238 3. 4. Roles of Site Design and Tree Selection on Tree Growth and Longevity Roles of Tree and Site Management on Tree Growth and Longevity TOPIC #1: DESCRIPTIVE STUDIES OF TREE GROWTH, LONGEVITY, AND MORTALITY Greg McPherson and Paula Peper, Ecologist with the USDA Forest Service, co-authored the keynote presentation for this topic, “Tree Growth Studies: Propelling Arborists to New Heights.” Researchers and presentations in this first group included Chris Martin (Arizona State University), “Tree Growth and Health in Phoenix”; Robert Fahey and Mar- lin Bowles (The Morton Arboretum), “Linking Composi- tion, Structure, and Productivity Across Chicago’s Urban Forest”; Lara Roman (University of California, Berkeley), “Urban Tree Mortality Rates: Concepts from Demogra- phy”; Bryant Scharenbroch (The Morton Arboretum), “A Soil Quality Index for Urban Trees”; and Julia Bartens (University of California, Davis), “Live Oak Growth in the Streets of Jacksonville, Florida: Can We Predict Its Future?” During the roundtable discussion, participants identi- fied common threads among the presentations and needs for future research. These five U.S.-based descriptive stud- ies represented very different geographic regions, from Flor- ida to the Midwest, and from Northern California to the arid Southwest, yet all of the researchers were committed to: * * * * investigating relations between trees and people improving quantitative mortality, and longevity integrating their research into improved arboricultural practices understanding human perception of “improved” site designs in urban areas Studies on urban tree growth and longevity are few and rather fragmented. Data collection for these studies relies heavily on regional networks and the International Tree Failure Database. Remote sensing techniques proved useful for collecting infor- mation in such studies, but their development and application could be more widespread. Analyses of these studies suggests that the development of coordinated databases that could be mined to identify correlations and causes of urban tree growth, longevity, and mortality, would be of a tremendous benefit to current and future researchers. Likely partnerships to foster further research and greater exchange of information were sug- gested between the nursery industry/growers and providers of tree care services, statisticians, physiologists, pomologists, and foresters. Potential resources for funding and collabora- tion were identified as being most likely among governmental agencies, corporations, and the tree care and growers’ industries. Symposium attendees provided many comments, questions, and suggestions for further investigation and development of descriptive studies. It was suggested that the relationship or influence of tree management on soil carbon flux be in- vestigated. A standardized database of information gath- ered during large-scale tree plantings and maintenance programs should be established and shared by research- ©2012 International Society of Arboriculture assessment of tree growth, Leibowitz: Urban Tree Growth and Longevity ers, practitioners, and citizens of municipalities. Decisions of what is important for future research and technology development should be based upon exchange between ex- isting networks of tree planters, managers, and scientists. Future research priorities for descriptive studies were ranked in the following order, with a tie for fourth place: 1. 2. 3. Determine the value of an urban site index and the next steps in its development. Establish a comprehensive, standardized monitoring network for long-term planting projects that includes data on social, biological, and management issues. Improve collaboration and data sharing among researchers. 4a. Standardize data to better facilitate sharing of information. 4b. Determine an appropriate tree response variable for tree growth, health, and belowground functioning. TOPIC #2: ROLES OF TREE PRODUCTION AND SALES ON TREE GROWTH AND LONGEVITY Edward F. Gilman, professor in the University of Flori- da’s Environmental Horticulture Department, authored the keynote presentation for the second topic, “Nursery Production Strategies Impact Tree Longevity and Perfor- mance—Don’t They?” Researchers and presentations in this group—addressing the roles of tree production and sales on tree growth and longevity—included Ed Mulrean (Arid Zone Trees, Phoenix, Arizona), “Propagation and Produc- tion for Dispersed Root Systems”; Matthew Stephens (New York City Department of Parks and Recreation), “What Should We Plant? New York City’s Plan to Diversify Its Ur- ban Forest One Tree at a Time”; and Henrik Sjöman (Swed- ish University of Agricultural Sciences), “Habitat Studies as a Selection Model in the Search for Future Urban Trees.” During the roundtable discussion it was noted that rela- tively few people are working on proper tree production tech- niques. The need to reduce the carbon footprint of containers (polypropylene plastic) also was discussed. Whether from the perspective of a producer or consumer, it was acknowledged that urban tree survival must be improved, generally, for both container and ball-and-burlap trees. The question then arose: over how long a period of time would a difference be observed in the survival rate among containerized or balled-and- burlapped trees? It was stated that increased root tips should be closer to the soil surface, yet a question was raised re- garding when new roots stop being generated from the root flare. A need for a deeper examination of native trees was dis- cussed, including the fine root structure of many native spe- cies, as well as more studies on the significance of tree size at planting and its relationship to the tree’s successful estab- lishment and survival. Nurseries and growers have opportu- nities to identify, at the earliest stages, the factors that may predict a tree’s health and longevity; can nurseries, through ge- netic engineering, produce superior specimens of urban trees? Selections for tree plantings can and should be based upon en- vironmental tolerances, with new selections carefully screened before planting to ensure the greatest chance for survival.
September 2012
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