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CAPSTONE PROJECT: THE EFFECTS OF TREE SPECIES DIVERSITY ON TREE MORTALITY RATES IN TORONTO DISTRICT SCHOOL BOARD (TDSB) PROPERTIES Rashid Azimov Master of Forest Conservation (MFC) Program Faculty of Forestry University of Toronto - 2018 Abstract Trees in schools of Toronto are important for providing shade to playgrounds, protecting children from the UV radiation and for cooling effects during hot days of the year. However, the current mortality rate of trees at school territories is relatively high. Probably, one of the main causes of the high tree mortality is the Emerald Ash Borer (EAB) infestation in the city. In urban forestry literature, researchers and forestry experts usually recommend increasing species diversity to avoid large-scale tree loss in the case of pest/disease outbreak. In this paper, we study how tree species diversity is changing and analyze potential effects of tree species diversity on reducing tree mortality rates in TDSB school properties. The analysis addressed the question if there is a significant statistical relationship between species diversity and tree mortality rates in the territory of 107 schools of TDSB. The potential relationship has been tested through using Simpson’s Diversity Index and estimated annual tree mortality rates. The regression analysis results showed a positive relationship between tree mortality rates and species diversity instead of the expected negative one. The existing literature in urban forestry explains this unexpected relationship with misuse of species in urban tree diversification process. ii ACKNOWLEDGEMENTS I would like to thank to Professor Sean Thomas, my academic supervisor from Faculty of Forestry of the University of Toronto for his valuable advices and guidance during the preparation of this paper. As well, I would like to express my gratitude to Mr. Justin Nadeau, Ms. Gail Bornstein, and Ms. Karen Dobrucki from Sustainability office of Toronto District School Board for provided information about tree management practices in TDSB schools. I also thank to Mr. Dean Klomp, my class fellow, for his kind support during collection and processing of the tree inventory data used in this project. iii Table of Contents Abstract ........................................................................................................................... ii Acknowledgements .........................................................................................................iii Table of contents ............................................................................................................ iv Introduction...................................................................................................................... 1 Goal, hypothesis and objectives ...................................................................................... 2 Methodology .................................................................................................................... 2 Data used for analysis................................................................................................ 2 Analyzing current tree diversity trends ....................................................................... 3 Calculating annual tree mortality rates ....................................................................... 4 Measuring species diversity ....................................................................................... 5 Regression analysis between the mortality rates and tree species diversity (Simpson’s diversity index) ........................................................................................ 6 Results ............................................................................................................................ 6 Current tree species diversity trends .......................................................................... 6 Estimation of the annual tree mortality rates ............................................................ 11 Tree species diversity calculation ............................................................................ 13 Regression analysis ................................................................................................. 13 Discussion ..................................................................................................................... 16 Conclusion and recommendations ................................................................................ 18 References .................................................................................................................... 20 Appendix 1 Share of tree species in total urban forest population of the studied TDSB schools in 2018 ............................................................................................................. 22 Appendix 2 Estimated tree mortality rates using average and actual interval periods ... 24 Appendix 3 Tree mortality rates in different tree size classes ....................................... 27 Appendix 4 Tree species diversity estimation using Simpson’s Diversity Index ............ 28 iv Introduction Trees in Toronto District School Board (TDSB) schools are valued for providing shade on playgrounds, protecting children from potential negative effects ultraviolet radiation and for cooling effects to all school territory during hot days (TDSB 2013). Recently researches discovered that trees also contribute to improvement of student academic performance at primary schools (Sivarajah 2018). However, currently trees in Toronto are experiencing stresses resulting from outbreaks of different pests, such as Emerald Ash Borer, Asian Long Horned Beetle, Gypsy Moth, etc. These pests are demonstrating considerable negative impact on overall status urban forest in the city (Cecco 2017, OMNRF 2018). In order to increase the resilience to such situations, researchers and urban forestry practitioners usually recommend increasing tree species diversity in city tree population (CAP 2007, Ordòñez et al. 2013). These recommendations are mainly based on generally recognized assumption about high possibility of severe tree loss mortality from outbreaks of pests, specific to popular tree species in single - species - dominant urban tree populations (Sanders 1978, Raupp et all. 2006, Lacan & McBride 2008). As example of such situations, researchers usually refer to Dutch Elm Disease and Emerald Ash Borer infestations in the cities of North America. Urban forestry specialists have developed several targets for increasing urban tree species diversity. The most popular one can be considered the “10-20-30” approach published by Santamour (1990). This formula tells that in order to minimize tree loss due to pest infestations, any urban forest should contain no more than 10 percent of any single tree species, no more than 20 percent trees from the same genus and no more than 30 percent trees from the same tree family (Lacan & McBride 2008). At the same time, other authors consider that counting only on species diversity may result in even higher tree mortality through planting less-adapted, untested trees in urban environments. According to them, tree adaptability is more important in decreasing mortality rates in urban tree populations than tree diversity (Richards 1983). Considering that currently the urban trees in Toronto have been impacted greatly by EAB, now is a good time to test these two contradicting opinions about the potential relationship of tree species diversity and urban tree mortality. In this capstone project, I analyze possible effects of tree species diversity on tree mortality rates at TDSB school 1 properties and make relevant recommendations for the urban forestry managers if species diversity can be used as an effective tool in reducing tree mortality at school courtyards in Toronto. Study goal, hypothesis and objectives The primary objective of this study is to analyze the relationship between tree species diversity and tree mortality rates at TDSB school properties. I hypothesize a negative relationship between tree mortality and tree diversity. That schools with more species diversity (richness and evenness) have lower the tree mortality rates; and schools with less species diversity tree mortality rates are higher, due to mitigation effects of diversity. In order to test this hypothesis, I conducted a four-step analysis: a) Analysis of current tree diversity trends; b) Estimation of annual tree mortality rates for the periods: 2004-2018, 2005-2018, 2006-2018 and 2007-2018; c) Measurement of tree species diversity at schools; d) Tests of the relationship between tree mortality rates and species diversity through linear regression analysis. Methodology Data used for analysis Currently TDSB possesses tree inventory database with information about 34,159 trees, which are located in the grounds of 547 schools. This database contains different tree measurement information, including tree trunk diameter, hard root surface, crown diameter measurements and general tree health assessment results. For my analysis, I used the tree inventory data of 107 schools, first collected in 2004- 2007 and updated in 2018. These updated inventory records allow us to assess changes for periods of 14, 13, 12 and 11 years. The data analyzed in this study covers tree measurements information in 107 out of 547 TDSB schools (19.5%). The schools 2 are located in Downtown, East York, North York, and West York areas of Toronto (see Figure 1). Figure 1. Inventoried TDSB schools. Green and purple

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