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Green Landscaping: Greenacres
Landscaping with Native Plants
Exploring the Environmental, Social and Economic Benefits Conference: December 6 - 7, 2004
Quantification of the Benefits of Native Landscaping Current Knowledge
Introduction
Native landscaping, sometimes called natural landscaping, uses plants that were native to a given region prior to European settlement. These native plants can be arranged in formally designed gardens or planted into a more natural meadow. Because native plants, once established, can require minimal irrigation, mowing, and chemical treatments, native landscaping is presumed to offer substantial savings and environmental benefits compared with conventional landscape designs. Native landscaping is promoted as a means to improve the quality of the air, soil and water, help to prevent flooding, control erosion, and enhance biodiversity. Native landscaping is also seen as a tool for sustainable urban development, as a means for reintroducing the natural heritage of an area, and as a vehicle for connecting urban residents to the natural world and promoting a conservation culture.
But how well are these various benefits quantified in the scientific literature? To answer this question we held a conference, Landscaping with Native Plants: Exploring the Environmental, Social and Economic Benefits, in Chicago in December 2004. Researchers evaluated the scientific literature pertinent to the Great Lakes basin to determine the current state of knowledge on native landscaping and its environmental, social and economic interactions. lose to 200 researchers, government officials, development professionals, environmentalists, landscape architects, civil engineers, natural resource managers and others reviewed the evidence.
The conference sponsors included: DePaul University’s Environmental Science Program and Institute for Nature and Culture; Chicago Department of Environment; U.S. Environmental Protection Agency; The Gutgsell Foundation; Peggy Notebaert Nature Museum; and University of Illinois at Chicago School of Public Health and Great Lakes Centers for Occupational and Environmental Safety and Health.
This document details the information presented at the December 2004 conference. Specifically, we examine the public perceptions of native landscaping; the economic benefits of native landscaping; the impact of native landscaping on water quality, air quality, and biodiversity; the fate of pesticides and fertilizers in native landscapes; and native plants’ effectiveness in containing or removing contaminants in soil (phytoremediation) and sequestering carbon.
In each section we provide a contact for the researcher(s) that compiled the information upon which this document is based.
During the conference we found that though there are many anecdotal stories about the benefits of native plants in the landscape, there are very few rigorous scientific studies quantifying the benefits. Many questions remain unanswered. Based on gap analysis discussions during the conference, native landscaping research needs was identified to give a systematic approach to addressing these gaps in knowledge. These identified research needs are included in Attachment A.
Attachment B contains case studies that were presented during the conference.
Public Perceptions of Native Landscaping
Researcher: Joan Nassauer [nassauer@umich.edu], University of Michigan <http://www-personal.umich.edu/~nassauer/>
Where one person sees beautiful wildflowers, another might see unkempt weeds. Public acceptance, or cultural sustainability, is equally as important as ecological functioning for a native landscape to deliver its intended environmental benefits—and perhaps even more so. Cultural sustainability is the capacity of ecologically beneficial landscapes to elicit public acceptance and appropriate care over the long term. Without cultural sustainability, native landscape installations will often be replaced by conventional plantings.
Four points are key to understanding public perceptions of native landscaping:
- Looking natural is not the same as delivering environmental benefits. City dwellers tend to view well-kept parks and gardens as “natural” and attractive, regardless of the chemicals and fossil fuel emissions required to maintain them, or their impact on storm water runoff. Research supports the claim that urban green delivers psychological benefits even when it does not deliver ecological benefits.
- Perception is not the same as function, i.e., natural looking is not synonymous with being environmentally beneficial. Different ecosystem types elicit different public responses. Prairies and wetlands are often perceived as messy and undesirable, for example, despite their environmental benefits.
- Public perceptions sometimes vary among different groups and can change over time. Children’s perceptions, for example, have been shown to be different from those of adults. Environmentalists, too, tend to have different ideas about what is valuable in a landscape. However, in general, public perceptions of landscape attractiveness are surprisingly consistent among different groups.
- A landscape’s visible characteristics are the basis for public perception.
Dense, messy plots are not acceptable.
A “well-groomed” area is assumed to be safe, and safety is a key concern to urban dwellers. Urban native landscapes also need to allow people to see through them; dense, overgrown landscapes are perceived as neglected and potentially dangerous.
Cues to care
Native landscape designers can build in “cues to care” to gain public acceptance. Structures such as fences, sidewalks, and viewing platforms indicate that a landscape is not neglected. Open water is perceived as desirable—as long as it doesn’t look dirty or smell bad. Picturesque curves and crisp edges and lines also have high appeal. If a “messy” installation such as prairie natives is surrounded by nicely mown turf, it becomes more acceptable. Studies indicate that a 1:1 ratio of mown turf to native plants has the greatest amount of public acceptance.
