Sustainable Urban Ecosystems

Statement of the Problem

We conjure up images of wide-open spaces when thinking of the West. That's because 96% of the population lives in urbanized areas. Within these cities and towns are over 25,000 km2 (15,000 sq miles) of greenspace containing over 500 million trees (USDA Forest Service 1999). This "green infrastructure" provides aesthetic, recreational, health, economic and environmental benefits that make our communities more livable. Westerner's spend about $2 billion ($40/capita) each year to obtain these benefits (Templeton and Goldman 1996).

Urban development has disrupted the flows of energy, water, wildlife and materials through the ecosystem. Instead of the slow, circular path taken by water, energy, and nutrients through "natural" ecosystems, in cities, flows are intensified and more linear. Open space is paved, thereby increasing the volume and rate of stormwater runoff, sometimes resulting in flooding. Over 50% of the water that is pumped and treated for human use is applied to the landscape during summer, at considerable economic and environmental expense. Fertilizers, pesticides, petroleum, and other pollutants washout into streams. Asphalt and buildings absorb sunlight, creating mini-heat islands throughout the urban region that increase demand for air conditioning and exacerbate air pollution. Lawn clippings, tree leaves, waste wood, and other materials are shipped to landfills, creating massive nutrient pools.

Communities throughout the West are struggling to meet the challenges of growth -- flooding, water pollution, water shortages, interrupted energy services, poor air quality, declining wildlife diversity and populations and landfill closures. Declining environmental quality makes it harder for cities to retain and attract new businesses. Governmental agencies are spending millions of dollars to rectify these problems, often in narrow and isolated fashion. Wildlife are often confined to small isolated patches or narrow corridors.

However, there are places where smart, green growth is happening at a local and community level. Residents are coming together to restore historic neighborhoods, protect valuable open space, turn shopping malls into village squares, and open the door to a more vibrant civic life. Increasingly we see that liveable communities are economically powerful communities; places where a high quality of life attracts the best-educated and trained workers and entrepreneurs, where good schools and strong families fuel creativity and a sense of community. The green infrastructure is a vital component of communities that are striving to be more than plots of bulldozed land, networks of roads, and collections of soulless buildings.


The impacts of growing urbanization and development in the West are being felt from the core of our cities to the wilds of our National Forests. Sprawling suburban growth reaches into agricultural and wild lands, fragmenting wildlife habitat, creating fire hazards, and reducing arable lands. Declining municipal budgets for tree care threaten the health of community forests.

We have failed to realize the full potential of our green infrastructure because we have designed and managed landscapes as "pictures" rather than as functioning ecosystems. Sustainable urban ecosystems recognize the interconnection of natural resources, human resources, site design, building design, energy management, water supply, waste prevention, and facility maintenance and operation. We define "sustainable urban ecosystems" as landscapes that are designed and managed to minimize impact on the environment and maximize the value received for the dollars expended in the long term. In principal, sustainable urban ecosystems are economically beneficial because the full life cycle of processes and products is evaluated and optimized. Costs and benefits are considered from initial design through the life of the project.

Sustainable urban ecosystems not only provide recreational and aesthetic values, but tangible benefits of cleaner air and water, conservation and reuse of natural resources, increased biodiversity, and other products that increase the livability of our communities. Creating sustainable urban ecosystems involves optimizing man-made greenspace based on considerations that are ecological and social. The science of sustainable urban ecosystems reflects our desire to connect human society with nature in a way that intimately influences everyday life. For example, sustainable ecosystems can be urban gardens that allow children to grow up knowing what it's like to eat locally-grown produce, open fields where we toss balls on a summer evening, natural ecosystems that are strolled through on an evening walk down the street, habitats with viable populations of a diverse mix of wildlife and municipal wastewater forests that recycle sewage, sequester carbon dioxide, and produce timber for local use.

Sustainable urban ecosystems are one means of reconnecting residents with natural processes. For example, instead of treating residential landscapes as "ornamental" they can be designed as functioning mini-watersheds that have environmental, economic, and social benefits. Through strategic tree planting, rainwater harvesting, mulching, and green waste recycling sustainable landscapes can regulate flows of water, energy, green waste, and nutrients in ways that are evident to residents and beneficial to the environment. Reconnecting people to the land through sustainable urban ecosystems can transform the way we live. It can instill a land ethic and a spirit of can-do cooperation. Moreover, sustainable urban ecosystems can foster more liveable neighborhoods, create jobs, and reduce governmental expenditures.

