The effect of moisture stress conditioning on the drought tolerance and performance of three open-pollinated families of loblolly pine (Pinus taeda I.) during water stress were investigated. Seedlings were subjected to prolonged sublethal drought treatments which included a watered control, a moderate stress treatment (MWS, seedlings watered only when needle water potential reached -0.8 MPa) and a severe stress treatment (SWS, seedlings watered only when water potential reached -1.4 MPa). After the conditioning period, numerous physiological and morphological parameters were measured, and performance of seedlings during water stress evaluated. Significant decreases in needle osmotic potential occurred in moisture stress conditioned seedlings. As a result, turgor in conditioned seedlings was equal to or greater than control seedlings even at lower needle water potentials. Photosynthesis vas decreased greatly with reduced needle water potential. However, the MWS and SWS seedlings maintained photosynthesis to water potentials 0.15 and 0.45 MPa lower than control seedlings, respectively. This response is likely the result of both osmotic adjustment, and an acclimation of the photosynthetic process resulting in less non-stomatal inhibition of photosynthesis at low needle water potentials. Initial needle conductance and transpiration, but not photosynthesis, were reduced greatly by the conditioning treatments, and resulted in improved water-use efficiency in conditioned seedlings. The response of stomata to changing vapor pressure deficit was increased through moisture stress conditioning. Boot growth was affected more by moisture stress than shoot growth, causing a decrease in root/shoot ratio. Changes in root morphology as a result of conditioning are not likely to improve the drought tolerance of loblolly pine seedlings. SWS conditioning significantly improved the height growth increment and resulted in slightly greater shoot and root biomass of outplanted, containerized seedlings after the first growing season, despite these seedlings being much smaller at the time of planting. Differences between seed sources did occur in the experiments, with a source from Texas generally showing the least response to moisture stress conditioning. / Ph. D.

A decline of eastern white pine, Pinus strobus L., has been observed for over 80 years in the eastern United States. The syndrome has not always been discussed as a decline but reported under a variety of names. Symptoms vary with time required for trees to die, but generally include chlorotic foliage, in many cases needle loss producing a tufted appearance, premature annual loss of needles, drooping of needles in some cases, shriveling of bark after a period of time, and eventual death after a period of months to years. An investigation into the causes of decline on landscape sites in Virginia included an indexing technique to compile and analyze, systematically, pertinent data from good and poor quality sites. Over 300 variables were studied from over 100 observations to narrow down the apparent causal factors for future investigation in a controlled environment. Observations were organized into two groups for analysis, one called the “decline habitat” and the other the “natural habitat”. Natural habitat observations consisted of trees from a site in the Jefferson National Forest (VA) and decline habitat observations consisted of trees from mostly western Virginia landscapes. After thorough study for a period of two years, a group of growth indicators were weighed against a group of site quality indicators. Growth quality indicators included: a height vs. age index, a 10-year compilation of tree ring increments and inter-branch whorl measurements converted to percent growth per year, and seasonal foliar color changes using a Munsell rating index. Site quality indicators centered around the soils with soil pH, clay content, amounts of compaction and soil disturbance as the most prominent factors derived from the study. Soil pH averaged 6.95 with a range of 5.9-8.1 for decline habitats; while the pH averaged 5.50 with a range of 5.0-6.0 for the natural habitat. Clay content averaged 37.05% for decline sites vs. 17.76% for the natural site for soils above and in the root zones of white pines. Clay content averaged 43.99% for decline sites vs. 17.95% for the natural site for soils beneath the root zones of white pines. Soils under decline habitat trees were highly compacted with measurements as high as 1806.1 psi to penetrate some decline habitat soils, while the natural habitat soils had little if any compaction, with readings of between 138 and 273 psi. Soil disturbance was not present in the natural site while present in most decline sites. The major cause of disturbance was construction and earth-moving activities around landscape sites. Important abiotic factors which worked in concert with soil factors included poor planting practices, competition with tree feeder roots from turfgrass, chemical pollutants, and mechanical damage by weather and man. Biotic factors were viewed as secondary agents attracted to already weakened trees after initiation of decline by the previously discussed factors. Separate studies of seasonal foliar color changes and the initial finding of the pinewood nematode in Virginia aided in identifying additional indicators of and contributors to decline. / Ph. D.

