Long-term Wetland Harvesting Study

Building off of the results of our small-scale harvesting experiment, in 2015 we began the implementation of a scaled-up harvesting experiment. With the help of funding provided by the EPA and GLRI, we purchased a Softrak wetland harvester, made by Loglogic. Using this machine we set up and implemented an experimental harvesting regime in Cheboygan Marsh. We laid out a network of 60 x 60 meter plots. We included plots that are harvested once per year, twice per year, plots that the cattails are crushed but not removed, and a set of control plots. Each treatment was replicated five times, with a total of 20 plots.

Through this work we will learn more about the impact harvesting has on plant community structure and Typha dominance. Unfortunately the Softrak harvester is not as thorough as hand removal, but it is the best tool available for Typha harvesting in Great Lakes coastal wetlands on a practical scale. Because of the differences between mechanized harvesting and hand harvesting, it will be important to see how this large scale harvest compares to the results of our hand harvesting experiment.  

We are also tracking the amount of nitrogen and phosphorus that is removed from the site in the form of harvested Typha leaf tissue. Our assumption is that by removing nutrients from the wetland once they are bound in Typha leaf-tissue, we will help mitigate the effect of legacy nutrient pollution in the wetland. To test this assumption, we are closely tracking the amount of phosphorus and nitrogen in the wetland’s sediments and pore water. We are also using plant root simulator (PRS) probes to look for differences in an array of plant micro and macro-nutrients between the treatments. PRS probes integrate the cumulative nutrient availability over a period of several weeks, which gives us a clearer picture of the nutrient conditions experienced by growing plants. These probes are typically used in agricultural fields, but we believe that the data they provide will help us gain an understanding of wetland nutrient dynamics. Much of the nutrient work at Cheboygan has been spearheaded by Kelsey Berke, our lab’s Masters student. While we are still waiting on further analysis, her mass balance calculations based on sediment phosphorus and phosphorus bound in aboveground leave tissue are leading us to believe that just 10 harvests of Cheboygan Marsh could remove the majority of the site’s legacy phosphorus.

Through our long-term harvesting experiment, we are also working to understand the influence these restoration treatments have on wetland carbon and nitrogen cycling. This work has been led by Dr. Beth Lawrence from the University of Connecticut.

This map shows the experimental treatment plots at Cheboygan Marsh, as well as the extent of invasive cattail as of 2010.

This map shows the experimental treatment plots at Cheboygan Marsh, as well as the extent of invasive cattail as of 2010.

The Softrak harvester cutting and collecting cattail biomass at the Cheboygan experimental plots.

The Softrak harvester cutting and collecting cattail biomass at the Cheboygan experimental plots.

In some areas of the harvested wetland, floating organic material acted as a “safe site” for seedlings to establish. Here you can see young cattails (Typha sp.) re-establishing, as well as seedlings of sedges (Carex sp.) that had been uncommon in Cheboygan Marsh before harvesting.

In some areas of the harvested wetland, floating organic material acted as a “safe site” for seedlings to establish. Here you can see young cattails (Typha sp.) re-establishing, as well as seedlings of sedges (Carex sp.) that had been uncommon in Cheboygan Marsh before harvesting.

Graduate student Kelsey Berke collects sediment cores from one of the control plots. By analyzing the nitrogen and phosphorus content of the sediment in different treatments, she is hoping to learn how large-scale macrophyte removal will impact wetland nutrient cycling.  

Graduate student Kelsey Berke collects sediment cores from one of the control plots. By analyzing the nitrogen and phosphorus content of the sediment in different treatments, she is hoping to learn how large-scale macrophyte removal will impact wetland nutrient cycling.