Cottonwoods (Populus sp.) and willows (Salix sp.) are generally limited to riparian landscapes in semi-arid regions of western North America. Water availability is a major determining factor for the establishment, growth and survival of these plants. Willows generally occur closer to the stream and at lower elevations than cottonwoods, suggesting reduced drought tolerance and increased flood tolerance. In the present thesis project, three related studies were conducted to investigate this hypothesis. Firstly, tolerable rates of water table decline and the impacts of the corresponding drought stress were investigated by growing cottonwoods and willows under water table decline rates from 0 to 12 cm/d. Willow saplings responded similarly to cottonwood saplings, but willow seedlings were more vulnerable than cottonwood seedlings to rapid rates of water table decline. In the second study, will saplings tolerated elevated water tables of 0 to 7.5 cm below substrate surface and the resulting flood stress for 152 days slightly better than cottonwood saplings. Finally, mature cottonwoods along Willow Creek, Alberta experienced water table decline from 1996 to 1998 due to water pumping in a nearby gravel pit; the water table recovered in 1999. The cottownwoods displayed physiological changes indicating drought stress in 1998 and recovered following restoration of the water table. This confirmed the cottonwoods' reliance on the water table as their primary moisture source. These studies indicate that the spatial separation of willows and cottonwoods may be particularly related to reduced drought tolerance of willows and these display only slightly increased flood tolerance of willos and these display only slightly increased flood tolerances. The studies confirm that both willows and cottonwoods are physiologically dependent on a sufficient riparian water table. / 85 leaves : ill. ; 28 cm.

Revegetation of riparian tree species along the lower Colorado River is currently a major activity for federal and state agencies. Revegetation methods for Fremont cottonwood (Populus fremontii), Goodding's willow (Salix gooddingii), and coyote willow (S. exigua) have historically consisted of cutting collection and vegetative propagation. If direct seeding could be implemented, large cost-savings could be realized while enhancing restoration results due to increased genetic and structural diversity. The following documents laboratory, greenhouse, and field studies conducted to establish seed storage practices, irrigation techniques, and seeding methods and rates which maximize germination and growth rates of these riparian tree species. Experimental seed storage study results indicated that seed viability was maintained for at least a two-year window by freezing, during which seed can be utilized for direct seeding or seedling production. Greenhouse study results include: (1) seed cleaning resulted in higher tree establishment; (2) adverse soil conditions reduced growth rates; (3) organic fertilizer amendment mitigated negative effects of sandy soil for Fremont cottonwood but not for willow; (4) mixed seeding resulted in cottonwood dominance, indicating that reduced rates or separate seeding of this species might be required to improve success of willow species seeding. Small-scale field study results include the following: (1) Fremont cottonwood establishment averaged 7% of pure live seed rates, whereas willow species establishment was less than 1%; (2) sprinkler irrigation did not affect establishment, and decreased tree growth rates; (3) hydroseeding resulted in higher canopy cover, establishment, and above-ground biomass compared to broadcast seeding for all three species; (4) furrow or border irrigation did not affect Fremont cottonwood or coyote willow establishment, but furrow irrigation resulted in higher Goodding's willow establishment. Volunteer species were abundant, with grasses dominating cover and biomass after one growing season despite application of grass specific herbicide. Saltcedar (Tamarix ramosissima) also established in abundance, but grew slower than Fremont cottonwood during the first growing season. Monitoring after three growing seasons indicated higher growth rates and survival of Fremont cottonwood compared to volunteer species. Larger-scale seeding studies are required to refine establishment rates and determine the cost-effectiveness of direct seeding for large-scale Salicaceae species revegetation.

Graduation date: 1997

Thesis (Ph. D.)--University of Canterbury, 2008. / Typescript (photocopy). Includes bibliographical references (p. 172-194). Also available via the World Wide Web.

Thesis (Ph. D.)--Oregon State University, 1999. / Typescript (photocopy). Includes bibliographical references (leaves 101-118). Also available on the World Wide Web.

Thesis (Ph.D.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (May 1, 2007) Vita. Includes bibliographical references.

Ramets of 14 clones of western black cottonwood Populus trichocarpa Torr. & Gray collected from the interior and coast of British Columbia were tested in the nursery for their growth performance after infection by the leaf rust Melampsora occidentalis Jacks. Linear relationships were demonstrated between various growth parameters (total dry weight, stem dry weight, root dry weight, volume, diameter and height) and disease severity rated as diseased leaf-weeks divided by total leaf-weeks. Losses due to rust infection included reduced total dry weight and volume growth in the year of heavy disease, the death of severely infected ramets during the following winter and reduced initial volume increment in the following growing season. The percentage reduction in yield (total dry weight) was greater than the cumulative percent leaf area infected, suggesting that the rust infected leaf parts act as sinks for photosynthate. The normal pattern of photosynthate allocation was altered in favour of the top growth of ramets. Ratios of stem/root dry weight increased rapidly as disease level increased. A threshold infection level, below which no loss occurred, was not detected in this pathosystem. Significant variation in rust resistance of black cottonwood clones was detected both within and between the two geographic areas. Clones from the coast or warm, moist areas were, on average, more resistant than clones from the interior or cold, dry climates. The phenomenon of induced resistance was not detected at either the local or the systemic levels in black cottonwood challenged by the rust. Variation in rust tolerance among black cottonwood clones was demonstrated. Rust tolerance was defined as the slope of the relationship between yield of ramets (expressed as a proportion of controls) and disease severity (expressed as the proportion of the total number of leaf-weeks infected). A negative correlation between rust tolerance and rust resistance was found. In the collection of clones tested, the positive effect of disease resistance on the growth of cottonwood clones was partially counterbalanced by the negative effect of reduced tolerance on the growth. The importance of this relationship in both natural and artificial selection of superior trees against disease is indicated. / Forestry, Faculty of / Graduate

