In Praise of Plants: Researchers Talk About Lessons Learned from Decade-Long Survey on Wisconsin Lakes

by Cassie Gauthier – When you think of a beautiful natural area, what do you imagine? Maybe you think of a lake at the top of a mountain with clear water and tall pine trees creating beautiful green reflections along the shoreline. Or maybe a desert with lizards scurrying around in the hot sun under and around orange-tinted rock formations lined with cacti as far as you can see. You could picture a pond with big lily pads covering the surface and frogs jumping between each one, or a rainforest so thick with large green leaves that you can’t see ten feet in front of you.

Regardless of where you thought of, it likely shared a common feature – plants. Why? Because everything needs plants. Plants provide food, shelter, and clean air to breathe. The more plants around, the more healthy, natural, and vibrant an area seems.

Using the long-poled metal rake, Carol collects aquatic plant samples. Photo: Carol Warden

It makes sense, then, that some scientists would spend their whole career studying and surveying them. Susan Knight and Carol Warden are two scientists who work at Trout Lake Station year-round and have dedicated their summer to conducting plant surveys of lakes in Northern Wisconsin for the Wisconsin Department of Natural Resources.

Part of Susan and Carol’s work this summer is to continue collecting long-term data of plant population surveys on 12 lakes. These lakes have been studied for more than a decade because they all contain a non-native plant, Eurasian watermilfoil. Half of the lakes they are sampling have been chemically treated to kill the Eurasian watermilfoil, while the other half have not. The goals of collecting this data are to better understand how this invasive species and each lake’s other aquatic plants vary over time with and without chemical treatment.

Susan and Carol collect their plant surveys by using a technique called point-intercept surveys. They do this by driving on a boat on a grid of GPS locations previously laid out for them throughout the lake. At each location they lower a rake with a long, 15-foot handle on it out of the boat and to the bottom of the lake. They spin the rake twice to gather plants and then raise it back up into the boat. They identify the overall abundance of plants on the rake on a scale of 0-3 (zero being no plants and 3 being the tongs on the rake are completely covered), the species of plants present, the abundance of each individual plant species, and the type of sediment on the lake bottom that the plants are growing in. This data is part of one of the longest running data sets of point-intercept plant surveys on lakes in Wisconsin, and possibly within the whole country.

“I know some people might think this type of sampling is tedious, but really we love being on the lakes,” Susan says. “For us, bringing the rake up and seeing rare plant species that we don’t usually see is like getting the best Christmas present.”

The map of Carpenter Lake shows an example of what the GPS grid Susan and Carol travel looks like when they survey a lake. Each dot on the map marks a location they sampled.

This map of Carpenter Lake shows the results of Carol and Susan’s survey work.

These types of plant surveys can provide important information about a lake. Some of the things they can accomplish are making maps of where a singular plant is within a lake (as shown with the green and orange dots on the Carpenter Lake map), calculating the frequency of occurrence of a plant within the lake, and providing an overall plant diversity analysis.

Before Susan and Carol began sampling, they hypothesized that Eurasion watermilfoil frequency in lakes without treatment would vary quite a bit, but never fully take over a lake. And, so far, they say their data has been showing this is true. They have also been finding that all aquatic plants, including Eurasion watermilfoil, vary quite a bit in population size from year to year, and that Eurasion watermilfoil has not had negative effects on native plant populations, although it can be a recreational nuisance in some areas of lakes by negatively affecting people’s abilities to boat and swim. Furthermore, there is evidence that management of Eurasion watermilfoil, particularly with chemicals, is negatively affecting native plant populations.

“I am a firm believer in long-term data sets,” Susan says. “We are learning a tremendous amount about lakes, non-native species, and the consequences of using chemical treatment.”

Though chemical treatments can kill invasive species they often also kill other native species, and remember, the presence of plants can signify a healthy, thriving ecosystem!

Susan and Carol will also do a number of what they call “wellness checks” on lakes throughout the summer. These checks include the kinds of plant surveys described above, as well as assessments of water quality, coarse woody habitat, aquatic invasive species, and shorelines – all of which tell a story about the health of a lake.

Carol says the meat of these wellness checks comes from the shoreline assessments. For part of the assessment, Carol and Susan drive around the shoreline of the entire lake and look at the type of vegetation that is within approximately 35 feet above the shore and 50 feet below. Lakeshore vegetation above the shore is crucial for the health of the lake because it can prevent direct stormwater runoff, minimize erosion and provide habitat. Vegetation within the lake can also provide habitat, prevent erosion, take up nutrients, and minimize impacts from waves.

Susan Knight IDs a plant collected during one of their surveys. Photo: Susan Knight

Carol and Susan assess each property on a lake and bring feedback to lake associations or shoreline homeowner groups to let them know what they are doing well and ways to improve the health of the lake. In a lot of cases, these groups can even apply for grants that give them money to offset costs to protect or improve their lakeshore.

“This is my favorite part of the project because people can become directly involved with improving the health and wellness of the lakes they live on by starting with their own property,” Carol says.

The best way lakefront homeowners can help improve lake health is to minimize their impact near the shoreline, Carol says. This can be done by building rain gardens, planting native plant species between a lawn and lake, or building diversion channels for water to travel through before it flows into the lake. You can find more information about how to successfully do these practices and other similar ones on the healthy lakes and rivers website.

An option that is simpler, less expensive, and perhaps most beneficial for the long-term health of the lake is to simply leave natural vegetation along the shoreline untouched. And if it has already been touched, perhaps mow, leaf blow, and weed whack a little less and leave a few more sticks near the shoreline.

After all, didn’t plants play a big role in the place you imagined when you were thinking of a beautiful and healthy piece of nature earlier? We need plants to stay healthy and so do lakes!