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Sustainable D.C.
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In Biophilic Cities: Integrating Nature into Urban Design and Planning, Timothy Beatley, Teresa Heinz Professor of Sustainable Communities at the University of Virginia, argues that cities must be designed so people feel intimately connected with nature. Beatley describes how “biophilia,” a term coined by famed sociobiologist and conservationist E. O. Wilson, can inform how we plan, design, and manage our cities. 

Wilson writes in the foreword: “The evidence is compelling that frequent exposure to the natural world improves mental health, it offers a deep sense of inner peace, and, in many ways we have only begun to understand by scientific reason, it improves the quality of life.”

Beatley then defines a “biophilic city” as one that puts nature first. “It recognizes the essential need for daily human contact with nature as well as the many environmental and economic values provided by nature and natural systems.” In addition, these cities are places where “residents spend time enjoying the biological magic and wonder around them. In biophilic cities, residents care about nature and work on its behalf locally and globally.” 

Within the District, the goal should be to increase connections to nature — locally, regionally, and globally. Institutions that could have particularly strong roles include botanical gardens, municipal zoos, natural history museums, and conservation groups.

Some sample questions used to guide the development of a biodiversity and environmental education action plan:

  • What is the percentage of time residents spend outside, understanding that climate must be accounted for?
  • What percentage of the population is active in nature or outdoor clubs or organizations? How many of these organizations exist in the city?
  • What percentage of the population can recognize common species of native flora and fauna?
  • To what extent are residents curious about the natural world around them?

Develop a biodiversity and environmental action plan based on the biophilic design work of Professors E.O. Wilson and Timothy Beatley. 

Washington, D.C.’s great riverfronts present opportunities for ecological restoration and preservation as a nature preserve. Tours could be offered through recreated wetlands, and recreation opportunities, including kayaking, could also be extended throughout the District’s river habitats. Native wildlife, including fish and water bird species, could be reintroduced in restored areas. 

Recreate wetland along riverfront edges and reintroduce native wildlife.

In 2009, the District adopted an urban tree canopy goal of 40 percent by 2035. Currently, the city has 35 percent tree canopy. According to Casey Trees, the District will need to add 2,401 acres of tree canopy to achieve the 40 percent goal. “Based on a mortality rate of 6 percent and using the rate of 100 trees equals 1 acre, 216,300 total new trees, or 8,600 trees a year, will need to planted over the next two decades.”

D.C.’s tree mortality rate is better than many cities, including New York. However, more could be done to ensure trees live long, healthier lives, thereby providing more environmental benefits. In a session at GreenBuild, Peter MacDonagh, the Kestrel Design Group, said the key to preserving larger older trees and keeping younger ones in place up to 50 years or more is to use large amounts of loam or bioretention soils that are 65 percent sand, 20 percent compost and 15 clay silt. These soils are not only the best growing mix for trees, but also filter out heavy metals, phosphorous, and nitrogen most efficiently. Nitrogen runoff can cause algae blooms and kill other life if it’s allowed to get to the watershed in large amounts.

The rule needs to be two cubic feet of loam for one square feet of tree canopy. So, for a tree that provides a 700 square foot canopy a designer needs to use 1,400 cubic feet of high-quality soil. These soils can be combined with “silva cells” that prevent soil compaction to enable the growth of tall, healthy trees. To prove this, MacDonagh showed the work of Bartlett Tree Lab’s Urban Plaza study, which demonstrated that loam soil grew trees that had 300 times more leaves and were 1.7 times taller than those grown in compacted soils. “This is important because the average street tree only lasts 13 years.”

In addition, the use of larger tree boxes with structured soils and permeable pavements around the trees enable the tree to both grow and get enough water, capturing stormwater in the process. 

The District should aim at further reducing the mortality rate of trees and extending their lifespan by enabling them to grow in larger tree pits. Use larger tree boxes with structured soils and add permeable pavements around the trees, which would enable the tree to both grow and get enough water, capturing stormwater in the process. As D.C. adds new trees, it should also ensure trees are distributed fairly between communities of different socio-economic levels.

Some cities grow trees elsewhere and then truck them in. In these instances, massive urban forestry campaigns may not be carbon neutral once all those transportation-related emissions are factored in. The city should ensure it uses only appropriate (native and adapted) plant species planted within 100 miles of the District. Other cities like Philadelphia and New York are exploring growing trees in nurseries within parks. 

Use appropriate trees grown locally for urban forestry campaigns. Experiment with growing trees in park nurseries.