Thesis (Ed.D.)--Teachers College, Columbia University. / Typescript; issued also on microfilm. Sponsor: Frederick Fitzpatrick. Dissertation Committee: Willard Jacobson, Phil Lange. Includes bibliographical references (leaves 124-144) and a ten-page bibliography of films available on conservation.

Thesis (M. Sc.)--University of Canterbury, 2008. / Typescript (photocopy). Includes bibliographical references (leaves 159-168). Also available via the World Wide Web.

The climate of the Southwestern United States and northwestern Mexico is marked by a bimodal precipitation regime with the majority of moisture arriving during (1) the cool season via intermittent frontal storm systems (November to February) and (2) intense, convective storms during the North American Monsoon (NAM) (July to September). Fire season in the region occurs primarily during the arid fore-summer in May and early June prior to the arrival of the NAM. Most long-term tree-ring based studies of fire-climatology in the region have evaluated only the role of winter precipitation. We used tree-ring width based reconstructions of both winter and monsoon precipitation, coupled with fire scar based tree-ring reconstructions of fire history from twelve mountain ranges in the US and Mexico at the northwestern margin of the NAM to quantify the historical role of both seasons of precipitation in modulating widespread fire years. Winter precipitation was the primary driver of widespread fire years in the region, but years with drought in both seasons had the highest fire frequency and most widespread fires. The timing and amount of monsoon precipitation can be important factors in ending the most severe fire weather conditions. Monsoon drought coupled with earlier snow melt in the spring appears to contribute to an extension of fire weather for longer periods, leading to more and larger fires.

The main purpose of this report is to develop an economic theory, along the lines of the Bergson- Samuelson social welfare theory, to regulate the utilization of natural resources in the long -term interest of a political- economic group of individuals and firms. The theory, called Collective Utility, qualifies as a "systems approach" because of its inherent flexibility, generality, and comprehensiveness. Collective Utility is a function of individual satisfactions and firm revenues, which are, in general, contingent upon the actions of other individuals and /or firms. Such interactions are called externalities. It is the contention of this report that efficient management of natural resources will follow from efficient control of externalities. A taxation - subsidy structure is suggested as an efficient control and the complete mathematics of determining and implementing such a structure are provided. Finally, the idea of externalities is integrated within the framework of Collective Utility to form an optimal policy for the utilization of natural resources using the techniques of calculus of variations.

Disturbances are key processes that alter environmental conditions which have consequences for species interactions; therefore, disturbances are important to maintenance of biological diversity. Climate, fire, livestock grazing, introduction of nonnative species, and humans all influence semi-desert grasslands of the southwestern United States. In southeast Arizona, a nonnative perennial grass, Lehmann lovegrass (Eragrostis lehmanniana), was introduced in the 1930s in an effort to restore degraded rangelands. I quantified annual fluctuations of Lehmann lovegrass and the response of native plants along a gradient of dominance by this nonnative grass. Biomass and richness of native plants declined with increasing dominance by Lehmann lovegrass. Substantial increases in biomass by Lehmann lovegrass in response to above-average rainfall did not result in decreases in native plants. Fire is an important disturbance in semi-desert grasslands. Herbaceous plants are favored over trees and shrubs in areas with frequent fires, therefore fire maintains grassland physiognomy. Humans have manipulated natural fire regimes however, by altering their frequency, season, and spatial extent. I experimentally investigated the possibility of a positive feedback cycle in grasslands invaded by Lehmann lovegrass by assessing whether the presence of Lehmann lovegrass was enhanced by fire to the detriment of native plants. In the two years post-fire, the proportion of Lehmann lovegrass on burned sites did not increased compared to unburned sites or to pre-fire conditions. I also detected no changes in species richness, diversity, or biomass of native plants in response to fire for 2-3 years after fires. Changes in biomass of all plants varied among years, especially due to exceptionally wet conditions during spring 2001, and varied if fires were set in spring versus summer. Lastly, I investigated the response of Agave palmeri to fire, a species that provides forage for a migratory bat that is federally endangered. Survival of agave varied with soil type, fire season, and size of the plant. In general, agave can tolerate up to 85% damage before mortality. Germination of agave seed was decreased by fire. Based on my research, I recommend setting fire at natural frequency and season for the maintenance of semi-desert grasslands.

