Landscapes - Winter 2015 - (Page LPplus4)

GROWING TREES CANOPY SIZE AND CLIMATE CHANGE: GROWING TREES IN CITY SIDEWALKS TREES ARE AN effective way to mitigate climate change impacts in urban areas. They capture stormwater runoff and pollutants and clean the air. They moderate temperature and cast shade, cooling down buildings and people on hot days. Despite their benefits, trees are vulnerable to the extreme weather effects of climate change. In urban areas, street trees are especially vulnerable as they are often planted in inhospitable conditions. Vandalism, compacted soil, lack of water, winter salt, low soil volumes and inadequate room for root and trunk growth in and amongst utilities are some of the conditions in which urban sidewalk trees are planted. While the cooling effect of trees grows exponentially with canopy size, trees in this environment rarely grow large enough to fully reap these benefits. Taking care to plant sidewalk trees so that they grow to full maturity has greater environmental benefit than planting many trees in harsh urban conditions. The City of Toronto has a goal to increase both the number and size of its street trees. Known as a green city with an extensive canopy cover, the City has approximately 10.2 million trees: 6.1 million (60%) on private property and 4.1 million (40%) on private property. Of the trees on public property, about 600,000 are street trees, many of which are struggling to survive and leave a poor impression on visitors to the city's core. The City aims to grow trees that live to at least forty years and have a girth of 40cm at breast height. Trees are recognized for their crucial role in healthy city infrastructure, providing enormous climatic, environmental, health, aesthetic and psychological benefits. This commitment is supported by a variety of policy documents, guidelines, bylaws, and planting detail standards. The current sidewalk tree planting detail for continuous soil trenches adds significant costs to road reconstruction budgets and does not provide options for retrofitting areas with existing planting or for projects where only part of the sidewalk is being reconstructed. 4 LANDSCAPES PAYSAGES In order to meet Toronto's ambition to grow more and larger urban trees, various departments came together to commission DTAH to evaluate current methods and how they might be improved through a two-part Tree Planting Solutions in Hard Boulevard Surfaces study. Three overarching directives guided the research and recommendations. 1] Solutions need to support large-sized urban trees. 2] Solutions must be acceptable to current City of Toronto standards, and affordable within the current fiscal climate. 3] Solutions must be viable from a utility access and maintenance point of view. They must be designed in a way that they can be realistically maintained. The study began with an evaluation of sidewalk tree planting practices in Toronto and eight North American municipalities with similar climate and density. The team found that Toronto fares well as a progressive centre for urban tree planting. This research was documented in the Context Review and Precedent Analysis of Toronto and Other Municipalities report. DTAH collaborated with Arup engineers, arborists at Urban Forest Innovations and urban forestry expert James Urban to produce a Best Practices Manual of the technical requirements necessary to create healthy growing conditions for trees planted in hard boulevard surfaces within the public right-of-way in Toronto. The document addresses how continuous soil trenches can be better implemented in the city to maximize the inherent benefits of tree planting projects, while minimizing costs and other encumbrances. Extensive consultation and coordination with multiple City departments, utility stakeholders, manufacturers and soil suppliers guided the final recommendations that included four key principles for larger, healthier street trees; construction methods

Table of Contents for the Digital Edition of Landscapes - Winter 2015

To Begin With | Pour Commencer
Our Writers | Nos éCrivans
Upfront | Prologue
Essay | Essai

Landscapes - Winter 2015