Date of Award

2013

Rights

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Document Type

Thesis

Degree Name

Master of Science (MS) in Biology

Department

Biology

First Advisor

Rebecca Brown

Second Advisor

Robin O'Quinn

Third Advisor

Suzanne Schwab

Abstract

"Invasive winter annual grass (IWAGs) abundance has increased throughout much of the western United States, with serious consequences for biodiversity and ecosystem function. While a variety of tools have been used to control IWAGS, they often fail to achieve the goal of creating a self-sustaining native plant community. Therefore, a major goal of my thesis has been to explore and test restoration approaches that might help realize such plant communities. These approaches include ecologically based invasive plant management (EBIPM) and assisted succession. EBIPM is a holistic approach that aims to restore ecological functions damaged by IWAGs with a combination of restoration tools that remove the IWAGs and promote native growth. Assisted succession can be used to further restore the native plant community by dispersing fast growing native annual seed (instead of native perennial), forcing competition with invasive annuals. It is thought that native perennials should be able to more easily succeed following the native annuals that they evolved with rather than invasive annuals. Both approaches seek to increase community resistance to invasion, which should promote self-sustainability. Community resistance to invasion in western bunchgrass communities is also enhanced by the presence of biological soil crust (biocrust), which is the moss, lichen, algae, and cyanobacteria growing on the soil. Biocrust has been shown to prevent seeds from establishing by creating a barrier between the seed and the soil but has only been tested in arid areas. Much of the west, including Turnbull National Wildlife Refuge, where my study is focused, is in semiarid habitat, with nearly twice the rainfall. It is not known how biocrust affects IWAG invasion in such conditions, or even how biocrust responds to invasive species control techniques such as herbicide and fire. I tested the effects of restoration techniques that control IWAGs, increase native species abundance, and promote community resistance to invasion on plant community and biocrust composition over a range of habitats in a Mirna mound Prairie at Turnbull National Wildlife Refuge (TNWR). Mima mounds are discrete mounds of soils, surrounded by shallow intermound soils; mound size and intermound vegetation growth is dependent on substrate type. The restoration techniques included prescribed fire (fall burn), Outrider herbicide applied in late fall, and native annual and perennial seed addition (seeds added in winter). I further tested the effect of boot trampling on biocrust. Plants were sampled before and the first growing season after application. I found that 1) V. dubia increased 15-fold on mounds from 2009 to 2013, and where V. dubia was abundant, lichen cover was low but moss cover was high, 2) Outrider® herbicide was the most effective technique at reducing invasive species and had minimal impact on natives, on mounds; on intermounds native cover actually increased with herbicide, 3) Fire effectively increased native species cover on mounds but had little effect on intermounds; fire had little effect on invasive cover, 4) annual seed addition effectively increased native cover while perennial seed addition had little effect the first year, and 5) in intermounds areas where biocrust was abundant, treatments had little effect on the biocrust community or on exotic plant species. My results can be used to help land managers decide appropriate restoration approaches to increase community sustainability in semiarid regions, however long-term monitoring is needed to test whether these results are truly sustainable"--Document.

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