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A Source Book on Natural Landscaping for Public Officials
THE "HOW TO" OF NATURAL LANDSCAPING
Designing, installing and managing natural landscaping projects will vary in complexity and approach depending upon the nature of the site and the project goals. There are different degrees of natural landscaping, ranging all the way from a small native flower patch, to a full-scale replication of a plant community covering many acres. An otherwise traditionally landscaped site may be installed with a "natural" stormwater lagoon with a fringe of native wetland plants and upland buffer to trap sediment.
Larger projects have the most at stake, financially and visually. They require a detailed and technical planning process. Some examples of larger scale projects include corporate campuses, university lands and large community parks.
ETHICS OF USING NATIVE PLANTS
Regardless of the scope or goals of your project, there are important ethical considerations regarding how to obtain native seeds and plant material for your project garden. Native seeds or plugs must be acquired from a reputable supplier. It is inappropriate under any circumstances for amateur gardeners or professionals to collect seeds or plants from "the wild," except by permission of the owner or as part of a restoration program.
Collection of too many plants or seeds can seriously reduce the
ability of the plundered site to replenish itself. Seed collecting
ethics are rigorously followed by volunteer groups working with
forest preserve districts, other owners of natural sites, and
professionals in the nursery business.
DEVELOPING AN APPROACH
Planning, even if informal, is a fundamental ingredient for a successful natural landscaping project. The greater the ambition or the shorter the timetable, the more planning and technical expertise will be required. A starting point for any natural landscaping project is to analyze the current amenities, opportunities and limitations of your site and articulate reasonable goals.
A basic underpinning for any natural landscaping project would be an understanding of current soil conditions. This knowledge will assist you with your decision about what you can plant where, since soil conditions can vary dramatically across a site. A soil scientist, such as your local agent from the U.S. Department of Agriculture's Natural Resources Conservation Service (formerly the Soil Conservation Service) can tell you the type of soil that you have and the kind of material from which it was derived. The more a project is oriented towards restoration, the more it must take factors such as particular soil conditions into account.
Prairie, woodland/savanna, and wetland/riparian projects have different requirements and will be treated separately in this chapter, although all could exist on one site. In addition, this chapter will discuss how to address stormwater management using natural landscaping integrated into a project's overall design.
The complexity of any natural landscaping project will be determined by a variety of considerations.
- Is this a small scale project with very limited budget and limited access to technical services? Or is it a large, well-funded project intended to achieve complex ecological restoration objectives?
- Do you know your soil types, the kind of vegetative community that is appropriate for your site, and your growing season sun and shade patterns?
- Does the vision for the project require the use of plants that are "fussy" about soil, drainage and other conditions? If so, prudence might dictate a look at alternative plants.
- Are professional assistance and field labor available at appropriate skill levels to undertake a complex project?
- What sources of labor are available for installation and follow-up stewardship?
- What are the local government regulations affecting the use and ongoing management of natural landscaping? Regulations may affect the location of natural landscaping on the site and the types of plants used. You need to know local weed ordinances and/or fire regulations before proceeding.
- What is the project's relationship to adjacent properties? Being a good neighbor is important, so a consideration of adjacent land uses is critical. Natural landscaping adjacent to existing natural open space is obviously much easier than the first introduction into a conventional turf subdivision. Educating adjacent landowners prior to installation is a valuable endeavor. Taking the longer view and adopting a willingness to phase in a project over a few years might be the pragmatic thing to do. It is quite possible, however, that the newly natural landscape will be so attractive that adjacent property owners will want to follow suit.
- Do any nearby or adjacent ecological restoration projects
suggest a theme or rationale, or a physical or institutional
NATURAL LANDSCAPING ON A SMALL SCALE
Many homeowners are looking for an alternative to the continuing efforts necessary to maintain the bluegrass lawn. They are particularly uncomfortable with the application of costly chemical herbicides and fertilizers. The shift to a more natural, environmentally friendly yard with groundcovers, shrubs, grasses and colorful forbs is an inviting alternative.
Individuals about to undertake the transition of a turf lawn to a natural landscape will find many helpful resource books in libraries and in larger or specialty bookstores. In addition, local restoration organizations such as the North Branch Prairie Project in the Chicago region, regional nurseries devoted exclusively to native stock, local nurseries that are enlarging their selection of native plants, and professional landscape architects who "design with nature" will readily share their knowledge.
Homeowners can volunteer with restoration organizations as producers of prairie and savanna seeds, beautifying their own yards in the process. It is important, however, that plants producing seeds intended for restoration grow in separate areas from those purchased at nurseries, because it is necessary to keep the native stock to be used for restoration "pure."
