Browsing by Author "Johnson, W. Carter"

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    Altered hydrology of the Missouri River and its effects on floodplain forest ecosystems
    Johnson, W. Carter; Reily, Peggy Weaks, 1953-; Andrews, L. Scott; McLellan, James F. (Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University, 1982)
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    Ecological and taxonomic studies of the Russulaceae and other ectomycorrhizal Basidiomycetes in the high-elevation forests of the southern Appalachians
    Bills, Gerald F. (Virginia Polytechnic Institute and State University, 1985)
    Temperate and boreal fungal floras indicate that species of the Russulaceae (the genera Russula andLactarius) are among the dominant ectomycorrhizal fungi in forest communities. The contribution of the Russulaceae to the communities of ectomycorrhizal Basidiomycetes fruiting in red spruce and adjacent northern hardwood forests in West Virginia was evaluated and compared with other ectomycorrhizal Basidiomycetes occupying the same habitats. The Russulaceae exhibited the greatest species diversity of any family of ectomycorrhizal fungi fruiting in the stands studied (44% of the species in spruce, 39% of the species in hardwoods). Species of Lactarius and Russula were among the most productive in both forests. Species diversity, productivity, and fruiting phenology of all ectomycorrhizal Basidiomycetes were compared between red spruce and northern hardwood stands for a 3-year period. Sporocarp numbers and sporocarp frequency in 384 four m² quadrats in each forest type was used to estimate productivity. Species richness was greater in hardwoods (36 species) than in spruce (27 species). Nine species were common to both forests. Most productivity was concentrated in a few species, while most species were rare. Species-area curves were constructed for both forests. Fungal species and tree species composition in both forests were compared by principal component analysis. Fungi in spruce forests were more productive than in hardwood forests. Productivity was highly variable among the three seasons studied because of climatic variability. Sporocarp abundance and frequency were positively correlated with basal area and density of mycorrhizal trees and were negatively correlated with fern cover in hardwood forests. Fruiting seasons extended from early July to late September or early October. Numbers of species fruiting from the same four m² quadrats ranged from 0 to 7 in spruce forests and 0 to 5 in hardwood forests. Spatial patterns of sporocarps of major species were characterized by the variance-to-mean ratio, mean crowding, patchiness, and spatial autocorrelation and were found to exhibit highly aggregated, contagious patterns. Interspecific associations between pairs of major species were measured by 2 x 2 contingency tables and Cole's index of association. A taxonomie and geographic survey of Russula and Lactarius in both the quantitative study areas and in similar habitats in the Southern Appalachians was presented.
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    Ecology of mule deer on the Pinon Canyon Maneuver Site, Colorado
    Gerlach, Thomas P. (Virginia Tech, 1987-01-15)
    Mule deer (Odocoileus hemionus) population dynamics, movements, and habitat use were studied on the Pinon Canyon Maneuver Site in southeastern Colorado during January 1983-December 1984. Thirty-eight adults and 28 fawns were radio collared, and 35 adults were color collared or ear tagged. Population estimates were 365 and 370 deer for 1983 and 1984, respectively. The sex ratio (yearling and adult) was 60 males: 100 females. Adult female pregnancy rate was 95%; the mean litter size for females over 1.5 years was 1.7 fawns. Annual fawn survival was 29% in 1983 and 22% in 1984. Coyote (Canis Iatram) predation was responsible for 76% of fawn mortality. Adult survival was 88% in 1983 and 87% in 1984; coyote predation accounted for 67%, and hunting for 33% of the annual adult mortality. The calculated annual rate of increase (λ) was 1.01, indicating a stable population. Seasonal home range size differed (p < 0.05) between males and females only in the fall. Females preferred pinyon-juniper woodland in all seasons, and shrub grassland in winter, summer and fall; proportional use of woodland/open grassland and shrub/open grassland edge was greater than proportional availability. Males preferred pinyon-juniper woodland and avoided open grassland in all seasons. Fawns preferred shrub grassland and shrub/open grassland edge; they avoided cholla/open grassland edge. Fawns selected bed sites with greater (P < 0.05) concealment cover at all 0.5 m intervals up to 2 m in height, and greater ground cover of trees, shrubs, and grasses (P < 0.01) than random sites.
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    The effect of hydroperiod on seed banks in semi-permanent prairie wetlands
    Poiani, Karen A. (Virginia Tech, 1987-06-05)
    In 1985, 24 bottom samples were collected in each of two slightly brackish,semi-permanent prairie wetlands (P1 and P4) with different hydroperiods. The main objective was to determine if hydroperiod affected seed pool characteristics. Additionally, 48 samples were collected in 1986 from wetland P1 to determine if seed bank composition changed annually without a change in mature vegetation. Seed bank composition was determined by placing soil samples in a greenhouse, then counting and identifying emerged seedlings. As a check against the seedling emergence method, seeds were separated and identified microscopically in one-third of the 1985 samples. Results indicated that the emergence method was an accurate technique for assessing seed pool composition. The wetlands did not differ in floristic composition (i.e., presence/absence) but did in species densities. The mean relative density of mudflat annuals in all seed pool samples was significantly greater in wetland P4 (82%) than in P1 (52%). A shorter hydroperiod in this wetland produces more frequent drawdowns and a greater input of mudflat annual seeds. Conversely, seeds of emergent species were more abundant in the seed bank of wetland Pl (48%) compared to P4 (17%). The former wetland has a longer hydroperiod and less frequent drawdowns, and thus, the primary seed input is from emergent plants.
