Tree Killers

What are the invasive species threats to trees? This resource discusses some of the biggest tree killers in Canada.


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What do I need to know?

What is an invasive species?

An invasive species is a plant, animal or disease moved to a new region where it damages native habitats or kills native species. They reproduce quickly, spread widely, and tolerate a range of conditions. The worst impacts occur when an invasive species is moved into an area without its natural predators that normally keep it in balance in its native habitat. This movement is almost always caused by human activity.

How do invasives kill trees?

Diseases and insects kill trees directly by blocking or consuming plant tissues used for water and nutrient transport. Vines can physically smother trees and saplings, robbing them of sunlight and nutrients. Other invasive shrubs and plants can crowd out tree seedlings and saplings growth. Still, some plants release toxic compounds into the soil.

Why is this important?

  • Invasive species are the second-biggest threat to biodiversity after habitat loss.
  • Trees provide habitat for a wide range of other flowers and wildlife.
  • From a purely economic viewpoint, trees provide forest products and tourism opportunities, which are a significant part of the world’s economy.
  • Invasive species control can be very, very expensive.

What are the common pathways for invasive species?

Quite frequently, invasive species first show up in, or adjacent to urban areas or other ports of entry. In many cases, wood crate packaging may contain exotic insects. Shipments of nursery stock may introduce the plant or a disease as do movements of fruits and vegetables which may transfer disease. Frequently, transporting firewood may introduce insects or disease and even the movements of people and pets may inadvertently transfer seeds.

Tree killers and the world

As world commerce increases, so do the number of species moved into new areas. Most invasive species thrive in disturbed habitats such as those found in urbanizing areas. As well, logging and forest clearing areas can leave the remaining trees more vulnerable to invasives. Once established, most invasive species are very difficult to eliminate. Canada’s extensive forests, especially those in proximity to urban areas are threatened by the same factors as elsewhere in the world.

Canadian should be aware of invasive species

Early detection allows time for control efforts (e.g.: the forklift operator in a Toronto-area warehouse who noticed the first Asian Longhorned Beetle in Ontario gave agencies time to respond and contain the insect). Awareness of the known pathways reduces spread of invasives (e.g. fuelwood sellers need to know not to move ash firewood from areas infested by the Emerald Ash Borer and residents with Dutch Elm Disease affected elm trees should remove and destroy them as soon as possible).

What can I do to help fight invasive species?

You can use this tool below to research known invasive species in Canada and help us identify and prevent these outbreaks in your area.

Broadly speaking, there are three (3) categories of invasive species that are threats trees in Canada

#1. Insects

150x150 insects

Asian Longhorn Beetle
(Anoplophora glabripennis)

Brown Spruce Longhorn Beetle
(Tetropium fuscum)

Emerald Ash Borer
(Agrilus planipennis)

European Gypsy Moth
(Lymantria dispar dispar)

Mountain Pine Beetle
(Dendroctonus ponderosae)

Sirex Wasp
(Sirex Woodwasp)
(Sirex noctilio)

#2. Diseases

150x150 diseases

Butternut Canker
(Sirococcus clavigignenti-juglandacearum)

Chestnut Blight
(Cryphonectria parasitica)

Dutch Elm Disease
(Ophiostoma ulmi)
(Ceratocystis ulmi)

White Pine Blister Rust
(Cronartium ribicola)

#3. Plants

150x150 plants

Black locust
(Robinia pseudoacacia)

Chelidonium
(Chelidonium majus)

Common Buckthorn
(Rhamnus cathartica)

Dog-Strangling Vine
(Cynanchum spp.)
(Vincetoxicum spp.)

English Ivy
(Hedera helix)

Garlic Mustard
(Alliaria petiolata)
(A. officinalis)

Glossy Buckthorn
(Rhamnus frangula)
(Frangula alnus)

Japanese Knotweed
(Fallopia japonica)
(Polygonum cuspidatum)

Norway Maple
(Acer platanoides)

Periwinkle
(Vinca minor)

Scotch Broom
(Cytisus scoparius)

Siberian Peashrub
(Caragana arborescens)

Tatarian honeysuckle
(Lonicera tatarica)

White Mulberry
(Morus alba)

White Poplar
(Populus alba)