A greenhouse study was initiated to asses P uptake, growth, colonization, total mycorrhizal P levels, and mycorrhizal polyphosphate levels in loblolly pine seedlings colonized with different ectomycorrhizal fungi and grown in a Piedmont soil. The pine seedlings were inoculated with one of four species of fungi (Scleroderma aurantium, Pisolithus tinctorius, Thelephora terrestris, and Rhizopogon roseolus). Uninoculated trees served as a control. The seedlings were grown in pots containing a Cecil sandy clay loam amended with one of the following: 75% sand, 25% sand, enamended, 56 kg P ha⁻¹, 112 kg P ha⁻¹. They were harvested ten months after planting. Shoot lengths, root lengths, biomass, and total P of all plant parts including mycorrhizae were determined. Mycorrhizae of T terrestris and S aurantium were analyzed for polyphosphates, and amended soils were analyzed before planting and after harvest for double-acid extractable Al, Fe, and P. Each fungus changed postharvest extractable P, Fe, and Al differently in the soil amendments. Seedlings colonized with S. aurantium were larger, contained more P, and had a higher degree of mycorrhizal colonization. There was no significant differences in growth among seedlings colonized with the other three fungi, but all colonized seedlings were significantly larger and contained more P than uncolonized seedlings. Soil amendments had no effect on the total levels of mycorrhizal P. Mycorrhizae of S. aurantium increased polyphosphate levels with increasing available P in the soil amendments. The pattern of polyphosphate accumulation in T. terrestris among the soil treatments was less definitive. Accumulation of foliar P was affected by the interaction of soil and mycorrhizal treatments. Control seedlings were P deficient in all soil treatments although foliar P increased as soil P increased. The accumulation of foliar P seemed to reflect the ability of each symbiont to survive, uptake P, and transfer it to the seedling. Seedlings colonized with S. aurantium were P deficient in sand-amended soils, while seedlings colonized with R. roseolus were P deficient in fertilized soils. Seedlings colonized with either P. tinctorius or t. Terrestris increased foliar P with the addition of sand the addition of P. This study indicates that S. aurantium is adapted to Piedmont soils such as the Cecil, is able to extract more of the vast amount of unavailable P present in these soils, and hence stimulate growth and P levels in loblolly pine. / Ph. D.

Site preparation is a required silvicultural practice for establishing loblolly pine plantations in the Piedmont physiographic region of the southeastern U.S.; however, relatively little is known about its effect on soil and site factors that influence growth and yield. In this study, the effect of seven different site preparation prescriptions on competing vegetation, tree nutrition, and the spatial distribution of planted seedlings was examined. Three treatments had a soil tillage component and differed with respect to the number of operations employed in removing residual trees and logging slash prior to discing. One treatment involved roller chopping and broadcast burning, one an application of the herbicide glyphosate followed by a broadcast-burn, one involved shearing all raking fogging-debris into windows, and one was no site preparation prior to planting. All treatments were applied to 12 sites in the South Carolina and Georgia Piedmont. After four years in the field, 756 trees within the site preparation treatment areas were randomly selected for analysis of foliar nutrients, soil nutrients, and competing vegetation. Herbaceous, woody shrub, and hardwood competition levels were not significantly different among site preparation treatment areas after four years. However, hardwood competition levels had increased at a faster rate during the last two growing seasons on chopped and disced areas than on the other areas. Hardwood competition became the predominant factor limiting pine basal diameter when 83% of the total basal area was in hardwoods or hardwood basal area levels exceeded 3.5 m²ha⁻¹. Potassium was identified as the most limiting nutrient 38% of the time, compared to 28% for phosphorus, 14 % for nitrogen, 7% for calcium, aiid 13% for magnesium. A significant linear relationship between soil and foliar nutrients confirmed these results. No treatment effect on nutrient deficiencies was evident. Foliar nutrient critical levels were derived using the Diagnosis and Recommendation Integrated System (DRIS) and were the same as those reported in the literature for nitrogen, phosphorous, and magnesium while potassium and calcium critical levels were determined to be twice as high as those reported (0.52% and 0.19%, respectively). The spatial distribution of seedlings at planting and after 2 years was determined. Spatial patterns varied from uniform to random as the degree of logging slash removal decreased. After two years, the spatial distribution shifted toward random and clustered. The degree of change was similar in all but the herbicide burn and untreated areas, which exhibited the greatest change and whose mortality tended to be clustered. / Ph. D.

