Ecological Restoration in Stormwater Ponds and Greenways

A brief overview in the history, objectives, management strategies and renewed approach to improve ecological biodiversity.

Photo of native plantings in stormwater pond.

About Stormwater Pond & Greenway Restoration

 Stormwater  ponds  and  greenways , designed to reduce the environmental impact of water pollution and flooding, also provide urban habitat and environmental corridors. Greenways are often reconstructed to stabilize eroding banks, improve water quality, or expand flood capacity due to increasing storm events. During this process, the existing habitat may be impacted and vegetation removed.

Removing vegetation, especially trees, can feel contradictory to environmental stewardship. However, vegetation removal and the subsequent restoration, addresses long-term goals of creating a resilient stormwater system while increasing urban greenspace biodiversity. The information presented here provides background, context, and transparency to ecological issues facing greenway restorations.

Greenway restoration during first growing season.

Greenway restoration during first growing season.

Staff conducting prescribed burn.

Historical Vegetation

Many of the wooded and turf greenways throughout our city provide wildlife habitat and urban greenspace.  These constructed greenways, while beneficial, do not provide the same ecological benefits as the oak woodlands and savannas, prairie, and wetlands that once covered southern Wisconsin. Where once fire played a critical role in these native ecosystems, this lack of fire now allows for the proliferation and spread of invasive woody plants - even in existing native woodlands. This has led to novel urban ecosystems; greenways that are typically densely shaded and dominated by the fastest-growing tree species and a thick invasive shrub understory. Novel ecosystems are human-influenced ecosystems that differ from ecosystems that historically prevailed.

Remnant prairie in Spring Green, Wisconsin

Restored prairie at Univeristy of Wisconsin Arboretum

Oak savanna, prairie, wet meadows, and emergent marshes were historically dominant in Madison. Tallgrass prairies now cover only 1% of their former acreage (Wisconsin Department of Natural Resources, 2015). Over 50% of the rare plants from the Southeast Glacial Plains Ecological Landscape are found in remnant tallgrass habitat and “even small, isolated, somewhat disturbed prairie, meadow and fen remnants are worth protecting here to maintain local genotypes and assemblages of species that may not exist elsewhere in the Southeast Glacial Plains.” (WDNR, Southeast Glacial Plains Ecological Landscape, 2015). Of the 109 vascular plants on the Wisconsin Natural Heritage Working List, 10 of these are listed as Wisconsin Endangered, 28 as Wisconsin Threatened, and 71 as Wisconsin Special Concern. These increasing pressures reinforce the importance of protection and restoration of urban ecosystem biodiversity.


Evolution of Madison's Stormwater Ponds and Greenways

19th Century Survey of Wisconsin

Finley's 1880's map of historical land cover based on his interpretation of Public Land Survey data. Southeast Glacial Plains Ecological Landscape contained mixture of upland forest, oak openings, prairie, and wetlands (WDNR, 2015).

Pre-1970's

Stormwater management system primarily consisted of farm ditches, rules of thumb and often resulted in pipes that were undersized by today's standards. Focus was to move stormwater away from urban areas as quickly as possible which contributed to piping intermittent streams and constructing concrete channel cunettes (concrete channels).

1970's

Stormwater management = cunettes, turf grass, hard-wrapped (metal sheeting) shorelines.

Mid 1990's

First greenways planted to natives.  Were not maintained and invasive vegetation out-competed native vegetation.

2000's

Vegetation management involved Madison Parks mowing all sites twice a year. Developer constructed public ponds and greenways required to be planted with native seed, but no requirements for maintenance set forth and quickly overrun by invasive plants.

2006

Engineering assumes management of stormwater system from Madison Parks. 

2012

Resident requests to Board of Public Works led to Selective Prairie Management Program, subsequent increased amount of land in “Managed Meadow” status which included mixtures of natives and turfgrass and reduced mowing.

2018 to present

Created Greenway Vegetation Coordinator position to look at stormwater system vegetation as a whole. City and developer constructed ponds and greenways and strict restoration standards to ensure long term success of native plantings.

