Assemble as many data sets as you can that describe the ecological, environmental, economic, and demographic features of your community. Your first stop will be your own community’s planning or GIS staff. Then you might consult your regional planning organization. Many will have collected at least some of the information you’ll need. Other sources include Community Commons, US EPA’s green infrastructure website, and US Forest Service research reports.
While stormwater projects must be designed to meet site-specific conditions, you can set priorities by mapping where trees are in your community, where they’re not, and where they should be planted. i-Tree Canopy offers a free, aerial-photo-based mapping tool. With trained volunteers or staff, you can create a canopy map showing different land cover types, that approaches 95+ percent accuracy when compared with field inventories. And it can be completed in a day or two.
High-resolution land cover mapping isn’t cheap, but many communities may have already collected it. For lower-resolution (but free, and still informative) map layers, check out the National Land Cover Database.
Air Pollution and Public Health
Trees planted for stormwater management do a lot of things besides slowing flow. Demonstrating their impact on reducing air pollution and improving public health can help make the sale.
First, check with your regional planning organization or state environmental agency. They’re likely to have watershed maps you can add as a data layer to your base map. Another place to look is EPA. Their EnviroAtlas provides a wealth of environmental data, including watershed and stream quality.
USDA has soil maps for 95 percent of the nation’s counties. Since soil volume and type are powerful predictors of tree health and survival, it helps to know what soils you’ll find in your communities. Remember though, that soils may vary from site to site; some may require additives to increase filtration rates. Don’t skimp on soil volume. Trees generally can’t survive without 500 to 1,000 cubic feet of soil for healthy root growth.
Climate Change/Temperature/Heat Island
It’s getting hotter; most cities have experienced increases in their heat island (i.e. the difference between the temperature in the city and the temperature in nearby rural areas). Some cities now suffer heat differentials as much as 20 degrees Fahrenheit. Since heat-related deaths approach 8,000 a year according to the CDC, planting trees to lower urban temperatures can help solve a critical public health problem.
Climate Central has the numbers for many cities.
As you review your community’s circumstances, you’ll find problems and natural solutions which can attract substantial support among stakeholders. Some may be directly related to stormwater management; others may offer important co-benefits when applied to stormwater management. Often public health impacts and reduction of heat island effects can help move public officials — and the public — toward more aggressive urban forestry and green infrastructure programs.
Don’t rely too heavily on case studies – especially from communities in a different climatic or soil zone. As one tree advocate from Southern California put it: “There’s not much we can learn from studies done in places where rainfall is three times what we get, and drought doesn’t matter.” Look to communities like yours and tap their experience.
Often, community-specific natural resource data won’t be readily available, or easily layered into GIS analyses. You can find alternatives – workable but less precise – from public data sources. Or, you can try to create a simple sample-based inventory by yourself. While most available inventory tools require highly-trained volunteers (often graduate students), they can produce accurate maps, and create the database necessary for long-term management and maintenance of city trees.