Date of Award:

2016

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Ecology

Advisor/Chair:

Karin M. Kettenring

Abstract

Phragmites australis (hereafter Phragmites) often forms dense monocultures, which displace native plant communities and alter ecosystem functions and services. Managers tasked with controlling this plant need science-backed guidance on how to control Phragmites and restore native plant communities. This study took a large-scale approach - to better match the scale of actual restoration efforts - to compare two herbicides (glyphosate vs. imazapyr) and application timings (summer vs. fall). Five treatments were applied to 1.2 ha plots for three consecutive years: 1) summer glyphosate; 2) summer imazapyr; 3) fall glyphosate; 4) fall imazapyr; and 5) untreated control. Dead Phragmites following herbicide treatments was mowed in the first two years. Efficacy of treatments and the response of native plant communities were monitored for three years. We report that fall herbicide applications were superior to summer applications. No difference was found between the two herbicides in their ability to reduce Phragmites cover. Plant communities switched from emergent to open water communities and were limited by Phragmites litter and water depth. Although, some plant communities showed a slow trajectory towards one of the reference sites, cover of important native emergent plants did not increase until year three and remained below 10%. These results suggest that fall is the best time to apply herbicides for effective large-scale control of Phragmites. Active restoration (e.g. seeding) may be needed to gain back important native plant communities. Methods to reduce Phragmites litter after herbicide applications should be considered.

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