Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii), a keystone species in western Washington, faces threats on plantations across this region from the invasive species Scotch broom (Cytisus scoparius (L.) Link), whose invasions on recently established stands can lead to mortality of Douglas-fir through overtopping. The susceptibility of sites to Scotch broom achieving dominance over Douglas-fir has been demonstrated as highly site dependent, however the site conditions that cause this have not yet been identified. Scotch broom has a demonstrated average maximum height of 3m, thus, after Douglas-fir exceeds this height, its risk of being overtopped is significantly reduced. This thesis strives to identify sites that were at the greatest risk Douglas-fir being overtopped by Scotch broom by first, identifying what factors improved growth of Douglas-fir during the period when they are at the greatest risk, and second, identifying factors that led to Douglas-fir outcompeting Scotch broom on sites they cohabitated. In Chapter 1, we utilized LiDAR scans, Soil Survey Geographic Database characteristics, and management histories to identify conditions that improved growth for Douglas-fir in ages 3-8. Individual tree detection was used to measure Douglas-fir heights, and a correction algorithm for LiDAR measured young Douglas-fir heights was established from field validation data. We identified that young Douglas-fir had improved growth on sites with lower elevation, flatter slopes, and finer textured soils. The factors identified were then transformed into four potential site index models based on mean stand elevation class, Mean stand elevation class and clay class, textural class and slope class, and textural class and Mean stand elevation class. In Chapter 2, we used paired field plots to examine Douglas-fir and Scotch broom competition on 19 sites across western Washington. Each site had 2 plots with only Douglas-fir and 2 plots with Douglas-fir and Scotch broom. Elevation, soil texture, and soil nutrient composition for carbon, nitrogen and available phosphorous were examined for influence on height and growth rate of both species. We identified that Scotch broom presence was negatively related to Douglas-fir height growth and that sites with either higher percentages of silt, lower concentrations of phosphorous, or higher percentages of Carbon were more likely to have growth patterns close to or exceeding Scotch broom. / Master of Science / Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) is a valuable timber species across western Washington that is commonly grown in plantations. In western Washington when Douglas-fir are planted on a site they often face competition from the invasive shrub Scotch broom (Cytisus scoparius (L.) Link). When Scotch broom invasions occur on a recently planted Douglas-fir stands, they can cause death of the trees if Scotch broom plants grow taller than the young Douglas-fir and obstruct their access to light, a process called overtopping. The risk of Douglas-fir being overtopped has been shown to be dependent on location, however what causes a location to be at risk of overtopping is yet unknown. Scotch broom has a demonstrated average maximum height of 3m, thus, after Douglas-fir exceeds this height, its risk of being overtopped is significantly reduced. This study aims to identify sites that were at the greatest risk Douglas-fir being overtopped by Scotch broom by first, identifying what sites generate the best Douglas-fir growth when they are young and at risk of being overtopped, and second, identifying site characteristics led to Scotch broom growing faster than Douglas-fir on sites they both occur on. To identify sites that produced greater young Douglas-fir height growth we used publicly available soil data from the Soil Survey Geographic Database and company management histories to predict tree heights measured through aerial laser scanning (LiDAR). We found that sites with soil textures that had higher percentages of smaller particles, were on lower elevations, and had gentler hillslopes could all produce greater Douglas-fir height growth. When attempting to identify what causes Douglas-fir to be at risk of being overtopped by Scotch broom we used plots with and without Scotch broom on a variety of field sites. This allowed us to not only identify which characteristics of sites where Douglas-fir was being outgrown by Scotch broom, but also identify if Scotch broom was changing how Douglas-fir grew. We found that reductions in Douglas-fir growth were related to Scotch broom being present and that increases in soil silt percentages, decreases in soil phosphorus concentrations, and increases in soil carbon percentages were related to Douglas-fir having height growth closer to or exceeding that of scotch broom.

Pseudotsuga menziesii, naturalized conifer from the North America, has been planted in the area of the present-day České Švýcarsko National Park (Czech Republic) from 19th century. These surveys concentrate on the question of environmental preferences of seedlings and saplings of Pseudotsuga, and characterize potential distance distribution of this tree. In conclusion, Pseudotsuga is still only naturalized species, but danger of becoming to be invasive is very high.

