Hasenbank Park Project
The Hasenbank Park Restoration project incorporates three distinct aspects to improve habitat, water quality and park usability over a period of three to five years (2022-2026). Project components include:
- Treatment of waters entering Powers Lake through a series of Stormwater Best Management Practices integrated into naturalized park spaces along the western and northern portions of the site.
- Vegetative restoration of Hasenbank Park that will focus on the protection of healthy oaks and other native trees, removal of buckthorn and other invasive species and the replanting of native species typical of oak savanna and oak woodlands. Practices will rely on the use of forestry mowing and goat grazing to remove invasive species in order to reduce the use of herbicides during site preparation.
- Development of plans for the vegetative restoration of wetlands and associated habitats surrounding Fish Lake, which is currently dominated by near monotypes of invasive reed canary grass and hybrid cattail.
Project planning will include consideration of features to provide access into and through restored natural areas and stormwater treatment practices as appropriate. Conversion to native plant communities will consider long term management strategies to support resilience and sustainability through periodic, but regular maintenance practices.
Goats & Restoration
The site is located on city property that receives maintenance only on an as-needed basis (hazardous tree removals). That said, the overall site plan being developed by the city and watershed district would provide a combination of connected project components that include improved ecological integrity of Fish Lake Wetlands, naturalized stormwater features to protect and improve water quality in Powers Lake and the full restoration of oak savanna and oak woodlands in the core of this site with the Hasenbank Park. Located within a nearly fully developed portion of the city, the 61 acres of Hasenbank Park best management practices will provide a large block of connected native plant community green space immediately east of Powers Lake and its associated forested edge.
Hasenbank Park provides an ideal location, on untilled soils, for the restoration of oak forest and oak savanna. Abundant and healthy mature oaks, currently on the site, provide a great opportunity for the restoration of oak dominated communities. Without restoration and maintenance, the native plant components of Hasenbank Park will likely decline through the continued growth and dominance of common buckthorn and non-native honeysuckles. This will eventually lead to the complete loss of the natural community components within the woodlands as regeneration of native species diminishes. Returning diverse native forest and savanna communities will provide enhanced habitat opportunities for a variety of native pollinating insects, birds, and other wildlife adjacent to diverse wetland and upland native plant communities. In addition, existing trails along the margins of the site will offer substantially enhanced opportunities for park users to observe and appreciate ecological function on this site.
The watershed district and city will use a multi-year combination of mowing followed by animal grazing to clear woody invasive species and encourage recruitment of native plant species through regrowth, replanting and seeding. This slow approach has been very successful at removing heavy buckthorn stands and subsequent garlic mustard infestations by weakening these plants numerous times as they re-sprout. The approach reduces the use of herbicides early in the process and allows for more targeted applications on already weakened individuals. This in turn reduces the potential for overspray and long-term effects of herbicide use.
Tentative Project Schedule
Schedule of activities in the coming years is as follows:
- Using qualified native plant contractors, woody invasive shrubs were mowed and mulched by forestry mowers (winter, 2022). Desirable native woody species were identified and protected during forestry mowing. Some continued hand cutting will complete this work.
- Prescribed goat grazing will occur for up to three full seasons in spring and fall to reduce the viability of invasive shrub species and knock back the expected flush of garlic mustard following initial removals.
- SWWD and City staff will survey the woodlands to assess canopy trees for removal. Removals will seek to create a more open canopy in Savanna areas (<50) and more closed canopy in Oak Woodlands (~70). Tree removals will first be driven by control of Oak Wilt, Emerald Ash Borer, and Dutch Elm Disease where potential or present, then by removal of less desirable species (boxelder, young cottonwood, and some black cherry) appropriate to promote target oak communities.
- Seeding of simple grass only native seed mixes will occur in the first year to provide ground layer cover and erosion control, but still offer opportunities to control broadleaved weeds. Mixed grass and forb broadcast seed rains will continue through subsequent years. Seeding just prior to grazing will help with seed to soil contact as goat hooves press seed into the ground.
- Project will create conditions to support future prescribed burns which will occur in future years to control the return of invasive shrub species.
- Tree, Shrub and Forb species for replanting will be identified and planted following assessment of site recruitment following invasives controls.
For years, buckthorn removal relied on a combination of hand pulling smaller stems and cutting/treating of small and large individuals with hand tools and herbicides. While both methods can be successful, they are both labor intensive among other drawbacks. Hand pulling can be very disruptive to soils, creating a bed for invasive weeds to easily establish and disturbing soil structure and underground ecosystems. Cutting and treating with herbicides can sometimes have negative and longer terms effects on recruitment of native species due to residuals or overspray.
Goat grazing to control buckthorn, honeysuckle and garlic mustard has proven effective in areas where these invasive species have become dominant. While the Hasenbank Park contains some native shrub and herbaceous species, common buckthorn was present in all locations and generally the dominant shrub. The site was at a point where a reset of the ground and shrub community was needed to create the potential for long term maintenance and resilience.
All approaches to remove significant buckthorn infestations require a multi-year effort to weaken and kill the species. In Hasenbank Park, forestry mowing, completed in winter 2022, cut and mulched in-place the large woody buckthorn individuals and shattered the stems, inhibiting rapid regrowth. The mowing will now be followed by five to six rounds of spring and fall grazing over three years. Goats favor the soft stems of woody undergrowth and will munch the buds and twigs of these plants, significantly reducing their ability to photosynthesize as shrubs struggle to create leaves. Successive rounds of grazing continually weaken and kill these plants. Goats also target garlic mustard, so timing the goat grazing to occur just prior to flower and seed set of this species has proved to reduce the aggressive establishment of this species which typically shows up after buckthorn has been removed.
An additional means of protecting soils and establishing native species understory within the woodlands and savanna will involve broadcast seeding of native grasses and flowers immediately prior to prescribed grazing. As the goats wander the site, their hooves press seed into soils throughout the site and essentially do work that often requires machinery that is difficult to operate in woodland settings. Seeding will take place using this method, in each of the three years, to begin building replacement cover as buckthorn is removed.
Following the third year of grazing, herbicide treatments will target the remaining (weakened) invasive shrub species. Herbicide treatments at this time will be far less intensive than using the approach early in the process. Treatments will be highly targeted at remaining shrubby invasive species. Native flowers, grasses, sedges, shrubs, and understory trees may be planted to augment site diversity.
Beyond Hasenbank Park
As Hasenbank Park sits between Fish Lake wetlands and Powers Lake, the city and watershed district are constructing additional improvements to improve overall water quality as it moves downstream from the two waterbodies. In 2022, the watershed lead an evaluation of the vegetation in and around Fish Lake, as a result vegetation improvements have begun in the wetland and adjacent storm water ponds. This will continue for numerous years to ensure the proper vegetation has a strong hold.
The partnership is also adding additional trail, educational and wayfinding features in conjunction with design of storm water best management practices in the open space directly east of Saint Johns Drive. The stormwater best practices have been designed to provide water quality benefits to the runoff before it reaches Powers Lake.
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