Native Plants and Ecosystems

Whether a new stormwater system is constructed or an old one is being repaired, the Engineering Department plants the area with native species typically found in oak woodlands, savannas, prairies, and wetlands.

The grasslands that once covered this corner of Wisconsin were comprised of herbaceous species with exceptionally large and deep root systems. These extensive roots systems can capture and infiltrate up to four times more water than the roots of turf grass (Dierks, 2011). The improved infiltration capacity of native plants makes them an excellent choice for stormwater ponds and greenways. Our native prairie and wetland species have the additional benefits of helping to control erosion and reduce nutrient runoff. They are also hardy, drought-resistant, a great habitat resource for wildlife.

Historically, stormwater land was planted to turn and mowed frequently. Today, Engineering's shifted management approach encourages the biodiversity of our native oak woodlands, savannas, prairie, and wetlands.

Management strategies include managed mowing, i.e. timing mows to control invasive species and favor native species; spot mows to control invasive plants while avoiding native plants; manual control of invasive species by digging, cutting or pulling; selective herbicide treatments of invasive species; prescribed burns to control invasive species and favor native plants; collecting and sowing native seed and planting native plants. 

Operation Fresh Start seeding prairie

Two measures of ecosystem health on engineering land are plant diversity - i.e. the number of different species - and the amount of area covered by invasive species. The more native plant species and the fewer invasive species present, the more beneficial the planting is to wildlife, and the more resilient the system is to fluctuating periods of drought and rain.  

Native canada milk vetch, coneflower (yellow and purple), cupplant, false indigo, golden alexander, and milkweed at Nesbitt Pond

Invasive Plants

The Southeast Glacial Plains Ecological Landscape possesses a rich flora, which is highly threatened by the destruction, isolation, and degradation of habitat needed by native plants. Ecological stressors such as development and urban sprawl, the spread of  invasive plants , hydrologic disruption, and high numbers of white-tailed deer continue to affect remnant natural communities with profound impacts.

In addition to those plants recognized on official state lists as “rare” via special designations (such as endangered, threatened, or special concern), many other components of the landscape’s flora warrant monitoring and conservation attention. Recent research has documented significant shifts in the understory composition of forests throughout southern Wisconsin with an overall decrease in native species diversity (Rogers et al., 2008). In particular, there is a region-wide increase of habitat generalists and weeds at the expense of species that are more sensitive and highly specialized.

Whereas native plants help improve stormwater infiltration, reduce erosion and pollution, provide habitat, and add recreation space, invasive plants may actually exacerbate some of the issues native plants may resolve.

For example, a common invasive shrub, buckthorn, can invade the understory of wooded greenways and shade out native shrub and herbaceous growth leaving exposed soil that can then wash out, causing erosion and pollution in our lakes. Purple loosestrife, a wetland invader, can create monocultures that leave pollinators without resources outside of its limited blooming period.

Buckthorn choked greenway

Japanese knotweed monoculture in woodland greenway

Invasive species control is among the most labor-intensive maintenance activities performed on stormwater land. Some species are so prolific that total eradication on all sites is impossible. Engineering staff may prioritize invasive species control by species, i.e. the most destructive species may be targeted first; by area, i.e. those areas with greatest native plant diversity or fewest invasive species may receive more control; or by land use, i.e. areas that are scheduled to be reconstructed in the near future may receive more control efforts to prevent spread during construction.

Most invasive plants produce abundant fruit and seeds that are widely dispersed and remain viable in the soil for years. Reconstruction projects will often expose these seeds, which makes native plant establishment particularly difficult during the first few years. Because of this, most city reconstruction projects are included in an annual ecological maintenance contract for the first few years. This ensures that the first crucial years of the restoration are successful and native plants can establish for long-term sustainable management of the area.

Public stormwater ponds and greenways that are constructed by private developers, not the city are required to create a vegetation maintenance plan and are encouraged to hire ecological restoration firms to maintain plantings until the City assumes responsibility. The pond or greenway must ultimately meet benchmarks for native and invasive plant coverage before the City will accept the land, and a surety is held by the City until acceptance.