Studies also show that large patches of native landscaping are more desirable than smaller ones. Large means at least an acre. People seem to inherently appreciate the value and beauty of a large flowing prairie over a small patch of prairie plants. However, even very small (less than .1 acre) patches of native plants will be perceived as attractive if they are designed to display cues to care. Studies suggest that the presence of wildlife is also a plus: people place higher value on landscapes that provide habitat for butterflies and other wildlife. Flowering plants are more acceptable than non-flowering plants, whether they are native or not.
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Designing for the long term
Although native landscaping designs may be quite different from traditional landscapes, they must exhibit and maintain a certain degree of order to ensure public acceptance. Native designs that look picturesque or vividly display human intention in their pattern, and suggest continual care for the landscape in their materials and condition, are likely to be accepted and sustained by the public. Designs that look too wild and overgrown to the untrained eye, especially smaller patches of prairie, can become vulnerable to compromise and replacement by conventional plantings. Native landscapes are often designed for their environmental benefits, but they must also be designed for public perception in order to be sustainable over the long term.
For further information about how to manage public perceptions of native landscaping, see:
- Nassauer, J. I. 2004. Monitoring the success of metropolitan wetland restorations: cultural sustainability and ecological function. Wetlands 24:4. pp. 756-765.
- Nassauer, J. I., Allan, J. D., Johengen, T., Kosek, S. E. and Infante, D. 2004. Exurban Residential Subdivision Development: Effects on Water Quality and Public Perception. Urban Ecosystems 7:3 pp 267-281.
- Nassauer, J. I., ed. 1997. Placing Nature: Culture and Landscape Ecology. Island Press, Washington, D. C.
- Nassauer, J. I. 1995. Messy Ecosystems, Orderly Frames. Landscape Journal. 14:2, pp. 161-170.
Click here to see identified research needs for Public Perception.
Economic and Cost Considerations
Researchers: John Haugland [haugland.john@epa.gov], US EPA, Hale Thurston [thurston.hale@epa.gov], US EPA
There is a perception that native landscaping is more expensive than conventional landscaping. This, however, is often not true when tested against both actual experience and cost/benefit models. Further, many environmental services provided by the native plants are not captured in traditional economic models. This section provides information on the economics of native landscaping - installation and maintenance, total development costs, and stormwater management.
Native plants provide economic benefits and positive externalities beyond the cost of landscape installation and maintenance. For example, the environmental services provided by native plants may include mitigating stormwater runoff and its associated problems, and filtering fertilizers thus preventing them from reaching a water body. These services have real economic value that communities would otherwise have to pay for. For example, communities might have to pay to construct additional stormwater infrastructure or address excessive algae blooms. Some benefits of native landscaping, like reduced air pollution from less mowing, are difficult to capture as economic values. Therefore, when considering the economic benefits of native landscaping, it is important to keep in mind the environmental value of native landscaping, which is often unaccounted for when considering the costs of installation and maintenance.
Installation and maintenance costs
In 2003, three Northern Illinois landscapers estimated installation and maintenance costs for turf-grass and native landscapes. All three concluded that turf grass is more expensive than native landscaping. Variations in conditions from site to site can create exceptions to this scenario. For residential sites that do not require irrigation systems, seeding turf can sometimes be cost-competitive with native landscaping. For large corporate campuses and residential developments with large common areas, native landscaping is more cost effectiveLandscape Treatment |
Low-End Estimate |
High-End Estimate |
Turf Grass | $7,800 | $14,825 |
Native Landscaping | $3,400 | $ 5,975 |
Figure A: First-Year Installation Costs Per Acre (Natural Landscaping for Public Officials: A Sourcebook. Chicago: Northeastern Illinois Planning Commission, 2004) |
Landscape Treatment |
Low-End Estimate |
High-End Estimate |
Turf Grass | $5,550 | $6,471 |
Native Landscaping | $1,600 | $ 1,788 |
Figure B: 10-Year Average Maintenance Costs Per Acre (Natural Landscaping for Public Officials: A Sourcebook. Chicago: Northeastern Illinois Planning Commission, 2004) |
Prairie Crossing, a residential development in Grayslake, Illinois, calculated installation and maintenance costs for open spaces planted with turf grass and compared these with areas on the property planted with native prairie and wetland species.
