Self-thinning quantifies the reduction in tree numbers due to density-dependent mortality. Maximum size-density relationships (MSDRs) are a component of self-thinning that describe the maximum tree density per unit area obtainable for a given average tree size, often quadratic mean diameter (D). An MSDR species boundary line has been defined as a static upper limit of maximum tree density -- D relationships that applies to all stands of a certain species within a particular geographical area. MSDR dynamic thinning lines have been defined as the maximum tree density obtainable within an individual stand for a particular D which have been shown to vary relative to planting density. Results from this study show that differences in boundary levels of individual stands cause the MSDR species boundary line slope estimate to be sensitive to the range of planting densities within the model fitting dataset. Thus, a second MSDR species boundary line was defined whose slope is the average slope of all MSDR dynamic thinning lines. Mixed-models are presented as a statistical method to obtain an estimate of the population average MSDR dynamic thinning line slope. A common problem when modeling self-thinning is to determine what observations are within generally accepted stages of stand development. Segmented regression is presented as a statistical and less subjective method to determine what observations are within various stages of stand development. Estimates of D and trees per acre (N) where MSDR dynamic thinning lines begin and end on the logarithmic scale were used as response variables and predicted as a function of planting density. Predictions of MSDR dynamic thinning line beginning and ending D and N are used in an alternative MSDR dynamic thinning line slope estimation method. These models show that the maximum value of Reineke's Stand Density Index (SDI) varies relative to planting density. By relating planting density specific Zone of Imminent Competition Mortality boundaries to a MSDR species boundary line, self-thinning was found not to begin at a constant relative SDI. Thus, planting density specific Density Management Diagrams (DMD) showed that self-thinning began at 40 to 72% for planting densities of 605 and 2722 seedlings per acre, respectively. / Ph. D.

Research in optimizing forest management has focused on single-stand problems to derive optimal harvest sequences in terms of residual basal area or residual stand structure for uneven-aged stands, and timing of pre-defined thinning treatments and clearcut harvests for even-aged stands. Recent research results provide various means of numerically deriving optimal management prescriptions for single-stand problems, thus considering all feasible solutions as opposed to considering only pre-defined harvest alternatives. However, forest-level problems involving aggregates of stands with similar management constraints are usually solved by evaluating pre-defined harvest sequences. Forest-level management optimization problems in which individual stands may be assigned to either even-aged or uneven-aged silvicultural systems have not been modelled. A dynamic forest management model is describer: that prescribes silvicultural treatments for stands within a multi-stand management unit. Results of an application of this approach to an Appalachian hardwood forest, comparisons of individual stand and whole forest optimal solutions, and efficiency of the solution algorithm are discussed. / Ph. D.

The thinning of loblolly pine plantations has a great potential to influence the fluxes and storage of carbon within managed stands. This study looked at the effects of thinning on aboveground carbon and mineral soil carbon storage, 14-years after the thinning of an 8-year-old loblolly pine plantation on the piedmont of Virginia. The study also examined soil respiration for one year following the second thinning of the same stand at age twenty-two. The study was conducted using three replicate .222 hectare stands planted using 3.05 by 3.05 meter spacing in 1980 at the Reynolds Homestead in Critz, VA. Using two different sample collection methods it was determined that soil carbon was evenly dispersed throughout thinned plots, and that random sampling techniques were adequate for capturing spatial variability. Soil carbon showed a significant negative correlation with soil depth (p=0.0001), and by testing the difference between intercepts in this relationship, it was determined that thinning significantly increased soil carbon by 31.9% across all depths (p=0.0004). However, after accounting for losses in aboveground wood production, thinning resulted in an overall 10% loss in stand carbon storage. However, this analysis did not take into account the fate of wood products following removal. Soil respiration, soil temperature, and soil moisture were measured every month for one year near randomly selected stumps and trees. In order to account for spatial variation, split plots were measured at positions adjacent to stumps and 1.5 meters away from stumps. Soil temperature and moisture were both significantly affected by thinning. Regression analysis was performed to determine significant drivers in soil CO2 efflux. Temperature proved to be the most significant driver of soil respiration, with a positive correlation in thinned and unthinned stands. When modeled using regression, thinning was a significant variable for predicting soil respiration (p < 0.0009), but explained only 3.4% of the variation. The effects of thinning were responsible for decreased respiration, however, when coupled with increased temperatures, soil respiration was elevated in thinned stands. / Master of Science

