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Invasive alien species at the urban-forest interface.

While focus on invasive alien species has been primarily on the economic and human health aspects, invasive alien species are the most significant threat to biodiversity after habitat loss and fragmentation. Many feel that the impacts from invasive species are irreversible in the environment, as alien species permanently modify habitats, hybridize with native species, and disrupt the natural interactions among species that determine key functions in forest ecosystems. Typically, with no natural enemies to suppress them in their newly invaded areas, alien species can reduce or eliminate native species by outcompeting them for resources, through predation or by inflicting disease. Invasive alien species may also have indirect impacts by modifying ecosystem processes such as fire. Fire management may increase the invasive potential for some organisms but invasion by alien species may also alter natural fire regimes. As a result of such ecological interactions, the potential impacts of invasive alien species are difficult to predict and are often cumulative. Although Canadian forest ecosystems are dynamic and adapted to change, the abrupt and unprecedented disturbances that result from invasive species have unique and far-reaching consequences for the ecosystem services provided by these forests, causing irreversible ecological damage and incalculable economic impacts.

Increased global movement of people and commodities has resulted in breakdown of the major biogeographical barriers that have historically separated floras and faunas in distinct continents and regional ecosystems. This human-mediated mixing of species has resulted in many aggressive alien species becoming widely distributed across the globe. Despite increased detection efforts at ports of entry, the frequency of introductions and the number of alien species continue to increase with increases in world trade. The future will see more species introductions as global trade, travel and climatic changes impact the current species balance.

This paper reports highlights from the two-part session on invasive alien species held during the Ecological Monitoring and Assessment Network (EMAN) National Science Meeting, November 2005. The morning symposium, organized by Natural Resources Canada's Canadian Forest Service (CFS), focussed on alien species at the urban-forest interface. It included presentations that reviewed the history of invasions in Canadian forests as well as the status of current programs. Pathways by which alien species invade and colonize forest ecosystems, their impacts, and the successes and failures of different management options were examined. Collaboration and partnerships were identified as crucial elements for addressing the risks associated with invasive aliens and in extirpating or mitigating impacts. A plenary talk was given by Don Duerr of the United States Department of Agriculture (USDA) Forest Service on the newly initiated Early Detection Early Response Program for alien species in the US. The morning symposium was followed by an open session where papers on various aspects of invasive species and the measures taken to control them in forested and other landscapes across Canada were presented.

As the main vector of invasive alien species, people are part of the problem but they can also be part of the solution for preventing introductions and mitigating the impacts of invasive alien species through collaboration and innovation. Public communication and awareness were identified during the symposium as the first lines of attack. Troy Kimoto, of the Canadian Food Inspection Agency (CFIA), described the important role of surveillance for all levels of government, industry and the public in order to detect new introductions, incipient populations and to successfully eradicate quarantine forest pests. Although the CFIA inspects imported commodities and conducts some surveys for forest pests, these measures alone are not sufficient to cover the vast landscapes of Canada, the immense volume of imports and the large numbers of vulnerable sites across the country. Better public education packages, improved coordination of surveillance and communication between federal, provincial, regional and municipal governments are needed. With humans at the heart of the problem, invasive aliens will continue to be most active at the urban-forest interface.

The recent successful program to eradicate Asian longhorn beetle from a Toronto suburb revealed the multi-partner complexity of the task. Jean Turgeon from the CFS described how this program challenged both scientists and citizens to come to terms with the necessity of removing hundreds of high-value amenity trees from the city landscape in order to contain the infestation. A variety of skills ranging from those of professional scientists, to politicians and to tree climbers were recruited to realize a community effort.

Lee Humble, also from CFS, reminded participants that invasion by alien species is not a new phenomenon. Beech bark disease (Nectria coccinea) and beech bark scale (Cryptococcus fagisuga) were first recorded on American beech in Canada in 1890. Chestnut blight (Cyphonectria parasitica) and Dutch elm disease (Ophiostoma ulmi), are two other well known invasive tree diseases that have devastated the American chestnut and the American elm, effectively eliminating them as significant components of the deciduous forests of south eastern Canada. The loss of these trees has permanently altered the forest ecosystems which they dominated, the wildlife that depended on them and the society for which they had both cultural and economic significance. For example, several moth species that fed exclusively on American chestnut are now extinct. Dutch elm disease, first isolated in 1930 from dying elms in Ohio, USA appeared in Quebec, in 1944. The disease is now transcontinental in the USA and British Columbia is the only Canadian province remaining free of the disease. The recent introductions of the Asian long horn beetle (Anoplophora glabripennis) in 2002 and the emerald ash borer (Agrilus planipennis) in 2003 similarly threaten the prominence of maple and ash as urban trees in Canadian cities. Their potential impact on natural forests is still unknown.

Don Duerr from USDA Forest Service shared lessons learned from his collaborative Early Detection, Early Response Program that was established to manage high-risk invasives. The early focus of the program has been on bark beetles because this group is among the most common and threatening species intercepted during port inspections and there exists good trapping methods for them. During the pilot program period 2001-2005, the need for more taxonomic expertise and more comprehensive trap installations were identified as major gaps. The results of the program to date also indicate that because some species cannot be trapped, the vigilance of educated volunteer groups including gardeners, nature societies, urban foresters and the public are essential to achieving early detection and control. The existence and availability of information about invasive alien species was also identified as a factor limiting risk assessments.

Risk assessment for invasive aliens in a particular region may utilize comparison of environments and organisms in potential source areas with similar Canadian habitats. For example, invaders to eastern North America may be anticipated from similar, humid northern temperate lands in east Asia. This region has relatively greater biodiversity than eastern North America and so the potential list of invaders is very high. In addition, east Asian and eastern North American species are reported to have been recently descended from common ancestors thus providing an increased possibility of hybridization between alien and native taxa. While models can be useful to determine the associated risks in the new environment, they require input on the basic biology of the organism, taxonomy and management practices. This information is often unknown. For example, although diseases have probably caused the major economic impacts to Canadian forests, fungi are one of the least known components of diversity globally with less than 5% of the species described.

Through advances in science and technology, and collaboration between research organizations, innovative new tools are helping to improve early detection of new introductions and new methods for mitigating the impacts of established alien species. Pierre Desrochers from the CFS described how detection and identification of various species such as Scleroderris canker (European strain), Dothichiza canker of poplar and brown spruce long horn beetle has been improved as a result of molecular identification kits, new traps and sampling methods.

The participants were left with the primary message that invasive alien species are a global and multi-faceted issue that needs to be addressed in a holistic manner. The focus has primarily been on eradicating the introduced alien and mitigating the impacts. To be successful in reducing the threats from invasive alien species, this approach needs to be broadened to consider the affected systems and to understand how removal of a dominant species may impact the rest of the ecosystem. A systems approach will only succeed if collaboration between managers, ecologists, economists, and the people living in communities at risk is fostered.

Brenda J. McAfee is Science Advisor, Biodiversity, at Natural Resources Canada in Ottawa. She can be reached at

C. Malouin works for the Canadian Forest Service of Natural Resources Canada in Ottawa.

V. G. Nealis works for Natural Resources Canada at the Pacific Forestry Centre in Victoria, B.C.
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Author:McAfee, B.J.; Nealis, V.G.; Malouin, C.
Geographic Code:1CANA
Date:Aug 1, 2006
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