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GEO-6 Regional Assessment for North America


2.3.5 Key stressors


Invasive species Invasive alien species are generally considered the second largest threat to biodiversity after land-use change; beyond predation, a dominant non-native species can seriously alter habitat of others, driving some close to extinction and threatening human economies and ecosystem health (Lodge et al. 2006; Pimentel et al. 2005). Both intentional and incidental introductions of non-native species into non- native ranges are a by-product of anthropogenic activities. In North America, driven mainly by economic factors (Keller and Perrings 2010), non-native species have been introduced into the Great Lakes Basin at an increasing rate, exceeding one per year between 1959 and 1999 (Dettmers et al. 2008).


The population expansion and ecological effects of Dreissenid mussels (zebra mussel, Dreissena polymorpha, and quagga mussel, D. bugensis) drastically changed the ecosystem in the Great Lakes and caused considerable economic damage to water systems. This particular trend shows no signs of abatement as new alien species continue to be introduced every 9–12 months (Hansen 2010). Notable pathways of introduction of aquatic biota include trade routes, such as the Erie Canal and St. Lawrence Seaway; ballast water releases from shipping; accidental introductions from fish hatcheries; the aquarium trade and live fish markets; the construction of roads and railways for trade and transport; and the culture of non-native bait fish. Meanwhile the US government is spending billions of dollars to prevent the spread of the voracious Asian carp, which have travelled north up the Mississippi River towards Lake Erie. In the West, the infestation of native mountain pine beetle over the last decade was of unprecedented intensity, damaging more than 163 000 square kilometres of forest (Safranyik et al. 2010). This expansion has had a tremendous impact on the forestry industry in Canada and the US and reflects the fact that not all invasive species are from distant lands, but due to climate change and other drivers, are encroaching on new areas where they face no natural predators.


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Invasive non-native plants are one of the greatest threats to Canada’s croplands, rangelands and natural areas. They degrade productivity and biological diversity; they are responsible for significant economic loss, and they affect trade with other countries. Approximately 1 229 (24 per cent) of the 5 087 known plants in Canada are not native. Of these, 486 are considered weedy or invasive. Great strides in the prevention, eradication, and control of invasive plants have been made, and the North American Plant Protection Organization, which derives its authority from the Food and Agriculture Organization of the United Nations (FAO), and a complex network of professional organizations, has worked to limit the spread of popular but invasive plants. Often the result of careless or ill-informed ornamental landscaping, they have also found their way through various trade routes, incidental releases of seeds and intended introductions for agriculture and ornamental horticulture. Well-known invasive plants in North America include various forms of kudzu (Pueraria spp.), knotweed (Fallopia japonica), the giant hogweed (Heracleum mantegazzianum), Dalmatian toadflax (Linaria dalmatica), English holly (Ilex aquifolium), gorse (Ulex spp.), the common water hyacinth (Eichhornia crassipes), hydrilla (Hydrilla verticillata) and, perhaps most commonly, purple loosestrife (Lythrum salicaria). However, it is important to note that invasive alien species do not necessarily destroy ecosystems, but alter them, making it more difficult for other species to co-exist, and in some cases, reduce the human benefits derived from ecosystem services.


Human, livestock and wildlife health may also be threatened by the link between invasive pathogens and the zoonotic and vector-borne infectious diseases they may transmit, such as West Nile or Lyme disease, in humans. In North America, the One Health Approach, which links ecosystem health with human health, is gaining traction and offers a more comprehensive approach to such environmental and anthropogenic triggers driving disease (Karesh et al. 2015).


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