The relationship between volume production and stand density, often termed the 'growth-density relationship', has been studied since the beginnings of forestry and yet no conclusive evidence about a general pattern has been established. Throughout the literature claims and counterclaims concerning the growth-density relationship can be found. Different conclusions have been attributed to the diverse range of definitions of volume and stand density among problems with study design and other pitfalls. Using data from two thinning studies representing non-intensively and intensively managed plantations, one spacing trial, and one thinning experiment a comprehensive analysis was performed to examine the growth-density relationship in loblolly pine. Volume production was defined as either gross or net periodic annual increment of total, pulpwood, or sawtimber volume. These definitions of volume production were then related to seven measures of stand density including the number of stems per hectare, basal area per hectare, two measures relative spacing and three measures of stand density index. A generalized exponential and power type function was used to test the hypothesis that volume production follows either an increasing or unimodal pattern with stand density. These patterns were tested using all combinations of the six definitions of volume production and the seven measures of stand density. Significance of the parameters indicated that different patterns existed depending on the type of management (intensive vs. non-intensive), if thinning is performed, and depending on the definitions of growth and density. The growth-density pattern was generally the same between gross and net production although different patterns emerged when comparing total, pulpwood, and sawtimber volumes. The definitions of stand density which used diameter as a measure of average tree size were more highly correlated with volume production and produced similar patterns while the number of stems per hectare was the least correlated. Further analysis was performed to evaluate Langsaeter's hypothesis which states that volume production is constant and optimal across a wide range of stocking. A mixed-model approach was used to test the equality in mean volume production across a range of planting densities and thinning intensities. To account for the effects of age, the equality in mean volume production was tested separately across a range of ages from 8 to 25 years within the spacing trial data and across a range of one to six years since thinning within the thinning experiment. A multiple comparison test indicate that pattern of volume production and stocking is highly related to the two stages of self-thinning. In young stands, within the distance-independent mortality stage, volume production increases with increasing planting density and therefor increasing stocking. During the distance-dependent mortality stage the assumption of constant and optimal volume production across a wide range of stocking is generally correct. However when mortality began to reduce canopy closure to the point that the residual stand could not recover gaps in the canopy a decline in volume production occurred resulting in a decreasing relationship with increasing stocking. Finally, a system of equations were constructed to describe volume production at the individual tree and stand levels. From this model it was determined that stand level volume production follow an increasing pattern with stand density. / Ph. D.

Commercial thinning in the South is a highly efficient mechanized operation which operates year round. Southern winters are typically wet; therefore, the potential for soil rutting and compaction exists when heavy machines are used. This study was undertaken to determine if mechanized thinning in wet weather impacted the soils and affected tree growth. Soil and tree growth data were collected from two natural loblolly pine stands located in the coastal plain of Arkansas that were thinned 4-5 years previously. The Demonstration Area was 1.9 acres in size and 26 years old, with a site index of 50 feet (base age 25). The second study area, the Deer Camp Area, was 4.0 acres in size and 31 years old, with a site index of 60 feet (base age 25). The soil physical conditions in both study areas were not significantly impacted by the mechanized thinning operation. In general, the soils had bulk densities below 1.3 Mg/m³, approximately 15% macropore space, 30% micropore space, and ruts were generally less than 6 inches deep. Trees growing greater than 12 feet from the skidding corridors were compared with trees growing 0-12 feet from the skidding corridors. In both study areas, radial growth of the trees next to the corridors exceeded that of those between corridors after thinning. Other results varied by site. On the Demonstration Area the trees in the 0-12 foot zone had larger DBHs and crown widths than the trees between corridors; but the trees growing more than 12 feet from the corridor were taller than the trees growing within 12 feet of the corridor. In the Deer Camp Area, the trees within 12 feet of the corridor had larger DBHs, total heights, and heights to the live crown than the trees growing more than 12 feet from the corridor. The main reason tree growth next to the corridors exceeded that of trees between corridors ( > 12 feet from corridor) was because of heavier thinning in the areas closer to the corridor. The only post-thinning growth reductions were found in trees growing near the deepest ruts (i.e. >6 inches deep). In both study areas, these trees had extremely poor radial growth responses after the mechanized thinning, increasing only 1.6% in the Demonstration Area and decreasing 4.7% in the Deer Camp Area. The trees located on ruts less than 6 inches deep had the highest radial growth responses to the thinning operation. The trees on 3-6 inch ruts responded 20.2% in the Demonstration Area and 28.6% in the Deer Camp Area; on 0-3 inch deep ruts, the trees responded 15.0% and 23.3%, respectively. Bole damage was also found to reduce the growth of residual loblolly pine. Damaged trees growing within 6 feet of the rut had the lowest increase in radial growth after thinning. On both study areas, the damaged trees located more than 6 feet from the rut did not seem to be adversely affected by the bole damage. Overall, mature loblolly pine seems tolerant of small amounts of soil disturbance and basal damage, but, if both occur, then tree growth is severely reduced. / Master of Science

