The Fraser fir (Abies fraseri (Pursh) Poir.) on Mt. Rogers is an isolated relic population and part of the southern Appalachian spruce-fir ecosystem. The population has, so far, been able to withstand the impacts of insect infestation and the possible influence of atmospheric deposition factors which may be causing mortality in other regions of the southern Appalachians. It was hypothesized that population vigor may be due to a unique genetic structure. The objective of this study was to determine the amount of genetic diversity within this population and to relate observed diversity to environmental variables. To quantify the genetic structure 304 trees from 35 plots were genotyped for 13 isozyme loci. Four loci were polymorphic using the 95% criterion. At a fifth locus there were two rare alleles with a combined frequency of approximately 3%. Range wide studies of eastern fir species have shown that other populations are more diverse. There were no significant differences in gene frequencies among three arbitrarily defined subpopulations or among the 35 plots. There were no significant correlations between any environmental characters and isozyme frequencies. There was a significant difference among subpopulations for seed weight and germination value as well as a slight, yet significant, correlation between seed weight and elevation, germination value and elevation, and germination value and aspect. Spatial autocorrelation analysis, Wright's F-statistics, Nei's genetic distances, and Gregorius' "𝜹" index all indicated little or no substructuring of the population. It is suggested that a population bottleneck (a drastic reduction of population numbers), which may have occurred following the last glaciation, is the cause for the relatively low genetic diversity found in the population. The lack of substructure is likely due to extensive gene flow. / Ph. D.

Fraser fir [Abies fraseri (Pursh) Poir.] is an important Christmas tree species in Virginia. Because it is responsive to fertilization, and because most Fraser fir growers fertilize their crop, a scientifically-based nutrient diagnosis and fertilizer recommendation system is needed. The objective of this study was to develop and test DRIS norms for Fraser fir Christmas trees grown in Virginia for the ultimate purpose of establishing a nutrition diagnosis and fertilizer prescription system. A total of 107 Fraser fir plantations were sampled for foliage, soil, and diameter measurements. These plantations represented the range in site conditions and management practices for Fraser fir Christmas trees grown in Virginia. Foliage was analyzed for N, P, K, Ca, Mg, Zn, Mn, Fe, Cu, and B. Soil was analyzed for extractable macro- and micronutrients. DRIS norms were developed from these data using standard DRIS procedures. A total of 42 nutrient ratios were significant discriminators of tree performance as measured by variation in ground line diameter. The norms were tested using sixth year data from a factorial fertilizer trial. Nutrient limitations due to both deficiencies and imbalance were detected and correctly diagnosed using the newly-derived norms. A complete validation is required, but this preliminary test showed that these norms are useable and useful in their present form. In the process of developing and testing the norms, modifications to traditional DRIS methods were used to meet the special conditions of this crop. DRIS symmetry was maintained by including non-significant ratios, but setting their standardization functions equal to zero. This reduced the influence of the non-discriminating nutrient ratios on the DRIS analysis. Norm ranges as opposed to discrete norms (ratio means) were used to correct for the influence of extremely variable micronutrient ratios on the DRIS analysis. Soil norms did not enhance diagnoses over and above using foliar norms alone. This is due to soil sampling variation, poor correlations of extractable nutrients with tree performance, and an incomplete understanding of fertilizer reactions and uptake chemistry in a variety of soils. Each crop presents unique challenges in the application of DRIS. DRIS should not be naively applied without investigating these problems. The DRIS norms established in this study, and the modifications to standard DRIS methods, provide a sound scientific basis upon which to build a nutrient diagnosis and fertilizer recommendation system for Fraser fir Christmas trees grown in Virginia. / Master of Science

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.