Arboriculture & Urban Forestry 41(1): January 2015 ticularly significant to the urban forest, as its high occurrence comes primarily from its common use as a hedge species (City of Toronto 2011). Faxinus, Prunus, and Picea are each between 5% and 10% of the total non-street tree population. Based on the inverse SDI, non-street trees have higher overall diversity, although both populations are below the recommended threshold of 10% (Table 1). When the city’s urban forest is explored below the city level, a few additional genera emerge as com- mon within one or more of the four management districts in the city. For street trees, Malus, Pinus, and Quercus are common (above 5%) in one or two districts in Toronto. For non-street trees, Ulmus, Gleditsia, Populus, and Pinus are also common in one or more district, but not above 5% citywide. Tree Planting Trends Table 2 shows basic characteristics and participa- tion rates of the four actors surveyed or interviewed. Seventy-six percent of landscape architects indicat- ed that their designs and plans include tree planting nearly all the time, and an additional 22% indicated that their plans include trees at least half of the time. The two NPOs surveyed collectively planted approx- imately 5,200 trees in Toronto last year, and both Table 1. Common tree genera citywide. Dashes indi- cate the proportion of the genus is below 5%. Genus No. of trees in analysisz Tree density No. of genera SDI Acer Gleditsia Tilia Picea Fraxinus Thuja Prunus Street trees 529,849 92.3/ km road 64 7.26 33.12 7.22 7.36 7.66 5.23 - - Non-street trees 2,505 10.3/ 400 m2 47 9.37 23.39 - - - 5.83 17.09 5.83 z The number of trees for street trees represents the total population, while the number for non-street trees represents a sample. plot 31 exclusively plant trees (and shrubs) native to On- tario and/or North America. For the garden centers and nurseries surveyed, trees made up a relatively limited proportion of their total stock. Most re- spondents (11 of 12) indicated that trees accounted for less than 25% of their inventory and sales. The most commonly selected or suggested genera for planting by the surveyed landscape architects are Acer, followed by Quercus, Gleditsia, Tilia, and Ginkgo (Table 3). The most commonly indicated individual species selected for planting were Ginkgo biloba, Acer rubrum, Quercus rubra, and Gleditsia triacanthos. At the genus level, NPOs also most commonly plant Acer, followed by trees of the Populus genus and then by Quercus (Table 4). Of the total 16 trees listed by the two organizations, only two overlap. Garden centers and nurseries indicated that a wide variety of tree species and genera were com- monly sold (Table 5), but Acer trees are again the most commonly sold trees; Acer palmatum was the most frequently identified species. Though most respondents indicated they sell various tree types (ornamental, coniferous, shade, and hedge varieties), garden-center sales appear to favor primarily ornamental species and genera. Considering municipal planting, just under 100,000 trees and shrubs were planted in 2012 by Toronto Urban Forestry. This includes plantings in natural areas and ravines (approximately 75,000 trees) and along streets (approximately 22,000 trees) (R. Vendrig, pers. comm., June 3, 2013; October 25, 2013). Toronto’s Urban Renewal section gen- erally uses two documents as reference for species selection purposes; both are available online (www. toronto.ca/trees). The first is a brochure available to residents interested in having a free street tree planted. The second is a native tree naturalization list, which is more of an internal reference docu- ment that includes more detailed planting infor- mation and requirements. Acer and Quercus have a strong presence on these documents, as well as trees Table 2. Participation rates and characteristics of actors engaged in tree planting in Toronto. Actor No. of respondents (% of potential participants) Landscape architects NPOs Garden centers and nurseries Toronto urban forestry 50 (45%) 2 (100%) 12 (60%) - Residential most common client-type; commercial and government also frequently identified One NPO primarily residential; the other primarily in parks and natural areas. Primarily private residents; also landscapers, contractors, and developers Responsible for all municipal tree planting on streets, other transportation rights-of-way, parks, natural areas, and other public property. Clients or planting areas ©2015 International Society of Arboriculture
January 2015
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