In terms of production forestry, more often than not any species that is not the crop species is considered a competitor as they are using finite growing resources that would otherwise be available to the crop species. With specific regard to Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) production in the Pacific Northwest, this study evaluated an array of morphological and physiological plant attributes to discern the relative competitive abilities of several common forest species and planted Douglas-fir in western Oregon during the first year of plantation establishment in the presence and absence of vegetation management treatments. The competitive ability of a species refers to the morphological and physiological characteristics associated with resource acquisition and internal allocation; a concept lacking a specific metric for evaluation. A conceptual model of plant resource utilization including proxy metrics for key aboveground plant-environment interactions was used a framework for synthetic assessment of species relative competitive ability. The relative competitive abilities of species were evaluated over a summer growing season with assessments of saturated specific leaf area (SLA[subscript SAT]) and saturated leaf dry matter content (LDMC[subscript SAT]), diurnal and seasonal leaf-level gas exchange (net photosynthesis (P[subscript n]), stomatal conductance (G[subscript s]), and derived instantaneous water-use efficiency (WUE)), midday leaf xylem pressure potential (��[subscript md]), aboveground proportional allocation of biomass into stem, leaf, and reproductive body components, leaf area index (LAI), and morphological development and growth (height, crown radius, and diameter and bud density for Douglas-fir). The study employed a complete randomized block design (RCBD) with four replicates (blocks) and three vegetation management treatment regimes: untreated control (C), site preparation only (SP), and site preparation with a spring and summer release (SP+R). The relative competitive ability of all species was evaluated in the C, whereas only dominant competitor species remained for evaluation in the SP treatment. Vegetation treatment effects were evaluated among remaining competitor species and Douglas-fir in the C and SP treatments, whereas the response of Douglas-fir was assessed across all three vegetation management treatments (C, SP, SP+R). Selected forest competitor species included two woody perennial shrubs, two ferns, one herbaceous dicot, and two herbaceous graminoid species: trailing blackberry (Rubus ursinus Cham. & Schlecht), snowberry (Symphoricarpos albus (L.) Blake), swordfern (Polystichum munitum (Kaulfuss) K. Presl), bracken fern (Pteridium aquilinum (L.) Kuhn), woodland groundsel (Senecio sylvaticus L.), California brome (Bromus carinatus Hook. & Arn.), and false brome (Brachypodium sylvaticum (Huds.) Beauv). Forest competitor species evaluated in the SP treatment were limited to trailing blackberry, swordfern, woodland groundsel, and California brome. Species relative competitive ability varied dramatically. However, similarities related to herbaceous and woody life forms were observed. Based on both univariate and multivariate response variable analyses, the relative competitive abilities of species examined in the study were ranked as follows: woodland groundsel > false brome > California brome > trailing blackberry = bracken fern > snowberry > swordfern > Douglas-fir. Although vegetation treatments effectively reduced total cover below 20%, a threshold of putative importance, with observed effects on soil moisture content and species performance, species relative competitive ability remained unchanged. Physiological responses were more variable than morphological responses for species performance and expressed greater sensitivity to vegetation treatment. Vegetation treatment effects were most pronounced for Douglas-fir in the SP+R treatment where mean total cover was 6.5%. In the SP+R treatment Douglas-fir exhibited decreased moisture stress coupled with significant increases in both diurnal and seasonal P[subscript n] and G[subscript s] rates and patterns. / Graduation date: 2013

I conducted field studies to determine the effect of insect herbivory and intraspecific plant competition on ragwort Senecio jacobaea. The objectives were to determine the patterns and causes in the distribution of the ragwort flea beetle Longitarsus jacobaeae foraging among varying densities of ragwort, to measure the behavioral and numerical responses of the beetle to changes in ragwort density, and to estimate the impact of insect herbivory and intraspecific competition on ragwort performance. Host density was manipulated by planting 1, 4, 8, or 16 plants per 0.5 x 0.5 m patch. Beetles were counted in each patch to assess the effect of host density on the beetle population. I measured four components of reproductive success represented by growth rate, development rate, reproduction, and annual survivorship to assess the effect of herbivory and intraspecific plant competition on ragwort performance In the first experiment, beetle populations were manipulated by establishing equal numbers of beetles in patches with unequal number of hosts (1, 4, 8, 16 plants per patch), which were then subsequently allowed to move freely about. Beetles rapidly re-distributed themselves, such that the number of beetles was strongly and positively correlated with the number of hosts. This indicates that ragwort flea beetles are highly sensitive to local distribution of their food plants. In the second experiment, host density was manipulated by planting ragwort in densities of 1, 4, 8, 16 plants per patch, and beetles were then allowed to colonize the experimental patches. Beetle behavioral response to a change in host density was dependent on host population size: the numbers of colonizing beetles increased asymptotically with increasing plant density. The number of beetle-days ranged from 261 for 1-plant patches to 1822 for 16-plant patches. In contrast, the numerical response (represented as observed multiplication rate per capita per generation per year) appears to be inexplicably low in the single plant population and levels off in the 4, 8, and 16 plant patches (grand mean for multiplication rate 1 was 5 and for multiplication rate 2 was 10.4 progeny per individual per generation). Combining these results, the beetles apparently respond to spatial variation in the density of hosts primarily by changes in their movement behavior rather than by changes in their per capita reproductive rates. These results highlight the importance of a natural enemy's colonizing behavior for controlling a sudden upsurge in pest abundance. Both insect herbivory and intraspecific competition had an effect on ragwort performance. For example, over approximately one year, ragwort's rate of biomass accumulation was 48% lower, and seed-head production was 18% lower in exposed compared to protected plots, while intraspecific competition reduced ragwort's rate of biomass accumulation and seed-head production, such that a 16-fold increase in host density (in protected patches) led to a 12-fold decrease in biomass per plant and a 11-fold decrease in the number of seed-heads per plant. Herbivore effects were independent of host density: variation in plant density from 1 to 16 plants led to no detectable change in magnitude of the herbivore effect. This suggests there is no density-dependent refuge for host plants operating at these local scales of observation. Keywords: Host density effects, behavioral response, reproductive response, biological control agent, Longitarsus jacobaeae, Senecio jacobaea. / Graduation date: 1995

Graduation date: 1993

Graduation date: 1994

Thesis (Ed.D.)--University of West Florida, 2007. / Title from title page of source document. Document formatted into pages; contains 252 pages. Includes bibliographical references.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 147-166). Also available via the Internet.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 2002. / Title from PDF t.p. (viewed on Dec. 10, 2005). Vita. Includes bibliographical references (p. 70-78).

Thesis (M. Sc.)--University of Stellenbosch, 2008. / Includes bibliographical references. Also available via the Internet.

Thesis (Ph. D.)--Oregon State University, 1997. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 1990. / Typescript (photocopy). Includes bibliographical references (leaves 88-92). Also available on the World Wide Web.