Resilience through diversity: Incorporating climate adaptation into wetland restoration
April 20, 2020
As our climate changes, so must our approach to ecosystem restoration
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Wetlands provide many services, including wildlife habitat, clean drinking water, flood protection, and recreation. After a century of intensive drainage efforts, Wisconsin has lost about half of its original wetlands. Today, we recognize the value of these wetland functions, and laws now require wetlands be restored to mitigate for activities that result in wetland loss.
A successful wetland restoration depends on achieving a balance that is neither too wet nor too dry. But a changing climate presents new challenges to restoring this balance, when so many factors are in flux. It has become increasingly vital for us to consider the impact of climate change in wetland restoration planning. In the past, we’ve often focused on restoring “historic” or “pre-settlement” wetland plant communities, but these may no longer be realistic targets for all sites. We felt it was time to bring a new approach to our site-specific restoration planning process, in order to address the risks and vulnerabilities associated with a changing climate.
A group of us in environmental services, working collaboratively with the Wisconsin Department of Natural Resources (WDNR), the US Forest Service (USFS), Northern Institute for Applied Climate Science (NIACS), and the Wisconsin Initiative on Climate Change Impacts (WICCI), hosted a two-day climate adaptation workshop focused on Stantec’s Bohn Farms Wetland Mitigation Site. At Bohn Farms, an 80-acre wetland restoration project in Winnebago County, Wisconsin, we’re designing and implementing a wetland restoration for the WDNR’s new in-lieu fee (ILF) wetland mitigation program. Using the Adaptation Workbook, a climate-change tool for land managers, we took a deep dive into site-specific restoration goals, assessed climate vulnerabilities, and adapted our restoration plan to face the challenges of a changing climate.
One of many seasonal woodland ponds at Bohn Farms, which hold water in spring but dry up by summer. These ponds are critical habitats for amphibians but are expected to dry out sooner under warmer future conditions. Retaining shade around ponds is a way to preserve these habitats.
As an outcome of the workshop, we determined that key challenges for this site are expected to include more frequent heavy rainfalls and floods, longer, hotter growing seasons, higher rates of evaporation and water loss, and more intense pressure from invasive species. We developed a site-specific climate adaptation approach to respond to anticipated challenges, with the goal of sustaining wetland functions over the long term. Our approach at Bohn Farms is shared in a project profile on the NIACS website.
Resilience through diversity
A highly diverse system—that is, a wetland with high biodiversity in plant and animal life—can better resist disease and invasive species and is more resilient to disturbance.
It has become increasingly vital for us to consider the impact of climate change in wetland restoration planning.
After more than 100 years of agricultural use, Bohn Farms had lost much of its original species diversity, making it more vulnerable to climate-related disruptions. In our site plan, we increased the number of species in our seed mixes and included a variety of native plants that are adapted to withstand broad ranges of moisture, from inundation to drought.
While diversity in general adds resilience, it was critical to select species that are likely to thrive under future conditions. Recent research indicates that ranges for many of Wisconsin’s native species are expected to shift north: species that currently occur south of our area are expected to thrive here in the future, while species currently near their southern range limits may retreat northward. We consulted species range maps when designing our seed mixes to achieve a mix with high floristic quality, high plant trait diversity, and including many native species that range to the south of the site.
Preserving a refuge for vulnerable species
Future climate conditions are expected to result in greater extremes of weather and moisture, from drought to floods, and overall higher temperatures. This will put stress on wetland flora and fauna. At Bohn Farms, we were particularly concerned about the vulnerability of wooded seasonal ponds, which provide key habitats for amphibians. To protect habitat for frogs, toads, and salamanders, we altered our restoration approach to limit tree clearing around these ponds. Retaining shade in these areas will preserve cooler micro-habitats and surface water, which these amphibians require to breed.
Pair of bumblebees on marsh thistle. Pollinators and wildlife depend on diverse plants for forage, and climate change will alter the mix of species on the landscape. Planting a high diversity of species will help to support many species of insects, birds, and mammals.
Designing with extreme weather in mind
In the past, wetland mitigation often relied on a simple design featuring large basins surrounded by tall berms. But we’ve learned that these types of restorations often result in low quality habitats that lack diversity.
Extreme rain events, which are projected to become larger and more frequent, can erode or overwhelm berms and outlets. For Bohn Farms, we designed and built numerous microtopographic features, such as hummocks and shallow depressions, instead of designing a single, large basin. Many small basins will disperse the energy of peak flows, increase infiltration, and reduce erosion, while providing shallow, dynamic wetland habitats that promote native plant diversity and extensive wildlife use.
Looking decades into the future
How do we know if our plan is working? Will our restoration designs be able to withstand the known and unknown challenges of a changing climate?
The full answer may not become clear for 10, 20, or 50 years. But early indications are promising. Shortly after construction in September 2019, a 4-inch rain event tested the structural design. Numerous small, shallow basins were holding water, and almost no surface flow was leaving the site. Long-term monitoring will be key to evaluating success of the climate adaptation tactics implemented at Bohn Farms and to developing effective adaptation approaches that we may implement on other ecosystem restoration projects.
It’s been rewarding to see how this project has started a conversation around climate adaptation across disciplines, including ecosystem restoration, engineering, and hydrology. We are excited to bring climate adaptation approaches to more projects and clients, as our communities realize that climate change, and its effects, are already here.