Native or introduced?

Organisms that occur naturally in Canada according to historical records are considered native or indigenous. Some common and widespread native organisms cause damage to trees during their life cycles. These include spruce budworm, forest tent caterpillar, mountain pine beetle, and lodgepole pine dwarf mistletoe. Although these native species may be among the most damaging pests, they also play significant roles in forest ecology and renewal. These species coexist with various natural enemies, including migratory birds, specific parasites and parasitoids, and pathogens. These natural enemies help maintain lower pest densities than would occur otherwise. Although these native pests are part of the forest’s biodiversity, excessive populations can raise concerns in the forest industry and among others using trees or forests for a variety of reasons. In response, pest or forest managers may intervene to reduce numbers and keep damage at tolerable levels.

In comparison, many non-native forest pests in Canada have been introduced inadvertently through trade routes, whether in nursery planting stock, contaminated wood products, or infested packing materials. During the 20th century, most of the pests introduced (e.g., satin moth, balsam woolly adelgid, and Dutch elm disease) came from Europe or the United States, with which trade was most common and where the climate was comparable to that of Canada. The rapid expansion in global trade in the last few decades has heightened the threat of introduced species, such as Asian longhorned beetle, emerald ash borer, and hemlock woolly adelgid, with recent invasions to Canada from climatically and botanically comparable regions of Asia.

Introduced insects and pathogens, typically entering Canada via trade routes and commodities, are often first noticed in urban and semi-rural settings, where disturbances and non-native tree species are common. Unlike native insects and pathogens that are usually only a concern when populations increase dramatically (outbreaks or epidemics), introduced species pose a significant risk merely by their presence. A risk-based approach is taken for introduced species, given the difficulty of predicting how far they could spread and what trees they might attack. Consequently, authorities favour preventative management of introduced species: assessing the risks of potential damage; enforcing quarantines and inspections of incoming goods; rigorous monitoring; and, where possible, eradicating recently introduced species to prevent their establishment and spread.