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  • Restoring Wetlands Dominated by Phalaris arundinacea (Reed Canary Grass) with Multiple Treatments: Haying, Spraying, and Establishing Aggressive Competitors
  • Olivia Clark (bio) and Meredith Thomsen (bio)

Phalaris arundinacea (Reed canary grass, hereafter RCG) is widely distributed within North America and Eurasia, where it is cultivated as a forage crop for agriculture and for erosion control. Most RCG strains in the United States are hybrids of native and European geno-types and behave invasively (Merigliano and Lesica 1998). RCG is a dominant wetland invader in North America that can outcompete native plant species and alter ecosystem diversity (Healy and Zedler 2010, Lavergne and Molofsky 2010). RCG is a clonal C3 grass that has a competitive advantage of early spring emergence in wet and disturbed conditions, which decreases light availability for other plants (Kercher and Zedler 2003).

Eradicating RCG in the long-term is challenging (Hovick and Reinartz 2007, Thomsen et al. 2012). After treatment, RCG can regenerate by rhizomes and seeds, the longevity of which can be 20 years or more. Studies suggest that multiple treatment strategies should be combined to suppress RCG and promote native plant growth (Lavergne and Molofsky 2006, Hovick and Reinartz 2007, Healy and Zedler 2010). In their review of RCG management techniques, Lavergne and Molofsky (2006) concluded that herbicide, tilling, fire, and planting native seeds show the potential to suppress RCG, though additional research is needed to find combinations that are effective in the long term.

In this study, we compared long-term haying to haying plus spring glyphosate application in terms of their effects on RCG and on other resident species. Furthermore, we evaluated the survival and growth of three native species planted as plugs in treated plots: Spartina pectinata (prairie cordgrass), Carex vulpinoidea (fox sedge), and Helianthus grosseserratus (sawtooth sunflower). [End Page 6]

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Figure 1.

Mean percent cover of RCG (A), graminoids (B), and angiosperms (C) in hayed-only (dashed line) and hayed plus herbicide (solid line) treatments throughout the summer. Measurements reported here were taken in subplots without planted plugs. Asterisks indicate significant differences between treatments.

Our study was conducted in a Mississippi River flood-plain site near La Crescent, Minnesota that was acquired by the U.S. Fish and Wildlife Service (USFWS) in 1994. The eight-hectare area was regularly hayed for the past 35 years and was hayed again in September of 2017. According to an oral history of the site, the establishment of the lock and dam system along the Mississippi River changed the site’s hydrology and limited the use of the land to haying and cattle grazing (Miller and Miller 1994). This same source indicated that the hay consisted of Phleum pretense (Timothy grass) and RCG, which was used for beef cattle feed and for mulching strawberries.

Timing on annual haying likely varied from year to year, but due to wet conditions the site is most reliably accessible in the late summer and fall. Annual haying may be responsible for the substantial component of graminoids and forbs which have persisted in the site despite high percent cover of RCG (Figure 1, hayed-only plots). Six members of Carex and nine native angiosperms were cataloged in the test plots during the summer 2018, with a mean coefficient of conservatism value of 3.0 (Table 1). The unusual persistence of native vegetation in an area dominated by RCG led to an interest in testing restoration strategies to augment native species richness, improve resident native plant performance, and decrease RCG cover in the site.

We established a total of 24 experimental plots, 3 × 3 m in size, in four rows near the north end of the site, with 2 m between plots. Sixteen plots were hayed only, while eight plots were hayed and also sprayed with glyphosate

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Table 1.

A list of graminoid and angiosperm species, their indigenous status and conservation value. The mean coefficient of conservatism of species found at the site was 3.0.

[End Page 7]

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Table 2.

Results of repeated-measures ANOVAs for the effect of herbicide treatment on resident plant performance in June, July, and...


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