Homeowners and owners of small sites who enjoy "digging in the dirt" may find the gradual approach to converting their lawns a less expensive alternative than a one-time project using a professional designer and installer. With this gradual approach comes the delight of experimentation with plants and their habitats. In addition, the maturing converted gardens can serve as plant nurseries for newly dug beds. Plants will teach the gardener where they like to grow and will relocate themselves over the years according to changing conditions of sun and shade. An ecologist who has tended a natural garden in Park Ridge for 27 years finds that a garden flows like a river; it is ever-changing.
In the natural perennial garden, treasured sentimental favorites, even exotics, can thrive intermixed with native plants to create an aesthetically and personally rewarding landscape. Gardeners can even try incorporating food plants, such as herbs and tomatoes.
It is tempting to begin with quick-spreading ground covers and perennials in order to make a beautiful display at the start and prevent soil erosion. Showy plants such as the exotic, early-blooming dame's rocket, and later-blooming native black-eyed susans and purple coneflowers can be used to brighten a garden reliably in its first year. However, it is important to avoid the trap of starting with extremely aggressive perennials and groundcovers that will then require much time and effort to dislodge.
In the first year, generous mulching will keep precious water in the soil and deter weeds and erosion. Eventually, the native flowers and grasses should out compete the non-natives, which are not so well adapted to the Midwest climate.
NATURAL LANDSCAPING ON A LARGE SCALE
Natural landscaping on medium to larger sites requires considerable advance planning because of the size of the initial investment and the cost implications of making serious mistakes. A rigorous program would include the following tasks, undertaken with the assistance of a qualified professional:
- inventory ecological resources, current site conditions and potential for restoration;
- study site history and review technical literature;
- develop goals and objectives for the overall project (and sub-areas of the site, as appropriate)
- develop a plan (site design, installation, and management) to accomplish the goals and objectives;
- design a monitoring program to assess project performance;
- implement the project (installation on the site);
- manage the project;
- evaluate the project and report on its progress.
Reputable and experienced guidance is the best insurance for a successful restoration program, whether from a staff manager, consulting ecologist, or other source.
CONSIDERATIONS FOR INSTALLATION
Prairies are open "grasslands" which are fire-climax communities. Historically, whether fires were started by lightning or by man, they beat back any trees and large shrubs which tried to grow and kept them at a low shrubby stage.
Prairies are dominated by perennial grasses and forbs. Soil type and hydrology are probably the primary determinants of different species composition on the prairie.
Site Preparation: Removal of Existing Undesirable Vegetation
The primary methods of preparing the site include: burning, baking under black plastic, herbicides, tillage, and removal by hand. Local conditions and personnel considerations may call for flexibility and creative approaches. Site conditions throughout the region have been so disturbed that successful approaches on one site, or one portion of a site, may not work on others.
Often techniques are used in combination. For small areas where appearance is not a factor, covering an area with black plastic for a growing season is a very environmentally safe method of killing turfgrass and other vegetation. This is not as practical with large sites. Here herbicide treatments may need to be conducted twice: once following an initial burn to remove litter and duff, and then several weeks later to eliminate any germinating or resprouting undesirable plants. Use a low toxicity, non-persistent herbicide.
Burning can occur early in the season at a time of low moisture. Tilling can occur as soon as soils thaw in the spring. It makes strategic sense to till after existing vegetation has germinated or sprouted in order to expose it to the stress effects of tilling and warmer weather.
Tillage can bring weed seeds to the soil's surface and create a longer-term weed problem. Where tillage is used, carefully timed repetition over several months, even for an entire growing season, has been used to control weeds. Cover crops may be used in-between tillage events to stabilize soils. Cover crops can include annual rye grass, barley, oats, and other annual species that grow quickly.
Site preparation and control of weeds are the single most important steps in the restoration process.
Procuring seeds and plants:
Seeds and plants can be acquired from many specialized nurseries. (See Appendix) It is most desirable to use local genetic stock from seed collected and propagated within a 150-200 mile radius. (Some restorationists recommend a 15 mile maximum radius.) The seed should be cleaned, should meet high quality seed test requirements, and should be accurately labeled. Locally collected seeds are also useful, (note ethics discussion above), but quality control may be a problem if the seeds are not cleaned and tested. More than one project has failed or been seriously delayed because of poor quality seed. Seeds are most economical for larger projects, while plants provide quicker results at a higher cost. A larger project can include strategically placed plantings in combination with larger seeded areas.
Highest priority should be given to creating a matrix of native grasses. Prairie forbs can be installed with the prairie grasses or introduced later. Some restorationists introduce special blends of pioneer grasses and forbs at the beginning and add carefully chosen matrices of more conservative plants over the years as the prairie matures. One common strategy is to include very colorful prairie plants such as black-eyed susans in the beginning. These may be short lived but will provide a highly visible, colorful and very positive initial impression.
Planting is largely a late fall or early spring activity. Planting in very hot and dry summer conditions may delay germination and growth or require irrigation. Irrigation of seeded areas, however, is usually not mandatory as native species will usually germinate when conditions are most appropriate. However, as with any planting, watering may be necessary to help a planting that has already germinated but is in early vulnerable growth stages when a drought or heat wave begins. An effective mulching system can usually address moisture retention and greatly help a young planting. As with any large-scale agricultural activity, however, the vicissitudes of nature can wreak havoc on even the best planned project.
