Past studies indicated that undisturbed spruce-fir species distribution tended to follow an elevation gradient: red spruce (Picea rubens Sargent) dominance changing to Fraser fir (Abies fraseri (Pursh) Poiret) dominance as elevation increased. Current stand composition at the Black Mountains and the Great Smokies also showed a shift from spruce to fir; however, Mt. Rogers NRA was an exception to that trend. As fir abundance increased with elevation there were increasing levels of balsam woolly adelgid-caused (Adelgid piceae Ratz.) mortality at the Black and Smoky Mountains where there was a greater proportion of standing dead fir than live fir. Unlike these two sites, Fraser fir on Mount Rogers still had escaped major damage from the adelgid.
Projected leaf area index (LAI)(m²/m²) was developed for spruce, fir and yellow birch (Betula lutea Michaux f.), based on predicted foliage weight from overstory biomass equations, as a quantifiable measure of forest productivity. Primarily old-growth spruce-fir stands at the Great Smoky Mountains had an average LAI (11.9) significantly greater than stands at Mt. Rogers NRA (9.1) or the Black Mountains (8.3) which both have a patchwork of disturbance histories. Some conversion to increased hardwoods may have occurred in second growth stands at lower elevations with a resulting lower leaf area capability. At higher elevations (1830-1980 m), LAI was predicted to decrease if the remaining adelgid-infested fir die for both virgin and logged sites.
Past studies have inferred information on mortality patterns from assessment of standing dead stems density. Overstory annual mortality was directly measured each year from 1985 and 1989 and found to vary among the four dominant overstory species; mountain-ash (Sorbus americana Marshall) had the highest rate (6.4 %), followed by fir (5.8 %), birch (2.7 %), and spruce had the lowest (2.1 %). Results suggested that enumerations of standing dead trees should not be used to assess mortality patterns since a substantial proportion (20-30 %) of all trees that died, fell to the ground in the same year, and were never part of the pool of standing dead stems. Comparisons of fir diameter distribution indicated that at sites where the balsam woolly adelgid was causing significant fir mortality, stand structure was shifting because of the elimination of larger (> 35 cm DBH) live fir stems. Prediction of individual tree mortality using logistic regression was unsuccessful for birch and mountain-ash, while equations to predict spruce and fir mortality depended on crown condition (amount of intact needles), as a predictor variable.
Since an accelerated rate of change in stand structure has been predicted to occur with increased mortality and reduced growth rates, a short-term (twenty year) projection model of forest composition and structure was developed. Individual tree basal area increment equations for red spruce, Fraser fir, and yellow birch, along with ingrowth and mortality information were combined to provide predictions starting from the year 1989 and ending in 2009. Where the adelgid has been dominating fir mortality patterns for several decades, such as in the Black Mountains, little overall change is expected. For most elevations basal area is projected to be stable while stem densities decrease. In the Smokies, where little fir is found at or below 1675 m elevation, stand structure is predicted to change little during the 20 year period. However, the highest elevations of the Smokies are predicted to eventually be similar to the current stand structure of high elevations of the Black Mountains. The adelgid infestation of the peaks of the central Smokies lagged by twenty-some years behind the Black Mountains and the model predicts a deterioration of fir as well as spruce in that area. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/38365 |
| Date | 06 June 2008 |
| Creators | Nicholas, N. S. |
| Contributors | Forestry, Zedaker, Shepard M., Burkhart, Harold E., Smith, David W., Webster, Jackson R., White, Peter S. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | xv, 176 leaves, BTD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 26247998, LD5655.V856_1992.N525.pdf |
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