Residential site designs that employ a suite of tools to address conservation goals are referred to as conservation developments. Conservation and conventional developments use different methods to manage stormwater. Conservation developments employ an array of environmentally sensitive development strategies and techniques such as: protecting natural features, including streams, wetlands, natural areas, and critical habitat; the use of natural drainage patterns; clustering built areas; the provision of common open space; and the use of native landscapes that are integrated into the stormwater management system. These are designed to reduce the on-site and off-site impacts of runoff by preserving and restoring natural hydrologic processes. Conventional developments, on the other hand, attempt to collect and move stormwater as quickly as possible to detention ponds, where it is stored and discharged at the legally allowable rate |
- Turf expenses included seed, mulch, fertilizers, and maintenance costs over five years (including mowing, fertilizer application, an irrigation system, municipal water, and aerating or de-thatching every other year).
- Native prairie plant expenses included seeding, planting plugs, mulching, and maintenance costs (including mowing in the first two years; spot herbicide treatment over five years; and prescribed burning in years two, three, and five).
- The native prairie cost 56 percent less than turf to install. For the total open space area in Prairie Crossing, prairie maintenance savings over five years averaged annual savings of $3,400 per acre.
Developments: Conservation vs. Conventional
Beyond installation and maintenance costs, native landscaping can contribute to larger total cost savings when used in conjunction with other conservation tools to develop a site. Landscaping is one component of a built system that interacts with other components of the system such as buildings and infrastructure. Certain landscaping choices can lower energy and stormwater costs, reduce infrastructure needs, avoid the need for irrigation systems and improve livability on the site.
In Southeast Wisconsin, the actual costs of conservation development were compared to engineering cost estimates for conventional designs at three residential subdivision projects. While native landscaping costs were higher than conventional turf in two of the three developments and costs were the same in the third, the total construction costs were less for conservation development at all three sites. The inclusion of native landscaping in the overall site design contributed to lower stormwater management costs for the conservation developments compared to the conventional estimates.
Cost models developed for the Conservation Research Institute compared conservation and conventional development for four types of land use on a hypothetical 40-acre parcel: commercial, moderate density residential, low density residential and rural residential. The use of conservation development methods was approximately 40 percent less expensive for commercial/industrial and low density residential sites, and slightly less expensive for rural and moderate density residential developments. Total per-lot development costs for conservation design also proved more cost effective for all four types of land use.
Accounting for Stormwater Management
Stormwater runoff can cause many serious problems that incur real costs to communities, including: flooding, pollution, groundwater recharge deficits, and damage to stream ecology. Reducing stormwater runoff is an issue of growing importance for urban planners, especially since many communities smaller than 100,000 residents must now comply with federal regulations for managing their stormwater. (Larger communities have been subject to these regulations since 1990.) Research suggests that native landscaping in the form of rain gardens, bioswales, and prairies, may provide a low- cost alternative to large-scale infrastructure solutions to reduce runoff.
Some communities are using stormwater management fee reductions as a way to tie economic incentives to the economic value of reducing the amount of stormwater running off of a site.
Stormwater fees are typically assessed based on the amount of impervious surface on a property and they represent the cost for the municipality to manage the stormwater generated throughout the city. Cities like Minneapolis, Minnesota and Columbus, Ohio are reducing stormwater management fees for property owners that implement effective stormwater best management practices (BMPs) that improve stormwater quality and decrease stormwater quantity generated on a property. Through the use of stormwater management fees and by providing fee reductions, municipalities recognize the costs associated with stormwater. Community members can then either pay for those costs or use BMPs that offset those costs.
In the Blackberry Creek watershed in Kane County, Illinois, researchers estimated the economic benefits of downstream stormwater management through the use of upstream conservation design practices. Analyzing within the 100-year floodplain, researchers estimated the benefits of flood risk reduction on property values and the cost of stormwater drainage infrastructure. When hypothetical conservation design practices, including native landscaping, were calculated, the researchers found that flood mitigation would create downstream property value benefits from $14,538 to $36,345 per acre for those properties no longer in the floodplain. There were lesser savings for those properties remaining in the floodplain, but experiencing reduced flooding. Conservation design practices would prevent the need to build new concrete culverts for stormwater diversion, saving $3.3 million to $4.5 million that would have otherwise been spent on culvert replacement or upgrades. When including both flood reduction and infrastructure savings are accounted for, the conservation development would be $301 to $681 less expensive per developed acre.
Click here to see identified research needs for Economics.
Hydrology
Researcher: James
Montgomery [jmontgom@depaul.edu], Associate Professor
Director of the Environmental Science Program, De Paul University,
Chicago, Illinois
What does available data in the scientific literature tell us?
