Alien species (insects, micro-organisms and plants) are species found outside of their natural range. They can be pests diseases, insects or weeds. Other alien species are competitors of indigenous species rather than pests. They do not cause damage to trees and plants, but they do change the natural biological diversity of local ecosystems by crowding out indigenous species. These species are termed invasive if they are able to modify indigenous ecosystems either as pests or competitors. The introduction of alien pests into a new environment, sometimes far away from their original environment, is most often accidental. Some plants introduced for horticultural or ornamental reasons become invasive weeds that invade and threaten natural ecosystems if allowed to grow wild.
To prevent damage by these alien pests, the Government of Canada has set up an Invasive Alien Species Strategy for Canada based on the prevention, early detection, rapid response and eradication, containment and control of invasive alien species in forests (IASFs) that nonetheless succeed in entering Canada. The Canadian Food Inspection Agency, the Canadian Forest Service of Natural Resources Canada and Environment Canada have put forward an Action Plan for Invasive Alien Terrestrial Plants and Plant Pests that outlines how the national strategy will be implemented in the forest and agricultural sectors.
There are numerous alien insects and diseases trying to enter Canada. However, very few succeed in establishing a home here because of Canada’s generally effective natural barriers, such as climate, a vast land mass and topography. Invasive alien species also have special requirements and can only establish themselves sustainably under certain conditions, such as the absence of predators, presence of a compatible host and temperatures promoting their reproduction. Of the species that manage to establish themselves in Canada, only a few can be termed invasive alien species or pests because of the extensive damage they cause and threats they pose to the integrity of our forest ecosystems. A very well known example is Dutch elm disease, which completely ravaged the countryside of the St. Lawrence Lowlands and many of Canada’s major cities. In Quebec alone, 600,000 elm trees were destroyed or chopped down between 1945 and 1965 because of this disease.
A growing phenomenon
The risk of introducing alien species (insects and diseases) will increase in Canada over the next few years for various reasons:
- More and more species reach our borders, particularly because of increased free trade;
- Modern-day forests are more vulnerable because they have been significantly modified by human activities;
- By definition, alien pests cause more damage than indigenous species because they have no natural enemies in Canada;
- Lastly, environmental considerations will limit the use of some control and eradication measures.
How do alien insects and diseases get into Canada? Like any traveler coming from abroad, they arrive by air, water or land. In fact, they can be found in all living or unprocessed plant matter (plants, seeds, tubers and greenhouse material) and in wood logs purchased outside Canada. It is suspected that the large-scale importing of pine logs from New England led to the introduction of pine shoot beetles into Quebec. They are also found in lumber used for packaging or securing cargo (wooden pallets, casings, dunnage, etc.), and even in the massive wooden spools imported from China that are used to wind cables, when these various products are made of green lumber. In short, the entry points for these unwanted guests are often the entry points of international trade. Because the United States, the world’s biggest importer, is our principal trade partner, many, if not the majority, of the alien pests that enter Canada have entered the United States beforehand. Moreover, with Canada building more and more trade links with other partners, such as Japan, China, South America and Europe, the origin and identity of alien pests entering Canada is changing. The introduction of these pests is usually accidental, but other pests may have been introduced intentionally, although their dispersal into nature can be accidental. For example, European gypsy moths were imported from France by an amateur entomologist who wanted to produce silk. In 1869, a few of the moths escaped and rapidly propagated. Today, this species is one of the major pests in Canada’s deciduous forests.
Invasive insects and diseases that attack Canada’s ecosystems and forests, and often its urban forests, are known to have ecological, economic and social impacts.
In ecological terms, the pests can cause significant damage to indigenous trees and plants that lack natural defenses against these invaders. They can slow their growth or kill them over vast areas. Consequently, they change the internal dynamics and possibly rupture the characteristic equilibrium of ecosystems, because the damage they cause adds to various natural or human disturbances. They attack plantations and certain valuable species, such as pine, elm, oak and butternut trees. Invasive alien species can become competitors or predators of indigenous species and their activities can eliminate habitats for some wildlife species through diminished biological diversity and even, in extreme cases, through the disappearance of particular species. As a result of chestnut blight, a disease introduced into Canada in the early 20th century, the chestnut species was placed on Canada’s endangered species list. Purple loosestrife has already altered many wetland areas in Canada.
In economic terms, alien pests have a considerable impact. They slow down growth, kill trees and plants, and reduce the quality of lumber and harvests. They also cause a reduction in activities related to plant resources, such as lost jobs and income in the forest, recreation and tourism industries. Restrictions on and reductions in commercial activities and related income (sale of products, taxes, etc.) are other impacts produced by alien pests.
In addition, a considerable investment has to be made in regulatory controls, possible processing of products intended for export, scientific monitoring of introduced pests, detection and control of epidemics, reforestation and sanitary measures, and, of course, prevention. It is difficult to calculate all of the expenditures related to alien pests, and the expenditures vary from one year to the next. But solely in terms of timber losses, we know that forest pests destroy about 400,000 ha of forest every year in Canada, which is slightly less than half of the 930,000 ha harvested annually by the forest industry.
Social impacts are even more difficult to assess, but the following, which are or may be affected to varying degrees, can be pointed out:
- Stability and well-being of rural communities, particularly those associated with the forest industry;
- Traditional Aboriginal activities;
- Esthetic and spiritual values that people associate with forest and natural ecosystems;
- The attraction of jobs in the forest and wildlife sectors;
- Health problems related to forest industry work and higher risk of accidents in disturbed ecosystems;
- Public perceptions of forestry and forest industry activities; and
- Credibility of governments in the area of forest and ecosystem management.
A list of our worst pests
CFS scientists estimate that over 80 alien insects or diseases have been introduced into Canada since 1882, including several that have proven to be extremely destructive for Canada’s forests.
The following is a list of the principal alien pests, along with their preferred hosts and estimated dates of arrival in Canada:
- Ambermarked birch leafminer
- Balsam woolly adelgid
- Bark beetle
- Beech scale
- Birch casebearer
- Birch leafminer
- Black stem borer
- Common pine shoot beetle
- Eastern spruce gall adelgid
- Elm leaf beetle
- European pine sawfly
- European pine shoot moth
- European pineneedle midge
- European spruce sawfly
- Gypsy moth
- Introduced pine sawfly
- Larch casebearer
- Larch sawfly
- Lesser shothole borer
- Lombardy leafminer
- Mountain ash sawfly
- Pear thrips
- Rusty tussock moth
- Smaller European elm bark beetle
- Winter moth