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Plant Ecology of Arid-land Wetlands; a Watershed Moment for Cienega Conservation

Posted on:2017-06-20Degree:M.SType:Thesis
University:Arizona State UniversityCandidate:Wolkis, DustinFull Text:PDF
GTID:2443390005462658Subject:Ecology
Abstract/Summary:
It's no secret that wetlands have dramatically declined in the arid and semiarid American West, yet the small number of wetlands that persist provide vital ecosystem services. Cienega is a term that refers to a freshwater arid-land wetland. Today, even in areas where cienegas are prominent they occupy less than 0.1% of the landscape. This investigation assesses the distribution of vascular plant species within and among cienegas and address linkages between environmental factors and wetland plant communities. Specifically, I ask: 1) What is the range of variability among cienegas, with respect to wetland area, soil organic matter, plant species richness, and species composition? 2) How is plant species richness influenced locally by soil moisture, soil salinity, and canopy cover, and regionally by elevation, flow gradient (percent slope), and temporally by season? And 3) Within cienegas, how do soil moisture, soil salinity, and canopy cover influence plant species community composition? To answer these questions I measured environmental variables and quantified vegetation at six cienegas within the Santa Cruz Watershed in southern Arizona over one spring and two post-monsoon periods. Cienegas are highly variable with respect to wetland area, soil organic matter, plant species richness, and species composition. Therefore, it is important to conserve the cienega landscape as opposed to conserving a single cienega. Plant species richness is influenced negatively by soil moisture, positively by soil salinity, elevation, and flow gradient (percent slope), and is greater during the post-monsoon season. Despite concerns about woody plant encroachment reducing biodiversity, my investigation suggests canopy cover has no significant influence on cienega species richness. Plant species community composition is structured by water availability at all cienegas, which is consistent with the key role water availability plays in arid and semiarid regions. Effects of canopy and salinity structuring community composition are site specific. My investigation has laid the groundwork for cienega conservation by providing baseline information of the ecology of these unique and threatened systems. The high variability of cienega wetlands and the rare species they harbor combined with the numerous threats against them and their isolated occurrences makes these vanishing communities high priority for conservation.
Keywords/Search Tags:Plant, Wetland, Cienega, Soil
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