In preparation for the December 2004 Native Landscaping Conference, researchers evaluated more than 220 scientific articles on the hydrologic impacts of native plants and those used in conventional landscapes, such as turf grass. Of special interest were studies of the processes most affected by urbanization, such as (1) infiltration, (2) evapotranspiration (water that evaporates and is transpired or passes through the plant leaves), (3) interception (the storage of water by leaf surfaces before it evaporates or drips down to the ground), and (4) runoff.
Infiltration
Infiltration rates varied widely among native grasses and
turf grasses, and between compacted and non- compacted soils. A 1996
study reported an infiltration rate of 7.5 inches per hour in native
switchgrass, while a 1979 study of urban sidewalk grass reported an
infiltration rate of 0.29 inches per hour. A 1970 study demonstrated
that as soil becomes more compacted, which is typical of urban
soils, the rate of infiltration decreases.
Evapotranspiration
Evapotranspiration measurements varied widely between region and
plant type. Northern semiarid grasslands had less than half the
rate of evapotranspiration as turf grass, indicating that more water
remained in the soil and less was lost via evapotranspiration.
Interception
In John Weaver’s classic 1968 study of the Midwestern prairie he
measured interception by different types of grasses, cereal and
forage crops. Native grasses such as little and big bluestem
intercepted 47-81 percent of precipitation.
Runoff
Studies show that surface runoff varied, from 3.6 inches per
year in native grassland, to 1.3 inches per year in compact lawn
turf. These numbers are not conclusive, however, since varying
conditions such as the slope of the land, and the type of soil
texture could strongly influence the amount of runoff.
Water Conservation
Native plants conserve water because, once established, they do not
need additional watering. Although it depends on climate, soil and
grass type, on average, turf lawns require about one inch of water
per week during the summer. This means that in the Midwest watering
an acre turf lawn for 12 weeks uses 325,848 gallons of
water. Watering a half acre turf grass lawn during the summer months
requires 162,924 gallons of water. This is equivalent to filling a
30-foot round, 4-foot deep, swimming pool almost 4.5 times during
the summer. Since native plants, once established, do not need
additional watering during the summer months, they could be a tool
for meeting local water conservation needs, especially in
communities with water usage restrictions.
Native Landscaping as a Management Tool
Native landscaping can be one option in a range of
stormwater best management practices (BMPs), which are used to
promote infiltration, reduce runoff, and improve the quality of
water.
Rain Gardens
One type of native landscaping is a rain garden planted with
indigenous plants. Rain gardens are built to reduce runoff by
capturing stormwater, allowing the water to infiltrate into the
ground. There are not enough quantitative data to state conclusively
that rain gardens improve the quality of the water that flows
through them, although studies measuring the ability of rain gardens
to reduce the amount of water running off of a site are underway.
In Burnsville, Minnesota, Barr Engineering Company is testing the ability of rain gardens to reduce the volume and improve the quality of storm water runoff entering nearby Crystal Lake. The company installed 17 rain gardens along one street, with existing curbs and gutters, in a 56.9-acre watershed. A street in an adjacent 81.9-acre watershed served as the control for comparative purposes. The gardens were constructed in fall 2003, with curb cuts added the following spring to funnel storm water from the street into the rainwater gardens. Two years before the gardens were installed, Barr engineers collected baseline data on storm water runoff rates and volumes from both the study and control streets. Water quality was also measured from a storm sewer pipe at the outlet of each watershed. Data will be collected for two years post-installation. Preliminary results show an 82 percent reduction in stormwater from the street with the gardens.
Click here to see identified research needs for Hydrology.
Air Quality
Impacts
Researchers: David J. Nowak [dnowak@fs.fed.us], USDA Forest Service, Northeastern Research Station, Syracuse, NY; Steven Rosenthal [Rosenthal.steven@epa.gov}, US EPA, :Jospeph Vaughan [jvaughan@mail.wsu.edu], Laboratory for Atmospheric Research, Washington State University
Air pollution is a significant concern in many American cities. At
the same time, trees – natural air purifiers - are being cut down
and fields are being plowed to accommodate growing urban and
suburban areas. This section provides information from the
scientific literature on the impact of landscaping on air quality.
Mowing and Air Pollution
One advantage of a native landscape is that it does not need
to be mowed regularly. A turf-grass lawn, on the other hand,
requires frequent maintenance, resulting in emissions of air
pollutants from lawn mowers, leaf blowers, and weed whackers. The
U.S. Environmental Protection Agency has calculated that standard
maintenance of 1000 acres of lawn will lead to the emission of 18
tons of VOCs per year, and that a gasoline-powered lawn mower
pollutes as much in one hour as does driving an automobile for 20
miles. According to calculations by the Illinois Environmental
Protection Agency, the use of lawn equipment in the Chicago Region
alone accounts for 50 tons of VOC emissions per day in the summer.
