Facilitation of Achillea millefolium increases at high levels of wind stress

Graduation Date

2006

Document Type

Thesis

Program

Other

Program

Thesis (M.A.)--Humboldt State University, Biological Sciences, 2006

Committee Chair Name

Jeffrey W. White

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

Abiotic stress, Pacific Ocean--Humboldt Bay, Facilitation, Humboldt State University -- Theses -- Biology

Abstract

Over the past several years, ecologists have begun to recognize that the role played by positive plant-plant interactions, specifically facilitation, in communities is under appreciated. Despite this recognition, little is known about how these positive interactions influence population and community dynamics. One theory posited by Bertness and Callaway in 1994, suggests that the relative importance of the effect of facilitation on plant distribution and abundance may depend on the level of abiotic stress. At high levels of stress, plants may create hospitable environments for neighboring plants (or sessile organisms), despite competition for limiting resources. In this experiment, I conducted a neighbor removal experiment in a dune ecosystem to test the relative importance of competitive and facilitative interactions at varying levels of abiotic stress. Stress levels were manipulated using PVC lattice shelters to decrease the effect of wind and associated stress. The effect of neighbor removal on the survival, aboveground biomass, stem length, leaf number, and reproduction of the target species was tested between high stress and low stress plants in treatments with and without neighbors, and in two habitat types. The strength and direction of the significant disordinal interactions between the variables indicated that plants sheltered from wind did better than plants exposed to wind, and in general, that this trend was not as apparent when neighbors were left intact. There was also evidence of interactions between shelter and neighbor treatments, indicating that the positive response of sheltering depended on the presence or absence of plant neighbors. Relative competition intensity values showed that positive interactions were more common in high stress sites. These outcomes are clearly consistent with the theory introduced by Bertness and Callaway that facilitation is more common at high levels of abiotic stress.

https://scholarworks.calstate.edu/concern/theses/j098zd49b

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