Why is reed canary grass such a problem?
The highly competitive reed canary grass (Phalaris arundinacea) now dominates seasonal wetlands and other sites throughout North America. Like purple loosestrife (Lythrum salicaria) and cattails (Typha x glauca), reed canary grass spreads quickly and forms dense monocultures with which few native species can compete, resulting in an overall loss of biodiversity, including reduced diversity of physical and abiotic features, flora, and fauna.
Some wetland flowers you may NOT see in a wetland
dominated by reed canary grass, from left to right: swamp milkweed (Asclepias
incarnata), blue-flag iris (Iris versicolor), Michigan lily (Lilium
michiganense). Photographs by Laura Phillips, 1998.
Impacts on native vegetation
For decades, the increased spread of reed canary grass in natural areas
has been accompanied by a decrease in native wetland and wet prairie
species. Barnes (1999) monitored the vegetation on a small river island in
western Wisconsin over a period of 15 years. During that time, a single
reed canary grass patch spread to become the dominate species of the wetland
zone up to one meter above the water level. Several forbs and grasses that
were abundant in this zone at the start of the study were reduced to near
complete absence during this period. The rapid spread of reed canary grass
during this period was attributed potentially to introduced aggressive
ecotypes of reed canary grass, as well as several years of low water levels,
which made the one-meter zone available to (that is, unflooded) reed canary
grass for a longer period of time each year.
Reed canary grass is believed to be a threat to many plant species, including the endangered annual aquatic plant, Howellia aquatilis, located on The Nature Conservancy’s Swan River Oxbow Preserve in Montana. Nine years after invading the preserve from a nearby national wildlife refuge, reed canary grass cover increased by 35% while H. aquatilis declined to near extirpation.
Despite numerous observations of similar trends in wetlands across North America, until recently it has not been clear that reed canary grass invasion was actually causing the decline of native species. It has been presumed that the aggressive grass species actively out-competes and displaces native species, but the possibility that reed canary grass spread and native species decline were two different processes both responding to some other environmental change could not be entirely discounted.
However, recent research seems to support the hypothesis that reed canary grass is directly displacing native vegetation. In greenhouse mesocosm studies, reed canary grass suppressed native sedge meadow vegetation across different nitrate-N levels, indicating 1) that reed canary grass displaces native vegetation, and 2) that this interaction is not dependent on nitrogen levels (as has been hypothesized) (Green and Galatowitsch 2001).
Impacts on wildlife
As reed canary grass forms dense monotypic stands, it reduces plant
structural diversity as well as species richness, which results in less
usefulness of the wetland for wildlife. In general, monocultures are less
useful to wildlife than diverse ecosystems, because they provide fewer and
less diverse overall resources. A diverse plant community provides food,
habitat, and other resources (such as nesting materials for birds, etc.) for
a greater variety of species than can any single monoculture.
Generally, reed canary grass is believed to have little value to wildlife, although its seeds may be eaten by some bird species (hence the common name), and its displacement of native vegetation is thought to negatively impact wetland wildlife, such as turtles, frogs, and some marsh nesting birds. Currently there is ongoing research in Minnesota and Wisconsin seeking to determine the comparative value of reed canary grass-dominated wetlands versus diverse wetland communities as wildlife cover and habitat for insects, amphibians, reptiles, birds, and mammals.
A frog suns itself on a milkweed leaf on the edge of a dense
reed canary grass patch. Reed canary grass is assumed to provide
little benefit for wildlife. Photograph by Laura Phillips, 1997.
Aesthetic impacts
In addition to the ecological impacts of reed canary grass invasion,
there are important aesthetic impacts as well. Humans seem to inherently
value biodiversity, and a vast expanse of reed canary grass monoculture
simply isn’t as pretty, interesting, or inspiring as a diverse wetland
community, with lush sedges and grasses, and different forbs flowering
throughout the growing season, and an abundance of wildlife using the site
Financial costs
Once reed canary grass is established, it is incredibly difficult and
costly to control, both in terms of financial costs for herbicide,
mechanical equipment, and native seeds/plants (to revegetate the site after
reed canary grass removal), and in terms of labor. Herbiciding, burning,
mechanical removal, replanting, and long-term monitoring are labor intensive
and time consuming activities, often requiring large numbers of volunteers.
Even after the first few years of initial removal, long-term control and
monitoring of reed canary grass may require more than one hundred hours per
year for many years. Control may need to be continued indefinitely.
Unless otherwise noted, information on this page is based on the following sources in addition to the author’s personal experiences: Apfelbaum and Sams 1987; Hutchison 1992; Kilbride and Paveglio 1999; Lyons 1998; and the Wisconsin DNR website.