Restoration ecologist battles invading plants
by Madeline Fisher
In the face of a pernicious invading foe, what’s a restoration biologist to do? If you’re the director of research at one of the world’s leading centers of restoration ecology – the art and science of rebuilding lost or threatened landscapes – you experiment.
 Joy Zedler, standing above, Aldo Leopold Professor of Restoration Ecology, works with graduate students to determine the degree of encroachment of reed canary grass in the UW–Madison Arboretum. Aided by runoff, this exotic plant has overwhelmed a large tract of Greene Prairie. Photo Jeff Miller.
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Joy Zedler, Aldo Leopold Professor of restoration ecology, is proposing just that as she confronts the menace of reed canary grass. Aided by urban runoff, this exotic plant has overwhelmed a large tract of the Arboretum‘s Greene Prairie, considered to be one of the world’s finest restored wet prairies.
The experiment, which involves introducing native plant species that might be able to stand up to the invader, may provide new insights into combating the mushrooming problem of exotic plant species, which aggressively displace native vegetation and cause loss of biodiversity.
In the large-scale experiment, Zedler envisions that six one-acre study plots would be cordoned off in the site. Three plots would act as controls of solid reed canary grass and three would receive a mosaic of treatments, including the planting of experimental native plant assemblages.
In addition to providing research and teaching opportunities for university faculty and students, Zedler hopes her strategy will educate the public about the problem of biodiversity loss.
“Until loss of biodiversity stares you in the face, it’s hard to comprehend,” Zedler says. “The experiment will provide a place to see side-by-side a diverse habitat with native plants, and monotypic reed canary grass. The public can then begin to form impressions about what they prefer.”
In the 1940s, Henry Greene, a UW botanist and prairie expert, almost single- handedly restored the prairie that bears his name after the former farmland became part of the Arboretum. Don Waller, professor of botany and former chair of the university’s arboretum committee, says Greene Prairie is “one of the best reconstructed prairies in the country” and one that has taught ecologists much about the science of restoration.
Although some varieties of reed canary grass are native to the United States, Zedler believes the plant now overrunning the prairie is a weedy European strain that has been extensively planted as forage for dairy cows and to prevent soil erosion. This variety not only aggressively displaces native plants, but furnishes poor habitat for native wildlife as well, Zedler says.
Across the country, invasive species such as reed canary grass, “are one of the four main engines of biodiversity loss,” says Waller. Human changes to the landscape tend to favor the growth of these weedy plants.
Surrounded by the city on all sides, the Arboretum’s fortunes have certainly been shaped by human activities. In particular, as urban development has expanded over the past 60 years, the Arboretum has received increasing amounts of storm water runoff from city streets. Ironically, a gutter system installed by the city in the early 1990s to divert runoff around the site’s southern end seems to have contributed to the current crisis in the prairie, says Zedler.
The gutters, which collect water that once flowed across Seminole Highway and directly onto Arboretum lands, discharge through a pipe just outside the southwest corner of the Arboretum near the prairie. Now, with every storm, a flood gushes from the pipe, and water that used to flow out over a large area completely inundates a relatively small one. The torrent pools under trees in the southwest corner, giving the woodland an uncharacteristic swampy appearance. From there it streams across the lower prairie, along the railroad tracks that mark the prairie’s southern border.
As the water flows, it carries with it sediments and nutrients, both of which, in addition to increased wetness, may favor the growth of reed canary grass, says Zedler. The grass now covers roughly seven acres of the prairie’s southern fringe and has approximately doubled its acreage in the last 10 years.
Once established, reed canary grass aggressively reproduces. Not only can the plant send stems snaking underground, guerrilla-style, to rapidly invade the territories of other species, but it showers the ground with thousands of seeds. For example, last semester Zedler’s restoration ecology class conducted a baseline study of the lower prairie and found that reed canary grass seeds composed 60-80 percent of the total seed bank in the soils.
Suzanne Kercher, a graduate student of Zedler’s in the botany department and a class member involved in the soil study, says the students’ results indicate that Greene Prairie must be replanted with native species in order to restore it.
But what plants can successfully repel the invader, especially under the water-logged and nutrient-rich conditions that now exist at the site? Unfortunately, the plants originally placed in the prairie by Greene are not likely to be contenders.
Instead, a group of “aggressive, weedy” native plants will probably be tried, says Zedler, including prairie cordgrass, Canada blue joint, and certain aster, goldenrod and sunflower species. As part of her doctoral research, this spring Kercher will begin to examine how these “mean and pretty” species tolerate flooding and high nutrient levels under controlled conditions in pots.
The next step will be to plant the tolerant species as assemblages in the lower prairie. Zedler’s current plan is to make 40 circular plantings within the three one-acre experimental plots. The plantings will be collared with plastic initially to prevent reed canary grass from moving in.
Within these protected circles, the grass, including its underground stems, called rhizomes, will be removed. Clean soil will be brought in and the native plants will be allowed to grow for a year. Then “the starting gates will be lifted,” says Zedler, referring to the removal of the collars, and researchers will “watch the rhizomes run.” They hope to see that at least some of the experimental native assemblages can prevent reed canary grass from reinvading and perhaps even expand their territories.
Although considered weedy themselves, the presence of native species in Greene Prairie should provide a host of environmental benefits that the European reed canary grass strain does not. For example, besides contributing to the biodiversity of the site, the native plants should promote more insect and bird diversity, says Zedler, although this will need to be documented scientifically.
But perhaps the largest benefit of the native plant reintroduction lies in the lesson to be learned by the public about the sheer difficulty of the endeavor. Says Zedler, “This experiment will demonstrate not only what we’ve lost, but how hard it is to put back. The message is ‘don’t lose it in the first place.'”
Tags: research