The Urban Forests of Philadelphia
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United States Department of Agriculture The Urban Forest of Philadelphia Northern Resource Bulletin Forest Service Research Station NRS-106 November 2016 Abstract An analysis of the urban forest in Philadelphia, Pennsylvania, reveals that this city has an estimated 2.9 million trees (encompassing all woody plants greater than 1 inch diameter at breast height [d.b.h]) with tree canopy that covers 20 percent of the city. The most common tree species are spicebush, black cherry, ash, tree-of-heaven, and boxelder, but the most dominant species in terms of leaf area are sycamore spp. (including London planetree), northern red oak, black walnut, red maple, and Norway maple. Trees in Philadelphia currently store about 702,000 tons of carbon (2.6 million tons of carbon dioxide [CO2]) valued at $93.4 million. In addition, these trees remove about 27,000 tons of carbon per year (99,000 tons CO2/year) ($3.6 million per year) and about 513 tons of air pollution per year ($19.0 million per year). Philadelphia’s urban forest is estimated to reduce annual residential energy costs by $6.9 million per year. The compensatory value of the trees is estimated at $1.7 billion. The city’s parklands constitute 9.3 percent of the total land area, have an estimated 1.1 million trees, 64 percent canopy cover, and account for 38.8 percent of carbon storage and 34.8 percent of air pollution removal performed by the city’s urban forest. The information presented in this report can be used by local organizations to advance urban forest policies, planning, and management to improve environmental quality and human health in Philadelphia. Quality Assurance This publication conforms to the Northern Research Station’s Quality Assurance Implementation Plan which requires technical and policy review for all scientific publications produced or funded by the Station. The process included a blind technical review by at least two reviewers, who were selected by the Assistant Director for Research and unknown to the author. This review policy promotes the Forest Service guiding principles of using the best scientific knowledge, striving for quality and excellence, maintaining high ethical and professional standards, and being responsible and accountable for what we do. Cover Photo Transportation corridor planting between railway and John F. Kennedy Boulevard in Philadelphia, PA. Photo used with permission from Philadelphia Horticultural Society. Manuscript received for publication 19 October 2015 Published by For additional copies: U.S. FOREST SERVICE U.S. Forest Service 11 CAMPUS BLVD SUITE 200 Publications Distribution NEWTOWN SQUARE PA 19073 359 Main Road November 2016 Delaware, OH 43015-8640 Fax: (740)368-0152 Email: [email protected] The Urban Forest of Philadelphia The Authors DAVID J. NOWAK is a research forester and project leader with the U.S. Forest Service’s Northern Research Station at Syracuse, NY. ALLISON R. BODINE is a research forester with Davey Tree’s Davey Institute at Syracuse, NY. ROBERT E. HOEHN III is a forester with the U.S. Forest Service’s Northern Research Station at Syracuse, NY. ALEXIS ELLIS is a research urban forester with Davey Tree’s Davey Institute at Syracuse, NY. SARAH C. LOW is a field station coordinator and biological scientist with the U.S. Forest Service’s Northern Research Station at Philadelphia, PA. LARA A. ROMAN is a research ecologist with the U.S. Forest Service’s Northern Research Station at Philadelphia, PA. JASON G. HENNING is a research urban forester with Davey Tree’s Davey Institute at Philadelphia, PA. EMILY STEPHAN is a research assistant with the SUNY College of Environmental Science and Forestry at Syracuse, NY. TOM TAGGERT is a research assistant with the SUNY College of Environmental Science and Forestry at Syracuse, NY. TED ENDRENY is a professor with the SUNY College of Environmental Science and Forestry at Syracuse, NY. Street trees in Philadelphia, PA. Photo by Sarah Tse, used with permission. CONTENTS EXECUTIVE SUMMARY .............................................................................................................................1 BACKGROUND ............................................................................................................................................3 METHODS .....................................................................................................................................................3 Tree Cover Assessment .......................................................................................................................3 Urban Forest Composition, Structure, and Values ....................................................................3 Tree Cover Change Analysis ..............................................................................................................9 Cobbs Creek Watershed Analysis ....................................................................................................9 Species Score .......................................................................................................................................11 RESULTS .......................................................................................................................................................12 Tree Cover Assessment .....................................................................................................................12 Urban Forest Structure, Composition, and Values ..................................................................12 Land Cover Change Analysis ..........................................................................................................33 Cobbs Creek Watershed Analysis ..................................................................................................34 MANAGEMENT IMPLICATIONS ..........................................................................................................37 Current Tree Size Distribution and Potential Species Changes ..........................................37 Invasive Species ..................................................................................................................................39 Insect and Disease Impacts.............................................................................................................39 Species Score .......................................................................................................................................41 CONCLUSION ............................................................................................................................................43 ACKNOWLEDGMENTS ...........................................................................................................................43 APPENDIX 1: Land Use Category Descriptions .............................................................................44 APPENDIX 2: Invasive Plant Species Assessed in Philadelphia’s Parkland Areas ...............46 APPENDIX 3: Ecosystem Services by Neighborhood ..................................................................47 APPENDIX 4: Potential Insect and Disease Impacts ....................................................................52 APPENDIX 5: Species Sampled in the Philadelphia Urban Forest ..........................................56 APPENDIX 6: Tree Species Distribution ............................................................................................59 APPENDIX 7: Relative Tree Effects ......................................................................................................63 APPENDIX 8: Temperature Index Map ..............................................................................................65 APPENDIX 9: General Recommendations for Air Quality Improvement .............................68 APPENDIX 10: Species Sampled in the Philadelphia Parkland Areas ....................................69 APPENDIX 11: Tree Planting Index Map...........................................................................................72 LITERATURE CITED ..................................................................................................................................74 Street trees in Philadelphia, PA. Photo used with permission from Philadelphia Horticultural Society. EXECUTIVE SUMMARY The urban forest in Philadelphia (i.e., all trees1 within the city) affects environmental quality and human health. In Philadelphia, local organizations are investing in tree planting campaigns to encourage the growth of a healthy urban forest. At the same time, insects, diseases, invasive species, climate change and development continually alter the urban forest. Addressing the challenge of developing a sustainable and healthy urban forest is complicated by a diversity of tree species, their dynamic character, a fragmented ownership pattern, and a lack of comprehensive information about the urban forest. To address these critical information needs, the U.S. Forest Service assessed Philadelphia’s trees to quantify its urban forest structure, and the associated services and values provided to society. This assessment consisted of field data collection and model analyses to inform and improve urban forest management. The i-Tree Eco model (www.itreetools.org) was one of the tools used to advance the understanding of Philadelphia’s urban forest. This computer model quantifies forest structure and associated ecosystem services and monetary values based on local data. Structure is a measure of physical attributes of the forest