A particular species of cattail, Typha spp., is spreading steadily throughout marshes in the Midwest, along with another invasive plant, a type of phragmites, a tall reed. Both are very large, very dense and very destructive to the ecosystem of native plants, fish, birds and amphibians in the coastal marshes of the Great Lakes. But the information gathered about these invasive species is being used in a new kind of computer model being developed by an SNRE faculty member that will increase our depth of understanding of ecosystems.
Plants like cattails and reeds degrade wetland habitat, decrease biodiversity and reduce ecosystem services, and because marshes provide a link between land and water, their health is imperative to maintaining the health of the entire Great Lakes Basin. But increased nutrient run-off (the result of urbanization and of nitrogen deposition in upland watersheds) has allowed the invasive marsh species to flourish, and land use and climate changes are likely to expand the species' spread.
Bill Currie, an SNRE associate professor and associate dean for academic affairs, has developed a computer model called "Mondrian" that incorporates satellite images and field data to track the movement of the cattails and phragmites and predict their expansion in different scenarios. Currie and colleagues Deborah Goldberg, the Elzada U. Clover Collegiate Professor and chair of U-M's Department of Ecology and Evolutionary Biology, and researchers from Michigan State University and Michigan Technological University, received a $1.5 million, three-year grant from NASA in May 2011 to map the risk of invasion and altered ecosystem services in wetlands around the entire coast of Michigan.
"This model links knowledge of plant communities—why plants are where they are, how plants compete and how invasive species take over—with our understanding of ecosystem processes, like flows of nutrients, carbon storage and water temperature," Currie said. The model breaks new ground in linking plant community changes and invasions to ecosystem understanding; Currie has been developing this model for three years.
At about 20 field stations in Lower Peninsula marshes, the team is collecting data and tracking the movement of the invasive species.
The team plans to combine information from the field studies, radar and optical images from satellites, and a large-scale model of human-driven changes in large watersheds with Currie's model of wetland ecosystems. Remarkably, the Mondrian model simulates every single plant in a given area individually and models its growth and reproduction. In so doing, the software allows the team to understand how invasive individuals compete on a plant-by-plant basis, and how that scales up to result in dramatically altered marshes.
"The sophisticated simulation software pieces together all you know in a model, then allows you to do experiments and create 'what if' scenarios," Currie said. He expects the model to be useful for other researchers examining invasive plant species across a range of ecosystems.