Partnering with nature instead of conquering it is at the heart of sustainable urban ecosystems. Sustainable planning and design recognizes systems that are best suited to human needs and capabilities, then creates and manages these systems to be as self-sustaining as possible. Self-sustaining or regenerating systems allow nature to manipulate the physical and chemical environment rather than relying on subsidies provided by humans. Self-sustaining landscapes, such as gardens with native plants, require less energy, water, and other resources to maintain than traditional landscapes, and they produce fewer pollutants.

Important ecological concepts that apply to the design and management of sustainable urban ecosystems include: (Graedel 1997; Mitsch and Jorgensen 1989; Lyle 1985; Mollison 1988;Van der Ryn and Cowan 1996; Wilson et al. 1998)


Research on the planning and design of sustainable urban ecosystems can link directly to the concepts adapted from the Guiding Principles on Environmentally and Economically Beneficial Landscape Practices on Federal Landscaped Grounds (EPA 1995). Major objectives of this Regional Research Project that focus on the benefits, costs and sustainability of urban ecosystems include:

1. Identify, Design and Promote Practices that Maximize Net Benefits and Minimize Adverse Effects on Urban Vegetation

2. Quantify Multiple Benefits and Costs

3. Seek to Prevent Pollution through design, installation, management practices appropriate use

4. Incorporate Knowledge of Plant-People Interactions

5. Use Regionally Native Plants for Landscaping as appropriate

6. Encourage biodiversity (plants and wildlife) within urban ecosystems

7. Create Demonstration and Extension Projects

1. Identify, Design and Promote Practices that Maximize Net Benefits and Minimize Adverse Effects on Urban Vegetation

Structures can be integrated with existing plant and animal communities and cultural (human) environments. Impacts on existing vegetation can be minimized by protecting and integrating plants into the site design and analyzing soil and irrigation water supplies to detect toxic or other undesirable materials. Limiting vehicular access to specified areas during construction and proper disposal of debris such as paints, chemicals, and concrete can minimize adverse impacts to natural habitat.

Potential research questions:

What is the optimum and/or necessary size, number and distribution characteristics of urban "open" green spaces?

What impacts may the emission of biogenic hydrocarbons have on the urban environment?

How does urban vegetation affect the urban infrastructure (e.g., sidewalks, curbs, sewer lines, etc.)?

What quantitative assessments can be made of the benefits (human psychological and emotional health) and liabilities (hazardous trees) of urban vegetation?

What design criteria need to be more completely understood or more thoughtfully implemented to meet the goals of a sustainable landscape?

What long-term management strategies (e.g., better detection, identification and monitoring of pests; biological control schemes) can be developed?

Disciplinary expertise required:

horticulture, landscape architecture, urban planning, environmental science, psychology

2. Quantify Multiple Benefits and Costs

Quantification of multiple benefits and costs of sustainable strategies serves as a basis for decisions concerning policy, investment, and management. For instance, development that incorporates street trees impacts capital and operating costs, urban heat island intensity, air quality, air conditioning costs, stormwater runoff, public safety, and resident satisfaction. Before implementing sustainable strategies it is necessary to assess the relative cost effectiveness of these strategies. Comparing benefits and costs (benefit-cost ratios) of sustainable strategies to traditional development and management practices provides baseline data for decision-making and helps target research areas with the greatest promise for implementation.

Potential research questions:

How are benefits and costs influenced by different levels of management? What mowing, pruning, burning, flooding, grazing, tilling, fertilizing, and monitoring cycles are most efficient for different urban ecosystem components?

How can municipal programs be configured to reduce costs and increase net benefits using trained volunteers, contractors, and different management technologies and practices?

What valid non-market valuation approaches are best applied to urban ecosystems?

What are the future costs of deferred maintenance of the green infrastructure and how are costs associated with future risks distributed?

Disciplinary expertise required:

economics, risk assessment, environmental science and policy

3. Seek to Prevent Pollution

The primary tenet of pollution prevention is: whenever feasible, pollution should be prevented or reduced at the source, and where pollution cannot be prevented, it should be recycled in an environmentally safe manner.

Manage Pesticides and Fertilizers. Improper use of pesticides and fertilizers contributes to pollution of surface and groundwater and can adversely impact human health. Plant Health Management (PHM) and Integrated Pest Management (IPM) can result in reduced use of chemicals contained in fertilizers and pesticides. PHM and IPM are decision-making processes that target interventions so that they are most effective, rather than indiscriminate application of chemicals as preventative or routine treatments.

Minimize Runoff. Uncontrolled runoff impacts the environment as a: 1) major contributor to soil erosion, 2) primary vehicle for pollutant transport to receiving water bodies, and 3) source of flooding that can damage property and threaten lives. Best Management Practices (BMPs) to reduce stormwater runoff include grass-lined swales, pervious paving materials, stream buffers, green parking lots, narrow streets, and watershed-based zoning.

