Trees are indicators of a community's ecological health. While urban ecology is more complex than just tree cover (it is technically green infrastructure) trees are good indicators of the health of an urban ecosystem because of the biological functions of the roots and leaves. When trees are large and healthy, the ecological systems that support them are also healthy. Healthy trees provide valuable environmental benefits which can be measured in terms of ecosystem services. The greater the tree cover and the less the impervious surface in a community, the more ecosystem services are produced. These services are measured as stormwater runoff reduction, increasing air and water quality, carbon storage and energy reduction.

American Forests has conducted an Urban Ecosystem Analysis (UEA) in more that 40 metropolitan areas in the country and documented the loss of tree cover in these areas. These reports calculate the ecosystem services provided by trees and their associated landscapes. The calculations use scientific and engineering models developed by agency experts in hydrology and air quality. The analysis starts with a detailed map of the land cover classified from high resolution satellite and aerial imagery. The land cover classification of the imagery produces a detailed map of the structure of the land.

American Forests advocates that every city set a tree canopy goal as an important step in ensuring that valuable green infrastructure is maintained at minimum thresholds, even as urban areas continue to grow. Details of our strategy and recommended targets have been published and are available at www.fundersnetwork.org.

American Forests has also developed the tools that local communities build capacity to o analyze and understand their own green infrastructure. CITYgreen software is a desk top GIS software available through our office for calculating the value of nature.

Many communities around the country have success stories to report as a result of their introduction to the Urban Ecosystem Analysis, green infrastructure assets and CITYgreen. Calculating the value of nature in urban communities has provided decision support materials to all reaches of the urban establishment from community leaders to educators. American Forests also organizes a national conference every two years to help communities develop the expertise they need to understand and manage their own green infrastructure assets.