City Engineering staff conducting prescribed burn to remove invasive plants

Tree Removals

Trees have many benefits, and are crucial to green infrastructure, bank stabilization, and ecological habitat. The construction of greenways often requires removing trees to stabilize slopes, widen channels, create stream meanders, provide maintenance access, etc. Construction of stormwater ponds can often mean creating flood storage areas. During design of a pond or greenway, a certified arborist will inventory tree species type, quantity, and health. While most wooded greenways are dominated by invasive understory and succession growth including honeysuckle and buckthorn, there are often healthy trees representative of the native ecological landscapes of Wisconsin.

A priority for pond and greenway restoration is to remove invasive species and improve the stormwater system’s overall biodiversity. The majority of trees that are removed in ponds and greenways are part of the city’s ongoing efforts to combat invasive species and are listed by the  Department of Natural Resources NR 40 Invasive Regulated (restricted or prohibited) Invasive Plants  and  DNR Invasive Non-Regulated plants . Oftentimes, other trees may need to be removed if they pose public safety risks (e.g. a decaying tree over power lines), impede reconstruction efforts, or are successional species detrimental to savanna, prairie, or wetland restorations.

Every effort is made to prioritize preservation of trees reflective of the native plant communities that historically dominated our local landscape.

Tree Lane Greenway restoration after construction showing selective tree removals (prior to seed establishment)

Hickory Hollow Greenway immediately after tree removals

Hickory Hollow Greenway summer after removals and native seeding

Wildlife

Ponds and greenways provide habitat to urban-adapted wildlife such as turkeys, deer, coyotes, foxes and many other mammals, birds and insects. While reconstructions of wooded greenways may displace these animals, such impacts are usually mitigated by several factors.

First, ponds and greenways complement shorelines, parks, golf courses and private land as a system of wildlife habitat corridors able to serve as refuges for displaced urban wildlife. Degraded woodlands similar to a typical wooded greenway are a common habitat type within this corridor system. Second, species that thrive in these densely wooded novel ecosystems tend to be those that are more generalist in their habitat needs. These generalist species are well-suited to finding alternative resources when faced with a disturbance such as reconstruction. For example, The Urban Canid Project has tracked foxes denning under porches as readily as in greenways and parks. Finally, reconstruction and subsequent restoration can provide habitat for a wider variety and a greater density of wildlife species, some of whom even have specialized habitat requirements.

Pollinators

Pollinators are one such wildlife group with more specialized needs. Many native pollinators require native plants to feed, shelter and complete their life cycles. In turn, pollinators help native plants to reproduce. Humans also rely on pollinators for the production of up to a third of our food crops, and many other non-food crops and plants. Ponds and greenways rich in native species are an increasingly important refuge for pollinators and can support surprising diversity. For example, urban areas may have higher rates of pollination than rural areas in the same region due to a greater density of flower-rich areas in cities (Halle-Jena-Leipzig, 2020).

Pollinators play a key role in ecosystem function and human health but face the threat of habitat loss, introduced diseases and increased pesticide use. Such is their significance and fragility that the City of Madison, following the lead of the Federal government, created a Pollinator Protection Task Force in 2015. The Task Force outlined strategies to help Madison become a more pollinator-friendly city. In 2019, the City became a  Bee City USA . In 2022, the City joined the  Mayors’ Monarch Pledge  – a program launched by the National Wildlife Federation as part of a tri-national partnership to prioritize monarch conservation. Increasing the biodiversity of the urban system as a whole will support not only pollinator health, but the wildlife, plants and people that depend on the pollinators.

Monarch butterfly on native prairie blazing star

Bumblebee on native Joe pye weed

Ctenucha moth on native glade mallow

Post Construction Restoration

Landscape and ecological restoration is integrated into the design and planning process for each pond and greenway.

This begins during the planning process with an evaluation of existing site conditions including trees, soil type, topography and condition of adjacent land. Seed mixes and tree and shrub planting plans are created based on post-construction site conditions include amount of sunlight the site will receive, slope, depth and duration of flooding anticipated, and additional site uses. For example, an upland pond slope might be planted with oak saplings and seeded with an oak savanna seed mix, while a nearby infiltration basin may be seeded with wet-mesic prairie species. Native seed mixes are encouraged and incorporated in most sites.

