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University of Calgary PRISM: University of Calgary's Digital Repository University of Calgary Press University of Calgary Press Open Access Books 2014 Historical GIS research in Canada University of Calgary Press "Historical GIS research in Canada". Jennifer Bonnell and Marcel Fortin, editors. University of Calgary Press, Calgary, Alberta, 2014. http://hdl.handle.net/1880/49926 book http://creativecommons.org/licenses/by-nc-nd/4.0/ Attribution Non-Commercial No Derivatives 4.0 International Downloaded from PRISM: https://prism.ucalgary.ca University of Calgary Press www.uofcpress.com HISTORICAL GIS RESEARCH IN CANADA Edited by Jennifer Bonnell and Marcel Fortin ISBN 978-1-55238-756-6 THIS BOOK IS AN OPEN ACCESS E-BOOK. It is an electronic version of a book that can be purchased in physical form through any bookseller or on-line retailer, or from our distributors. 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Acknowledgement: We acknowledge the wording around open access used by Australian publisher, re.press, and thank them for giving us permission to adapt their wording to our policy http://www.re-press.org 6 Mapping Ottawa’s Urban Forest, 1928–2005 Joanna Dean and Jon Pasher Like many HGIS projects, this research began with a question that could not be answered with traditional historical sources. Municipal records showed dramatic shifts in attitudes to city trees in the mid-twentieth century. We wanted to know whether these cultural shifts reflected changes in the urban forest itself.1 Were there too many trees in the 1920s, as critics charged? Were there too few in the 1960s, as environmentalists claimed? And how many trees are too many, anyway? The question was of more than academic interest. Urban foresters have established that trees provide significant health and climate benefits by cleaning and cooling city air. Trees can live for decades, and historical analysis can contribute to our understanding of forest growth and improve manage- ment in the future. Our pilot project assessed the use of historical aerial photographs to measure canopy cover on selected neighbourhoods in Ottawa. The techniques for measuring forest canopy cover from aerial photographs and satellite images are well tested, but little historical analysis has been done, and the use of historical aerial photographs complicated the project in a variety of ways.2 We found that it was possible to measure canopy cover within a reasonable margin of error. It appears that the critics may have been right, that tree cover was dense in central parts of the city in the early twentieth century and that it subsequently declined. It appears that the environmentalists were also right to worry about trees in the 1960s, when the inner-city decline was matched by the deforestation in early suburbs like Alta Vista. 111 What was interesting, however, was that the urban forest, with very little experience geospatial analysis took the research beyond in HGIS, focussed on the applicability of the the original question: not only could we draw method for environmental history. The pro- connections between canopy cover and shifts ject described here was a pilot project, funded in popular opinion, but we could also correlate with a small SSHRC grant, and possible only canopy cover to social indices such as class, in- because of the generosity of colleagues in the come, or race. Inner-city neighbourhoods were Geomatics and Landscape Ecology Laboratory subjected to close scrutiny for urban renewal at Carleton. We analyzed only five carefully in the postwar period, and a wealth of statis- selected areas, and, as in any good pilot pro- tics are available. Our pilot project had not ject, we learned from our mistakes. We offer been designed with this analysis in mind, but the following observations as “lessons learned,” even so the correlation of income and canopy intended to be useful to others interested in cover is clear. The statistics allow us, follow- incorporating historical air photos into their ing Nik Heynen in the United States, to insert HGIS research. the urban forest into an environmental justice framework as an environmental benefit that is socially produced and unevenly distributed.3 CONTEXT The project also offered an opportunity to move beyond statistics. Our methodology created maps of canopy cover that can be read Urban forests have been the subject of much visually and stacked in a dynamic time series. recent analysis in Europe and North America. This has the potential to alter our perception The recognition of the environmental bene- of the urban forest. Trees appear to humans to fits or services provided by city trees led to a be static entities, and their growth is only rec- growing demand for the quantification and ognized retrospectively: it is a common trope monetization of these benefits, and the devel- of memoir writers to observe with surprise oping science has provided the context for our 4 that a childhood tree has grown. The dynamic research. The term “urban forest” was coined changes of canopy cover visible in a time series by Erik Jorgensen, at the University of Toronto reminds us that forests are living agential com- Faculty of Forestry, and has been widely adopt- munities that move and respond to changes in ed. The term is generally understood to include the built environment. all urban trees: the street trees that line roads, While our own work and experiences are as well as single trees and groups of trees in focussed on urban forests, the methods and gardens, yards, cemeteries, parks, and wood- issues are applicable to other HGIS applica- lands. Although the urban tree is normally tions. The observations arise from the differ- distinguished from shrubs and other vegeta- ent perspectives of project team members. Jon tion by its trunk and crown (the urban tree is Pasher, who was completing his doctorate in defined as “a woody perennial plant growing in Geography at the time of the project, focussed towns and cities, typically having a single stem on the methods, development, and accuracy or trunk − and usually a distinct crown − grow- of the statistics. Joanna Dean, a historian of ing to a considerable height, and bearing lateral 6 MAPPING OTTAWA’S URBAN FOREST, 1928–2005 112 branches at some height from the ground,”5) But the consensus is that the services outweigh most observers include shrubs within an urban the disservices, or have the potential to do so forest. For those involved in canopy cover an- if well managed, and so the emphasis in the alysis of aerial photographs and remote sens- literature is on improved understanding and ing, it is often difficult to distinguish between management of urban trees.10 trees and shrubs, and, as the ecoservice bene- Because of the focus on these ecosystem fits are similar, the inclusion of shrubs makes services, and the interest in assigning mon- sense methodologically. Ecologists sensitive to etary values, many urban forest studies adopt the interrelationships between plants and ani- quantitative methods: field surveys for smaller mals tend to think more broadly, and the term areas and GIS, aerial photography and remote urban forest is sometimes extended to include sensing for larger areas.11 The science has de- grass, and even the related biota in an urban veloped with advances in remote sensing and ecosystem.6 spatial analysis. It is often possible to acquire Urban foresters have established that urban high-resolution satellite images with a spatial trees provide a wide array of ecosystem servi- resolution of 60 cm and as well many muni- ces: they moderate air temperature, attenuate cipalities have acquired low-altitude aerial storm water flooding, mitigate urban heat is- photographs, which, although often intended land effects, and reduce noise and air pollution.

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