This study was established to determine the effects of competition control on loblolly pine (<i>Pinus taeda</i> L.), woody plant diversity, and wildlife habitat quality in Virginia Piedmont plantations 12-14 and 24-27 years of age. The responses of loblolly pine and competing woody vegetation in plantations 12-14 years of age were analyzed at 8 levels of competition control: total, 2/3, 1/3, or no woody stem control in combination with either total or no herbaceous vegetation control. As woody stem (plus herbaceous) control increased, pine yield increased, and percent hardwood basal area (PHWD BA) and overstory plant diversity (Shannon index (H’)) decreased. Understory percent woody cover, and woody plant species richness, evenness, and diversity (H’) were not affected at any of the competition control levels. Regression analysis was used to determine relationships between loblolly pine yield, hardwood dominance and overstory plant diversity. Pine yield was negatively correlated to PHWD BA (R²=0.74), while overstory diversity (H’) was proportional to PHWD BA (R²=0.97) and inversely related to pine yield (R²=0.77). The relationship between diversity and PHWD BA was consistent for plantations 12-14 and 24-27 years of age, while relationships of yield to PHWD BA and to diversity were altered in the older plantations. In plantations 12-14 years, competition control reduced proportions of oak and hickory species and reduced canopy structural heterogeneity, but increased proportions of other fruit bearing plant species, and increased deer browse availability and ground stratum heterogeneity. In plantations 24-27 years, competition control altered plant species composition and increased structural heterogeneity. / Master of Science

The pine bark adelgid, Pineus strobi (Hemiptera: Adelgidae) is a native herbivore of eastern white pine, Pinus strobus (Pinales: Pinaceae), in eastern North America. It is a sessile insect that settles on P. strobus and inserts its stylet bundle to feed on the tree’s phloem. Although P. strobi is not considered a serious pest, it shares its range with the invasive hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae). Predators introduced as biological control agents of A. tsugae interact with P. strobi and its native predators, including Laricobius rubidus LeConte (Coleoptera: Derodontidae). Prior to this study, little work had been done to document the phenology or predators of P. strobi, particularly in its southern range. In the present study, the phenology of P. strobi is reported in southwestern Virginia. Patterns in overwintering population dynamics varied notably from those described from this species’ northern range. The number of annual generations could not be measured due to overlap following two distinct spring generations. Adult body size varied seasonally and was greatest in the spring. Variation between observations from the northern and southern ranges of P. strobi indicate phenological plasticity that informs biological control efforts and offers insight into implication of climatic effects on population dynamics of this and related species. Arthropod predators associated with P. strobi in forests of southwest Virginia were collected during a two-year survey. Morphology and DNA barcoding were used for identification. Species of predators found included: Laricobius rubidus (Coleoptera: Derodontidae), a native adelgid specialist, and two species from the dipteran family Chamaemyiidae, Leucopis piniperda Malloch and L. argenticollis Zetterstedt, which are adelgid specialists. Members of the families Cecidomyiidae, Coccinellidae, Chrysopidae, Hemerobiidae, and Syrphidae were also recovered. Most diverse were the Cecidomyiidae, with 15 different species inferred from their DNA barcodes. Additional work was performed to quantify supercooling points of L. rubidus collected from November – December 2016. These will be compared to those of other Laricobius species in a parallel study. Knowledge of this predator complex is beneficial to describing P. strobi ecology, and also with regard to potential biological control of invasive adelgids in the same region. / Ph. D. / The pine bark adelgid, Pineus strobi (Hemiptera: Adelgidae) is a native herbivore of eastern white pine, Pinus strobus (Pinales: Pinaceae), in eastern North America. It is a sedentary insect that settles on P. strobus bark, branches, and needle bases where it inserts its mouthparts to feed on the tree’s fluid nutrients. Even when P. strobi populations are dense, it does not harm the tree and is not considered a serious pest. It does, however, share its range with the invasive hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae). Predators introduced as biological control agents of A. tsugae also interact with P. strobi and its native predators, including Laricobius rubidus LeConte (Coleoptera: Derodontidae). Prior to the current study, little work had been done to document the natural history or predators of P. strobi, particularly in its southern range, both of which are relevant to the management of other invasive adelgid species found there. In the present study, the natural history of P. strobi is reported in southwestern Virginia. Patterns in the frequencies of various life stages present during the winter varied notably from those described from this species’ northern range. The number of annual generations could not be accurately measured due to the degree of overlap following two distinct spring generations. Adult body size varied seasonally and was greatest in the spring. Variation between observations from the northern and southern ranges of P. strobi indicates that its natural history can vary with the climate, which not only informs biological control efforts, but also offers insight into implication of climatic effects on the population dynamics of this and related species. This study also describes arthropod predators associated with the pine bark adelgid in forests of southwest Virginia found during a two-year survey. Physical characteristics and molecular techniques were used in identification. Species of predators found include: Laricobius rubidus (Coleoptera: Derodontidae), a native adelgid specialist, and two species from the family Chamaemyiidae, Leucopis piniperda Malloch (Diptera: Chamaemyiidae) and L. argenticollis Zetterstedt (Diptera: Chamaemyiidae), which are known adelgid specialists. Members of the families Cecidomyiidae, Coccinellidae, Chrysopidae, Hemerobiidae, and Syrphidae were also recovered. Most diverse were the Cecidomyiidae, with 15 different species genetically identified. Additional work was performed to quantify the bodily freezing points of L. rubidus collected from November – December 2016. These will be compared to those of related biological control agents in a parallel study. Knowledge of this predator complex is beneficial to describing P. strobi ecology, and also with regard to potential biological control of other invasive adelgids in the same region.