Sowing can be accomplished by use of tractors and appropriate drills or broadcasters on larger projects while hand broadcasting can often be used in smaller projects. Native plants are installed the same way as any other potted or bare root stock by digging a hole large enough so it will not constrict root systems. Mulching is often necessary to ameliorate soil and moisture conditions and ensure successful seed germination and early growth. Straw mulches, or alternatively, cover crops including oats, barley, etc., can be seeded simultaneously with the prairie seeds and plants to provide protection against erosion and desiccation, and also to control subsequent weed germination. Cover crop seeding rates should be light to moderate so they do not compete with developing seedlings.
The cost of installation can be reduced by using volunteers who are often eager to be stewards and learn about natural landscaping.
After cover crops (and some inevitable weeds) reach a height of 1-2 feet, usually by late June of the first year of planting, mow the planting to a height of no lower than 6-8 inches. Use a rotary mower that does not leave thick mats of clippings, which smother young prairie seedlings. Noxious weeds such as thistles may need extra attention. Hand removal or direct application by wick treatment with herbicides may be sufficient.
Occasional mowing may be necessary for 2-3 years to keep weeds down and prevent them from suppressing young prairie plants. There is no prescribed season or number of times for mowing, but weather will be an important factor in growth of the newly planted prairie and will affect the mowing schedule. The services of a qualified professional will be invaluable in decision-making about maintenance during the first years. In the spring following the first year of planting, prescribed burning can be used to begin the maintenance process. Noxious weed management may also be needed at this time.
Routine maintenance will primarily involve use of prescribed burning. Prescribed burns can be conducted anytime plant fuel is combustible. However, late spring and early to mid-summer burns, alternated with fall burns, have been very useful. Do not be reluctant to burn annually if necessary to accelerate the rate of performance of the prairie during the first 4-6 years.
to expect for the first 5 years:
Expect cover crops and weeds during years 1-3 as the prevailing vegetation. Usually, in years 3-5, native grasses and a series of early successional native flowers (e.g., black-eyed susan and yellow coneflower) will dominate. Depending on the species mix, prairie restorations usually become better, more diverse, and more aesthetic with time. Uniform mowing maintenance as described above not only helps the prairie develop but also improves public relations during the first couple of years of establishment.
Strategies For Being a Good neighbor with Natural Landscaping
|Conflicts with neighbors can be
avoided by following a few simple rules:
Adapted from: "To Mow or Grow", by Brett Rappaport in Wildflower, Spring, 1996
|Sorghum, Silver Grass, Indian Grass|
|Click on the figure above to get a larger image!|
SAVANNA AND WOODLANDS
Woodlands are a major component of the region's natural environment. They originally existed in upland areas in a delicate, see-saw relationship with prairies, and in lowland areas as well. Their location and density depended largely upon climate changes. The Chicago metropolitan area is world renowned for its oak savannas, an open woodland form dominated by oak species such as bur oak.
Dense oak/elm/ash/maple "big woods" contained many fire-intolerant fast-growing tree species with thin bark. This "forest" community probably experienced fire much less often than "oak openings," whose dominant oak tree has thick, fire-resistant bark. Both woodland types share many, but not all, of the same understory plants.
There is considerable academic interest and debate regarding the historical predominance of oak woodlands and relationships with other forest trees such as maple, hickory and elm. The natural transition from one type of vegetation to another in a woodland and in the transition zone between woodland and prairie and savanna is also still being studied.
Much of the remaining oak woodland has been included within the
holdings of the forest preserve districts. Other woodlands have
become highly desirable locations for subdivisions and estate homes.
Oak woodland and conventional turf-dominated landscaping are not
compatible, however. In our region the cultivation of turf grass
under established oaks, and the soil compaction which accompanies
it, results in the slow, but certain, demise of the oak. Therefore,
remaining oak groves should be protected and restored. Landowners
might even want to begin a woodland "from scratch." The process of
woodland restoration is even less well understood and defined than
prairie restoration, yet this should not deter the property owner
from beginning to grow woodland plants and working towards
re-establishing healthy ecosystems.
Creating a woodland "from scratch" is a long-term, if not multi-generational project. The time required for the maturing of trees, creation of more natural woodland soil conditions, etc. requires patience and vision on the part of the project sponsor. The effect can be enhanced through the strategic introduction of some faster growing but short-lived trees, which can jump start the creation of shaded conditions to support woodland understory vegetation and soil building. These will be replaced later by maturing oaks, maples, or other species, depending on the type of woodland you are building.
Existing savannas and woodlands throughout the region are often seriously degraded and dominated by such plants as European buckthorn and garlic mustard. Thus, natural landscaping often means taking a highly degraded existing forest remnant, eliminating exotic species and re-introducing species that have been eliminated.
