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Forest Invasivesbreadcrumb separatorIntro to Invasivesbreadcrumb separatorImpacts of Invasive Speciesbreadcrumb separatorThe Urban Forest

The Urban Forest

In many cases, outbreaks of invasive species begin in urban settings. The spread of invasive species is heavily influenced by human activity, following common shipping and trade routes among urban ports of entry (See ‘Pathways’). In urban settings, individual trees are valued for their many environmental and economic services and for the social and health benefits that they provide. These include, increased property values, reduced energy costs for homes with trees near them, improved air and water quality, and aesthetic values, among others. In fact, TD Bank recently released a report that places a dollar value on urban trees in Toronto, which can be seen by clicking here.

Invasive forest pests can have huge economic costs to Ontario and Canada for prevention efforts, control efforts, and other mitigation and regulatory efforts. The costs associated with such prevention and regulatory controls, as well as with scientific monitoring and research of introduced pests, reforestation of impacted areas, and potential processing and treatment of wood products intended for export can be extremely high and hard to predict (FIAS, NRCan, 2013). The City of Toronto, for example, estimates that it will cost $37 million over five years to cut and replace the city-owned ash trees that are killed by the emerald ash borer (EAB). Further, as of 2012, the Canadian Food Inspection Agency had already spent over $30 million to manage the invasion of EAB and had cut over 130,000 trees to slow the spread of the beetle (Ontario Ministry of Natural Resources, 2012). Over the next decade, some estimates from the United States suggest that 17 million trees will need to be removed and replaced within communities alone. This would cost approximately $10.7 billion, but could double if both urban and rural land is taken into account (Kovacs et al, 2010). These estimates only take into account one invasive pest, the emerald ash borer. Costs continue to rise as more invasive pests and pathogens spread throughout North America.

Invasive species also have the potential to cause extensive ecological impacts on individual urban trees, as well as to the overall urban tree canopy. As invasive species can cause damage to various parts of the tree, can reduce its health, or even kill a tree, they subsequently have a negative impact on the health of the overall urban forest. By damaging or killing trees, forest pests can reduce habitat or food sources for native animals within urban centres. Further, the quality of the environmental services that trees provide - such as shade, water and air filtration, and oxygen production - can be greatly impacted by invasive species in cities. 

The social impacts related to forest pest infestations are the most difficult to value, but they can also be extensive. Many communities, especially in rural northern Ontario rely on forestry for their livelihoods and reduced harvest levels due to forest pest infestations can greatly impact the stability and well-being of these communities. Damaged forest ecosystems could also mean a negative impact on tourism and recreation, especially in areas where a healthy forest or green space is highly valued for outdoor activities, such as campgrounds, or hiking trails. Many invasive species infestations begin in urban areas, attacking trees on streets and in parks. This can negatively impact the aesthetic value of neighbourhoods, communities, and cities.

Photo: Joseph O'Brien, USDA Forest Service, Bugwood.org