For comparison, even the largest sources of VOC emissions, like a
large auto assembly plant, produce about two tons of VOC emissions
per day; the cumulative use of lawn equipment produces 25 times that
amount. In addition, evaporative emissions from gas cans, which are
used primarily to support lawn maintenance activities, emit about 22
tons per day of VOC emissions in the Chicago Region.
Ecologic Benefits of Controlled Burns
Controlled burns have many ecological benefits, and are
vital to the maintenance of some ecosystems, like prairies. Native
plants are able to survive a controlled burn, while nonnative and
invasive plants are killed without resorting to the use of
herbicides. Burns increase plant biodiversity by preventing any one
species from becoming dominant. They also prevent the invasion of
shrubs and trees into the prairie.
Growing awareness of the essential role of fire in maintaining natural landscapes argues for increased use of fire as a management tool. However, there is also concern about the impact of smoke on human health and tighter pollution standards for constituents of smoke. These concerns coupled with the growing number of fire-maintained prairies within urban and suburban communities, necessitates examination of fire as a management tool.
There is a surprising lack of research on the air quality and health impacts from controlled burns in prairies. While there is existing research on the effects of fire in the Western United States and burning of agricultural land, it is unknown if this information transfers to the quick burning controlled prescribed fires used to manage prairie ecosystems and native landscapes.
Note: Information on air quality and plant emissions, pollution removal and carbon sequestration is currently being peer reviewed. It will be added to this document when available.
Click here to see identified research needs for Air Quality.
Biodiversity
Researchers: Liam Heneghan [lhenegha@depaul.edu], Associate Professor, Environmental Science Program, DePaul University, Chicago, Illinois; Mary Carol Hunter [mchunter@uga.edu], Assistant Professor, School of Environmental Design, University of Georgia
Why is biodiversity important?
Biodiversity allows for a rich array of microbes, insects,
plants, birds, and animals. Communities are interested in promoting
and preserving biodiversity for several reasons. Ecosystems with
greater biodiversity are considered by many to be more resilient to
physical disturbances, natural disasters, and invasive species.
Diverse ecosystems also provide ecological services that are
expensive to replicate, like air and water purification, attracting
pollinators, and providing natural material for advances in science
and medicine. Ecologically rich areas also provide aesthetic value
and reinforce a sense of place for urban dwellers, bringing a bit of
nature into the city.
What factors determine biodiversity?
Urban and suburban areas have many physical structures
(e.g., buildings) and disturbances (e.g., mowing). When designing
projects using native plants on large tracts of urban land,
biodiversity can be supported, in part, by replicating the
historical disturbance regime found in nature. For example, in the
case of native prairie plants, this is often accomplished through
the use of controlled burns. When seeking to improve biodiversity on
smaller parcels of land in the built urban environment, designers
should take into consideration many aspects of local ecosystem
structure including ecological niches, the texture, size and shape
of the native landscape, and their distance from natural areas.
Does native landscaping improve biodiversity?
A landscape with a high level of biodiversity is important
because it provides multiple ecological services and aesthetic
value. Designed landscapes in backyards, corporate campuses, and
city parks are often created to emulate nature. These designed
landscapes offer opportunities for cities to increase
biodiversity. A review of scientific literature finds few formal
quantitative studies addressing the biodiversity benefits of native
landscapes.
If the plants we plant attract local insects, we can assume that the native birds will follow to feed on those insects. A study of ground arthropod diversity in and around Phoenix sampled 24-sites over six different land uses. The highest diversity was found in areas three habitats where native plant species dominated. Less arthropod diversity was found in areas dominated by non-native plants.
A second study examined biodiversity among certain insects, particularly spiders. Yards landscaped with non-native drought-resistant plants imported from Australia, Africa and South America had diversity of species roughly equivalent to industrial sites. The lesson here seems to be that if a community’s plant and animal life have not evolved together (as native flora and native fauna have), non-native plants may not appeal to local fauna (spiders, birds and pollinators). This seems to be true even if the imported plants perform the same function as natives, such as being hardy and drought resistant.
A research project in Birmingham, England demonstrated the importance of disturbance in impacting biodiversity. There, researchers compared carabid (ground beetle) biodiversity at 65 sites across an urban-rural gradient. They found that the time since last disturbance was a key predictor of carabid diversity. In urban areas, if there are more, or different, disturbances than would naturally occur, then biodiversity is expected to decrease. Abandoned sites, with the absence of land management, reduced disturbance, and wetlands had the highest biodiversity and also provided habitat for scarce species. In addition, the smaller the fragment and further it was from a habitat corridor, the lower the biodiversity.
