Definition of Urban Forests

What comes to mind when thinking of an urban forest? Street trees? Trees in containers on sidewalks? Forests in ravines? Backyard trees on lot lines? In fact, urban forests encompass all those things and more. 

Since the mid-20th century, urban areas in Canada have experienced significant growth and increased population density, which has brought many environmental, ecological, and social problems to the surface. These have underscored the importance of developing greener cities and heightened the need for the conservation and management of urban trees. Over time, urban greening attention has moved from a tree-by-tree management approach to one that recognizes the importance of all trees in urban areas (Konijnendijk et al., 2004).  Terms like “urban forest,” “urban forestry,” and “urban tree canopy” have emerged, and their definitions have developed over time. While these three terms are related and often used interchangeably, it is important to recognize the differences between them.

Key Terms in Urban Forestry

There are several detailed definitions of urban forest and forestry that have been used in Canada. In general, the urban forest is defined as a collection of all trees, woody plants, and vegetation within urban areas (Jorgensen, 1974). Broadly speaking, urban forestry is a specialized yet multidisciplinary branch of forestry focusing on forest and tree management techniques and practices that range from planning, planting, maintaining, and protecting trees to public engagement and education (Deneke, 1993). Urban tree canopy is a two-dimensional expression of an urban forest and a measure of the extent of tree canopies that shade the ground (CSLA, 2024; Vogt, 2020). Easily mappable using modern spatial technologies, the urban tree canopy is often used as a simple and general measure of urban forests, enabling urban forest quantification, comparison, and monitoring over space and time (Tree Canada, 2019).

The approach to thinking of trees in urban areas as a forest was prompted by the loss of American elms (Ulmus americana) due to the impacts of Dutch Elm Disease (DED) in North American cities in the 1960s. DED, a vascular wilt fungus, killed most American elms in urban areas and devastated the tree canopy cover in many Eastern American and Canadian communities. The sudden loss of tree canopy left streets and neighbourhoods without sufficient canopy cover and shade, leading to a significant public outcry for conserving and managing urban trees. The movement mobilized forestry professionals and scientists to recognize and value urban forests as critical natural resources in urban areas. Society had started to recognize that urban forests were critical for providing diverse environmental and social benefits and making urban areas livable. 

Subsequently, the importance of all trees growing in urban areas was recognized, and the terms “urban forest” and “urban forestry” were coined. The terms were defined in 1965 by Dr. Eric Jorgensen at the Faculty of Forestry, University of Toronto, Canada. Dr. Jorgensen first defined the term “urban forestry” as “a specialized branch of forestry and [it] has in its objectives the cultivation and management of trees for their present and potential contribution to the physiological, sociological, and economic well-being of urban society. These contributions include the overall ameliorating effect of trees on their environment, as well as their recreational and general amenity value.” (Jorgensen, 1974). He also believed that urban forestry extends beyond “the city trees or single street management, but rather the tree management in the entire area influenced by the urban population.” (Jorgensen, 1974).

Definitions Over Time

Dr. Jorgensen’s original definition of urban forestry was enhanced and developed over time. In 1993 at the first Canadian Urban Forest Conference, Frederick Deneke expanded on the term, stating: “Urban forestry is the sustained planning, planting, protection, maintenance, and care of trees, forests, greenspace, and related resources in and around cities and communities for economic, environmental, social, and public health benefits for people. The definition includes retaining trees and forest cover as urban populations expand into surrounding rural areas and restoring critical parts of the urban environment after construction. Expansion at the urban/rural interface raises environmental and public health safety concerns, as well as opportunities to create educational and environmental links between urban people and nature. In addition, urban and community forestry includes the development of citizen involvement and support for investments in long-term ongoing tree planting, protection, and care programs.” 

Over the years, with growing knowledge and a better understanding of the significance and value of the urban forest, more foresters and professionals began working in the field of urban forestry, and urban forest definitions started to surface in professional documents and acts in Canada. For example, the Ontario Government’s Professional Foresters Act of 2000 defines urban forests as “tree-dominated vegetation and related features found within an urban area, and includes woodlots, plantations, shade trees, fields in various stages of succession, wetland and riparian areas.” In 2021, the Act’s urban forest definition was enhanced, and the term “urban woodland” was added to include urban natural areas such as “woodlands found in an urban environment, including those in riparian areas, ravines and wetlands” (Professional Foresters Act, 2000).