Almost all conifer ovules produce a liquid secretion as part of reproduction. This secretion, termed an ovular secretion, is produced during ovule receptivity and is involved in pollen capture and transport. Historically, examinations of the ovular secretion have focused on how they are part of pollination mechanisms. As a result, the chemical composition of the ovular secretion has not been examined systematically. Investigations into the constituents of the ovular secretion were limited to analyses for simple water soluble compounds such as sugars, minerals, amino acids and organic acids. More recently, the protein component of the secretion has been investigated using mass spectrometry-based proteomics. Proteins involved in processes such as carbohydrate modification, proteolysis, and defence have been identified in conifer ovular secretions. This biochemical complexity suggests a broader view of the function of the ovular secretion is warranted. However, protein identifications only provide putative information on function. Functional characterization of these proteins is needed in order to fully understand how they contribute to ovular secretion function. The research outlined in this dissertation describes the first functional characterizations of proteins found in conifer ovular secretions. Three proteins - invertase, chitinase, and thaumatin-like protein - were characterized in the ovular secretions of Douglas-fir (Pseudotsuga menziesii) and hybrid yew (Taxus × media). The Douglas-fir ovular secretion is capable of converting sucrose to glucose and fructose, confirming that invertases present in the secretion are functional. The invertase activity was maximal at pH 4.0. Activity was 77% of maximal at pH 4.5, the physiological pH. This indicates that post-secretory hydrolysis of sucrose occurs in situ in the Douglas-fir ovular secretion. Invertases in the ovular secretion are likely involved in controlling the movement of carbohydrates to developing pollen and could facilitate pollen selection. Chitinases present in the Douglas-fir ovular secretion are functional at physiological conditions. All three modes of chitinolytic activity, i.e. endochitinase, chitobiosidase and β-N-acetylglucosaminidase, were detected at physiological pH. β-N-acetylglucosaminidase activity was 80 % of maximal at physiological pH. Chitinases are pathogenesis-related proteins capable of hydrolysing chitin in fungal cell walls. These results suggest the ovular secretion is capable of defending the ovule against infection by phytopathogens. Thaumatin-like protein was immunolocalized to the cell wall and amyloplasts in Douglas-fir and yew nucellar tissue in a pattern consistent with a defensive role. It was also localized to the cell wall of fungal spores and germinating hyphae that were present in the micropyle of a yew ovule. These results provide additional evidence for an antifungal role for the ovular secretion. Functioning enzymes involved in pollen-ovule interactions and ovule defence are present in the conifer ovular secretion. The ovular secretion has functions beyond pollen capture. A revised functional model for the conifer ovular secretion is proposed. / Graduate / 2021-08-17

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The western spruce budworm (Choristoneura occidentalis Freeman) is the most widespread and destructive defoliator of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests in British Columbia. Over the past two decades, western spruce budworm outbreaks have been sustained and widespread in the interior of British Columbia, leaving the forest industry and many forest-dependent communities increasingly vulnerable to the economic consequences of these outbreaks. While a great deal is known about the impact of western spruce budworm outbreaks on tree growth and form, substantial knowledge gaps remain as to the historic variability of western spruce budworm outbreaks and the consequences of defoliation on fundamental characteristics such as wood structure. This research focused on describing historic and contemporary western spruce budworm outbreaks across multiple spatial and temporal scales in south-central British Columbia using dendrochronology and wood anatomy techniques. Outbreak histories over the past 435 years were reconstructed using a network of tree-ring chronologies from central British Columbia, revealing that 12 western spruce budworm outbreaks have occurred since the early 1600s, with a mean return interval of 30 years. Further, the research illustrates that outbreaks observed over the last 40 years are not unprecedented, which does not support the perception that western spruce budworm is moving northward into central British Columbia. To evaluate the effects of a single western spruce budworm outbreak on the anatomical characteristics of Douglas-fir stemwood, tree ring data was collected from permanent sample plots that sustained both periodic and chronic western spruce budworm feeding. In mature even-aged stands of Douglas-fir, a documented outbreak occurred from 1976 to 1980 in the coastal transition zone of southern British Columbia. Based on microscopic wood anatomical measurements it was shown that the tree rings formed during this outbreak had significantly lower percentages of latewood, reduced mean cell wall thickness and smaller radial cell diameters relative to wood formed during periods without budworm feeding. Western spruce budworm defoliation temporarily modified cellular characteristics, which has implications for wood quality. In uneven-aged stands of mature Douglas-fir, located in the xeric southern interior of British Columbia, there has been a sustained western spruce budworm outbreak since 1997. Tree rings formed during this outbreak had progressively larger earlywood lumen area and radial cell diameter, reduced latewood cell wall thickness, latewood radial cell diameters, and lower percent latewood. Mixed-effects models revealed that climatic variables, defoliation severity, defoliation duration, and in limited cases canopy class were the best predictors of xylem features. The severity and duration of western spruce budworm defoliation, as well as site factors that influence moisture conditions effect the degree and direction of anatomical changes in the stemwood of Douglas-fir. This research fills a number of knowledge gaps by providing insights into the temporal and spatial dynamics of western spruce budworm outbreaks in central British Columbia over multiple centuries, and the plasticity of anatomical features in the stemwood of Douglas-fir during discrete western spruce budworm outbreaks. These research findings suggest that Douglas-fir forests are resilient to western spruce budworm outbreaks over space and time. / Graduate