Date on Master's Thesis/Doctoral Dissertation

12-2014

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Biology

Degree Program

Biology, PhD

Committee Chair

Carreiro, Margaret Mary

Committee Co-Chair (if applicable)

Weintraub, Michael

Committee Member

Remold, Susanna

Committee Member

Emery, Sarah M.

Committee Member

Eason, Perri

Subject

Urban forestry; Invasive plants--Ecology; Honeysuckles--Ecology; Earthworms--Ecology

Abstract

Invasive species are one of the leading causes of biodiversity loss and their presence can significantly impact the structure and function of native ecosystems. In this dissertation, the impacts of the invasive honeysuckle shrub, Lonicera maackii, on exotic earthworm populations, leaf litter decay responses, and inorganic and organic nutrient pools in an urban woodland park are assessed. Chapter 1 provides a brief review of honeysuckle's effects on forest ecosystems. Chapter 2 describes honeysuckle’s effects on exotic earthworm populations and the seasonal importance of macroinvertebrates to leaf litter decomposition in urban woodlands. This study revealed that L. maackii promoted higher exotic earthworm biomass and density and that macroinvertebrates actively decomposed litter across all seasons. In Chapter 3, the effect of macroinvertebrate activity (including earthworms) on the decomposition and nitrogen dynamics of honeysuckle and sugar maple leaf litter mixtures during the late winter were assessed to determine if they contribute to honeysuckle success. Without macroinvertebrates, litter mixtures imported nitrogen in late winter, reducing nitrogen availability to plants. With macroinvertebrates, nitrogen release coincided with honeysuckle leaf expansion in late winter. Since no other woody plants exhibited such early leaf expansion phenology, honeysuckle is in an advantageous position to take up this nitrogen pulse. The results of Chapters 2 and 3 together provide strong support for a positive feedback between honeysuckle and soil processes and the existence of invasional meltdown between earthworms and honeysuckle. In Chapter 4, the temporal dynamics of inorganic, organic, and microbial biomass C and N pools were assessed with respect to honeysuckle presence and time since honeysuckle removal. The results from this analysis indicated that neither honeysuckle shrub presence nor time since removal were important factors in determining inorganic, organic, or microbial nutrient pools. Percent bare soil and soil moisture content were the most common factors predicting soil nutrient dynamics during each season. Overall, these results suggest that honeysuckle and exotic earthworms may form an ‘invasional meltdown’ leading to increasing rates of invasion and/or increased impacts on native communities and ecosystems. However, other factors may be more important in determining soil nutrient dynamics than L. maackii presence alone.

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