The effects of crop tree release and fertilization of young yellow-poplar on low and medium quality Southern Appalachian sites were compared. In June of 1989 96 individual 10 year-old yellow-poplar crop stems were treated in factorial combinations. The crop trees were either released, using a 4% triclopyr ester in kerosene basal spray. fertilized with 224, 291 and 243 kg/ha of N, P, and K; released and fertilized, or left untreated. These treatments were repeated in June of 1992. In 1992, treatments were slightly different. Crop trees were released mechanically, and only nitrogen was applied at 224 kg/ha. After five years, only release resulted in significant growth responses. Released trees responded positively to increased sunlight and horizontal space by increasing their uptake of nitrogen and iron - elements essential for photosynthesis. This led to an increase in foliage production, and presumably, an increase in total photosynthesis. Released trees reacted to the increased growing space by filling in the space created by release. Released trees increased both diameter and crown volume growth; unfortunately, they did so at the expense of height growth, which was decreased by crop tree release. Current stem wood volume, was therefore not increased. / Master of Science

The influence of thinning at age eight on the photosynthetic rate, needle conductance, xylem water potential, water use efficiency and growth of loblolly pine trees was studied during their ninth and tenth growing seasons. Litterfall dynamics were monitored throughout the study period as well. At the end of the second post-thinning growing season, trees in thinned plots had greater stem diameters, greater live crown ratios, greater live crown diameters and greater average volumes and basal areas than did trees in control plots. Significant physiological changes due to thinning were observed only in the lower crowns where needles were found to adapt to the sudden increase in available light by adjusting their physiology to resemble that of sun needles. Lower crown photosynthesis and needle conductance in thinned plots were more similar to upper crown values for these parameters than to lower crown, control plot values. Foliage produced during the current year and measured after full elongation had a higher average photosynthetic rate, needle conductance and lower average water potential than did foliage in its second growing season during both 1988 and 1989. Additionally, the water use efficiency of current-year foliage was significantly greater than that of the second-year foliage. In both thinned and control plots, significant diameter growth and photosynthesis continued throughout the dormant season although at a slower rate than during the growing season. Litterfall timing did not differ between thinned and control plots, nor did the amount of litterfall per unit basal area during the first year following thinning. Partial second-year data suggest that subsequent litterfall amounts will mirror the greater average crown size in thinned plots. / Master of Science

Hydrophobic interaction plays an important role in biology, daily lives, and a variety of industrial processes such as flotation. While the mechanisms of hydrophobic interactions at molecular scale, as in self-assembly and micellization, is relatively well understood, the mechanisms of macroscopic hydrophobic interactions have been controversial. It is, therefore, the objective of the present work to study the mechanisms of interactions between macroscopic hydrophobic surfaces in H-bonding liquids, including water, ethanol, and water-ethanol mixtures. The first part of the present study involves the measurement of the hydrophobic forces in the thin liquid films (TLFs) confined between two identical hydrophobic surfaces of contact angle 95.3o using an atomic force microscope (AFM). The measurements are conducted in pure water, pure ethanol, and ethanol-water mixtures of varying mole fractions. The results show that strong attractive forces, not considered in the classical DLVO theory, are present in the colloid films formed with all of the H-bonding liquids tested. When an H-bonding liquid is confined between two hydrophobic surfaces, the vicinal liquid molecules form clusters in the TLFs and give rise to an attractive force. The cluster formation is a way to minimize free energy for the molecules denied of H-bonding with the substrates. Thus, solvophobic forces are the result of the antipathy between the CH2- and CH3-coated surface and H-bonding liquid confined in the film. A thermodynamic analysis of the solvophobic forces measured at different temperatures support this mechanism, in which solvophobic interactions entail decreases in the excess film enthalpy and entropy. The former represents the energy gained by building clusters, while the latter represents loss of entropy due to structure building. Thus, hydrophobic interaction may be a subset of solvophobic interaction. The solvophobic forces are strongest in pure water and pure ethanol, and decrease when one is added to the other. Adding a very small amount of ethanol to water sharply reduced the solvophobic force due to the adsorption of the former with an inverse orientation. An exposure of the OH-group toward the aqueous phase decreases the antipathy between the surface and H-bonding liquid and hence causes the hydrophobic (or solvophobic) forces to decrease. The second part of the study involves the measurement of the hydrophobic forces in the wetting films of water using the force apparatus for deformable surfaces (FADS). This new instrument recently developed at Virginia Tech is designed to monitor the deformation of bubbles to determine the surface forces in wetting films. In effect, an air bubble is used a force sensor. The measurements have been conducted with gold, chalcopyrite, and galena as substrates. The results obtained with all three minerals show that hydrophobic force increases with increasing water contact angle, suggesting that hydrophobic forces are inherent properties of hydrophobic surfaces rather than created from artifacts such as preexisting nanobubbles and/or cavitation. A utility of the intrinsic relationship between hydrophobic force and contact angle is to predict flotation kinetics from the hydrophobicity of the minerals of interest. / Ph. D.

