The services people enjoy from healthy ecosystems are the unobtrusive foundation of daily life. Yet people often underestimate or simply ignore the values from these "ecosystem services" when making land-use decisions— only to realize later how difficult, expensive, and sometimes impossible it is to replicate services once they are lost. The central message of the Sustainable Sites Initiative is that any landscape—whether the site of a large subdivision, a shopping mall, a park, an abandoned rail yard, or even one home—holds the potential both to improve and to regenerate the natural benefits and services provided by ecosystems in their undeveloped state.
While standards exist for sustainable structures—“green buildings”—there are no comprehensive guidelines and performance benchmarks for those who want to create and measure sustainable landscapes. Yet landscapes have great potential for both environmental good and severe environmental damage. For example:
Greenhouse gas emissions. Vegetation and soil help reduce the amount of carbon dioxide, a greenhouse gas, in the atmosphere by capturing and storing it for use in producing roots, leaves and bark. In the United States, urban trees capture up to 25 million tons of carbon each year.1
Urban climate. Use of vegetation, shade structures, and other techniques to cool the air can reduce costs associated with urban heat islands. Vegetation provides cooling through shading and evapotranspiration. Evapotranspiration alone can reduce peak summer temperatures by 2 to 9 degrees Fahrenheit.2
Control of invasives. Invasive species compete with and harm plant and animal communities. Approximately 85 percent of the invasive woody plant species in the U.S. were introduced for landscape or ornamental use,3 and approximately 5,000 plant species have escaped into natural ecosystems, resulting in millions of dollars in control costs.4 Through competition with native plant species, invasive species are a threat to native flora and fauna.
Water waste. Irrigation of unsustainable landscapes accounts for more than a third of residential water use—more than 7 billion gallons per day nationwide.5 Typically, half of irrigation water can be wasted as a result of evaporation, wind, improper system design, and overwatering.6
Water pollution. Around the country, polluted and contaminated stormwater runoff accounts for 70 percent of water pollution in urban areas and is the leading cause of poor water quality and the degradation of aquatic habitat.7 According to the U.S. Environmental Protection Agency’s Wadable Streams Assessment (WSA) in 2006, 42 percent of U.S. stream miles are in poor condition compared to the best available reference sites in their ecological regions. The WSA found that the most widespread stressors across the country are nitrogen, phosphorus, excess sedimentation, and riparian disturbance(i.e., evidence of human disturbance in or alongside streams).8
Yard waste. Retaining and recycling land-clearing materials on-site avoids the cost of waste disposal and reduces the need for new purchased materials and soil amendments such as compost and mulch. In 2007, approximately 33 million tons of yard waste entered the municipal waste stream,representing 13 percent of total municipal waste in the United States.9
Health and well-being of site users. Research by social scientists and psychologists shows that, for both adults and children, encounters with everyday nature—a green view from an office window, a lunchtime stroll through a nearby park, well-tended landscapes around schools—restore the ability to concentrate, calm feelings of anxiety, and reduce aggression.10 In addition, a Chicago study links tree and grass cover to fewer property crimes, fewer violent crimes, stronger ties among neighbors, more frequent use of common neighborhood spaces and a greater sense of safety.11
Energy consumption. When development results in an overall reduction in tree canopy cover, buildings are more exposed to both direct sunlight and wind. This exposure increases the demand for air conditioning in the summer and for heating in the winter. Studies conducted by American Forests found that tree canopy reduces residential home cooling costs, saving an average of between $11 per household per year in Portland, Oregon, and $28 per household per year in Atlanta, Georgia.12 Multiplied across the region, this household benefit can add up: in the Atlanta region, savings in home cooling costs amount to $2.8 million per year.