Browsing by Subject "Salix"

Now showing 1 - 4 of 4
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    An ecological and evolutionary perspective on functional diversity in the genus Salix
    (2010-05) Savage, Jessica Anne
    Natural selection, along with biochemical and architectural constraints can limit the trait combinations expressed by plants, creating functional trade-offs across species. These trade-offs often play a critical role in limiting species distributions by preventing them from performing well under all environmental conditions. For this dissertation, I examined the role of functional trade-offs in limiting species distributions at two geographic scales, focusing on species in the genus Salix (the willows). First, I examined whether species exhibited niche differentiation across a local water availability gradient, and investigated the extent that plant function and functional similarity influence species distributions and patterns of co-occurrence. For this analysis, I examined species distributions in relation to physiological and functional data collected in the field and in a greenhouse common garden. I also estimated a phylogeny of the species to examine patterns of species phylogenetic community structure and trait evolution. Second, I examined whether there was evidence for a trade-off between freezing tolerance and growth that could explain species range limits. This analysis involved comparing species freezing tolerances and growth rates under different environmental conditions and determining the extent that these traits related to species distributions. Overall, I found evidence that functional trade-offs are important in determining species distributions both within local plant communities and across broader geographic distributions. On a local level, species exhibit niche differentiation across a water availability gradient, and this differentiation is driven by a functional trade-off between drought tolerance and relative growth rate. Traits related to species drought tolerance and recruitment strategies also demonstrate correlated evolution with species water availability niches. At a broader geographic scale, species demonstrate a trade-off between freezing tolerance and growth. This trade-off is primarily the result of species dependence on photoperiod cues for growth regulation. The strong correlation between species growth rates, their freezing tolerances, and their modeled geographic ranges suggests that this trade-off could influence their geographic distributions. This research demonstrates the importance of functional trade-offs in determining the distributions of species in an ecological and economically important genus. It also demonstrates the value of integrative research that draws on physiological, evolutionary and ecological methodology.
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    The snow in the willows: assessing the use of shrub-willows for living snow fences in Minnesota, USA
    (2015-12) Ogdahl, Eric
    Blowing and drifting snow adversely affect winter driving conditions and road infrastructure in Minnesota, often requiring removal methods costly to the state and environment. Living snow fences (LSFs)—rows of trees, shrubs, or grasses installed on fields upwind of roadways—are economically viable solutions for controlling drifting snow in agricultural areas and can provide a range of environmental benefits, such as carbon sequestration and wildlife habitat. Despite incentives and financial assistance by state and federal agencies, farmer adoption of LSFs is low, in part due to concerns about removing cropland from production. Shrub-willows (Salix spp.) have been proposed as a LSF species to meet landowner needs, given their potential to reach effective snow fence heights and densities soon after planting and provide a marketable biomass product. As part of evaluating the use of willow LSFs for multiple benefits in Minnesota, this thesis sought to 1) assess the establishment and snow trapping ability of three willow varieties in two- and four-row planting arrangements in a LSF in south-central Minnesota, and 2) compare the establishment and growth of both native and hybrid shrub-willow varieties and species to species traditionally used in Minnesota LSFs (i.e., Gray dogwood and American cranberrybush). In the first study, willows had an average survival rate of 89% and average growth of 1 meter after two growing seasons. Over the 2014-15 winter, no differences were found among willow varieties in their ability to trap snow; however, four-row arrangements caught more snow than two-row arrangements. Blowing snow models indicated that two- and four-row arrangements should be able to trap all of the mean annual snow transport for the study region after three and four growing seasons, respectively. In the second study, all species showed good establishment, and all willows exceeded the growth of traditional LSF species after the second growing season. Additionally, a native willow (S. petiolaris) had similar growth to the top-growing hybrid willow varieties, suggesting it may provide a suitable local source for future LSFs. Overall, these results suggest that willows may provide effective LSFs earlier than traditional LSF species and add to the LSF design practices for transportation agencies, natural resource managers, and landowners.
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    Wetland Mitigation in Abandoned Gravel Pits
    (Minnesota Department of Transportation, 2010-03) Johnson, Kurt W.
    It is becoming increasingly difficult to provide on-site mitigation for wetland impacts due to road construction in northeastern Minnesota counties that retain greater than 80 percent of their pre-settlement wetlands. Abandoned gravel pits are one of the few remaining areas that can serve as wetland mitigation sites. The overall goal of the project is to develop cost-effective methods for creating functional mitigation wetlands on abandoned gravel pit sites to compensate for wetland impacts due to road construction. Two approximately 1-hectare wetland creation demonstration sites were established in adjacent abandoned gravel pits within the U.S. Trunk Highway 53 reconstruction corridor to evaluate techniques for wetland establishment. Wet meadow and shrub swamp wetlands were attempted on one site, and wooded swamp and bog wetlands on the other. Wetland seed mixes provided both positive and negative effects on the developing plant communities on both sites initially but their effect was limited to the first year. Alder thicket and bog donor soil applications had positive effects but not until the third year of the study. Hardwood willow cuttings were effective for establishing a shrub component. Conifer seedlings did not survive unless planted on soil mounds. Fertilizer proved ineffective for promoting wetland plant growth during the study period. The use of straw mulch is questionable on saturated wetland sites such as those in this study.