The anatomical properties of loblolly pine (Pinus taeda L.) and cottonwood (Populus deltoides Barto ex. Marsh.), both from intensively managed woodlands, were quantitatively characterized using the principles of stereology. Physical and mechanical properties were also determined for each growth increment of six sample trees of both species. Anatomical parameters measured were correlated to certain mechanical properties. The numerical values obtained for the anatomical properties were derived from simple counting measurements. They included size distribution parameters of individual anatomical elements as viewed on transverse sections. The parameters were determined both in terms of within growth ring variability and in terms of changes from pith to bark within the species studied. Average mechanical properties of the two species were shown to increase significantly from pith to bark. In the regression models constructed for predicting physical and mechanical properties, up to three anatomical variables were found to significantly account for the variation in the strength properties. Close to 87% of the variation in MOR and 86% in MOE could be accounted for by the three anatomical parameters in loblolly pine. About 82% of the variation in the crushing strength parallel to grain could be explained by the anatomical variables. The three anatomical parameters selected for predicting strength properties in cottonwood were all related to fibers, suggesting that the most important anatomical elements determining strength in cottonwood are the fibers. Overall predictability in cottonwood was not as good as in loblolly pine. Less than 40% of the variation in MOR could be explained by fiber properties alone, while almost 70% in MOE was accounted for. Over 55% of the variation in maximum compression strength parallel to grain could be explained by fiber properties alone. About 84 to 94% of the variation in specific strength properties was accounted for by three anatomical variables unrelated to specific gravity in loblolly pine. Addition of specific gravity improved the model with R² values between 92-97%. In cottonwood, 65-85% of variation in specific strength properties was accounted for by three anatomical variables unrelated to specific gravity. The R² values also improved by addition of specific gravity (82-92%). / Ph. D.

Thesis (Ph. D.)--Mississippi State University. Department of Entomology and Plant Pathology. / Title from title screen. Includes bibliographical references.

This study was designed to investigate the relationships between spectral properties of cottonwood plantations and defoliation by the cottonwood leaf beetle (CLB), Chrysomela scripta F., as well as to develop and analyze the spatial structure of CLB and associated defoliation using geospatial information technology. Multispectral imagery data from airborne platforms were acquired using three remote sensing systems: (1) GeoVantage remote sensing system with 450 nm, 550 nm, 650 nm and 850 nm wavelengths; (2) RDACS (real time digital airborne camera system) with 540 nm, 675 nm, 695 nm and 840 nm wavelengths; and (3) Kodak DCS420 digital camera with the 500-810 nm wavelengths (red, green and near infrared). In addition, multispectral and hyperspectral radiometric data were collected using spectroradiometer. Analyzing reflectance values for simulated CLB defoliation indicated that the 0% and 25% defoliation could be differentiated from the 75% defoliation in the near infrared (NIR). Utilizing normalized difference vegetation index and a simple vegetation index, 0% and 25% defoliation could also be separated from 50% and 75% defoliation. Reflectance values for natural defoliation by CLB and various ground covers indicated that NIR was the best indicator for distinguishing different ground cover types. Heavy feeding by CLB could be detected but light or no feeding could not be discriminated from each other using these systems mentioned above. Spectral spatial analysis of a first year rising cottonwood plantation indicated that a wave (hole-effect) variogram model could be used to describe the spatial structure at omnidirection. Within the 1.90 - 2.48 m range, there is a significant spatial autocorrelation of reflectance. Spatial structure of adult and larval populations indicated that spatial dependence varied among dates and directions. Spherical and Gaussian functions provided the best statistical fit for CLB adult and larval spatial distributions, which were aggregated. The signature analysis for hyperspectral data indicated that when comparing the 0% defoliation to the 25, 50 and 75% defoliation, maximum reflectance differences were found near 294 nm in the ultraviolet, 550 nm in the visible spectrum and 764 nm in the near infrared spectrum. The highest reflectance sensitivity occurred between 528-557 nm in the visible spectrum. High sensitivities were also found between 730-740 nm and 930-940 nm in the infrared spectrum. Bands from 892-894 nm were best for separating various defoliation levels. This study has first demonstrated the application of remote sensing combined with GPS and geostatistics to CLB defoliation of cottonwood. The defoliation level of cottonwood can be detected and assessed using different remote sensing systems. Spatial models can be used to map CLB population densities and defoliation rates in landscapes. These maps can be used for site specific CLB management.