Click here to see identified research needs for Biodiversity.
Soils
Pesticide and Fertilizer
Impacts
Researcher: J. Marshall Eames [jeames@depaul.edu], De Paul University, Chicago, Illinois
Native landscapes are thought to reduce the amount of fertilizers and pesticides from entering lakes, streams and rivers. Much of the science supporting these claims is borrowed from an extensive and growing body of literature in related fields—for example, from agricultural studies on the impact of buffer strips for farm nutrient management, and the use of native cover for sediment control in mine reclamation.
The Problem With Generalizing
Pesticide and fertilizer impacts depend on a range of
conditions, including: soil type, density of the plantings, the
types of planting used, the slope and size of the plot, and most
importantly, the decision whether to use pesticides and fertilizers
by the property owner. Much of this information is poorly
documented in the scientific literature. This limits the
conclusions that we can reach regarding whether the use of native
plants impacts the effects of pesticides and fertilizers.
With these caveats in mind, researchers reviewed available studies comparing native landscaping, such as prairies and savannas, with conventional landscaping, i.e., a turf grass lawn. They distinguished between small-scale landscapes, measuring less than half an acre and large-scale native landscapes, which are characterized as areas up to 640 acres, such as parks, corporate campuses and brownfield sites.
The literature reviewed suggested the following benefits from native landscaping: (1) native plants may not require the fertilizers and pesticides needed to maintain conventional landscapes, i.e., turf grass; (2) native plants may reduce the impact of fertilizers through direct uptake of nutrients—nitrogen and phosphorous— from runoff that otherwise would contaminate the water supply; (3) via facilitation, native plants may create sub-soil conditions that reduces the levels of nitrate entering drinking water; and (4) through filtration, native plants may physically remove sediment particles and nutrients that bind to soil particles, i.e., phosphorus. Native plants also reduce soil erosion. Native prairie plants have extremely deep and thick root systems, and once established these plants anchor the soil, preventing wind and water erosion. Preventing soil erosion is very important for improving water clarity and fish habitat.
- Reduced Use
While more than 60 studies have documented the fertilizer and pesticide requirements and impacts of conventional landscapes, few studies are available comparing these to native landscapes. We know that when nitrogen and phosphorous are properly applied to turf grass and managed well, there is very little release to the environment. Over-fertilized or badly irrigated turf grass, on the other hand, does release nutrients. Many in the native plant nursery industry do not recommend using fertilizers.They believe that fertilizers are unnecessary and may provide a competitive advantage to weeds. Herbicides use may be reduced or eliminated if manual weeding is used or after native plantings are established and can out-compete invasive weeds. But regardless of fertilizers and pesticide necessity, some gardeners and land managers may still employ fertilizers, herbicides, and pesticides in an attempt to achieve larger and longer lasting blooms. The decision to use pesticides and fertilizers is always a personal and cultural preference and is often made independent of the plants actual need. - Direct Uptake
Direct uptake of nutrients occurs with native and non-native plants alike. Plants use these nutrients in order to grow and stay healthy.However, nutrient requirements vary by plant species. At this point, the scientific literature does not contain information showing that native plants are more efficient than non-natives at nutrient uptake. - Facilitation
Microbial activity responsible for decomposition of plants removes nitrogen from soil and water and releases it into the atmosphere in a process called denitrification. Denitrification is important because it prevents the excess nitrogen in the groundwater from flowing into waterways and causing algae blooms. It also reduces the quantity of nitrates entering drinking water. Significant factors that influence the rate of denitrification include: the availability of a carbon food source for the denitrification microbes, soil hydrology (how wet it is), and the amount of available nitrogen in the landscape. Native plants, particularly prairie plant species, may do a better job of facilitating denitrification than non-natives because they have dense root systems. This root system maximizes the rhizosphere - the zone surrounding the roots of plants – and decaying roots provide nutrients and energy to denitrifying microbes. However we do not know with certainty whether native plants are better at denitrification than nonnative plants. - Filtration
Phosphorous enters the landscape either as a particulate or in soluble form. Plants need phosphorous to grow, but excess phosphorous that is not taken up by plants can end up running off into waterways. Phosphorous is a problem in lakes because it feeds algae blooms, which cloud the water and lower the amount of oxygen available to support aquatic life. Because phosphorous is often bound to soil particles, the mechanisms for removing it from the environment are nearly the same as those for retaining sediment. There are several factors to keep in mind when using plantings to manage phosphorous: placement of plantings, stem density, and slope of the land. Dense native prairies do well at conserving soil and reducing runoff but we do not know if native landscaping shares these same capabilities.
