Date of Award

2021

Document Type

Dissertation

Degree Name

Ph.D.

Department

Biological Sciences

First Advisor

Anna A. Sher

Second Advisor

Shannon Murphy

Third Advisor

Robin Tinghitella

Fourth Advisor

Jing Li

Fifth Advisor

Eduardo González

Keywords

Biological control, Functional traits, Invasive species, Plant communities, Riparian, Spatial analysis

Abstract

Invasive species have become an inextricable part of the landscape, particularly in riparian plant communities, and removal is often a key component of restoration programs. Biological control (biocontrol) is a method of removal that is often both efficient and effective. However, the impact of biocontrol on target species and indirect effects from invasive species removal can be hard to predict. While monitoring the impact of invasive species removal usually involves some species-based assessment such as changes in diversity, historically dominant species or native species, these strategies do not typically provide insight into the mechanisms underlying plant community response to removal.

My research that I present here seeks to expand our understanding of the drivers underlying variations in impact of a biocontrol beetle (Diorhabda spp.) on a dominant invasive tree (Tamarix spp.) in the southwestern United States. I used spatial modeling to uncover underlying structure in the response of Tamarix to Diorhabda. I found evidence for compensatory growth in response to defoliation. I also showed that a large portion of spatially structured variation in Tamarix cover was not associated with abiotic conditions, suggesting that biotic factors may be more important in determining the impact of biocontrol.

Biocontrol defoliation creates a natural gradient of invasive species cover across the landscape. I examined Tamarix dominated sites across a large geographic extent to understand how both the abiotic environment and varied levels of Tamarix influence the functional composition of underlying plant communities. I found that Tamarix cover encourages shade tolerance, sexual reproduction and short life cycles in the understory plant community. To better understand the long-term effect of Tamarix defoliation and the response to a specific defoliation event, I examined traits and functional diversity over the course of 8 years, up to 14 years after initial defoliation. This study provides evidence that understory plant communities stabilize after an initial defoliation event and supports the previous findings on plant community functional response to Tamarix. My research adds to the body of knowledge regarding the role of environmental filters in structuring the plant communities and aids land-managers in anticipating plant community response to invasive species removal.

Publication Statement

Copyright is held by the author. User is responsible for all copyright compliance.

Provenance

Received from ProQuest

Rights holder

Annie L. Henry

File size

178 pgs

File format

application/pdf

Language

en

Discipline

Conservation biology, Natural resource management

Available for download on Tuesday, April 19, 2022

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