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    Environmental determinism and forest structure and composition: a naturally replicated experiment
    Schiffman, Paula M. (Virginia Tech, 1990)
    Ecological theory states that forest succession is largely environmentally determined. Many investigators have suggested, however, that stochastic processes can frequently alter successional pathways. In particular, the colonization phase is thought to be very stochastic. This study utilizes a unique series of 6 naturally replicated sites on Brush Mountain (Montgomery Co., VA) to determine whether forest structure and species composition is primarily deterministic or stochastic in nature. Although the canopy stratum of the mature forest at these environmentally similar sites was very Similar in structure and species composition (p>0.05), the composition of the subcanopy strata vegetation differed Significantly among sites (p<0.05). This indicated that stochastic events (e.g. low intensity ground fires, deer browsing, cattle grazing) were were important factors during the development of understory and ground layer vegetation. Site-to-site differences in subcanopy species composition remained apparent during the first 2 years following disturbance (removal of canopy cover) of 4 sites. Brush Mountain lacked a significant seed bank (< 1 seed/m²), and the dominant sub canopy species reproduced largely by vegetative sprouting. Post-disturbance colonization of the sites was very stochastic, but had relatively little immediate effect on vegetation structure and composition. In the future, however, as colonist species reproduce and increase in density, stochastic colonization events may become an important aspect of forest development at some of the sites.
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    The influence of water and light on the physiology and spatial distributions of three shrubs in the Southern Appalachian Mountains
    Lipscomb, Mary Virginia (Virginia Tech, 1986-06-11)
    In order to understand vegetational gradients which develop in response to environmental gradients, the physiological capabilities of each species must be examined in relation to the observed environmental gradient. The distributions of three temperate zone shrub species which occupy different positions on the spur ridges of Brush Mountain may be influenced by their tolerances to light and moisture. Greenhouse studies indicate that R. maximum has a 60 % reduction in photosynthesis at water potentials below -1.0 MPa. R. nudiflorum has only a 30 % reduction and K. latifolia has less than 10 % reduction. Seasonal pressure volume curve determinations, conductance measurements, and water potential measurements of plants in the natural environment indicated that photosynthesis is not affected by water potential in K. latifolia. R. maximum has a significant reduction in conductance during drought which may limit photosynthesis. R. nudiflorum appears to begin senescence prior to severe drought in this area. Greenhouse experiments of adaptability to increasing light intensity show that K. latifolia and R. nudiflorum can significantly increase their light saturation point and maximum rate of photosynthesis in high light environments. R. maximum does not increase its photosynthesis rate in high light environments and appears to undergo chloroplast degradation when grown in high irradiance. Gradient analysis of vegetation on Brush Mountain shows that R. maximum reaches its highest importance in low light, high moisture sites. K. latifolia is most important in low moisture, high irradiance sites. R. nudiflorum is infrequent in the study area but occurs mostly in moderate moisture and irradiance sites. The distributions of R. maximum and K. latifolia appear to match their experimentally determined physiological tolerances. The results for R. nudiflorum are inconclusive.
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    Interspecific competition in young loblolly pine plantations on the Virginia Piedmont
    Bacon, Catherine G. (Virginia Polytechnic Institute and State University, 1986)
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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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    Population ecology of Pinus pungens in pine-oak forests of southwestern Virginia
    Williams, Charles Edward (Virginia Polytechnic Institute and State University, 1989)
    I studied aspects of the population ecology of table mountain pine, Pinus pungens, in pine-oak forests on Brush Mountain, Montgomery County, Virginia. The objective of this study was to examine the age structure and recruitment dynamics of P. pungens, a fire-adapted conifer, and to determine whether P. pungens populations would persist in the absence of fire. The age distributions of P. pungens on the Brush Mountain study sites were bimodal, with peaks in seedling and canopy age classes and a major trough in the sapling and understory age classes. Age and diameter of P. pungens understory and canopy trees were positively related, but diameter was a poor predictor of age. The sparse representation of P. pungens in the seedling, sapling, and understory strata of the Brush Mountain sites strongly indicates that under current disturbance regimes, maintenance of P. pungens populations is unlikely. The prevalence of oak advance regeneration ard other gap-exploiting woody species such as ard Sassafras albidum and Nyssa sylvatica suggests that gap replacement processes would favor these species and not P. pungens Recruitment of P. pungens was not limited by seedfall from serotinous cones or from seed predation by animals. Seedfall occurred throughout the year at low levels and was concentrated in the spring and summer months. The unavailability of seedling habitat strongly limited recruitment of P. pungens seedlings. Litter depth and type were important determinants of P. pungens seedling habitat; seedlings occurred almost exclusively in shallow pine litter. There was little overlap between the distributions of habitat variables for seedlings and random points in the forest, indicating that suitable seedling habitat was rare. Summer drought and substrate were important factors influencing the establishment and survivorship of seedlings. Greenhouse studies were conducted to determine the influence of leaf litter and water regime on early establishment of P. Pungens. Emergence of seedlings was consistently highest in pine litter and lowest in hardwood litter at all water regimes and in litter-free treatments at low watering intervals. Survival of seedlings was enhanced by litter at low water regimes. Significant litter/water interactions indicated that the effects of litter and water regime were not independent; litter significantly decreased the loss of soil moisture from experimental treatments. Evidence suggests that depression of P. pungens seedling emergence in hardwood litter was due to physical-mechanical effects.
