Juncus gerardii has a moderate environmental impact in the Great Lakes.
Juncus gerardii cannot invade areas with existing vegetation or dense litter (Ericson 1981 in Jutila 1999). Juncus gerardii seedlings also have little resistance to burial by wrack (floating plant material); significant amounts can lead to burial and ultimately seedling death (Brewer et al. 1998). For these reasons, J. gerardii becomes established in the first stages of succession after a disturbance (Bouzillé et al. 1997)
Juncus gerardii poses a competitive threat to the native and naturalized Juncus spp. in the Great Lakes, especially those listed as threatened or endangered, including J. alpinus auct. non Vill., J. ambiguus Guss., J. balticus Willd., J. biflorus Elliot, J. marginatus Rostk. var. biflorus (Elliot) Alph. Wood, J. brachycarpus Engelm., J. brachycephalus (Engelm.) Buchenau, J. dichotomus Elliot, J. diffusissimus Buckley, J. ensifolius Wikstr., J. greenei Oakes & Tuck., J. interior Wiegand, J. militaris Bigelow, J. pelocarpus E. Mey., J. scirpoides Lam., J. secundus P. Beauv. ex Poir., J. stygius L., J. stygius L. ssp. americanus (Buchenau) Hultén, J. subcaudatus (Engelm.) Coville & S.F. Blake, and J. vaseyi Engelm. (USDA NRCS 2012c).
There is little or no evidence to support that Juncus gerardii has significant socio-economic impacts in the Great Lakes.
Many Juncus spp. serve as a host for larvae of Coquillettidia, a genus of mosquitoes that can serve as a vector for various animal- and human-borne diseases (Sérandour et al. 2010).
The vegetative parts of J. gerardii are round, stiff, and sharp enough to puncture human skin (College of Environment 2012).
Juncus gerardii may be confused with or pose a competitive threat to native rushes that are culturally important, including J. arcticus ssp. littoralis and J. effusus (USDA NRCS 2012b).
Juncus gerardii has a moderate benefit in the Great Lakes.
In the native portion of its range, J. gerardii is often a preferred species for restoration (especially post-Phragmites control) because its lower growth forms a more open landscape (Casagrande 1997).
Numerous animals feed on the seeds of rushes, including waterfowl, songbirds, quail, cottontail, muskrat (also feeds on roots and rhizomes), porcupine, and other small mammals (Martin 1951 in Stevens and Hoag 2003).
Juncus spp. provide habitat for amphibians and various wetland birds, as well as spawning ground for some fish species (Stevens and Hoag 2003).
The dense root and rhizome system of Juncus spp. enable them to survive periods of stress (drought, flood, etc.), accumulate soil, and provide erosion control (Stevens and Hoag 2003).
Cattle, horses, and sheep will graze on Juncus spp., but J. gerardii’s specific value as fodder is unknown (Centre for Aquatic Plant Management 2004, Cosyns et al. 2005).
The rhizome matrix can support numerous bacteria that can be useful in wastewater treatment (Stevens and Hoag 2003). Use of the plant has been explored for phytoremediation of cadmium (Podlipná et al 2011), boron (Türker et al 2016) and other heavy metals (Milic et al 2021).
Phenanthrenes isolated from J. gerardii have been examined for cytotoxicity against cancer (Stefkó et al 2020) and the plant has also been investigated as a source of antioxidants (Grigore & Oprica 2015)