38 Vander Vecht and Conway: Comparing Species Composition and Planting Trends trees likely overlooks some rare species. However, such omissions would likely only have minimal effects on the relative dominance of the most com- mon species and would not represent major concerns from a pest-vulnerability perceptive. With regard to the tree planting data, while the results represent the planting activities of a variety of important actors participating directly or indirectly in urban forest management, they are not comprehensive of all tree plantings occurring in Toronto. The results are also based on individuals’ perceptions of what genera and species they most commonly planted or sold. It would be worthwhile to further investigate actual tree purchasing and planting records. There are lim- itations with the generalizability of these results, but this work represents a good first look into the overall picture of what is being planted in the City of Toronto and how it will likely influence pest vulnerability. Additionally, it is important to note that pest vul- nerability, and the use of a tool like the PVM, is only one of many components to urban forest manage- ment. Understanding overall pest vulnerability and the ways current planting trends are affecting that vulnerability should be one of several considerations when planting and maintaining the urban forest. Pest issues are also influenced by more than the pres- ence (or lack) of susceptible hosts—there are many other relevant aspects to consider. For example, maintaining a diverse age structure is important as tree age can influence susceptibility to, and the ulti- mate impact of, a pest or disease. It is also important to have complex and appropriate vegetation struc- ture so that birds and other beneficial organisms are attracted to, and can thrive in, urban environments and help control problematic pest populations. In summary, Toronto’s urban forest will likely see a decrease in vulnerability to tree pests moving into the future based on the genera that are now frequently planted. Invasive, non-native pests continue to be a major source of concern and vulnerability for the urban forest. Likewise, the over-dominance of and heavy reliance on a few genera are problematic. In general, the diversity of both street and non-street tree populations could be improved, in part, through increasing the pro- portion of coniferous trees, reducing the number of ornamentals, and relying less on the standard urban tree genera like Acer, Tilia, and Gleditsia. Acknowledgments. This research was supported by the Social Sciences and Humanities Research Council through the Joseph- Armand Bombardier Canada Graduate Scholarships—Master’s award. The authors would also like to thank all the individuals who took the time to participate in the surveys and interviews for this research. Special thanks to Igor Laćan for providing the origi- nal PVM and to J. Ric of the Forest Health Care unit in Toronto’s Urban Forestry department for his help with modifying the PVM for Toronto. LITERATURE CITED CFIA. 2013a. Asian Long-horned beetle eradicated from Canada. News Release. Accessed 12/18/2013. CFIA. 2013b. Asian long-horned beetle found in Mississauga. News Release. Accessed 12/18/2013. City of Toronto. 2011. Every tree counts: a portrait of Toronto’s ur- ban forest. Accessed 03/27/2014. City of Toronto. 2012. Street tree general data [Metadata file]. Parks, Forestry & Recreation and Urban Forestry, Toronto, Ontario, Canada. City of Toronto. 2013a. Toronto’s geography. Accessed 03/27/2014. City of Toronto. 2013b. Urban Forestry: Forest Heath Care. Accessed 03/27/2014. Czerwinski, E., J. Pollard, and T. Scarr. 2006. Forest health alert: Sirex Woodwasp [Sirex noctilio (F.)]. Accessed 05/23/2013. D’Amato, N.E., T.D. Syndor, and D.K Struve. 2002. Urban foresters identify Ohio’s tree needs. Journal of Arboriculture 28:291–301. Dillman, D.A. 2007. Mail and internet surveys: The tailored design method, second edition. Jon Wiley and Sons, Toronto, Ontario, Canada. Dreistadt, S.H., D.L. Dahlsten, and G.W. Frankie. 1990. Urban forests and insect ecology. BioScience 40:192–198. Dykstra, M.D., and M. Sabourin. 2012. Pests and diseases of the eastern white cedar (Thuja occidentalis). Report no. PDCF-006 of the Pest Diagnostic Clinic. Accessed 05/22/2013. Escobeder, F.J., T. Kroeger, and J.E Wagner. 2011. Urban forest and pollution mitigation: Analyzing ecosystem services and disser- vices. Environmental Pollution 159: 2078–2087. Farrar, J.L. 1995. Trees in Canada. Fitzhenry & Whiteside Limited and the Canadian Forest Service, Markham, Ontario, Canada. Gamfeldt, L., T. Snäll, R. Bagchi, M. Jonsson, L. Gustafsson, P. Kjel- lander, M.C. Ruiz-Jaen, et al. 2012. Higher levels of multiple ecosystem services are found in forests with more tree species. Nature Communications 4:1340. Haack, R.A., and R.E. Acciavatti. 1992. Two-lined Chestnut Borer: Forest Insect and Disease Leaflet 168 of the US Department of ©2015 International Society of Arboriculture
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