Recycle Landscape Trimmings (Green Waste). A significant percentage of the total waste stream is comprised of leaves, grass clippings, plant trimmings, and woody material. These elements are desirable for composted material, mulches, and landscape amendments. By using these products we can effectively and economically enrich the soil, promote plant growth, preserve soil moisture, reduce erosion, and inhibit weed growth. Per capita, California homeowners are estimated to produce 180 kg of green waste (lawn clippings, tree/shrub prunings) per year (Statutes of California and Digests of Measures, 1989). This green waste is a significant component of the municipal waste stream that can be reused or recycled. In 1989, California passed legislation requiring every city/county to divert 25% of all solid waste from landfills through source reduction, recycling and composting by 1 Jan. 1995 (Statutes of California and Digests of Measures, 1989). By 1 Jan. 2000, these municipalities will be required to divert 50% of their solid waste. While the legislation permits any strategy (reduction, recycling) to reduce the amount of green waste, the method of greatest interest to horticulturists and urban foresters is composting.

Composted green waste has very good potential for use as a plant growth medium, soil improver or as a landscape mulch. It is suitable for use as a partial or complete substitute for peat, particularly when mixed with coir. Widespread use of composted green waste should lead to a reduction in peat usage, to a reduction in environmental damage and to reduced waste disposal costs.

Challenges facing urban dwellers in the use of composted green waste include accessibility of the product (unless they make it themselves), variable quality (e.g., % organic matter; nitrogen, and other mineral, content) and the potential presence of phytotoxic constituents.

Implement Water and Energy Efficient Practices. Irrigating landscapes can account for a significant proportion of total municipal water consumption, particularly during the peak watering period. Water efficient landscape practices contribute to the preservation of fresh, potable water and the conservation of energy used to pump, distribute, and treat water. Water conservation practices include careful selection and siting of plants, use of mulches, on-site water harvesting, design and maintenance of efficient irrigation systems, and use of reclaimed water (recycled or gray water).

Strategic siting of plants to shade buildings and cool paved surfaces can improve human thermal comfort and reduce building heating and cooling loads. However, improperly located plants can increase heating costs by blocking winter solar access. By transpiring water and shading surfaces, plants lower local air temperatures, thereby reducing ozone levels. In the absence of the cooling effects of plants, higher air temperatures contribute to ozone formation. Although trees provide air quality benefits by 1) absorbing gaseous pollutants (ozone, nitrogen oxides) through leaf surfaces, 2) intercepting particulate matter (e.g., dust, ash, pollen, smoke), 3) releasing oxygen through photosynthesis, many trees also emit various biogenic volatile organic compounds (BVOCs) such as isoprenes and monoterpenes that can contribute to ozone formation. The ozone forming potential of different plant species varies considerably.

Try New Models of Landscape Design. Apply the California Landscape Garden model developed in Francis and Reimann (1999) to a series of home and public garden case studies in California to explore how this approach minimizes energy consumption, creates regionally appropriate landscapes and improves garden design and management. This could be done by developing demonstration gardens, evaluating outcomes utilizing interviews, observation, habitat analysis and water use with potential outcomes to include: improved garden and planting design practices for home and public gardens.

Potential research questions:

How can landscape tree fertilization programs be best designed and implemented to minimize adverse environmental impacts?

What strategies can be employed to minimize the use of chemical pesticides and fertilizers in and around urban vegetation?

What novel irrigation practices can be used in the urban setting to maximize the efficient use of water and minimize its loss through runoff?

How can recycled green waste be effectively used in the urban ecosystem?

How and in what quantities do mineral nutrients move throughout the traditional turfgrass systems and in more sustainable landscapes?

What is the species response to water quality?

Disciplinary expertise required:

pest management, horticulture, soil science, environmental toxicology, entomology, plant pathology

4. Incorporate Knowledge of Plant-People Interactions

Adoption of sustainable urban ecosystem practices depend on the values, attitudes, and lifestyles of designers, managers, and their customers. Understanding how these factors influence decisions and behaviors is critical to developing education and marketing strategies. For example, "caring" for one's garden and the neighborhood is often manifest in clean and tidy landscapes that mimic orderly, agricultural fields. The "controlled wildness" that is often characteristic of sustainable landscapes can be misconstrued as disregard or neglect, rather than another expression of "caring." Promoting an ecological aesthetic and articulating its theoretical underpinnings will require a greater understanding of plant-people interactions. Substituting the ecological know-how required to manage dynamic, sustainable landscapes for the more formulaic maintenance practices now in-place will require our best social science. The following procedures will be involved in studying this area: behavior mapping; interviews with developers, users; site analysis; urban design analysis. We envision possible outcomes to include improved design methods and practices for creating open space-oriented development.

