Date of Award

Spring 1-1-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology & Evolutionary Biology

First Advisor

Sharon K. Collinge

Second Advisor

Nichole N. Barger

Third Advisor

Kendi F. Davies

Fourth Advisor

Paula J. Fornwalt

Fifth Advisor

Timothy R. Seastedt

Abstract

Invasive species are considered one of the top five threats to biodiversity worldwide and when established can quickly degrade a system. In response to this degradation a large number of ecological restoration projects have been implemented to mitigate the effects of invasion. Using a long term vernal pool restoration project that has documented invasive encroachment over time, I sought to tease apart the mechanisms underlying exotic plant invasion through exploration of positive feedbacks in both above and belowground plant communities. My results demonstrated that a thick litter layer deposited by the invasive species not only decomposed at a slower rate than native litter, but also strongly hindered native species abundance. This invasive litter layer created a positive feedback that allowed for invasive species recruitment while hindering the majority of natives from reaching the aboveground vegetation. However, vernal pool native species were maintained at continually high densities in the seed bank and the abundant aboveground invasives had a much lower presence belowground. These results were corroborated by my comparisons of the existing seed bank community to the historical aboveground vernal pool vegetation (5-8 years prior) versus more recent aboveground vegetation (1-3 years prior). Here I found a strong legacy effect in seed banks; i.e., seed banks had a composition with greater similarity to the historical aboveground vegetation than to the more recent aboveground vegetation. Finally, to test if similar relationships as those observed for above and belowground vernal pool vegetation were present in other, more widespread systems, I conducted a seed bank study in three Colorado conifer forests types. The forests had all undergone a mechanical fuels reduction treatment aimed at restoring historical fire regimes. Under thick mulch layers of treated woody materials, the seed banks tended toward increased density when compared to the untreated, but seed banks generally did not differ among treatments. These results coupled with the vernal pool findings show that the aboveground vegetation and seed banks are often quite divergent. Therefore when implementing and monitoring a long term restoration project it is important to understand drivers of both the above and belowground responses to fully understand restoration success.

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