Oak trees of any species often do not reproduce in their own shade and need openings for sprouting and maturing. Also, ground cover is shade suppressed by European buckthorn and other nonnative and native shrubs and trees. To create the conditions for oak regeneration and the growth of savanna grasses and forbs, both native and nonnative shrubs need to be reduced. The procedure should include manual or machine cutting and treatment of stumps with an herbicide to prevent resprouting.
The follow-up can be a wait-and-see-what-comes-up strategy, or the introduction of seeds and plants. Seedbank testing (placing soil samples in a flat and seeing what germinates) will often verify that native species are present and that they will be stimulated to germinate by removal of the shade suppressing shrubs and trees. If the seed bank is depleted, seed purchase or local collection may be required. Using the same guidelines as for procurement of seeds for prairies, appropriate species and quantities should be installed.
Introduction of the herbaceous layer into a woodland or savanna can be by simple hand broadcasting, usually in late fall, winter, or early spring (mid- November through March). In especially bare soil areas that might be erosion prone, light raking of the soil surface may accomplish better seed incorporation required for germination and minimize seed loss to erosion.
It should be noted that nurseries market non-native trees such as the Norway maple which, with its deep shade, self-propagating vigor and widely-spreading surface roots, eliminate vegetation underneath them. Maples in general have this effect but some of the cultivars are a particular problem and should be avoided. Lack of light beneath them will retard the growth of the understory and promote erosion, loss of topsoil and nutrients.
Certain profusely growing, "weedy" native trees, such as box
elder, are often considered a detriment to regeneration of desirable
plants and are removed. These trees are often valued by the public
which often doesn't distinguish among species and which values
vegetation largely for scenic buffering and wildlife purposes.
Therefore, removal of vegetation should be approached carefully with
a regard for adjacent property owners. Education, evaluation of the
need for removal, and the phasing of project components can help
Initial management and follow up:
In a woodland or savanna, other than spot removal of noxious weeds (e.g., garlic mustard, Canada thistle and resprouting buckthorn), prescribed burning is both the initial and long-term management and maintenance tool. Initially, prescribed burns should be light ground fires.
There are different professional opinions as to whether spring or fall is the best time to burn. The timing of burns can be varied, however, and the results monitored. Often a late spring date (mid April - mid May) is most effective at controlling the noxious weeds that have already leafed out and have minimal root energy reserves. Thus, burning at this time is most stressing to them. There is a perceived conflict with burning at this time; spring ephemeral plants (e.g., trout lilies, spring beauties, may apples and trillium) are often in bloom. Burning will of course initially set these species back. However, most will immediately re-grow, and all will bloom the following year with apparent indifference to fire. A burn plan can divide the project into thirds. Subsequent burn rotations every third year will provide cover for wildlife escaping the fire.
Expectations for the first five years:
Savanna and woodland sites with an intact seed bank will respond very quickly to management. A lush native grass, sedge and wildflower cover is the ultimate goal in conjunction with regenerating oaks, hickories, and other native trees and shrubs. In most degraded sites, all native trees are of a single age; expect babies, juveniles, adolescents, and middle age trees in the future rather than just the older existing trees. These varying age classes will scatter throughout and contribute to a parkland aspect as times goes on.
Repeated removal of resprouting buckthorn and other undesirable shrubs and trees should be expected management challenges during the first five years. Once a ground cover sedge and grass layer is present, the aesthetic will increase substantially, and the management requirements will diminish.
WETLAND, STREAM AND LAKE SHORE HABITATS
Wetlands, streams and lakes can be important amenities on a development site. Waterfront (or riparian) property, in particular, can substantially enhance real estate values. Natural landscaping is particularly applicable in the vicinity of wetlands and waterbodies for the following reasons: 1) Natural landscaping can enhance degraded conditions which commonly exist prior to development; 2) Natural landscaping can protect existing high quality wetland and water amenities; 3) Natural landscaping techniques can be used to "fix" problems in these areas (e.g., shoreline erosion) more cost effectively than conventional approaches. Each of these natural landscaping opportunities is discussed below.
Natural landscaping for enhancement of wetlands and riparian zones
Over time, many of our wetland, streamside, and lake shore environments have become degraded by human-induced disturbances which not only affect their natural functions but also reduce their aesthetic value. One such disturbance is the introduction of invasive non-native plants, including reed canary grass, purple loosestrife, European fragile willows, and buckthorn. Such species reduce habitat value, contribute to an unkempt, weedy appearance, and obscure the waterbody from view. Wetlands and waterbodies also may be disturbed by land development activities in adjacent areas and in upland areas within the watershed. These disturbances, resulting in sediment deposition, nutrient enrichment, and increased stormwater flows, present a landscaping challenge in wetland and riparian environments.
Natural landscaping to enhance degraded conditions in wetlands and riparian environments should focus on two zones.
