Arboriculture & Urban Forestry 45(1): January 2019 series of controlled experiments. In one experiment, Norris had twelve experienced arborists assess two different sets of trees with a multitude of targets, failures, and consequences. Each arborist used eight assess- ment methods. In looking at the ratings, Norris (2007) concluded that risk assessment methods can yield a wide range of output values when used on the same tree in the same situation; and that the validity, complete- ness, robustness, repeatability, base assumptions, and underlying modeling of any risk assessment method must be evaluated if it is to be widely adopted. Norris also noted that the evaluations of arborists varied greatly. This was attributed to differences in each arborist’s individual attitude toward risk (Norris 2007). To this point, Koeser and Smiley (2017) noted a correlation between arborists risk tolerances for financial loss and their tree risk ratings. No similar relationship existed between assessed tolerances for physical injury and tree risk ratings. Few studies have tested the validity and consis- tency of risk assessment methods (Matheny and Clark 2009; Klein et al. 2016; Koeser and Smiley 2017; Koeser et al. 2017). Despite this, experts have pub- lished articles both in support of (Ellison 2005a; Fink 2009) and against (Gruber 2008; Bond 2010) the underlying logic and assumptions associated with a given risk assessment method. More research is needed to compare how risk assessment methods handle sce- narios with differing targets and tree defects. More importantly, research should investigate the consis- tency or risk ratings among trained users and how the various methods used influence actual tree mitigation measures. Research has shown that visual assessment of likelihood of failure using the ISA BMP Method can be both consistent (Koeser and Smiley 2017; Koeser et al. 2017) and accurate (Koeser and Smiley, unpublished data). Future research should identify methods or technologies for reducing unnecessary variation in the assessment of likelihood of impact. Similarly, research is needed to provide meaningful criteria for consequences of failure with regard to injury and death. Lastly, no research has addressed the impact of timeframe (e.g., one, three, or five years) on risk assessment ratings, rating variability, and rat- ing accuracy. Public Perceptions of Trees and Open Spaces in an Urban Area Public perception of the risks posed by trees has mostly focused on groupings of vegetation in natural 33 areas or recreational space (Schroeder 1982; Schro- eder 1983; Talbot and Kaplan 1984; Smardon 1988; Jorgensen et al. 2002; Roovers et al. 2006; Jorgensen and Anthopoulou 2007; Zheng et al. 2011). Fewer studies explore the perceived risk associated with individual tree failure (Wyman et al. 2012; Davison and Kirkpatrick 2014). Studies that established how people perceive visual aesthetics of plants in land- scape settings frequently use photographs and surveys (Schroeder 1982; Schroeder 1983; Talbot and Kaplan 1984; Smardon 1988; Jorgensen et al. 2002; Roovers et al. 2006; Jorgensen and Anthopoulou 2007). Schro- eder et al. (2006) explained that research has consis- tently shown that urban residents have positive perceptions of trees and that the benefits of trees typ- ically outweigh their annoyances. Contacts with nature are fundamental to human health and the well-being of people in built environments (Rohde and Kendle 1994; Kuo et al. 1998; Ozguner and Kendle 2006). People often rate a positive association with urban vegetation and natural spaces (Miller et al. 2015). In a telephone survey of Charleston, South Carolina, U.S., following the destruction resulting from Hurricane Hugo in 1989, Hull (1992) found that over 30% of the respondents mentioned some com- ponent of the urban forest as one of the most import- ant physical features destroyed by the hurricane. Similarly, Wyman et al. (2012) conducted a study where they assessed and compared the perceptions of tree-related risk among community leaders from Hill- sborough and Broward Counties, Florida, U.S. They found that even though these areas are highly suscep- tible to hurricanes and the resulting damage caused by trees, 57% of the respondents agreed it was import- ant to increase the size of their urban forests. CONCLUSION Overall, this review found a limited body of literature that focuses specifically on the perceptions of risk as related to tree failure (Wyman 2012; Davison and Kirkpatrick 2014; Koeser et al. 2015; Koeser and Smiley 2017). Though the currently available litera- ture related to risk perception provides insight into the differing perceptions given gender, age, educa- tion, and cultural background, there is still a gap in the understanding of how property owners perceive and accept the risk of trees. Given the global importance of our urban forests and the impact that they have on the bulk of the ©2019 International Society of Arboriculture
January 2019
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