For some forest landowners in the southern USA, multiple ecological and economic objectives are met through the conversion of longleaf pine (Pinus palustris) plantations to uneven-aged stands. This study was conducted in eight similarly-aged longleaf pine plantations at The Jones Center at Ichauway in southwestern Georgia. The stands were disturbed by commercial thinning in 2014 and partially disturbed by Hurricane Michael in 2018 and half of the stands were seeded with native grasses and a forb in 2015. I developed explanatory models of groundcover biomass and longleaf pine seedling occurrence and density. I detected a community composition difference in groundcover species assemblages between seeded and unseeded stands. For recruited longleaf pine regeneration, my model indicated that lower amounts of groundcover biomass were correlated with greater occurrence and density of pine regeneration. Partial stand disturbances and restoration of native groundcover set stands on a trajectory to resemble a more natural condition.

Mountain pine beetles (Dendroctonus ponderosae) are native insects that have decimated millions of hectares of mature pine (Pinaceae) forests in western North America. The purpose of this study is to investigate biophysical and climatic correlates of Mountain Pine Beetle (MPB) insect outbreaks in the Crown of the Continent Ecosystem (CCE) from 1962 to 2014 using Aerial Detection Survey (ADS) and climate data. Specific objectives were: 1) to develop statistical models to determine how selected biophysical correlates (slope, aspect, elevation, and latitude) and 2) to understand how local and global climate variables relate to the extent of the MPB infestations in the CCE, and 3) to contextualize the results of the models with historical climate data. Overall, the major findings of this study are: 1) despite its limitations, the ADS data seems suitable for analysis of beetle damage with respect to climate and topographic factors, on a regional scale, 2) there appears to be a link between local biophysical factors and winter precipitation and TPA within the CCE, and 3) a combination of a negative-phase PDO and La Niña is important in forecasting a decline in MPB spread, during a given year. This study is the first, to our knowledge, to explore spatio-temporal patterns of MPB outbreaks using biophysical factors, and both local and global climate variables, over a fifty-year timespan in the CCE. In the future, additional geospatial analyses may enable a landscape assessment of factors contributing to variability of MPB infestation and damage as this insect continues to spread. / Master of Science / Mountain pine beetles (Dendroctonus ponderosae) are a native insect that has decimated millions of hectares of mature pine forests in western North America. The purpose of this study was to investigate, using GIS-derived variables, biophysical and climatic factors that have influenced past mountain pine beetle insect outbreaks, as evident by beetle-induced tree mortality in the Crown of the Continent Ecosystem (CCE) from 1962 to 2014. Specific objectives of this study were to determine how selected biophysical variables (slope, aspect, elevation, and latitude), regional climate variables (temperature, precipitation, and drought) and global climate oscillations (ENSO, PDO, NAO, AO, and PNA) relate to bark beetle infestations in the Crown of the Continent Ecosystem from 1962 through 2014, as measured by aerial surveyrecorded tree mortality. We sought to contextualize the results of the statistical models with historical data to further understand the relationship between increases and decreases of tree mortality by comparing these trends to geopotential height and sea-surface temperatures that may influence CCE climate. Our work revealed first, that while the aerial survey data has important limitations, overall it is a useful dataset for analyzing historical spatio-temporal patterns of insect infestations. Second, there appears to be a link between local biophysical factors, such as latitude, elevation, and winter precipitation (as opposed to global climate factors) and tree mortality within the CCE. Local climate analysis revealed the importance of winter precipitation to be the biggest influence of MPB decrease or increase along with lower geopotential heights during a decline in MPB spread over the CCE. Finally, a combination of a negative PDO and El Niño was important in forecasting a decline in MPB spread, as shown by damage, during a given year. This is the first study to use aerial survey data in a geospatial analysis incorporating biophysical variables for the US portion of the Crown of the Continent Ecosystem. Additionally, this study is unique to explore the potential relationship between global teleconnections and regional climate in the CCE area, and the spatio-temporal extent of mountain pine beetle infestations.