Upland transitional zone:
Land that is adjacent to the normally wet or inundated area is a critical upland transitional zone. This transitional zone is extremely important to the health, function, and appearance of the wetland or waterbody. Natural landscaping in this transitional zone should be based on the same principles and techniques previously described for prairies and savanna/woodlands. An assessment of early surveyors' data may provide a good indication of the type of plant community to strive for in this zone.
While description of the techniques for prairie and savanna/woodland landscaping will not be repeated here, one particular consideration is worth mentioning. Most of the existing stream and river environments in northeastern Illinois bear little resemblance to the natural conditions which existed prior to settlement in the mid-1800's. The typical stream is now densely tree-lined (commonly with European buckthorn, box elder, and other invasive species). Not only do these trees often completely obscure the stream from view, they also shade out understory plants which are important for soil stabilization, pollutant filtering, and aquatic habitat. Part of the natural landscaping challenge in these areas is to develop acceptance of a new aesthetic for riparian areas and dispel the notion that the removal or thinning of trees along streams is undesirable. Fortunately, there are some high visibility restoration projects in the region, notably the Skokie River restoration at the Chicago Botanic Garden in Glencoe and the Des Plaines River Demonstration Project in Wadsworth, which effectively convey the beauty and functionality of rivers meandering through prairie and open savanna landscapes.
There are varying recommendations for the width of riparian buffer zones. Standards adopted by some northeastern Illinois communities range from about 25 to 50 feet on both sides, although narrower widths may be appropriate adjacent to intermittent streams or small wetlands. Buffers will be discussed at greater length later in this section.
Wetland/open water zone:
Wetland and open water zones range from having saturated soil below the ground surface (such as in a wet meadow) to being completely inundated with water (such as a lake shoreline or a streambank). These areas can support a range of wetland plant species ranging from various sedges and shrubs which are intolerant of inundation, to emergent species, to submerged or floating leaved plants. Some of the basic principles of wetland landscaping -- such as the importance of determining site history and previous vegetation -- are similar to prairie and woodland principles, but many other factors are unique to wetlands.
The most important consideration in wetland landscaping is hydrology. Hydrology defines the presence of water in a wetland, including such factors as average and maximum depth, duration of inundation, and degree of soil saturation. Hydrology establishes the soil and plant conditions which distinguish different wetland types and streambank and shoreline environments.
It should be noted that certain types of activities in wetlands, lakes and streams require a Section 404 permit from the Army Corps of Engineers. (The Corps' Chicago District regulates activities in the six-county northeastern Illinois region.) Regulated activities include filling, draining, and regrading. Most natural landscaping activities which are limited to vegetation management are not subject to a Corps permit. If a permit is needed, a formal wetland delineation also will be required and more explicit mitigation criteria must be met. Wetland mitigation guidance is beyond the scope of this Source Book. You should check with the Corps of Engineers, U.S. Fish and Wildlife Service, or Natural Resources Conservation Service to determine possible permitting and mitigation requirements. (See Appendix for more information.)
Restoration of Degraded Plant Communities
In dealing with existing wetlands with degraded plant
communities, reduction of nonnative vegetation can best be addressed
by using the techniques presented for prairie, savanna and woodland
systems. Once undesirable species are under control, wetland
enhancement may require temporary cover crops, modest species
enrichment, or in extreme cases, complete reseeding or replanting.
Most wetland sites have a seedbank (both native and nonnative) that
will respond once weeds are reduced. However, if deep sediment
burial has occurred, seed banks may not be present. Understanding
the history of sediment burial is a key to determining the
regenerative capability of the existing site. In some cases, it may
be desirable and feasible to remove accumulated sediments to expose
the seedbank and to create depressions and open water zones. This
type of restoration can enhance the aesthetics and marketability of
the new development. (The project designer can find assistance from
the Natural Resource Conservation Service or a consulting wetland or
soil scientist regarding appropriate restoration techniques.)
Restoration of Drained Wetlands
Another important consideration in wetland landscaping is an appreciation of the fact that extensive draining of naturally wet (or hydric) soils was done to accommodate intensive agriculture. Hydric soils are often found on farmland that has been (or is about to be) converted to urban uses. One of the simplest ways to "create" (or expand) a wetland landscape is to identify the location of hydric soils and the presence of drain tile systems or surface drainage ditches. Restoration of wetland hydrology can be accomplished by breaking up or plugging the drain tile or eliminating the ditch. This method is fairly reliable and is less expensive than excavating a wetland depression. Good technical planning is essential so that neighboring properties are not adversely affected with undesired nuisance wetness. Once the hydrology is restored, wetland plants are likely to reappear. Supplemental seeding or planting may be appropriate if greater diversity is desired.
