34 Vander Vecht and Conway: Comparing Species Composition and Planting Trends Acer I or D or S Probable Cause ↓ I Adelgids: Cooley spruce gall adelgid, Pine bark adelgid, Hemlock adelgid D Maple (Acer spp.) Box elder (Acer negundo) Apple, Crabapple (Malus spp.) Ash (Fraxinus spp.) Honey locust (Gleditsia triacanthos) Spruce (Picea spp.) Acer neg. MalusFraxinusGleditsia PiceaPinus 2 Pine: scots, nigra, sylvestris, resinosa sugar, brutia, jeffrey Quercus decTiliaAcerCeltisGinkgoGleditsia GymnocladuTiliaUlmus new Oak - deciduous (Quercus spp.) Linden (Tilia spp.) Maple (Acer spp.) Hackberry (Celtis spp.) Maiden-hair tree (Ginkgo biloba), Ginkgo Honey locust (Gleditsia triacanthos) Coffee tree (Gymnocladus dioica), Kentucky coffee tree Elm - new cultivars Linden (Tilia spp.) (Frontier, etc.) (Ulmus spp.) Pest count → 10 677437 10 3102 0403 6 11 Anthracnose: Apiognomonia; Cylindrosporium; Marssonia; Glomerella. 11 11 I Aphids - OTHER: Braggia spp., Aphis sp., Sitobion sp. Euthoracaphis, Dilachnus 111 D Apple Scab 1 D Armillaria root rot or Oak root fungus. 11 1 I Ash plant bug; Ash tingid (Leptoypha minor) 1 I Asian Ambrosia Beetle, Xylosandrus crassiusculus 1 I Asian Longhorned Beetle Anoplophora glabripennis 11 I Bark beetles - Dendroctonus 1 I Boxelder bugs. 11 S Clearwing borers 11 I Cynipid gall wasps. 1 D Cytospora Canker 1 11 D Dematophora root rot. 1 S Diplodia canker, Sphaeropsis sapinea = Diplodia pinea 1 I Elm leaf beetle. 1 I Emerald Ash Borer (Agrillus planipennis) 1 I Eriophyid mites, aka "gall mites", Aceria and Vasates spp. 11 11 1 1 1 11 1 1 1111 11 Figure 2. Pest Vulnerability Matrix for street trees comparing current common street trees with municipal planting trends. Columns with grey-toned headers (right) represent the planting trends; columns with white headers (left) represent current species assem- blages. Low severity pests are shown in light gray, moderate severity in medium gray, and severe pests in dark gray. The parallel white curved lines indicate not all the individual species in the genus are susceptible to the given pest. Black text indicates an invasive non-native species of pest or disease. I, D, and S represent insect, disease, or secondary condition. Black, double-lined boxes indicate pest-tree interactions noted as problematic in Toronto due to public perception of pest and frequency of genera. Based on the results from the PVM, overall pest vulnerability is likely to decrease in the future for Toronto’s urban forest, with the number of both severe and moderate severity interactions decreas- ing. However, some significant concerns remain. For both the current and future urban forest com- position, the most concerning issues are typically from invasive non-native tree pests and diseases. These results concur with findings by the City of Toronto; Urban Forestry considers A. glabripennis, L. dispar, A. planipennis, and Ceratocystis ulmi (Dutch elm disease) to form some of the biggest ©2015 International Society of Arboriculture risks for Toronto’s urban forests with the poten- tial to do over six billion dollars of structural damage to the forest (City of Toronto 2011). Agrilus planipennis is currently a major focus of the city’s FHC unit. It is assumed that every single ash tree in Toronto is now infested and that by 2017 only ash trees that have been treated will remain standing (J. Ric, pers. comm., July 10, 2013). The FHC is imple- menting a coordinated management plan where thousands of city-owned ash trees in good condition showing low levels of infestation are being treated with injections to halt or slow the progress of the
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