Cyclamens are deemed an essential cold season crop for supplementing the income of commercial growers during winter. However, cyclamens have the reputation of being a demanding commercial crop mainly due to difficulty in successful crop cultivation, lengthy production time and production costs. The economic and environmental landscape in South Africa dictates that careful consideration be given to reducing production time and costs, but still improving the quality of the commercial crop for market readiness. Growth medium are considered an important factor contributing significantly to the quality of commercially grown container cyclamens in a controlled environment. The focus of this study was on establishing the most suitable growth medium for commercially grown cyclamens in a South African environment in order to improve the quality of the commercial crop. Only one F1 variety of cyclamen was used as the sample population with a sample size of five plants per growth medium mixture planted according to a randomised block design in a specified area within a greenhouse. Seven commercially available growth medium mixtures, five locally available and two imported, were subjected to a typical production cycle of commercial cyclamens in a controlled greenhouse. The growth medium mixtures for comparison were Cyclamen Mix; 45 Mix; 50% Cyclamen Mix - 50% 45 Mix; 49 Mix; 7 Mix; coarse coir; Klasmann base 4 Substrate mix . The measuring instrument used in the study was adapted from existing instruments used in the comparison of cyclamens and growth medium. It included various measurements and observations: Plant height, plant diameter, plant weight, number of leaves, leaf width, foliage fresh weight, number of flowers, diameter of tuber and root fresh weight. The results obtained in the comparison determine the most suitable growth medium for container cyclamens for South African circumstances. The physical properties of peat retain water for a longer time which is beneficial for the production of container cyclamen. The results of this study therefore indicate that growth mediums containing peat performed better than mediums containing no peat. / Agriculture and  Animal Health / M.Sc. (Ornamental Horticulture)

High-dose verbenone, verbenone plus nonhost volatiles (NHVs), and both semiochemicals in combination with aggregant-baited funnel traps were tested for stand- level protection against mountain pine beetle attack for two consecutive years (2004-2005) at three seral high elevation whitebark pine sites in the Greater Yellowstone Ecosystem. In 2004, two 0.25-hectare treatments comprised of 25 high-dose verbenone pouches or verbenone pouches combined with single baited funnel traps were tested in a push-pull strategy. In 2005, 25 high-dose verbenone and 25 NHV pouches, or verbenone and NHV in combination with baited funnel trap clusters were tested. In both years, treatments were compared to 0.25-hectare control plots with no semiochemicals or funnel traps. The proportion of trees attacked by mountain pine beetle in treated plots was significantly reduced, when compared to control plots, at only one site treated with verbenone in 2004, and at only one site in 2005. High-dose verbenone alone, verbenone and NHVs, and both semiochemicals combined with baited funnel traps in a push-pull strategy did not consistently reduce the proportion of mountain pine beetle attacked trees relative to control plots. No covariates tested, including stand density, beetle population size, or tree size were consistently significant in explaining proportion of trees attacked.