Restoration of Channelized Streams
A natural landscaping opportunity for stream corridors is the restoration of meandered channels to replace artificially straightened channels. There are numerous opportunities for this type of restoration in northeastern Illinois since over 40 percent of the existing stream miles have been straightened or ditched. Several recent residential developments have incorporated stream channel restoration into their site plans to enhance the aesthetics and marketability of their projects. Once the natural contours have been restored, native wetland and prairie plants are planted on the streambanks to provide soil stabilization and aquatic habitat benefits.
Enhancement of Streambanks and Lake Shores
Natural landscaping of streambanks or lake shores typically begins with the elimination of invasive overstory plants which shade out native wetland species. In many cases, emergent wetland plants will then propagate on their own. If not, planting of live plugs or tubers is recommended. Native wetland and prairie plants are much more protective of waterbody edges than conventional turf grass which is intolerant of extended inundation. While wetland plants are expected in many streambank and lake shore settings, there are some locations where wetland plants will not grow. For example, rocky substrates or large river/lake systems with large fluctuations in water levels may not support wetland plants.
An additional consideration for natural wetland landscaping, particularly near open water, is the need to protect plantings from geese. If geese are likely to be present, special "goose cages" should be provided to protect new plantings. Once the plantings are well established, they will be able to withstand predation.
Plant species selection:
Selection of plants for wetland, streambank, and lake shore zones is closely tied to the hydrology of the site, particularly water depths and flood durations. Other factors such as shading and water clarity also must be taken into account. Planting in open water areas typically involves the use of tubers, plugs, and potted plants. Planting in non-ponded wetland zones often involves both seeds and live plants. You need to learn your plants and their hydrologic and soil requirements to choose species that will work. Field tests may be useful for delineating planting zones on a site which contains a range of wetness regimes.
It is important to get a desirable mix, or diversity, of wetland plants and not a monotypic stand of reed or cattails. Certain aggressive species which are very easy to establish, such as non-native reed canary grass, should not be planted. Extremely aggressive wetland plants will out-compete and eventually dominate less robust colonizers. (See Appendix for plant lists and other sources of information.)
Initial and long-term management and maintenance:
Noxious weed control is needed in wetland areas, as in other natural landscapes. Prescribed burning is a commonly used technique for wetlands as well as natural streambanks and shorelines. Timing is important as these areas burn well only at very specific times of the year. Fires in wetland areas can be very intense, especially where cattails and giant reed grass (Phragmites communis) are present. Therefore, extra care is warranted. A two to three year rotation is generally appropriate for wetland burning.
Chemical weed control also may be needed, especially for species (e.g., purple loosestrife and reed canary grass) which are difficult to eliminate. Herbicide techniques are different from upland sites primarily because herbicides have to be licensed for use in or near waterbodies, wetlands and other aquatic systems. Read the product labels, and make sure that only a licensed herbicide applicator conducts this work.
What to expect:
If hydrologic and soil conditions are conducive, wetland plantings often respond very rapidly. Extensive cover of native plants often can be achieved during the first growing season. Often, noxious weed control via herbicides, mowing, or pruning is necessary during the first several years. Some replanting also may be necessary. A stable, diverse, and aesthetic wetland/riparian landscape may take three to five years to achieve.
Purple loosestrife is a particularly aggressive, noxious wetland weed and merits special attention here. If it gets out of control, the landscaping project may be in trouble. When the weed is present in a limited area, it may respond to hand pulling or to several doses of herbicides. It is important to attack before it goes to seed. Recently, biological controls for purple loosestrife have been introduced in Illinois. Information on the European beetles of the Galurecella sp. which damage purple loosestrife is available through the Illinois Department of Natural Resources, Natural Heritage Division, as well as county forest preserve districts (see Appendix for details).
Natural landscaping buffers to protect high quality wetlands and waterbodies
Wetlands, streams and lakes do not exist in isolation. Their long term health is heavily dependent on the management of adjacent landscapes as well as upland areas in upstream watersheds. Native vegetation can be used to establish buffers along wetlands, stream edges and lake shores, known as riparian zones. Native vegetation buffers help to stabilize streambanks and shorelines, filter out sediment and other runoff pollutants from adjacent developments, protect the habitat in sensitive nearshore areas, preserve aesthetic values, and provide access for maintenance and/or trails.
Natural landscaping buffers are recommended on all sites containing wetlands, streams, or lakes. The design and management of riparian buffers should follow these general criteria:
The minimum buffer width should be 25 feet. Wider buffers (e.g., 50-100 feet) should be established for larger or more sensitive streams, lakes or wetlands.
Buffers should be planted using native vegetation indigenous to the riparian zone (See Appendix for plant lists).
Applications of fertilizers or pesticides should be avoided once the buffer is established. Maintenance should be limited to occasional mowing or controlled burns necessary to control weeds and maintain native plant diversity. If certain noxious weeds need additional control, limited use of approved herbicides may be appropriate in localized areas.
NIPC has published a Model Stream and Wetland Protection Ordinance that may be used by municipalities to protect stream corridors.