In addition, the green spaces of our cities and neighborhoods provide extensive, profound benefits for people who live and work in cities. Other benefits have been documented for people as they actively participate in community greening projects. Nearby nature in urban environments helps alleviate people's stress and anxiety, aids in health and well-being, boosts worker satisfaction and productivity, relieves driver stress in traffic and helps create attractive retail settings to attract consumers. Such benefits are achieved not just by the mere presence of plants and trees, but also by the form and configuration of site planting and management (Kaplan, Kaplan & Ryan, 1998). We can learn how to maximize multiple functions of urban ecosystems, creating "green infrastructure" that is ecologically sustainable and provides liveable, nurturing places for people.

Potential research questions:

How can the impacts of vegetation and open space on new community design including smart growth community development be assessed?

How have plants and landscapes been managed in the past and how can this knowledge apply to management of more sustainable urban ecosystems?

What demographic, scientific, economic, and religious trends are most likely to shape urban dwellers attitudes towards nature and their behaviors impacting landscapes?

Why do people participate in more ecologically sustainable landscapes and how does this interaction affect human health and the community's quality of life?

How can urban ecosystems be planned, restored and managed to optimize psycho-social benefits for individuals?

What are the positive impacts of community-based green projects on small groups and organizations that participate?

How might we economically value human benefits so that cost/benefit analyses include quality of life factors?

What makes homeowners adopt or reject the choice to grow native plants?

Disciplinary expertise required:

landscape architecture, psychology, sociology

5. Use Regional Landscape Ecology in Landscaping

Where the appropriate conditions exist, regionally native plants may offer the advantages of natural adaptation to the climatic and geologic environments. The goal is to integrate knowledge of regional water regimes, plant associations (not just individual plants as ornamentals) and wildlife habitat requirements into residential, commercial and public landscape schemes. Use of regionally native plants can enhance wildlife habitat and diversity and promote a "sense of place" and regional identity.

Potential research questions:

What production methods (e.g., propagation, plant and ecosystem management, transplantation) are best utilized for native plants?

What urban environments are most suitable for native plants? Where can native plants be used most effectively?

What strategies can be employed to control / minimize the spread of exotic plants that may threaten native plants?

What are the potential problems associated with growing populations of native plant species in urban settings?

6. Encourage Biodiversity (Plants and Wildlife) Within Urban Ecosystems

Since so many animals trek across landscapes such as butterflies and birds--not conforming to state or regional boundaries--thinking of our cities in a larger context of being inside of wildlands may shape the kinds of activities we enact in our cities. Some of the best ways to get urban dwellers interested in wild nature is through witnessing, learning about, welcoming, and facilitating the recurrent event of a major biological phenomenon such as the return of the salmon in northern California, or the return of the monarch butterflies--in Seaside and Pacific Grove, California. These migrations occur in every region and could be significant focal points around which to rally support for "sustainable urban ecosystems." Thinking about how we might better link our wildlands and agricultural lands to our cities will aid us in the design of more sustainable urban ecosystems. Planting a butterfly and bird garden, for example, and looking for the return of wildlife visitors each year and understanding their individual life cycles, may be the best way to educate oneself about nature and the interconnectedness of places. It also provides a way for people to become stewards of nature--within their own backyards or local parks.

Potential research questions:

What criteria should be used to determine optimum openspace (patch) size, distribution and level of connectivity, habitats capable of sustaining viable wildlife communities in urban ecosystems?

What criteria should be used to determine optimum corridor width and vegetative structure to connect urban habitat patches?

What implementation strategies can be employed to minimize fragmentation of existing patches and corridors and optimize connectivity?

What impact does the multiple use of most urban openspaces have on wildlife communities?

Disciplinary expertise required:

Wildlife and fisheries science, environmental planning, landscape ecology and restoration

7. Create Demonstration and Extension Projects

Sustainable demonstration and extension projects can 1) promote public awareness and education, 2) serve as inspiration for similar initiatives, and 3) showcase partnership opportunities among industry, academia, government agencies, neighborhoods, and non-profit organizations. Extension projects can directly connect researchers with extension agents and their customers to more effectively promote and share information about approaches to plan, design, and mange sustainable urban ecosystems.

Potential extension/outreach activities:

Assist with development of outdoor demonstrations and monitor their performance.

Develop on-line design and management tools to audit landscapes and rate their sustainability

Prepare and deliver extension courses and workshops to build local capacity.

Learn, develop, apply, and evaluate the use of inventory/management software and GIS-based programs

Develop and disseminate information about pests, beneficial organisms and sustainable pest management strategies to the urban public and professional landscape managers.

Disciplinary expertise required:

Environmental education, horticulture, environmental planning, communications,


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