Katerina Morici Mortality in the Urban Forest May 12 2008 p. 1 Mortality in the urban forest: a comparative analysis of tree survival in West Oakland with respect to planting entity Katerina Morici Abstract Urban forestry is the practice of managing trees in urbanized landscapes for the benefit of the surrounding human population. Trees are an essential component of urban areas all over the world. The economic, environmental, social, and psychological advantages of establishing and maintaining healthy urban trees are well established. However, due to the difficulty of gathering long-term data in the heterogeneous urban landscape, little is known about the processes which regulate tree planting success. This study is a comparison of mortality between two different planting agencies: the City of Oakland and Urban Releaf, a nonprofit community-based organization, to determine if trees planted by a community organization had a greater survival rate. Two tree inventories with a one-year time lapse were completed of 1108 trees in West Oakland. The results were inconclusive regarding the role that planting entity plays in tree mortality due to inherent variation in study site, tree species, and size class. Trees with smaller diameters were found to display significantly higher mortality. Variation due to species and land use was also established as a source of significantly different mortality rates. Understanding the principal factors in tree mortality may help forest managers determine how to efficiently allocate funds to maintain a healthy and viable urban forest.Katerina Morici Mortality in the Urban Forest May 12 2008 p. 2 Introduction Street trees provide a broad range of benefits that include improved economic, ecological, human health, and community conditions (Dwyer et al. 1992). A well-maintained urban forest is a financial asset for a community. Urban greening has been proven to increase the surrounding property values (Tryvainen 1997, Anderson & Cordell 1985). This indicates that trees are a desirable feature of the urban landscape. An analysis of the cost-benefit ratio of the urban forest in Modesto, California revealed that benefits exceed management costs by a factor of two to one (McPherson 1999). The ecological and environmental benefits that trees provide are accumulated over their lifespan. An Australian study of 400,000 trees planted over the last 100 years estimated the monetary contribution due to energy savings, carbon sequestration, and pollution mitigation to be between $20 and $67 million during a four-year period (Brack 2002). A recent study of five US cities demonstrated that, per year, each dollar spent on maintaining the urban forest has an estimated return of $1.37 to $3.09 in storm water control, temperature reduction, and air quality improvement (McPherson et al. 2005). In addition, tree shade lowers both asphalt and ambient air temperature, which reduces the need for air conditioning and decreases pavement distress (Asaeda 1996, McPherson and Muchnick 2005). It is apparent that urban trees serve functions far more varied than improving streetscape aesthetics. Trees have also been shown to augment physical and psychological health. For example, Ulrich (1984) demonstrated that hospital patients with a tree view had shorter stays, used less medication, and had better rapport with the nurses than patients in the same condition that had a view of a brick wall. Likewise, people suffering from depression experienced increased health and well-being after volunteering at a local tree management organization (Townsend 2006). Caring for urban trees fosters a sense of community and connection with nature (Austin 2002). This is especially important in economically disadvantaged neighborhoods for several reasons. First, public open space is limited in multicultural, economically disadvantaged areas (Johnson & Shimada 2005). Second, urban greening may provide a forum for community interaction and participation. Third, it is more cost-effective to maintain existing trees in a healthy state than replacing dead trees. For all the benefits they provide, street trees face a number of challenges associated with living in an urban environment. Stresses due to vandalism, cars, poor air quality, restrictedKaterina Morici Mortality in the Urban Forest May 12 2008 p. 3 growing space, and contaminated urban soil decrease a tree’s ability to cope with naturally-occurring stresses, such as insects, disease and drought. Mortality due to vandalism is unusually high in areas of lower socioeconomic status (Nowak et. al 1990). In a study conducted in Berkeley and Oakland, tree death two years after planting was not significantly correlated with species, but was related to socio-economic status of the surrounding neighborhood (Nowak et al. 1990). Vandalism was reported to be a recurring cause of mortality. In a survey of European cities and towns, up to 30% of newly planted trees were affected by vandalism (Pauleit 2002). It is clear that human-induced damage to urban trees is a common problem. However, it has been demonstrated that a reduction in the incidence of injury to trees due to vandalism is correlated with increased community participation and direct contact with individuals (Cole 1979, Gobster & Dickhut 1995). While the psychological, social, and environmental benefits of trees in urban settings have been clearly established, there are few authoritative studies regarding the survival rates of city trees. In this study I investigate whether trees planted and maintained by a community organization exhibit significantly different mortality rates than trees planted and maintained by the city. In order to gauge the effect of community involvement in tree survival, I investigate the efforts of Urban Releaf, a local nonprofit organization that focuses on employing youth to plant trees in economically disadvantaged areas of Oakland and Richmond. The goal of this organization is “to revitalize these communities by planting trees, providing environmental awareness education, and providing on-the job training to disadvantaged and at-risk youth” (www.urbanreleaf.org). The two main planting entities in the West Oakland I consider in this study are Urban Releaf and the City of Oakland. Trees may also be planted by private property owners, however this was not considered in the present study. If inner-city planting by
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