United States and provides useful advice that could be used by many agencies that work on urban forestry. The report explores how urban sustainability can move beyond analyses devoted to single disciplines and sectors to systems-level thinking and effective interagency and intergovernmental cooperation. It concludes that it is critical to better integrate science, technology, and research into catalyzing and supporting sustainability initiatives; find commonalities, strengths, and gaps among rating systems; and incorporate critical systems needed for sustainable development in metropolitan areas.

Discussion

Dr. Bartuska was asked how USDA is defining “sustainability” in the context of an increase in population, economy, and agriculture. She said there is a balance of three factors in the context of sustainability: people, planet, and profit. USDA does have a sustainability office and they must continue to be aware of what constitutes sustainability and sustainability practices. For example, USDA’s Beginning Farmers and Ranchers Program ensures that participants address water and air issues, as well as biodiversity issues and then incorporate these into practice. Dr. Bartuska also noted that the USDA Agricultural Research Service has a project in small and organic farms in urban areas.

URBAN FORESTRY WITHIN THE GREATER URBAN ECOSYSTEM
Moderator: Marina Alberti

Urbanizing regions pose enormous challenges to ecosystem’s capacity to deliver important ecological services (Alberti, 2010). At current rates of urban growth, global urban land cover will increase by 1.2 million km2 by 2030, nearly tripling the global urban land area of 2000, with considerable loss of habitats in key biodiversity hotspots (Seto et al., 2012).

Scientists have made significant progress during the last few decades in studying the role of urban forests in both mitigating urbanization’s impact and providing a variety of ecosystem services. Yet scientific understanding of key mechanisms governing ecosystem functions across multiple scales is incomplete. There are important tradeoffs across scale and between functions. There is also great variability across metropolitan areas and biophysical regions.

The goals of this panel were to (1) explore the role of trees within the greater urban ecosystem and the ecosystem services they provide, and (2) review current understanding of the ecosystem services provided by urban forests, and identify research needs.

Urban Ecosystems and their Potential to Provide Ecosystem Services
Richard Pouyat, United States Forest Service (USFS)

The environmental changes and landscape alterations typical of urban areas make it difficult to be “green.” Urban areas have highly modified environments, sealed surfaces, and species introductions that are human-caused and thus represent novel habitats made up of novel assemblages of plants and animals. From an evolutionary perspective, these assemblages are relatively new, since cities have been around for only 5,000 or so years. As a result, urban landscapes are typically thought of as artificial, harsh environments where cultivated plants grow outside their native habitats, and where animals introduced as pets (such as domesticated cats) wreak havoc on prey species such as native song birds.

Despite these alterations, urban ecologists are finding high levels of biological activity and biodiversity in urban areas (Gregg et al., 2003; Ziska et al., 2004). Measurements thus far suggest there are high flux rates, large sinks for carbon and nitrogen, and high resource



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