Thesis (Ph. D.)--Leland Stanford junior university, 1907. / Cover title. Also issued in print.

Thesis (M.S.)--Oregon State University, 1999. / Typescript (photocopy). Includes bibliographical references (leaves 105-122). Also available on the World Wide Web.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1980. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

A study is described on the occurrence of wetwood in black cottonwood, found in the Lower Fraser Valley of British Columbia, Canada. Wetwood first appears when trees are 8 to 10 years old, and in 12 year and older trees, wetwood is always present. Further extension of wetwood is similar to that of a normal heartwood, A large number of microorganisms with different 0₂ requirements (i.e., aerobes as well as facultative and obligate anaerobes) were found in the wetwood. Wood-destroying fungi were absent in the wetwood. In the majority of the black cottonwoods examined, very low 0₂ concentrations (<0.1% or microaerobic conditions, detected by a Field-lab 0₂ analyzer) were found in the wetwood during the summer. Generally the 0₂ concentration increased during the winter while the reverse was true for CO₂ (detected by gas chromatography). CH₄ was also present, but only in small quantities, in most trees. Mechanical wounding of wetwood resulted in an increase in the 0₂ concentration and decrease in the CO₂ and CH₄ concentrations. However, sealing of the wound re-established the original gas composition. Presumably the microbial flora of wetwood is primarily responsible for the microaerobic conditions. The ability of 2 wood-destroying fungi (Polyporus delectans Peck and Ganoderma applanation [Pers.] Pat.) to cause a weight loss in wood under microaerobic and aerobic conditions (10 weeks incubation each) was determined, using a soil-block experimental technique, Microaerobic conditions prevented weight loss in wood (average 0.1%) and therefore wood decay, whereas under aerobic conditions, the average weight loss was 41.7%. Special characteristics of wetwood such as high pH (average 7.8) or high moisture content (approximately 160%) did not contribute significantly to the decay resistance. Also, microorganisms associated with wetwood showed no antagonism to the growth of wood-destroying fungi. Exposure of wood-destroying fungi to microaerobic conditions subsequent to aerobic conditions arrested their growth and ability to cause weight loss. On the other hand, exposure of these fungi to aerobic conditions following the microaerobic conditions, induced a significant weight loss in wood (average 10.9%), but it was considerably less than when the fungi were grown under aerobic conditions alone (average 41.7%). The 2 wood-destroying fungi survived 10 weeks exposure to microaerobic conditions, A 13 weeks exposure to anaerobic conditions (<0.002 % 0₂), however, resulted in the death of these, wood-destroying fungi. Eight wood-destroying fungi differed in their abilities to survive under anaerobic conditions; generally brown-rot fungi tolerated anaerobic conditions better than the white-rot fungi. Therefore, if anaerobic conditions exist in the tree trunks for long durations, some fungi (probably white-rot fungi) may die during that period while others (probably brown-rot fungi) may survive such an exposure and resume decay activity when 0₂ becomes available. These findings led to the concept that the microaerobic conditions found in the wetwood of black cottonwood may prevent the development of decay. / Forestry, Faculty of / Graduate

In the northwestern prairies, the cottonwoods Populus deltoides Batr., P. balsamifera L., P. angustifolia James, and inerspecific hybrids, form the foundation of the riparian forest ecosystem. The present project characterized the phenotype and 391henology of each tree in a mature cottonwood grove (N=391) for the purposes of clone-delineation. In order of their utility, tree sex, general leaf-shape, six leaf dimensions, and phenology of flowering, leaf-flushing, senescence,and leaf-abscission were utilized. The population's 391 trunks represented only 115 individuals, 67 of which were clones which ranged from 2 to 58 trunks each. Thus, 88% of all trunks belonged to clones which ranged from 2 to 58 trunks each. Thus, 88% of all trunks belonged to clones, and this high clonal content reflects the senior age of the population. Clone structure explained the population's apparent spatial-clumping, female-skewed sex ratio, differential spatial distributions of the sexes and species, and complexity in trunk-size classes. Trends suggest that P. balsamifera and P. angustifolia are more strongly clonal than P. deltoides, partially explaining their differences in environmental preferences. The observed extent of asexual regeneration has implications for riparian resource management and analyses of cottonwood reproductive ecology. / xv, 201 leaves : ill. ; 28 cm.

