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infrastructure strategist at CNT and one of the principal authors of the guide. “Establishing a framework for calculating the benefits of green infrastructure is a first, key step to making it a mainstream practice.” The guide distills key considerations involved in assessing the merits of green infrastructure practices. It examines the steps nec- essary to calculate a variety of performance benefits gained by implementing green infrastructure strategies, and, where possible, demonstrates simplified illustrative examples that estimate the magnitude and value of these benefits. The guide focuses on five green infrastructure practices: green roofs, tree planting, bioretention and infiltration, permeable pave- ment and water harvesting. However, the following excerpt focuses on the implications of tree planting. Overview of the benefits of planting trees Whether measured on a tree-by-tree basis, or on a larger scale such as an urban forest, tree planting has a multitude of benefits above and beyond a tree’s ability to manage stormwater. For example, tree planting: Reduces stormwater runoff: • Trees intercept rainfall and help increase infiltration and the ability of soil to store water. • Tree canopies diminish the impact of raindrops on barren surfaces. • Transpiration through leaves minimizes soil moisture, which reduces runoff. Increases groundwater recharge: • Trees can contribute to local aquifer recharge and to the improvement of watershed system health, from both quantity and quality standpoints. Reduces energy use: • When properly placed, trees provide shade, which can help cool the air and reduce the amount of heat reaching and being absorbed by buildings.In warm weather, this can reduce the energy needed to cool buildings. • Trees reduce wind speeds.Wind speed, especially in areas with cold winters, can have a significant impact on the energy needed for heating. • Trees release water into the atmosphere, resulting in cooler air temperatures and reduced building energy consumption. Improves air quality: • Trees absorb air pollutants (e.g.NO2,SO2, and O3) and inter- cept particulate matter (PM10). • Trees reduce energy consumption, which improves air quality and reduces the amount of greenhouse gases, including N2O and CH4. Reduces atmospheric CO2: • Through direct sequestration, trees reduce atmospheric carbon www.arborage.com dioxide levels. • Tree planting reduces energy consumption, which in turn reduces CO2 levels. Reduces urban heat island: • The various cooling functions of trees help to reduce the urban heat island effect, thereby reducing heat stress-related illnesses and fatalities. Improves community livability: • Trees provide beauty and privacy, which improve community aesthetics. • Planting trees increases recreational opportunities for com- munities by improving pathways, creating places to gather and providing shade during warm weather. • Trees provide a sense of place and well-being, which can strengthen community cohesion. • Trees help to reduce sound transmission, reducing local noise pollution levels. • Tree planting may provide opportunities for urban foraging and food production. Improves habitat: • Planting trees increases wildlife habitat, especially when plant species native to the region are used. Cultivates public education opportunities: • Managing future economic and environmental constraints will require full community participation and partnership.Green infra- structure provides an opportunity to develop community awareness and understanding around the importance of sustainable water resource management. • Community tree planting provides a valuable educational opportunity for residents to become more aware of the benefits of green infrastructure. The following section describes and quantifies tree planting benefits in the realm of water management, energy use, air quality and climate change. Water Water interception estimates, determined on a per-tree basis, are needed to calculate the amount of stormwater runoff reduced from a given project.Therefore, it is necessary to know the number of trees being planted and their size and type. For example, the larger leaf surface area on one kind of tree will intercept more rainfall than will a smaller tree or leaf. In addition, the rate at which trees intercept rainfall is significantly impacted by a site’s climate zone, precipitation levels and seasonal variability, which affects evapotran- spiration rates. The Center for Urban Forest Research of the US Forest Service, utilizing its STRATUM model,compiled a set of Tree Guides that take into account many of these factors and estimate the level of benefits provided by trees: http://www.fs.fed.us/psw/programs/cufr/tree_guides.php Arbor Age / March 2011 17