Browsing by Subject "Scale"

Now showing 1 - 5 of 5
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    Consequences of Biodiversity in Tree Diversity Experiments
    (2018-05) Grossman, Jacob
    This dissertation reports on four studies that explore the consequences of changes in tree biodiversity for three ecosystem processes (growth, leaf herbivory and disease, and leaf decomposition) in tree-dominated ecosystems in eastern Minnesota, USA. In Chapter 1, I present the Forests and Biodiversity (FAB) experiment and assess the role of taxonomic, phylogenetic, and functional diversity in this experiment on stem growth of 12 species. Over the third to fifth years of the experiment, trees with more diverse neighborhoods produced more biomass than trees in less diverse neighborhoods. This complementary overyielding effect was associated with species richness (taxonomic diversity) and was better predicted by tree diversity at larger (12 m2) rather than smaller (0.25 m2) spatial scales. I also measured three forms of invertebrate herbivore damage and two forms of disease damage on leaves of nine FAB species; results from this study are presented in Chapter 2. I assessed the consequences of diversity for damage across four spatial scales. Herbivory and disease responded to a variety of metrics of community diversity and these effects were species-specific. Damage, regardless of what kind, was better predicted by community structure and diversity at small spatial scales (1-4 m2) than large scales (9-16 m2). Chapter 3 consists of the presentation of results from the Biodiversity in Willows and Poplars (BiWaP) experiment, in which both the genetic diversity and species diversity of three Salicaceous species was manipulated, and tree growth and herbivory were measured. Diversity did not have a consistent effect on productivity because one dominant species suppressed hetrospecific neighbors. In contrast, specialist gall formation was best predicted by genetic identity and genotypic diversity suppressed leaf mining. Finally, through a separate litterbag decomposition experiment designed in parallel to FAB and presented in Chapter 4, I measured the consequences of leaf chemical diversity for decomposition over two years. When litter from multiple species were mixed, it did not lose mass, cellulose, or lignin differently than would be expected based on monoculture. But more labile carbon fractions (soluble contents and hemicellulose) decomposed more slowly in more functionally diverse litter mixes.
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    The molecular weight effects of poly(acrylic acid) on calcium carbonate inhibition in the kraft pulping process.
    (2011-05) Dubay, Matthew Richard
    Calcium carbonate scale reduces process efficiency and control in kraft pulping operations. The formation of scale can be alleviated or at least reduced by the addition of antiscalant chemicals into the process line. A number of different antiscalants are commercially available but still little is known about their mechanism of inhibiting scale formation. This project focused on one class of antiscalants, the polymeric antiscalants, which are carboxylic acid containing copolymers, with the majority of their monomer residues being poly(acrylic acid). Scale inhibition performance at high pH and temperatures was characterized using a number of different experimental setups and the mechanisms involved were investigated. Performance tests yielded that the most influential characteristic of the polymeric antiscalants was the molecular weight (MW), and consequently, the molecular weight distribution (MWD) of the polymer species. Since commercial poly(acrylic acid) (PAA) samples have a broad MWD, atom transfer radical polymerization (ATRP) was utilized to create relatively monodisperse samples of PAA. These PAA samples synthesized via ATRP were used to investigate the effects of MW and MWD on antiscalant performance along with the mechanisms responsible for the observed optimal MW range of ~10,000 under laboratory kraft pulping conditions. The information presented here is useful both in identifying important properties of polymeric antiscalants and in understanding the mechanisms by which they inhibit the formation of calcium carbonate crystalline deposits in kraft pulping.
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    Multiple scale spatial dynamics of the moose-forest-soil ecoystem of Isle Royale National Park, MI, USA
    (2008-11) De Jager, Nathan R.