Streambank and shoreline stabilization techniques
Conventional landscaping, particularly turf grass, is generally unsuitable for most streambank and shoreline applications. Turf grass is very shallow-rooted and is intolerant of extended inundation which is common in low-lying areas. As a consequence, bare soil and erosion are common occurrences on conventionally landscaped lake shores and streambanks. Native vegetation is increasingly being utilized as a low-cost alternative for restoring and stabilizing these areas. It provides several important advantages over conventional landscaping.
- Appropriate native vegetation is tolerant of inundation, even surviving extended floods.
- The deep, dense root systems of native plants hold the soil firmly in place.
- Native plants dissipate wave and current energy and protect erodible banks.
In addition to these advantages, native vegetation also has several advantages over conventional engineering solutions, such as riprap or steel pilings, which have been traditionally used to stabilize eroding streambanks and shorelines. It enhances aquatic habitat and aesthetics. It provides shading for nearshore areas. Once root systems become established, the ability to stabilize erosive banks increases over time.
Native plants can be used alone or in combination with other materials in what are commonly called bioengineering methods. Several common bioengineering methods are described below.
Native prairie, wetland or woodland vegetation can be planted as seeds, dormant cuttings or plant plugs. Planting generally follows removal or thinning of non-native trees or shrubs. Common plantings include prairie grass plugs or dormant willow poles on streambanks, or emergent wetland plants on lake shores. These approaches work best where bank slopes are moderate (e.g., 1:1 or flatter) and erosive velocities are not severe.
|Examples of Bioengineering techniques
for bank stabilization
These methods utilize layers of dormant tree or shrub branches -- typically willow or dogwood species -- alternating with layers of soil. The protruding ends of the branches physically deflect erosive flows and the brush roots eventually stabilize erodible soils. These methods can be applied to a range of slopes and velocities.
Fiber rolls are constructed of coconut fibers which are densely packed into a cylindrical shape and wrapped with a polypropylene mesh. Fiber rolls are partially submerged at the toe of an eroding streambank or shoreline and secured with construction stakes. Native vegetation is planted into the fiber roll and on the slope above it. This method is most appropriate in low to moderate velocity zones where the toe of the slope is eroding.
A-Jacks and lunkers
These techniques rely on hard-edged materials to stabilize the toe of the slope in combination with native vegetation planted on the upper banks. Concrete A-Jacks structures, resembling children's jacks, are placed in a linear nested arrangement along an eroding bank or shoreline, backfilled with soil, and planted with stabilizing vegetation such as willow poles. Lunkers are rectangular boxes constructed of wood or plastic lumber and built into the toe of the bank. Both of these techniques are effective in stabilizing the toe of an eroding slope and should be integrated with native plants.
An excellent description of alternative stabilization techniques has been developed by DuPage County Department of Environmental Concerns. Its Streambank Stabilization Program report (1995) describes the advantages, disadvantages, and installation techniques of a range of natural vegetation and bioengineering approaches.
NATURAL LANDSCAPING FOR IMPROVED STORMWATER MANAGEMENT
As previously described, natural landscaping provides an environmentally conscious alternative to conventional methods of addressing stormwater management and other water resources concerns. This section describes the implementation of several natural landscaping techniques for conveying and storing stormwater runoff in a more environmentally conscious and cost effective manner.
On an undisturbed site, there is very little surface runoff. Most precipitation infiltrates into the ground and slowly recharges underground aquifers or moves laterally to recharge streams, lakes and wetlands. When surface runoff does occur, it moves slowly across the vegetated landscape, through natural depressions, and via swales into larger streams.
In contrast, the developed site produces dramatically more surface runoff due to impervious surfaces and soil compaction. Conventional drainage relies upon curbs, gutters, channels and sewers to quickly convey the water away. As a consequence, pollutants in stormwater runoff are flushed downstream and the pulsating flows contribute to increased flooding and destabilization of downstream channel systems.
Natural drainage designs attempt to replicate elements of the pre-development drainage scheme by:
- minimizing disturbances of the original drainage network and the area of impervious surfaces and
- maximizing opportunities to infiltrate surface runoff, to hold runoff water in natural depressions, and to release it slowly through surface swales and drainageways.
While it will be impossible to replicate completely the pre-development hydrologic conditions of a site, studies estimate that natural drainage designs can substantially reduce both surface runoff volumes and pollutant loads compared to conventional drainage designs. For example, for a clustered, naturally drained residential development in Grayslake, Illinois, estimates suggest a 65 percent reduction of surface runoff. Recommended elements of a natural drainage approach, or runoff reduction hierarchy, are described below.
Preserve Natural Drainage Systems
Existing swales, depressions, wetlands and stream corridors should be preserved in the site plan wherever possible. In some cases this will require clustering the development around these important features. By siting the buildings, homes or other structures on only a portion of the total site, clustering has the added benefits of reducing the total impervious area associated with roadways and minimizing soil compaction associated with mass grading activities.