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    Response of semi-permanent prairie wetland to climate change: a spatial simulation model
    Poiani, Karen A. (Virginia Tech, 1990)
    The objective of this research was to assess the potential effects of global warming on the hydrology and vegetation in semi-permanent wetlands located in the glaciated prairie region of North Dakota. As a means to that objective, a spatially-defined simulation model of the vegetation dynamics in these wetlands was constructed. A hydrologic component of the model estimated water levels based on precipitation, runoff, potential evaporation and transpiration. Amount and distribution of emergent cover and open water were modeled using a geographical information system. Vegetation response to changes in water level was based on seed bank composition, seedling recruitment, establishment and plant survivorship. Simulation results were compared to actual distributions from aerial photographs (1979-89). Results showed that the model was relatively good at calculating changes in water level for average years. Late-summer water levels were overestimated during dry years due to limitations in the Thornthwaite method of calculating potential evapotranspiration. In general, changes in the ratio of emergent cover to open water were accurately simulated. Tests of the model elucidated two areas that needed improvement. First, seedlings germinated too quickly on exposed mudflats in the model when drawdown occurred late in the season. The actual wetland had a thick mat of dried, submergent vegetation on top of the mudflats which impeded germination, which the model did not consider. Second, model conversions between open water and deep marsh vegetation were not always timed correctly. If water depth crossed a threshold value for a given period of time a cell would change its type. In reality, tolerance of emergents to deep water is more complex. A probability function with respect to time and water depth rather than a threshold value would better represent this relationship. The model was used to assess the potential effects of global warming on the cover cycle in one wetland. An 11-year simulation was run using a normal versus greenhouse climate. Although water level fluctuations still occurred, peak values were significantly lower in the warming scenario and the wetland dried in most years. Simulations also revealed a significant change in the vegetation, from a nearly balanced cover ratio to a completely closed basin with no open water areas.
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    Vegetational change resulting from forest conversion in the central Piedmont of Virginia and their implications for wildlife
    Felix, Antone Costa (Virginia Tech, 1981-05-15)
    Conversion of natural forest to loblolly pine plantations has become a common practice on commercial forest land in the central Piedmont of Virginia. To gain insight as to bow habitat conditions for wildlife vary over time, vegetation composition and structure were quantified in 21 converted stands at two state forests. The stands represented three replications of seven developmental stages ranging in age from 1 to 22 years. Six natural forest stands Which typify sites presently being converted were selected for comparison. The seral process can be exemplified by comparing vegetative changes in species richness, evenness, and vegetative coverage in the ground stratum (<1m). Richness and vegetative coverage showed the same trends: high values in stands 1 to 5 years of age followed by a decline from 5 to 15 years, at Which point canopy closure was complete and these variables were relatively stable for the next seven years. Evenness over time was fairly constant, except for three-rear-old stands where a decline occurred due to predominance by Andropogon virginicus. Trends in richness and evenness differed from the old-field successional model due to a diverse reservoir of propagative units at the initiation of succession and the rapid closure of the canopy by co-developing pines and sprout hardwoods. From an analysis of habitat variables, it appeared that one-year-old stands satisfied requirements of bobwhite quail and wild turkey; stands aged three years were deficient in food plants and probably too densely vegetated. Nine-year-old stands still provided browse for white-tailed deer. Post-canopy closure stands (15 to 22 yrs) were of little value to wildlife. In native forest stands (72 yrs), understory forage production was comparable to the post-canopy closure stands, while mast production, as estimated by Oak basal area and density, was more than adequate for good deer and turkey habitat. The present value of converted stands to wildlife depends on their size and interspersion with native forest and other cover types. Their future value could vary significantly depending on the silvicultural treatments applied.