Browsing by Author "Johnson, J.D."

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    Oak regeneration after clearcutting on steep slopes in the ridge and valley province of southwest Virginia
    Ross, Michael S. (Virginia Polytechnic Institute and State University, 1982)
    The development of oak stems of advance regeneration and stump sprout origin was studied during a two-year period following clearcutting and whole-tree removal in eight midslope stands in the Ridge and Valley Province of southwestern Virginia. Oak regeneration was also characterized in several older clearcuts. Height and diameter of oaks of stump sprout origin in the two-year-old stands was significantly greater than that of advance regeneration stems, and the difference in size among regeneration types appeared to persist into the oldest (17- and 28-year-old) stands sampled. Chestnut oak, which had been the dominant oak species in most pre-harvest stands, had higher density of advance regeneration stems, higher frequency of stump sprouting, and greater sprout production per stump than scarlet or black oak two years after harvesting. However, shoot growth of advance regeneration during the two-year period did not differ among oak species when initial stem site and vigor were accounted for taller stump sprouts in the two-year-old stands were associated with more productive sites (as indicated by site index, topographic variables, and vegetation composition), whereas biomass production per stump was less closely related to site quality. Height and diameter growth of oak advance regeneration during the two-year post-harvest period were significantly greater on sites of medium quality than OD sites of low quality. Density of well-established oak stems of advance regeneration origin two years after harvest was greatest in stands of site index 55-65 (base age 50), and fell off on sites of higher and lower quality. Models developed to predict two-year stump sprout production from characteristics of the parent tree generally explained less than 40 percent of the variation among stumps, while models describing growth of advance regeneration individuals from pre-harvest measurements accounted for as much as 82 percent of the variation. Regeneration in most of the two-year-old stands appeared adequate for restocking of oaks to at least their pre-harvest level, although stems will probably be widely spaced and mostly of stump sprout origin on both the poorest and the most productive sites.
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    Physiological response of loblolly pine seedlings to moisture-stress conditioning and their subsequent performance during water stress
    Seiler, John R. (Virginia Polytechnic Institute and State University, 1984)
    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.
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    Seed dormancy and germination of northern red oak
    Hopper, George Martin (Virginia Polytechnic Institute and State University, 1982)
    Northern red oak (Quercus rubra l.), a valuable timber in species in the eastern United States, has a delayed growth in the early years of establishment. Freshly harvested northern red oak seed exhibit dormancy that may be broken by stratification or pericarp removal. In this research, germination, seedling growth and adenylate energy metabolism of northern red oak with pericarp removed and intact was measured during stratification (5C) for two consecutive years. Two seed moisture levels (50% and 70% d.w.) during stratification were tested on intact acorns, pericarp removed seeds and acorns intact during stratification and then the pericarp removed prior to germination. Pericarp removal increased germination five-fold at harvest (from 10% to 55%), but almost half the naked seeds were still dormant. There was a deepening of dormancy during the first 4 weeks of stratification; but, stratification for 6 to 8 weeks significantly increased germination and germination rate. Etiolated seedlings grew taller and faster from acorns that had been stratified 8 to 12 weeks than from acorns with no or only 4 weeks of stratification. Significant increases in root, shoot, and axial dry weight and lengths, and root/shoot ratios were observed as early as 14 days after germination. Pericarp removal had no significant effect on seedling growth. Relative growth rates of seedlings were compared by pericarp treatment and stratification time. There were no significant differences in germination or seedling growth between 50% and 70% seed moisture content. Adenylate (ATP, ADP, AMP) levels were measured using the luciferin-luciferase assay). Energy charge (EC) increased during stratification at 2 weeks when germination was low. Thereafter EC decreased before increasing at 8 weeks of stratification. This second rise in EC was concurrent with an increase in germinability. ATP concentrations during the 28 day growth time appeared to be associated with surges in relative growth rates of roots and shoots.