When using plants to manage phosphorous, placing plants in the flow path of sediment runoff is critical for managing phosphorous. Runoff or surface flow directed through 15 feet of planted buffer (small strips of vegetated land, designed to intercept pollutants and manage other environmental concerns) will remove 30-60 percent of phosphorous; a 30-foot buffer removes 75-85 percent of phosphorous. Stem density also has an impact. Higher plant densities act as a mechanical filter, straining out phosphorous bound to sediment particles. The final factor is slope— or the grading of the native plantings. By grading the landscape with a flatter slope rather than a very steep slope, the velocity of runoff is reduced, allowing for greater phosphorous removal and sediment retention.
Do Native Landscapes Reduce the Impact of Fertilizers and
Pesticides?
Possibly. The maintenance of native plants could potentially
impose a lighter chemical burden on the environment than
conventional landscaping, but this depends largely on the choices
that people make when maintaining their landscapes.
Native Landscapes and Climate Change
Researcher: Mitchell Pavao-Zucherman [mzucker@email.arizona.edu], University of Arizona
Carbon circulates in an endless cycle between Earth’s atmosphere, the oceans, plants and soil. There is a fixed amount of carbon in Earth’s system, and it is stored in (or sequestered) and exchanged among various sinks, or pools in forms ranging from atmospheric carbon dioxide to organic matter in the soil. Sequestering carbon in the soil, and thus removing carbon dioxide from the atmosphere, is a strategy for offsetting carbon emissions and addressing climate change. Sequestration of carbon in the soil also promotes soil quality and health. Plants facilitate the sequestration process by removing carbon dioxide from the atmosphere during photosynthesis and storing it as biomass, which later decomposes to organic matter in the soil.
Why Carbon Sequestration is Important?
As concern grows about the potential harmful impact of rising
atmospheric carbon dioxide concentration, so does interest in
“carbon sequestration” -the net removal of carbon dioxide from the
atmosphere via photosynthesis and its storage in vegetation and soil
- as a mitigation strategy to offset carbon emissions and abate
climate change. While carbon sequestration is not a stand alone
solution to rising atmospheric carbon dioxide and climate change, it
is a useful strategy that can complement other solutions.
Soil carbon sequestration is one potential tool for combating climate change, because soil and plants offer a large carbon sink. Researchers have suggested that globally, soils have the potential to sequester 24 percent of the total emissions from fossil fuel combustion. Earth’s soils contain roughly three times as much carbon as all plant biomass.
How Soils Store Carbon?
Carbon is stored as soil organic matter in soil clumps, or
aggregates, for different lengths of time. These aggregates range in
size. Many variables influence the formation of aggregates,
including temperature, rainfall, and soil fauna and mineralogy, as
well as land management. In smaller aggregates the organic matter
bonds physically to the minerals in the soil; some soil organic
matter pools can store carbon for centuries.
Prairie Restoration and Carbon Sequestration
At FermiLab, west of Chicago, tallgrass prairie plots have been
established every year since 1975 on cropland that had been
cultivated for more than a century. Researchers are studying the
effects of prairie restoration on carbon cycling and sequestration
over time.
Researchers found that soil aggregates increase rapidly following prairie restoration—35 times faster than carbon accumulates in the soil. However, after ten growing seasons, soil carbon concentration was only 45 percent of virgin prairie, which underscores the importance of preserving remaining virgin prairie fragments. Practices that promote the sequestration of carbon include residue management (leaving plant biomass in place to decompose); soil amendments like manure and peat; minimizing disturbances to the soil; maintaining root biomass in the soil; and other practices that mimic the natural ecosystem. Prescribed fire in prairie restorations, for example, keeps the canopy relatively thin and warms the soil. Warmer soil promotes decomposition, which in turn promotes carbon sequestration.
Native Landscapes and Carbon Sequestration
It is fiendishly difficult to generalize about the relationship
between native plants and landscapes and soil carbon sequestration.
Not only do variations in urban soils have an impact on carbon
sequestration—so, too, does the urban environment itself, which is
fundamentally different from undisturbed systems. Cities are heat
islands that typically have higher temperatures than the surrounding
areas, with more air pollution, denser cloud cover, more
precipitation, more exotic species, greater fragmentation, and
higher disturbance regimes than rural or undisturbed systems. Due to
variations in urban soil types, research done in one place in the
city may not apply two blocks away. At least one study from USDA
conducted in and around Baltimore, Maryland suggests that plants in
cities are more productive than plants in more rural areas.
