Urban natural areas are not wilderness. They are too small and have been altered too drastically to function as fully intact ecological systems. Without stewardship, these areas degrade ecologically. The city and many residents actively manage natural areas. Activities typically focus on monitoring and planning, controlling invasive plants, and restoring native plant communities.
Site Analysis & Planning
Managing a natural area, or restoring a site to natural conditions, begins with understanding what's there, setting goals for the site, and developing a plan to achieve those goals. The city does this for its natural areas and encourages homeowners with naturalized yards do it as well. Understanding what is currently on the site is important. If native plants exist on the site, these may serve as the building blocks for the restoration and you don't want to destroy them unknowingly.
Goals for a natural area vary based on soil and site conditions, personal needs and preferences, and budget. On some public sites our plans include goals such as:
- Increase types of habitat
- Improve habitat for songbirds
- Reduce knapweed and increase native grasses
The plan then defines the methods that will be used to achieve the goals. As management activities are conducted, the site is monitored and strategies are adjusted to respond to what happens on the landscape - an approach called adaptive management.
Managing a Site With Existing Native Habitat
On sites with native plants, it's important to select management methods that protect and enhance existing native species. Management often includes activities such as burning, mowing, cutting, spot herbiciding, overseeding or interplanting.
- Some of our local habitat types are fire-dependent and benefit from prescribed burns. The city uses prescribed burns on areas of prairie, oak savanna, and oak woodland. This can be very effective in invigorating native grasses, preparing a site for native seeding, and helping set back weeds. In Maplewood, prescribed burns may be conducted by experienced contractors and require a permit signed by the city's Fire Marshall. Burning typically doesn't kill perennial plants.
- Mowing and cutting can be used to control some invasive weed species. It won't necessarily eradicate them, but it can help set them back or prevent seeding for that year.
- Spot herbiciding is sometimes used to control weeds or invasive plants that threaten the long-term well-being of a natural area. Many weeds are not a threat - they don't spread uncontrollably or outcompete natives and don't necessarily need to be managed. But invasive species such as buckthorn and spotted knapweed, can outcompete natives and change a habitat, resulting in loss of diversity. Controlling these species may include spraying single plants with a backpack sprayer or spraying larger areas with a boom sprayer.
- Seeding and planting can be used to increase the diversity in a natural site. In woodland areas, there is often bare soil that can be seeded or planted directly. In grassy areas, interseeding or planting can be done after a prescribed burn on some sites. Survival of the new plants is not ensured in grassy areas since competition from surrounding plants is intense.
Restoring a Site to Native Habitat
Yard areas or degraded naturalized areas can be restored to native habitat.
- Planting (as opposed to seeding). On small projects, plants (rather than seed) are typically used to establish natural areas. If the existing vegetation has been killed, and the planting area will be mulched, it is usually not necessary to till the site if the soils are loose enough to penetrate with a trowel or shovel. Plugs or 4" pots are common planting sizes for prairie and woodland grasses, ferns, and flowers. Bareroot plants or large pots are typically used for shrubs and trees. In this situation, the whole planting areas is typically mulched with shredded wood mulch to suppress weeds and maintain moisture.
- Removing existing vegetation. If there are no native plants on the site, the 1st step is often to kill existing vegetation (except for trees and native shrubs). There are many ways to remove or kill existing vegetation - digging out sod, using an herbicide, or smothering the vegetation under black plastic. Each has its pros and cons.
- Seeding. On a large sites slated for prairie restoration, using plants is cost-prohibitive so seed is typically used. Site preparation typically includes a combination of mowing or burning, herbiciding, and shallow discing to kill all vegetation in the planting area. The seed is then drilled or broadcast over the site, along with a cover crop. It takes three to five years to establish a prairie from seed and during that time the site will look very weedy.
Managing Invasive Plants
Much of the effort in managing a natural area goes towards managing invasive plants. Determining the most effective control measures depends on the species, size of the infestation, site conditions, and time of year, and other factors. Using multiple methods - integrated pest management - is usually is more successful than using a single method. Common methods are:
- Biological. Biological control (biocontrol) is the use of an organism that targets and consumes a specific species to control an invasive plant or pest. It our region, biocontrol is available for controlling purple loosestrife, leafy spurge, and spotted knapweed. Researchers have not yet been successful in finding a biocontrol for common buckthorn. Biological controls undergo rigorous testing in the lab and in field test sites to ensure they will only impact the targeted species.
- Chemical. Herbicides are frequently used in restoration. In some situations, this may be the only type of control that is effective. But caution should always be at the forefront. Herbicides are poisons and in addition to killing the targeted plant, they can be harmful to people, animals, non-target plants, water, and soil, and soil organisms. A given herbicide will only be effective on specific plants. It's important to select the right product and to use it according to the label.
- Mechanical Control. This includes pulling, cutting or mowing. These methods may be an option on some sites, for some species, but they can be labor intensive and may disrupt soil and cause other problems. For example, in a woodland with lots of native wildflowers and sedges, pulling buckthorn could be very damaging to the native groundcovers. It that situation it would be better to cut and stump treat the buckthorn in fall, when the wildflowers are dormant. (Cutting alone is not effective for buckthorn since it will resprout.)
When determining what methods to use, it's essential to consider effectiveness as well as the environmental and ecological impacts of the treatment.