    Moose (Alces alces) make foraging decisions at scales that range from plant stems (centimeters) to home ranges (kilometers). These decisions determine the spatial distribution of forage consumption and the consequent impacts on plant communities and nutrient cycles. From the fine scale changes in the size and density of plant stems to the distribution of plant patches and community assemblages across landscapes, the effects of moose browsing at one spatial scale may amplify spatial heterogeneity at scales that are orders of magnitude larger than the scales at which the interactions originally took place. In this thesis, I focused on how gradients of moose browsing in two valleys at Isle Royale National Park, MI, USA influenced plant fractal geometry and how such changes to plant geometry feedback to moose foraging across larger previously browsed landscapes. I also examined changes in larger scale patterns of forage availability, plant community composition, and soil fertility in response to recent declines in island-wide moose population density. Increasing moose browsing influenced the geometry of deciduous and conifer species differently. The fractal dimension of bite density, bite mass, and forage biomass of aspen saplings all responded quadratically to increasing moose browsing and were greatest at intermediate browsing rates. In contrast, fractal dimension of bite density, bite mass, and forage biomass of balsam fir all declined steadily with increasing moose browsing. These different responses of plant canopies to increased browsing as well as seasonal changes in bite mass altered the distribution of foraging mechanisms across larger previously browsed landscapes. At the larger scale, recent (2005-2007) landscape patterns of available and consumed browse became decoupled from each other and distributions of available forage, plant species composition, and soil fertility were qualitatively different from patterns documented in the early 1990's. These changes are coincident with and likely driven by recent declines in the island-wide moose population of Isle Royale. Collectively, these two studies suggest that large scale landscape patterns of browse availability, species composition, and soil fertility may emerge from finer scale impacts of browsing on plant geometry and the feedbacks to larger scale foraging decisions that moose make in addition to population density. The long-term dynamics of landscape patterns in boreal forests are therefore dependant on both fine scale foraging decisions and large scale population dynamics.
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    Retail therapy: A qualitative investigation and scale development.
    (2009-05) Kang, Minjeong
    The principle goal of this research was to enhance understanding of retail therapy, defined as shopping to alleviate negative moods. The specific research objectives were to 1) analyze the conceptual foundations of retail therapy, 2) qualitatively investigate the phenomenon of retail therapy, and 3) develop and validate a scale measuring retail therapy. Through a detailed conceptual analysis of the two existing approaches to the study of retail therapy, the researcher articulated how these approaches are related. In addition, the exploration of relationships between retail therapy and other consumer behaviors further clarified the concept of retail therapy. In-depth interviews were conducted to qualitatively investigate consumer experiences of engaging in retail therapy. 43 self-identified therapy shoppers participated in one time interviews. Interview findings revealed the nature of retail therapy during three shopping stages: pre-shopping, shopping, and post-shopping. Retail therapy scale development consisted of three phases: initial item generation, scale purification, and scale validation. 43 initial scale items were generated based on interview findings and included in the survey questionnaire. 258 survey responses from the general population were used for scale purification through which four factor measurement model was developed with 22 items retained. The refined measurement model was validated using a separate sample of 272 general populations. Implications of research findings were provided in three areas: consumer behavior research, retailers and marketers, and consumers and therapists.
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    Spatial vegetation-environment relationships and distributional changes in the presettlement Minnesota prairie-forest boundary.
    (2009-02) Danz, Nicholas P
    The prairie-forest boundary region in Minnesota spans 650 km along a northwest-southeast axis and is often considered one of the most abrupt grassland-forest transitions in the world. Historically, this region separated tallgrass prairie vegetation to the south and west from forest vegetation to the north and east, while land conversion since presettlement has eliminated over 95% of original prairie and continues to convert and fragment forested lands. Ecological boundaries such as the prairie-forest transition are considered critical landscape elements that control the fluxes of organisms, materials, and energy between ecosystems. While the significance and characteristics of ecological boundaries has been often discussed in scientific literature, there are few studies that provide empirical support for boundary concepts. In particular, studies are lacking that evaluate vegetation-environment relationships across boundaries. In this thesis, I use the presettlement prairie-forest boundary as an example of an ecological boundary to address the following issues: 1) the influence of spatial scale and spatial heterogeneity in the controls of vegetation, 2) the spatial nature of a vegetation-climate relationship across the boundary, and 3) range distributional shifts since presettlement in tree taxa common to the boundary region.