Along with the definition of urban forests and urban forestry, the importance of strategic and planned urban forests and their management became apparent. Kenney (2003) pioneered the idea of strategic urban forest management planning and emphasized the importance of strategically managing all urban forest components and associated biotic and abiotic elements across a wide range of urban areas, from large to small communities, and in the areas between them. As such, strategic management of urban forests across a range of urban spaces, such as streets, parks, cemeteries, arboretums, private properties, and natural forest fragments, was implemented. All urban forest elements were recognized as the backbone of green infrastructure, and the contribution of urban forest to connecting urban and rural green areas and its contribution to improving the urban environment (GIOC 2015; NRCan and Canadian Forest Service, 2022).

Building on Kenney’s (2003) idea of the importance of strategic urban forest management and recognizing the ecological and social importance of urban trees within and outside the boundary of urban areas, the 2019-2024 Canadian Urban Forest Strategy (CUFS) defines urban forests more comprehensively as the “trees, forests, greenspace and related abiotic, biotic and cultural components in areas extending from the urban core to the urban-rural fringe” (Tree Canada, 2019). Additionally, the CUFS definition of urban forestry also includes “the sustained planning, planting, protection, maintenance, management and care of trees, forests, greenspace along with related resources in and around cities as well as communities for economic, environmental, social, and public health benefits for people.” It also recognized “techniques associated with retaining trees in the context of densification, forest cover in the context of urban expansion into surrounding rural areas, and greening critical parts of the urban environment after development and urbanization.” The CUFS acknowledges that “As the geographic and social distinctions between urban and rural become less clear, urbanization raises environmental and public health and safety concerns, thereby creating a need for educational and environmental links between urban people and nature. Urban forestry is multidisciplinary and multifaceted, comprised of many actors in research, policy, practice, and community engagement. Urban forestry includes the development of citizen involvement and support for investments in long-term on-going tree planting, protection, and care programs.”

Defining Urban Areas

While definitions of urban forests use the term “urban” to describe the bounds of the urban forest, this raises the question of how to define the term “urban.” In Canada, the definition of urban areas has evolved over the years. In the 1931 Canadian Census, an urban population is defined as a “population residing inside boundaries of incorporated cities, towns, and villages, regardless of size.” After 1951, however, urban areas in Canada began to be defined by their population size and, later, by population density. The 1971 Canadian Census, based on population count and density at the time, stated, “An urban area has a minimum population concentration of 1,000 persons and a population density of at least 400 persons per square kilometre.” In 2008, Statistics Canada recognized that there are two classes of populated areas in Canada: urban areas and rural areas, and they further define urban population specifically as “all population living in the urban cores, secondary urban cores and urban fringes of census metropolitan areas” (Statistics Canada, 2008). 

Consequently, as the definitions of urban areas and urban population have evolved spatially and structurally, the definition of urban forest also advanced to include trees and associated vegetation found in areas deemed metropolises, cities, towns or villages, and areas impacted by the urban population. It has also been recognized that urban forests and urbanization are interdependent and that urban forests extend beyond the city limits and are not constrained to municipal borders (Tree Canada, 2019). Urban areas and their populations benefit from the forests and woodlands outside urban boundaries. These forests and trees, between urban and rural areas, within the zone of urban influence often termed peri-urban forests (FAO, n.d.; Salbitano et al., 2016), provide recreational opportunities for urban dwellers, support biodiversity conservation, and, although outside urban areas, contribute to regulating urban climate and hydrology, improve air and water quality, and provide aesthetic and cultural value. However, the pressures from urbanization, development, and the urban population negatively impact forests and the natural environment in peri-urban areas, often resulting in fragmented forest patches and forests that are permanently lost or altered due to development (Puric-Mladenovic, Kenney & Csillag, 2000). Understanding and recognizing the interdependence of urban and peri-urban areas, as well as the similarities and connections between peri-urban and urban forests, is critical for strategic urban forest management and planning (Kenney & Rosen, 2003; Konijnendijk et al., 2004; Salbitano et al., 2016).