The Bouteloua curtipendula (Michx.) Torr. complex (BCC) is composed of 11 species and five varieties distributed in North and South America with its center of diversity in Mexico. It is characterized by tremendous morphological variation and taxonomic complexity that is most likely due to reticulate evolution, phenotypic plasticity, and the development of asexual reproduction (apomixis). Climate-induced range changes over evolutionary time may explain the origin of the morphologically diverse BCC as suites of species came into contact over time, hybridized, and created new species, cytotypes, and reproductive modes. I investigated the origins of the BCC by creating habitat suitability models based on present-day occurrence records for eight BCC taxa and hindcast these models to paleoclimate reconstructions for the Last Glacial Maximum and Last Interglacial. By estimating range dynamics over time, coupled with phylogenetic data, I inferred the locations of contact zones among taxa and identified likely progenitor taxa for various cytotypes found in the BCC. Species with large and environmentally heterogeneous distributions may have large ranges due to plastic responses to environmental variation for adaptive traits or they may maintain differently adapted ecotypes to specific habitats. I evaluated phenotypic plasticity for stolon and rhizome production in the three taxonomic varieties of B. curtipendula. My results indicate that expression of these traits is correlated with specific, local environmental conditions and not to broadly defined environments in geographic space and that phenotypic plasticity accounts for a greater proportion of trait expression than does total genetic variance. Apomixis, asexual reproduction via seed, most likely results from interploidy hybridization. There are many possible pathways that lead to asexual seed formation and understanding these pathways is important to understanding genetic diversity, demography, and evolutionary potential in apomictic and mixed apomictic-sexual populations. I discovered that B. curtipendula var. caespitosa, the only recognized apomictic taxon in the BCC, is pseudogamous, indicating that although fertilization is unnecessary to produce the embryo, it is necessary to produce the endosperm. These data also indicate that meiosis is highly irregular and results in sperm nuclei with variable chromosome numbers, which affects endosperm production, fertility and demographics in apomictic B. curtipendula.

Online homework is becoming a common type of assignment for math courses in secondary and post-secondary schools in the U.S. This study attempts to determine whether in this setting immediate feedback offers any advantage over delayed feedback in promoting learning gains in high school math. To this end, a study involving two comparable groups of students was performed, one group receiving immediate and the other delayed feedback. Both groups received their feedback in a computer-assisted environment. No significant difference in achievement between the two feedback groups was found.

This study aims is to discover the best methods for geometry students to master proof writing. Students who are taught how to write proofs in a traditional setting find proofs to be very difficult - struggling throughout the school year writing proofs on their own. Studies have been conducted regarding the use of dynamic geometry software in proof writing. To further study the effects of proof writing using dynamic geometry software, forty-eight freshmen students enrolled in an honors geometry course at a high performing suburban high school in Louisiana were given several proofs to complete, along with self-reflection surveys. During phase one of this research, twenty-four students were allowed to use Geometers Sketchpad (GSP) while writing their proofs, while the other twenty-four students were using only paper and pencil to explore the figure involved in the proof. During phase two of testing, the control and experimental groups swapped places to uphold the equality standards of the course. Student self-reflection surveys show that some students enjoy writing proofs when using GSP, while others are indifferent. Along with the student surveys, the present study is an analysis of student work from those who had access to GSP to improve proof writing skills.

Research continues to reinforce that student centered classrooms and interactive engagement (IE) strategies, when used effectively, can produce considerable gains compared to traditional instruction methods. In this study, IE strategies, primarily modeling instruction, were compared to traditional instruction in a middle school classroom to determine if IE strategies would have an impact in two specific areas: graphing ability and science reasoning skills. Class mean scores on tests were compared over time to show that IE strategies produced greater gains in graphing and science reasoning than traditional instruction for one group. The other group did not see significant differences in graphing or science reasoning based on instructional method. Student scores were also analyzed based on math preparations, and it was noted that students enrolled in pre-algebra math classes saw statistically significant gains in graphing. Results from this study suggest that using IE strategies in middle school science may have a positive impact on graphing ability and science reasoning skills.

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