Utilize vegetated filter strips
A critical consideration in designing a natural drainage plan is to identify opportunities to disperse runoff from impervious surfaces -- rooftops, streets and parking lots -- onto the pervious, vegetated areas of the site. These vegetated areas, or filter strips, allow runoff to infiltrate into the ground before it is conveyed to swales or other conveyance devices. Runoff is directed to filter strips in several ways. It can be conveyed from rooftops via downspouts. From roads, driveways or parking lots, runoff is directed to filter strips as sheet flow or through slotted curbs.
Filter strips are suitable on most types of development but are probably most effective in settings where there are relatively wide expanses of pervious area adjacent to impervious surfaces. Filter strips are readily accommodated in the following development situations:
- office and industrial campuses
- expressways and rural roadways (where right-of-way is adequate)
- buffer zones adjacent to sensitive environments
There are several basic design considerations for filter strips which will maximize their performance and reliability:
- A robust stand of vegetation should be established.
- Ground slope should ideally be relatively flat (i.e., preferably less than 5-10 percent slope).
- A width of at least 10-20 feet is recommended.
- Runoff onto the strip should be evenly dispersed.
- Contributing drainage areas should be relatively small (less than five to ten acres.)
Healthy vegetation is important to minimize erosion and to improve the filtering of pollutants in the runoff water. Where high concentrations of salt are expected due to roadway de-icing, salt tolerant vegetation should be planted. Native prairie vegetation is ideal in most filter strip applications. (Choose salt-tolerant species where necessary.) Its deep root zones and extensive biomass give it performance advantages over turf grass. Forested filter strips also can be effective because of their ability to take up certain pollutants from the root zone and store them in their biomass.
Utilize Vegetated Swales
Swales function much like filter strips except that their purpose is to convey concentrated flow. Unlike conventional storm sewers, swales move water more slowly and allow a portion of the runoff to infiltrate the ground.
Swales are suitable alternatives to storm sewers for many types of development , particularly where the number of driveway crossings is not large. Swales are easily implemented on the rolling to gently rolling topography which is common in northeastern Illinois. Swales are strongly recommended in the following development situations.
- large lot residential sites (e.g., ½ to 1 acre or larger)
- office and industrial campuses
- roadways where right-of-way widths are adequate
- parking lot medians and edges
Where feasible, runoff should be routed into swales from filter strips. Runoff also can be directly conveyed from parking lots or roadways via sheet flow or through slotted curbs. Swales in parking lot medians represent a departure from the conventional design which elevates landscaped islands or medians above the pavement. It is recommended instead that medians be excavated to collect runoff. Parking lot swales also are useful for the disposal of plowed snow.
Design guidance: The design guidance for vegetated swales is similar to the criteria for filter strips.
- Slopes should be adequate to minimize nuisance ponding -- roughly 1-2 percent as a minimum.
- Where existing gradients are steep (e.g., greater than 5-10 percent) and erosion is a concern, the effective slope of swales can be reduced through the use of drop structures.
- Swales should be wide and shallow with side slopes no steeper than 3 horizontal to 1 vertical.
- Swales can be vegetated with turf, prairie or wetland vegetation as appropriate. If high salt concentrations are expected in runoff, salt tolerant plant species should be utilized.
Utilize Natural Detention Basin Designs
Before runoff leaves the development site, it should be routed through a detention basin to further slow the peak flow rates and to provide an opportunity to remove runoff contaminants. While most northeastern Illinois communities require detention via subdivision ordinances, most conventional basins are very "engineered" in appearance, with hard edges or concrete channels. Natural landscaping of detention basins incorporates native plants and gradual side slopes to enhance the removal of stormwater pollutants, improve aesthetic appearance, and reduce maintenance needs.
There are two recommended natural detention basin types. A wet bottom basin has a large, deep permanent pool in the basin bottom. A wetland basin contains smaller deep pools near the outlet and/or inlets. The remainder of the basin bottom, which either has very shallow ponding or is dry between storm events, is vegetated primarily with wetland plants, sometimes in combination with prairie vegetation or turf grass.
Design guidance: The basic philosophy of natural detention designs is to replicate the components of natural lake and wetland systems. The following design considerations are important.
- Shoreline slopes of open water areas should be relatively flat (e.g., 5:1 to 10:1).
- Shoreline zones and frequently flooded areas should be planted with native wetland vegetation.
- Where feasible, basin side slopes should be vegetated with prairie grasses and forbs.
- Basin shapes and open water contours should be irregular to enhance appearance.
|A natural approach to detention basin design|
An important caution: Because natural wetlands are often in the lowest spot in the landscape, there is sometimes a temptation to convert them to detention basins. This generally should be avoided, particularly for wetlands containing sensitive habitats or diverse plant communities, because the subsequent changes in water levels and pollutant loadings associated with urban runoff will hasten their degradation