TWIN CITIES URBANIZATION AND IMPLICATIONS FOR URBAN FOREST ECOSYSTEM SERVICES A DISSERTATION SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL OF THE UNIVERSITY OF MINNESOTA BY Adam Michael Berland IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Steven M. Manson, Adviser May 2012 © Adam Michael Berland, May 2012 ACKNOWLEDGEMENTS Many people deserve thanks for their help with this research. First, I would like to thank my adviser, Dr. Steven Manson. Steve, I appreciate your generosity, patience, sense of humor, and practical professional advice. Thank you for supporting me as I developed and carried out this project. I am grateful to my dissertation committee: Dr. Marvin Bauer, for the opportunity to develop my remote sensing skills, Dr. Kurt Kipfmueller, for your valuable feedback on my project ideas; and Dr. Katherine Klink, for the guidance to consider my research from the perspective of the general public. Dozens of faculty members at Minnesota and St. Thomas have influenced my thinking and prepared me for the future, especially Bryan Shuman, David Kelley, Paul Lorah, Robert Werner, Kyle Zimmer, and Rebecca Montgomery. The completion of this work relied on field assistance from Brewster Malevich, Paul Berland, and Larry Berland. Chris Boche of St. Paul Forestry generously allowed me to borrow the city’s tree planting records. I value my project discussions with the following municipal foresters: Ralph Sievert (Minneapolis), Paul Edwardson (Bloomington), Chris Link (Richfield), Dave Grommesch (Burnsville), Jeff Kehrer (Apple Valley), and Mick Higgins (Lakeville). I am also thankful for positive interactions in the HEGIS lab with Dave Van Riper, Chris Crawford, Sami Eria, Dudley Bonsal, and the others who have circulated through the lab. Finally, I want to thank my family. Megan, thank you for your patience and support during this long haul, and for willingly reading everything I put in front of you. i Mom and Dad, I could not have done any of this without you. To the rest of my family (in-laws included), I appreciate all you have done for me over the years. Portions of this research were supported by a Doctoral Dissertation Research Improvement grant (Award #1003138) from the National Science Foundation, a Doctoral Dissertation Fellowship from the University of Minnesota Graduate School, a Thesis Research Grant from the University of Minnesota Graduate School, and the Graduate Research Partnership Program from the University of Minnesota’s College of Liberal Arts. These organizations have not endorsed this publication. Any views and errors are mine alone. ii For her patience and support, I dedicate this work to Megan. iii ABSTRACT Urbanization affects ecological structure and function by impacting the provision of ecosystem services, or benefits we derive from the natural environment. It is broadly acknowledged that ecosystem services should be formally considered in land management decisions, but inadequate scientific understanding of urban ecological systems is a key obstacle to achieving this goal. In this dissertation, I address this shortcoming by assessing the relationships between urbanization and the urban forest, a key urban ecological component. The three studies described here demonstrate spatial and temporal effects of urbanization on urban forest structure, function, and value in Minnesota’s Twin Cities Metropolitan Area. In the first study, I used historical air photos to analyze past trends in tree canopy cover related to urbanization and other land cover changes. Urbanization events generally reduced tree canopy cover, but urban sites rapidly afforested following development. Older urban neighborhoods typically had higher tree canopy cover than newly developed areas. In the second study, I used factor analysis on a suite of urbanization indicator variables to derive an urbanization gradient that is more sophisticated than a simple urban-rural distance-based gradient. This synthetic gradient was strongly related to more types of urban forest structural variables than the distance- based gradient, highlighting the influence of secondary urbanization trends on urban forest structure. In the final study, I stratified the study area by property parcel land use, and compared estimated urban forest structure, function, and value across land use classes. Residential and undeveloped areas both had higher urban forest values than non- iv residential developed areas, but were not statistically different from one another. This study showed which types of urban land uses promote good urban forest structure and function, and the results can be used to guide future urban forest study designs. All three studies demonstrate the need to consider complexities associated with human-environmental systems. Two major themes were the importance of temporally lagged tree growth and nonlinear urban-ecological relationships. Specifically, urban forest structure was typically greatest at intermediate levels of urbanization where urban intensity was not too great, and where adequate time since urbanization had allowed ample tree growth to occur. By making these complexities more visible, this research will improve the design of future work, so that we can develop a more complete and nuanced understanding of the effects of urbanization on the urban forest. v Table of Contents Acknowledgements ............................................................................................................ i Dedication ......................................................................................................................... iii Abstract ............................................................................................................................. iv Table of Contents ............................................................................................................. vi List of Tables .................................................................................................................... ix List of Figures ................................................................................................................... xi List of Abbreviations ...................................................................................................... xii CHAPTER 1. Introduction—the state of urban forestry and motivations for this research ...........................................................................................................1 Overview ...................................................................................................................1 Literature review .....................................................................................................2 The urban-rural gradient approach ........................................................................3 The importance of the urban forest .......................................................................4 Research challenges in urban forest ecosystem service science ...........................8 Summary of chapters ............................................................................................11 CHAPTER 2. Long-term urbanization effects on tree canopy cover along an urban-rural gradient ..................................................................................14 Overview .................................................................................................................14 Introduction ...........................................................................................................15 Methods ..................................................................................................................18 Study area............................................................................................................18 Data preparation ..................................................................................................21 Data analysis .......................................................................................................24 Results .....................................................................................................................28 vi Land cover ..........................................................................................................28 Tree canopy cover ...............................................................................................29 Canopy responses to land cover change .............................................................33 Distance from the urban core ..............................................................................35 Intensity of urbanization .....................................................................................35 Age of urban development ..................................................................................35 Discussion ...............................................................................................................38 Urbanization, agricultural legacies, and tree canopy cover ................................38 Spatial structure of tree canopy cover .................................................................40 Conversion to urban land cover ..........................................................................43 Study limitations .................................................................................................44 Conclusions ............................................................................................................46 CHAPTER 3. Patterns