It can take several years post construction for the groundlayer to establish in new ponds and greenways. During these early years, sites are managed with a higher level of maintenance to prevent establishment of invasive species. A typical pond or greenway reconstruction will be placed under contracted maintenance with an ecological restoration firm for the first 1-2 years following planting. The first two years tend to require the most intense labor with timed mowing, regular weed control, and possible reseeding or replanting required. Following the initial maintenance period, the sites are placed on a rotational maintenance regimen and cared for by Engineering ecological restoration staff. Ongoing maintenance includes targeted invasive species control, prescribed burns, occasional site mows and reseeding or replanting as needed.

Tree Lane Restoration Year One

Vision for the Future

Encouraging biodiversity of ponds and greenways is a key goal to addressing the steadily increasing pressure on natural and semi-natural habitats. For Madison, increasing biodiversity requires removing invasive species, adding native herbaceous and woody species via seeding and planting, and given the opportunity, converting heavily invaded woodlands to more biodiverse native savannas, prairies and wetlands. The Wisconsin Department of Natural Resources recognizes:

  • Oak openings and upland prairies supply critical habitat for rare plants.
  • Recent research has shown that forests in southern Wisconsin are demonstrating increases in exotic species and habitat generalists at the expense of more sensitive native plants.
  • The key to protecting populations of many of these rare species is to ensure that the natural communities they depend on are managed appropriately and in ways that can accommodate short-term environmental change.
  • Habitat and population isolation, coupled with the spread and explosive increase in invasive species pose major threats to the native flora of the Southeast Glacial Plains.

Healthy urban ecosystems are playing an increasingly important role in addressing environmental degradation, habitat loss and fragmentation, and preservation of species, including  keystone pollinators . Local impacts such as tree removals, herbicide applications, and temporary displacement of wildlife are necessary in order to address long-term goals of improving resilience and biodiversity.

Please see the  interactive map  for a tour of pond and greenway ecological landscapes in the City of Madison.

Sources

Wisconsin Department of Natural Resources. 2015. The ecological landscapes of Wisconsin: An assessment of ecological resources and a guide to planning sustainable management. Wisconsin Department of Natural Resources, PUB-SS-1131 2015, Madison.

GEI Consultants, Inc., & Dierks, S. D. (n.d.). Developing a Stormwater Control Measure Sizing Credit for the Infiltration Improvements Attributable to Plants. Https://Www.Washtenaw.Org/DocumentCenter/View/14315/Dierks_Infiltration-on-Marginal-Soil-in-Rain-Gardens. https://www.washtenaw.org/DocumentCenter/View/14315/Dierks_Infiltration-on-Marginal-Soil-in-Rain-Gardens

About the UW Urban Canid Project. UW. (n.d.). Retrieved April 4, 2022, from http://uwurbancanidproject.weebly.com/about-the-project.html

Pollination is better in cities than in the countryside: Plants benefit from more bees, especially bumble bees. (n.d.). ScienceDaily. Retrieved April 4, 2022, from https://www.sciencedaily.com/releases/2020/01/200129091438.htm

Greenway restoration during first growing season.

Remnant prairie in Spring Green, Wisconsin

Restored prairie at Univeristy of Wisconsin Arboretum

Operation Fresh Start seeding prairie

Native canada milk vetch, coneflower (yellow and purple), cupplant, false indigo, golden alexander, and milkweed at Nesbitt Pond

Buckthorn choked greenway

Japanese knotweed monoculture in woodland greenway

City Engineering staff conducting prescribed burn to remove invasive plants

Tree Lane Greenway restoration after construction showing selective tree removals (prior to seed establishment)

Hickory Hollow Greenway immediately after tree removals

Hickory Hollow Greenway summer after removals and native seeding

Monarch butterfly on native prairie blazing star

Bumblebee on native Joe pye weed

Ctenucha moth on native glade mallow

Tree Lane Restoration Year One