• Start-up
  • Planning
  • Action
  • Evaluation
The Bohn Farms project was developed as a wetland compensatory mitigation site through Wisconsin’s In-Lieu Fee program, to restore wetland hydrology and native plant communities to fields that had been drained and farmed for over one hundred years. The Wisconsin Department of Natural Resources (WDNR) and Stantec developed and implemented the restoration design, constructed the site, and initiated a five-year monitoring and management period, beginning in 2020. The Bohn Farms project incorporates climate adaptation approaches into the hydrologic restoration design, native plantings, vegetation management, and vegetation and hydrology monitoring. The site has features that may enhance adaptability to climate change, including its location on a sub-watershed divide, location near the northern range limits of many plant species, extensive contiguous conservation lands, and existing species and habitat diversity. The eastern portion of the site contains a mosaic of moderately degraded remnant upland and wetland habitats.

Project Area

Site (Photo credit: Josh Sulman)
The Bohn Farms site (79 acres) was a family farm for over 100 years – consisting of pasture, woodlots, and row crop cultivation. The adjacent land uses include residential development, agriculture, and conservation lands owned by WDNR and Ducks Unlimited. In 2018 the Wisconsin DNR acquired the property for the purpose of establishing a wetland mitigation site. The site has rolling lake plain topography, with a mosaic of ephemeral wetlands and upland forest in eastern one-third of the site. The western two-thirds of the site has been tilled and extensively drained, resulting in a loss of historic wetland hydrology, native plant diversity, flood storage capacity, and wildlife habitat value. Unique to this site is the remnant ephemeral ponds, which are significant habitats for amphibians and other wildlife but are especially vulnerable to climate change.

Management Goals

Ephemeral ponds (photo: Josh Sulman)

The Wisconsin DNR's goal is to restore the Bohn Farm site to a healthy wetland, that provides long-term sustainable wetland functions, diverse plant and wildlife habitat, stormwater storage, groundwater function, and recreational values. To help achieve long-term management goals, WDNR and Stantec developed a restoration plan that restores ecosystem and hydrologic function to the site, assesses site-specific climate change impacts and vulnerabilities, and incorporates climate adaptation approaches and tactics. 

The following are objectives for the restoration of Bohn Farms:

  • Restore drained croplands to diverse native herbaceous wetland communities, by filling ditches, restoring microtopography, and re-establishing diverse, native wetland vegetation.
  • Slow runoff from the site, increase stormwater storage capacity and provide a gradual release of clean water to the downstream watershed. 
  • Increase grassland/wetland wildlife habitat (birds, herps, pollinators).
  • Control invasive species including reed canary grass (Phalaris arundinacea), invasive Phragmites (Phragmites australis subsp. australis), non-native cat-tails (Typha angustifolia, T. X glauca), common buckthorn (Rhamnus cathartica).

Climate Change Impacts

For this project, the most important anticipated climate change impacts include:
Precipitation projections point to increases in annual precipitation, potential for reduced growing season precipitation, and continued increases in intense precipitation events.
Increasing winter and spring precipitation, that may result in lower snowpack and less infiltration. Rain in winter and spring increases risks of erosion, can affect early stages of vegetation establishment.
Dry and droughty conditions may affect plant establishment, especially on clay soils. Reduced soil moisture is of concern in mid-elevations, and in formerly cropped areas with compromised structure and less organic matter.
Ephemeral ponds are vulnerable to changes in water depth, and warming temperatures.
Invasive species are expected to get worse over time. Non-native invasive species and woody species may outcompete vegetation, particularly early prairie plantings. Reed canary, invasive Phragmites are already on site, and hybrid cat-tail exist nearby.
Prominent upland forest and savanna species onsite, including white, bur, and swamp white oaks, are projected to have suitable habitat on site by end of century.

Challenges and Opportunities

Climate change will present challenges and opportunities for accomplishing the management objectives of this project, including:

Challenges

Increased competition and spread from invasives, particularly during establishment phase.
Heavy rainfalls could wash away seed, injure/uproot plants during vulnerable life stages, or reintroduce invasive propagules.
Sedge meadow species and hummock microtopography may be vulnerable to sedimentation.
Drought could wipe out young plantings.
Canopy openings may have negative impacts on ephemeral ponds by increasing water temperatures and changing how ponds receive precipitation, affecting amphibian breeding.
Brush invasion may become a challenge to maintaining herbaceous species diversity in forest and savanna groundlayers, prairie, and herbaceous wetlands; atmospheric nutrient enrichment may increase woody vigor and growth rates.
Enhanced invasive species vigor due to longer growing seasons may become difficult to control, and existing control measures (e.g. herbicide application) may conflict with native plant establishment.
Prescribed burning windows may become increasingly narrow and/or unpredictable limiting options for managing reed canary grass and brush invasion.
There is uncertainty about future precipitation and hydrological conditions that may conflict with restoration project specifications.
Extreme rain events and frequent inundation could erode or overwhelm water control features (e.g. berms).

Opportunities

The site is located in the Tension Zone, near northern range limits of many species; offers flexibility for using a range of prairie and savanna species that are likely to migrate north.
Increased opportunities for including more southern species in planting mixes. Wet prairies and sedge meadows are inherently adaptable to variable hydrology; this is the mechanism behind hummock formation. Longer growing seasons can help establishment.
Prairie species are intrinsically heat- and drought-tolerant. Wet prairie species will be more flexible to accommodate fluctuating water levels, and drought.
If climate change promotes greater growth of prairie and wetland plants, the resulting biomass and thatch, may help fuel fires.
Opportunity to increase water storage capacity for stormwater due to amenable site conditions, earthmoving equipment, budget.
Mature oaks (swamp white and bur) on sites are drought tolerant and can tolerate upland and wetland conditions, offering flexibility with changeable moisture regimes. Oaks are expected to have more suitable habitat in the future.

Adaptation Actions

Project participants used the Adaptation Workbook to develop several adaptation actions for this project, including:

Area/Topic
Approach
Tactics
Entire site
Monitor sites that are vulnerable to invasive species invasions (e.g., areas prone to flooding); and control new infestations before they become dense.
Conduct prescribed burns to restore savanna and wetland communities.
Open Wetlands (wet prairie and sedge meadow
Plant diverse seed mixes of species that can tolerate a broad range of moisture regimes (including inundation and drought) and soil types.
Seed species broadly across edaphic gradients to allow plants to occupy spaces according to moisture and nutrient tolerances.
Implement passive hydrological control by designing small check dams/ditch plugs to retain water on site.
Design perimeter berms to withstand extreme storm events and retain water on site.
Examine adjacent off-site water levels and flow patterns during extreme rain events to determine if there is potential for invasion by invasive species (e.g. Typha, etc.).

Monitoring

In 2020, Year 1 of the monitoring period, groundwater hydrology was monitored at 17 wells across the Site. A total of 183 native plant species and 58 non-native species, were recorded within the Site. In addition, 75 species of birds, and six herpetiles, were observed.

Overall, project participants identified several monitoring items that could help inform future management, including:
Invasive species: Annual meander surveys and quadrat surveys (species and percent cover, if >20% cover implement control measures)
Acres of wetland: Following 5 year delineation (total acreage of wetland onsite will be delineated, and compared to baseline delineated acreage, prior to construction--2018)
Prescribed burn implementation: Post burn inspection - acres burned, percent black, percent cover of native vs. invasive/wood plants, grassland birds
Shallow groundwater hydrology: monitoring wells across Site wetlands will record water table data for the first 3—5 years following construction

Project Documents

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Keywords

Planting
Savanna/ open woodland
Water resources
Wetlands

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