In forest communities, the composition and abundance of plants in the understory is generally mediated via a complex interplay between herbivory and competition. Nonetheless, most research assesses the effect of herbivory and competition independently and rarely investigates potential interactions between the two factors. In this dissertation, I examine how herbivory and competition, alone and in concert, influence forest understory plant diversity. At one extreme, herbivory is hypothesized to reduce interspecific competition, thus allowing for greater species coexistence in the understory. In chapter one, I test this hypothesis in the herbaceous community of a tropical forest in central Panamá. I found mammals limited the abundance of the dominant herbs while simultaneously limiting the establishment of rare species. In contrast, intense herbivory may reduce the diversity of the most palatable species allowing browse-resistant species to rapidly expand and overtake the forest understory. In chapter two, I explore this alternative by reviewing the processes leading to the formation of recalcitrant understory layers worldwide and summarizing the mechanisms by which these layers inhibit tree seedling regeneration and alter forest succession. In chapter three, I experimentally examining how a recalcitrant understory layer limits tree species recruitment via direct competitive as well as indirect, apparent competitive interactions. Specifically, by providing a favorable microhabitat for small mammals, a dense understory canopy can facilitate increased granivory, thereby indirectly limiting tree recruitment. I found a dense hay-scented fern (Dennstaedtia punctilobula) understory exerts strong apparent competitive effects on the emergence of black cherry (Prunus serotina) and strong competitive effects on emergence and survival of red maple (Acer rubrum). In chapter four, I explore the potential interactions between white-tailed deer (Odocoileus virginianus) and a dense canopy of hay-scented fern. This work demonstrates that in light limited, closed-canopy forests, a dense understory layer strongly suppresses germination and survival of several shade intolerant tree species. Furthermore, I argue that century-long legacy of deer overbrowsing has resulted in a depauperate forest community that predisposes future declines in plant diversity and increased monodominance. In all, these findings stress the need to discriminate among multiple ecological factors and assess their relative importance in structuring natural communities.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-08042005-214212 |
| Date | 10 October 2005 |
| Creators | Royo De Sedas, Alejandro |
| Contributors | Rick Relyea, Walter P. Carson, Stephen B. Horsley, Joseph Merritt, Steve Tonsor |
| Publisher | University of Pittsburgh |
| Source Sets | University of Pittsburgh |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.pitt.edu/ETD/available/etd-08042005-214212/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Pittsburgh or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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