For deciduous trees, the growth season becomes progressively shorter with increasing latitude or elevation. To overcome the challenge of sufficient growth and development within the limited interval, deciduous trees may have adapted with increased physiological capacity. To test this ‘latitudinal compensation’ theory, I investigated the growth, foliar morphology, and some foliar biochemical and gas exchange characteristics of narrowleaf cottonwoods originating from the full range of its distribution. This study was carried out in a common garden at the University of Lethbridge, Alberta, Canada, near the northern limit of the species’ distribution. Across 167 genotypes from 9 populations representing the full 16º latitudinal range, heights and stem diameters were associated negatively (p<0.1) with the latitude of origin, while foliar morphological characteristics of blade width and leaf mass tended to be positively associated with latitude (p<0.1), and leaf mass per area (LMA) was positively associated (p<0.05). Foliar chlorophyll (chl) and nitrogen (N) content were also significantly associated with latitude, and carbon isotope composition (δ13C) was positively correlated with chl and N. With a more intensive analysis for a subset of three populations from near the southern middle, and northern limits of the distribution, these same patterns were confirmed and additionally, stomatal ratio was higher in the leaves for the northern population. Subsequently, the light-saturated photosynthetic capacity (Amax) was higher in genotypes from the northern population. I conclude that increased foliar morphological and biochemical characteristics of narrowleaf cottonwoods contribute to increased photosynthetic capacity for northern populations, providing evidence for latitudinal compensation in a deciduous tree from the northern hemisphere. / ix, 91 leaves ; 29 cm

Leaf surface area present on black cottonwood (Populus trichocarpa) and Douglas hawthorn (Crataegus douglasi) was measured indirectly using a point frame, photographs, and a canopy analyzer. Each was compared to directly measured leaf surface area. Six black cottonwood and 3 Douglas hawthorn shrubs were selected in 1996 and 9 black cottonwood and 3 Douglas hawthorn shrubs in 1997. Shrubs were selected based on size and isolation. Each indirect method was applied prior to removing a portion of leaves from each shrub. Shrubs were defoliated in 3 to 7 increments and leaf surface area of each was measured. After shrubs were completely defoliated increments of measured leaf areas were added to subsequently removed leaf areas to determine the measured leaf area present on a shrub each time indirect methods were applied. Measured leaf areas were paired with indirect method values and regression equations were developed. Correlation coefficients for regressions were 0.76 for black cottonwood and 0.70 for Douglas hawthorn for the point frame, 0.91 for black cottonwood and 0.79 for Douglas hawthorn for the photographs, 0.62 for black cottonwood and 0.61 for Douglas hawthorn when shrub volume was included for the canopy analyzer. Photographs took 20 minutes to set up and take pictures followed by 1.5 hours for processing images in Idrisi and Picture Publisher. The point frame required 45 minutes to 1.5 hours field time and 5 to 10 minutes to process data. The canopy analyzer was the most rapid of the techniques requiring less than 5 minutes to secure a field measurement and enter this value into the regression equation. Canopy analyzer reliability was the lowest of the methods studied. / Graduation date: 1999

No description available.

No description available.

Cottonwoods are poplar trees that are adapted to riparian zones that are naturally occasionally flooded. Like all Salicaceae, cottonwoods are dioecious and prior studies have indicated that males are more drought-tolerant than females and found more often in poorer, drier sites. We investigated sex differentiation of cottonwoods in response to the opposite water-stress, flood, and predicted that the increased water-stress tolerance of males in drought would also apply to flood-stress. Twenty-one clones of male and female narrowleaf cottonwoods (Populus angustifolia) were grown in a greenhouse along with three female clones of the hybrid native lanceleaf cottonwood (P. x acuminata) for comparison. It was anticipated that the hybrids would show the fastest growth owing to the genetic contribution from the P. deltoides parent and its rapid intrinsic growth rate. Flood reduced heights and the numbers and sizes of leaves and roots, and consequently dry weights, abaxial stomatal conductance and leaf chlorophyll. Inundation increased carbon:nitrogen, but did not alter stomatal density, leaf water potential, or δ13C. The hybrid saplings were much larger than the narrowleaf saplings but their proportional growth reduction with flooding was greater than in the female P. angustifolia, suggesting higher flood-tolerance of the narrowleaf cottonwood. P. angustifolia sexes performed similarly under reference conditions but the males were proportionally more inhibited by flood, suggesting sex differentiation in flood-tolerance. This study indicates that riparian cottonwoods are reasonably flood-tolerant but slight differences exist between the sexes and to a greater extent, across taxa. While prior studies have indicated males are apparently more tolerant of drought, females are probably more flood-tolerant. / xiii, 117 leaves : ill. ; 29 cm