Researchers planted lambs’ quarters in three environments: urban,
suburban and rural. The urban environment provided 21 percent more
atmospheric carbon dioxide and higher temperatures than the rural
site, thus resulting in twice as much plant biomass in the city
plants. Does this higher productivity enhance transfer of carbon to
the soil? That question remains to be answered.
For further information:
The FermiLab project aims to use the information learned about carbon cycling in restored prairies in order to develop restoration practice guidelines for enhancing the natural carbon cycle and improving carbon sequestration (see http://www.uic.edu/labs/meler/fermi.htm).
The USDA has two urban soil programs that are relevant to the sequestration of carbon in soils in native landscaping. (1) The Forest Service’s Northeastern Research Station in Syracuse, New York, established in 1978, investigates the effects of urban forests and their management on human health and environmental quality. http://www.fs.fed.us/ne/syracuse/ .
The National Resource Conservation Service has a program entitled “Urban Soil Issues.” Its goals are to provide nationwide leadership in soil science to meet the needs of urban customers. The define urban broadly, so their activities will likely apply to suburban and exurban landscapes http://soils.usda.gov/use/urban/ .
Click here to see identified research needs for Pesticide/Fertilizer and Climate Change.
Phytoremediation Using Native Plants
Researcher: M. Christina Negri [negri@anl.gov], Argonne National Laboratory
Phytoremediation is the use of plants to remove, alter, or
contain contaminants on a site. Phytoremediation occurs when
contaminants in either the soil or groundwater are drawn into the
root system of a plant. Once in the root system the contaminants
are absorbed, sequestered, degraded, or volatilized into the
atmosphere. This section provides information from the scientific
literature regarding the use of phytoremediation using native plants
as a natural tool for cleaning up polluted soil and groundwater.
Soil Remediation
Scientists have studied many plant species to determine their
ability to remediate specific contaminants. Plants are selected
according to climate and contaminant cleanup objectives.
Non-native plants are often employed for specific tasks. Cleanup of heavy metals, for example, requires genetic traits of tolerance and uptake selectivity. Relatively few plants fit the bill, and those that do are contaminant-tolerant exotic species that have evolved on soils rich in the metal of interest. Two examples are Pteris vittata, a fern from Asia that is good for extracting arsenic, and Thlaspi caerulescens, a European plant that accumulates zinc. When non-natives are used for phytoremediation, precautions are taken to prevent them from becoming invasive. Sunflowers and other crops, coupled with chemical soil manipulation, can also phytoextract heavy metals.
Native plants work best when the functions required for remediation are tied to the plants’ effect on soil fertility, microbial populations, water consumption, or to their effectiveness as ground cover, since native plants often have a positive effect on these attributes. As an alternative arrangement, native plants may be planted after non-natives have finished a cleanup, to make the transition to a native landscape.
For example, at Argonne National Laboratory near Chicago, non-native trees are performing the specialized task of cleaning up contaminated soil and groundwater. The lab planted 800 hybrid poplars and willows in 1999. These tree species were selected because of their fast growth rate and deep roots that could reach a 30-foot-deep aquifer contaminated with trichloroethylene and other solvents. By the fall of 2000, the solvents were absorbed into the tree tissue, demonstrating that phytoremediation was occurring. Argonne’s goal is to restore the site to a native landscape after cleanup is complete, progressively planting native oak in the areas now dominated by willows and poplars.
Roots
Prairie plants have dense root systems, and native plants are
good at degrading hydrocarbons in the rhizosphere, the zone
surrounding the roots of plants. Decaying roots provide nutrients
and energy to biodegrading microorganisms. Dense root systems also
stabilize the soil and protect it from runoff and wind erosion. At
the Bunker Hill, Idaho Superfund site in the Coeur d’Alene River
Basin, the second largest Superfund site in the nation, revegetation
with native and nonnative plants is helping to prevent soil that is
contaminated with a variety of heavy metals from eroding into the
river system.
Native Plants
Phytoscapes are landscapes that are designed to deliver
phytoremediation benefits. Atlantic Richfield Company is pioneering
the use of native-prairie and wetland plants to prevent small spills
from spreading, and to clean up spills around its neighborhood gas
stations.
Some native plant species not only tolerate but actually remediate gasoline in the soil. While gasoline- tolerant species are now being used to prevent small spills from building up, and to clean up leaks that have already occurred, intolerant native plant species are being used as leak detectors. Like canaries in the mines, the death of an intolerant “sentinel” plant indicates that there has been a gas leak. These intolerant plants are especially useful because they can detect leaks sooner than conventional detection methods.
Tolerant Species
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Figure XX: Information courtesy of David Tsao, Atlantic Richfield – British Petroleum |
Click here to see identified research needs for
Phytoremdiation.