By increasing fruit exposure to sunlight and influencing fruit development, leaf thinning in the fruit zone can improve grape quality and lower disease incidence; however, further investigations on the timing, varietal response and intensity are needed to optimize results and to better understand underlying physiologic responses. Fruit zone leaf thinning was applied at different timing and intensities to evaluate its effect on cluster health and fruit composition in Cabernet Sauvignon and Chardonnay. Treatments consisted of control (C), pre-bloom leaf thinning (PB) and two levels of fruit-set leaf thinning (three leaves, PF3 and six leaves, PF6). In an additional project on Cabernet Sauvignon, two levels of hedging (17th node, NH and 12th node, H) were integrated with no leaf thinning (L) and fruit set leaf thinning (LR, three leaves). All leaf thinning treatments consistently reduced disease incidence compared to control vines in both varieties, with the reduction extent varying between 2017 and 2018. Yield was not negatively affected by leaf thinning treatments, even though PB reduced cluster compactness by decreasing the number of berries per cluster of Chardonnay in 2017. Control vines tended to have greater titratable acidity than defoliated vines, while Brix and pH responses varied between seasons. No direct positive correlation was found between sunlight exposure and norisoprenoids concentration. Post fruit set leaf thinning PF6 consistently increase free norisoprenoids at harvest, while pre-bloom defoliation never did. Heterogeneous responses were observed for bound and total norisoprenoids. In Cabernet Sauvignon free, bound and total 1,1,6-trimethyl-1,2-dihydronaphtalene (TDN) was consistently increased by PF3. Hedging negatively influenced Brix and anthocyanins accumulation in 2017, and increased free norisoprenoids while decreasing the bound and total fraction. Results revealed that a high level of stress possiblt caused by excess sunlight and/or reduced photosynthesis might negatively affect norisoprenoids glycosylation. / Master of Science in Life Science / This project evaluates the effect of a grapevine canopy management practice on grape quality. The objective was to find a suitable technique to expose the fruits to sunlight in order to increase grape aroma concentration and improve grape sanitary status of Virginia vineyards. Leaves were removed from the fruit zone with different intensities at two grape developmental stages, in two varieties (Chardonnay and Cabernet Sauvignon). Treatments consisted of control, three leaves removed before blooming (PB) and three or six leaves removed after fruit set (PF3 and PF6 respectively) In an additional project with Cabernet Sauvignon, the effect of canopy height was integrated with the fruit zone defoliation. Results showed that the removal of leaves from the fruit zone is effective in improving grape sanitary status at harvest, with the improvement extent depending on the season climatic conditions and on the amount of leaves removed. Crop yield was not negatively affected by treatments. Non defoliated grapes tended to have greater acidity at harvest, while sugar responses were inconsistent. Aroma compounds responded heterogeneously to fruit zone defoliation, but volatile odorants were consistently greatest in the most exposed grapes (PF6) compared to all other treatments at harvest. Pre-bloom defoliation instead, never increased volatile aroma compounds compared to control at harvest. Generally, non-volatile odorants were greater in less severely defoliated vines or control. An overall positive effect was observed with PF3. Canopy height was demonstrated to be able to indirectly affect grape quality and composition, with the short canopy reducing grape’s sugar and color content and increasing grape’s volatile aroma compounds concentration at harvest in 2017. The removal of three or six leaves from the fruit zone in post fruit set could be a suitable practice to improve grape quality in the Virginia environment.

