Seeing the forest and the stream: assessing the influence of riparian invasion by the exotic shrub amur honeysuckle (Lonicera maackii) on terrestrial-to-aquatic linkages

Date of Award

2017

Degree Name

M.S. in Biology

Department

Department of Biology

Advisor/Chair

Advisor: Ryan W. McEwan

Abstract

Terrestrial-to-aquatic linkages are an important vector for the transfer of nutrients from one habitat to another. Therefore, the biology of headwater streams is strongly influenced by the surrounding terrestrial riparian vegetation. Amur honeysuckle (Lonicera maackii) is an invasive shrub that thrives in disrupted habitats including stream riparian zones. Although, extensive research has shown the detrimental effects of L. maackii on terrestrial systems, little research has been done on how cross boundary subsidies such as leaves and woody debris are impacted by the dense and often overarching L. maackii invasion in headwater stream riparian zones. Therefore, the aim of this study is to understand the influence of a gradient of L. maackii density in riparian habitats on the contribution of organic subsidies in stream systems in Southwestern Ohio. Across the established gradient of L. maackii invasion leaf litter biomass, fruit biomass, falling twig biomass, terrestrial and aquatic fine woody debris (0.5-9.9 cm diameter) volume and count, and terrestrial and aquatic coarse woody debris (>9.9cm diameter) volume were accessed. We hypothesized that sites with a higher density of L. maackii would have a decreased total leaf litter biomass deposition due to the dense overarching riparian L. maackii over the stream increasing the potential of litter getting caught in the canopy. Additionally, based on the intentionally established gradient of sites we also expected L. maackii leaf biomass to increase as invasion intensity increased. Lastly, we hypothesized that woody biomass in the form of both fine and coarse woody debris would decrease along the invasion gradient due to the dense shrub architecture. The only significant treatment effects in regards to site were found for L. maackii only leaf litter biomass (p = <0.0001), count of aquatic fine woody debris (p = 0.03292), and fruit biomass (p = 0.00597). In all cases the observed treatment effect did not follow our hypotheses. The results of overall biomass and fruit biomass suggest that impact along the L. maackii gradient was not strong enough to overcome the impact of the riparian zone species heterogeneity and spatial differences. Additionally, the unique physiology of L. maackii appears to have strong potential influences on the biomass of leaf litter created by L. maackii as well as on the amount of fine woody debris generated that is also greater than the impact of the unique dense L. maackii canopy architecture. Despite the lack of support for our hypotheses of increasing loss of subsidies as L. maackii riparian density in the form of an overarching architecture increases, the increased presence of L. maackii in aquatic stream systems still has a myriad of negative consequences including potential bottom up effects.

Keywords

Forest litter Ecology, Honeysuckles Ecology, Invasive plants Ohio, Stream ecology Ohio, Land-water ecotones, Ecology, Biology, Lonicera maackii, Amur honeysuckle, invasive species, terrestrial-to-aquatic linkages, invasion ecology

Rights Statement

Copyright © 2017, author

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