Management of Horicon Marsh Wildlife Area

Following the illegal ditching and draining of Horicon Marsh in the early 1900s, marsh waters were restored by the construction of a dam on the Rock River. That dam is still in use today and allows wildlife managers to adjust the timing, depth, and duration of flooding in the marsh. 

Wetlands naturally experience variations in water levels because of seasonal and climatic precipitation cycles. Wetland productivity depends on this cycle of drought and flood. During dry times, when marsh sediments are exposed, wetland plants germinate from the seed bank, and mud flats and shallow water provide critical habitat for shorebirds, dabbling ducks, sandhill cranes, herons, and other species. This stage of the cycle also consolidates wetland soils and helps to improve water clarity. As precipitation and water depth increase, diverse emergent plants form the base of a food web that includes invertebrates, waterfowl, amphibians, and semi-aquatic mammals like muskrats and mink. Eventually, deep or persistent flooding kills emergent wetland plants, and the marsh takes on the appearance of a shallow lake. At this stage, the wetland loses productivity and wildlife use declines. Wetland managers use the Horicon dam and other infrastructure like embankments, pumps, and stop-log structures to mimic this wetland cycle. Wetland impoundments (engineered systems of embankments, pumps, and stop log structures) give managers a greater range of water level adjustment and, in turn, a better ability to mimic the wetland cycle.

Since the 1980s, the wetland plant community in Horicon Marsh has changed dramatically because of the spread of invasive ‘hybrid’ cattails. Today, nearly all of the emergent vegetation at Horicon Marsh is hybrid cattail, which has greatly reduced the productivity and suitability of the marsh for wildlife. Hybrid cattails are tolerant of a wide range of water depths, from nearly dry soil to water 3-4 feet deep, and they thrive in stable water rich in nitrogen and phosphorous. Under these conditions, hybrid cattail grows taller than 10 feet, and the dense plant growth accumulates each year, creating a mulch that inhibits the growth of native wetland plants. Control of hybrid cattails is a primary goal of wetland managers. Methods of control include mimicking wetland drought and flood cycles to stress cattail and establish native plants, burning wetlands to reduce cattail litter, and clearing away old cattail stems to increase the effectiveness of herbicide application. Herbicide is targeted at historically open water areas like small potholes or old river channels where treatment is expected to have a longer-term effect.

In uplands, grasslands are managed using prescribed fire, herbicide, mowing and tree removal to prevent woody and invasive plant spread. Timber harvest and timber stand improvement activities are used in forests to promote the regeneration and growth of tree species highly beneficial for wildlife, particularly oak. Oak trees were historically abundant around the marsh. Oak seedlings require abundant sunlight and establish best on forest edges or under very open forest canopies, often in the presence of fire. Without fire or timber harvest, oak forests become invaded by tree species more tolerant of shade and eventually, oaks and the incredible wildlife benefits they provide are lost from the forest. Management is done at this property to prevent the loss of oaks and foster new oak growth.