Coal has been and will continue to be an important energy source in the U.S. for the foreseeable future. Surface mining for coal is one of the methods employed to extract this resource from below the ground. The process of surface mining removes native topsoils and any native vegetation that was support by these native soils. In the Appalachian coal-producing region of the United States, the pre-mining landscape is predominantly forested. Prior to the Surface Mining and Reclamation Act of 1977 (SMCRA), surface mined lands were commonly reclaimed to forests. Subsequent to the passage of SMCRA, reforestation of surface mined lands has decreased. As a result, thousands of hectares of land that were forested prior to mining are being reclaimed using grasses and legumes. This is done in spite of the fact that the SMCRA requires that land be reclaimed to an "equal or higher land use." The decline of reforestation stems from two main issues, namely: (1) reclaiming land to pasture is an easy and low-risk way for mining companies to obtain bond release; and (2) SMCRA reclamation requirements have led to unfavorable conditions for tree establishment and growth. Recent interest has been shown in reverting these surface mined lands that have been reclaimed to pasture back to forests for reasons related to the environmental, economic, and carbon sequestration benefits that forests are believed to have when compared to pasture land. It is believed that forests can be established on existing reclaimed pasture land through the use of silvicultural treatments, that mature stands of trees growing on surface mines will respond to treatment similarly to stands growing on native soils, and that mature stands growing on relcaimed surface mines have different soil properties controlling their growth than those that have been found for younger stands. The purpose of this investigation was to understand the biological feasibility of restoring forests on post-SMCRA surface mined lands in the Appalachian coalfields reclaimed to pasture and to understand the productive potential and factors governing the productive potential of pre-SMCRA surface mines supporting mature forests in an attempt to show the benefits of reclaiming these lands with forests. A 3x3x3 factor random complete block design was used to assess first-year survival and growth of three species assemblages under three levels of silvicultural treatment intensity at each of three study sites having different site characteristics. The native hardwood species assemblage was found to have the best survival across all three sites, with 80 and 85% survival for sites with spoils derived from shale and oxidized sandstone, respectively. White pine generally had the lowest survival of all species and ranged from 27% across treatments on siltstone spoils to 58% across treatments on oxidized sandstone spoils. Hardwood and white pine grew little over the first year, ranging from -3.7 to 8.9cm in height compared to hybrid poplar, whose height growth ranged from 22.4cm to 126.6cm. Response to silvicultural treatment was variable by site and species, but weed control in combination with tillage generally resulted in the highest survival. Greatest height growth (126.6cm) occurred on the oxidized sandstone spoil, where hybrid poplar was treated with weed control plus tillage in combination with fertilization. Hybrid poplar was found to have the greatest growth after one year compared with the hardwood and white pine and also had the greatest height growth at each level of silvicultural intensity for all sites. This superior growth should give hybrid poplar an advantage over the others used to revert these grass lands back to forests, as the amount of height growth observed (>50cm over one year in the weed control plus tillage treatment at all sites) may be enough to ensure that these trees will not succumb to aggressive competing vegetation without further weed control. The results of this study show that based on first-year data, reforestation of these lands does appear to be biologically feasible, given the species and treaments used. In an attempt to quantify the productivity of a 26-year-old white pine stand established pre-SMCRA, a random complete block experiment was used to compare the response to a thinning that occurred in this stand at age 17. Site index of the stand was found to be 32.3m at base age 50, indicating that this is a very productive stand. Neither stand volume nor stand value was statistically different at age 26 between treatments with volumes and values ranging from 290m3ha-1 and $5639 ha-1 to 313 m3ha-1 and $5478 ha-1 for the thinned and unthinned treatments, respectively. The difference in mean breast-height diameter, however, was significant at age 26, and this was confirmed by a significant difference in a repeated measures analysis of annual diameter data for these treatments (P < 0.0001). Projection to age 30 revealed that both stand volume and value would be significantly higher in the thinned treatment by margins of 8.7 m3 ha-1 and $2457 ha-1. Regression analysis of soil data within the observed rooting depth of the trees from this stand indicated that nitrogen mineralization index, bulk density, sand percentage of the fine soil fraction, and percentage of oxidized sandstone in the soil profile were the most important variables in determining the stand's productive capacity (R2 = 0.7174). It was also found that of the five different spoil types encountered in the stand, the oxidized sandstone spoil had the most favorable physical and chemical properties for tree growth. Common root-restricting layers were found to have high soil density or increased levels of soluble salts. It has been shown that reclaimed surface mines can grow productive forests if the appropriate spoil materials are returned to the surface in sufficient depth. It has also been shown that surface mined lands reclaimed to pasture can be successfully reforested using silvicultural treatments to ameliorate unfavorable conditions for tree establishment and growth, though these treaments may not be cost-effective, and the success of these treatments was variable based on the soil characteristics of each site. / Master of Science