“Eventually, all things merge into one, and a river runs through it.”— Norman Maclean, A River Runs Through It
To many people, the Arboretum represents a destination for regular respites from the hustle and bustle of the city. We also provide a beautiful setting for exercise, whether on foot, a bike, or cross-country skis. To others, the Arboretum is a place to learn—during public talks, field trips, guided walks, or summer camp. All of these uses represent services that the Arboretum provides for people who visit us. But Arboretum land also provides services beyond visitor enjoyment. In the past few decades, nature’s contributions to people’s well-being, often called “ecosystem services” in science circles, have received a great deal of attention, especially as we lose species and ecosystems that help provide these services.
Nature’s contributions to human society fall roughly into three categories: material resources like food, minerals, and lumber; non-material resources like the inspiration gained by visitors to the Arboretum; and regulatory functions like pollination, protecting water quality, and attenuating erosion. A study published last month in Science highlighted the regulatory functions of nature by mapping where these services are most needed and who bears the brunt of the problems when they are lost. The authors created amazing interactive maps to accompany the article, illustrating global patterns of ecosystem services now and in 2050.
The Arboretum’s native plant communities support many pollinators, and pollinators are vitally important to ecosystem functioning. However, pollination services are usually quantified using the monetary value of crops that require animal pollinators. Since we are located in the middle of a city, there aren’t many crops close enough to benefit from the pollinators that thrive here. It is thus difficult to quantify the value as a conventionally defined “ecosystem service,” but the importance of pollinators to healthy and diverse ecosystems is undeniable.
The Arboretum’s important impacts on water quality can, at least partly, be quantified. About 300 million gallons of stormwater runoff flow every year into the Arboretum, which lies at the bottom of the Lake Wingra watershed. There is a cost to this influx: trails are eroded and other parts of the infrastructure are damaged; nitrogen and phosphorous carried in the water alter nutrient levels to the benefit of invasive species; and changed water levels negatively affect many restored plant communities. However, Arboretum land provides some clear “downstream” benefits, with the support of hydrological engineering projects called stormwater ponds.
Most of the water bodies in the Arboretum were constructed by people. At first, this construction focused on wildlife habitat. Spring Trail Pond (aka the Duck Pond) was dredged to provide (of course) duck habitat before the Arboretum existed. Stevens Pond, Ho-Ne-Um Pond, and Teal Pond were dug in the 1930s after the land was acquired by the University of Wisconsin. The goal of Arboretum founders and early leaders in creating these ponds was to support ecosystem services (although that phrase was not yet in use) by providing wildlife habitat, to serve the Arboretum’s wildlife research mission, and to give Madison residents a place to observe wildfowl and rare bog plants. Stormwater wasn’t a big issue then, before Madison’s growth led to widespread construction of impervious surface in the watershed.
Marion Dunn, Manitou, and Curtis ponds were dug at the Arboretum to handle the water flowing in from the surrounding city. The ponds temporarily hold the water to allow sediments and nutrients to settle out before it flows through Arboretum land and marshes to Lake Wingra. The land, marshes, and ponds all function to slow the flow into the lake by absorbing some and cleaning the rest. The water volume and untrapped nutrients present challenges, but the ponds provide a net benefit to the quality of water that flows into Lake Wingra, and then the Yahara, Rock, and Mississippi rivers, and eventually the Gulf of Mexico.
Arboretum land provides key ecosystem services, but it needs help from surrounding communities. We are working with the Cities of Madison and Fitchburg, Town of Madison, and State of Wisconsin to mitigate impacts and increase our capacity to improve water quality before stormwater flows into Lake Wingra. There are many ways that you can help decrease the quantity and increase the quality of water flowing through the Arboretum. For ways to prevent stormwater pollution and reduce runoff and flooding, please read the Homeowner’s Guide to Watershed Health, a handout created by Laurie Elwell, a Friends of the Arboretum board member and Wisconsin Master Naturalist volunteer. Together, we can make a difference in our neighborhoods and the many downstream places to which we are connected by water.
—Karen Oberhauser, Arboretum director