Beech Bark Disease

Beech Bark Disease

One of the many iconic forest trees in Central Ontario is the American Beech (Fagus americana). This tree is most well known for it's smooth grey bark with a broad crown. Beech trees are easily identified in all seasons due to their smooth bark which some people refer to as "elephant legs" in the forest. Beech trees are slow growing, however, they can live for 200 years or longer.


Beech trees are mostly found in upland forest communities, and are typically associated with sugar maple, eastern hemlock, and other hardwoods such as red oak, white ash, ironwood, and basswood. Beech leaves are large, alternate, short stalked, and egg shaped, pointed at the tip and have a leathery feel to them. They are dark bluish-green in the growing season and turn golden bronze in the fall. Some leaves will persist into winter. Beech trees also produce an edible nut that are popular with many birds and mammals, they grow in pairs in bristly reddish-brown husks.


Beech trees are known as "mast trees" in the forest due to the abundance of nuts they produce for wildlife, including black bears. The fresh nuts are very high in protein and were historically an important food for Aboriginal peoples; they are still a very important source of protein for a number of wildlife species.Ā  Black bears will actually make "nests" in the top of beech trees while feeding on beech nuts. They will climb to the top of the trees, sit in a crotch of branches, reach out to grab branches, break them off in order to eat the nuts, and then stuff them underneath themselves when finished to make a "nest". It's not uncommon to come across beech trees with bear claw marks up the bark and a big pile of branches at the top!

Unfortunately, beech trees are currently in decline across their range due to beech bark disease. This disease is caused by a combination of an introduced beech scale insect from Europe, coupled with a nectria fungus. Beech scale arrived in Canada in 1890 in Nova Scotia and has slowly been making its way across the provinces and is now in Ontario. While the fungus is likely native to North America, the introduced scale insect provides an opening to a new host tree for the fungus. The disease begins with many of the scale insects feeding on beech sap while they form a covering of white wooly wax over their body. Once the scale has opened up a wound in the bark of the tree, the fungus begins to colonize the bark, cambrial layer, and sapwood of the tree. This stage of the disease produces cankers or raised blisters and calluses on the outer bark covering much of the trunk. This infection severely weakens the tree and exposes it to other stresses. "Beech snap" is a common occurrence once a tree is infected - the tree can appear to be reasonably healthy, but has declined so quickly that it begins losing branches in the canopy quite quickly.


This disease has resulted in severe die-back in mature beech trees, potentially creating a significant threat to wildlife, biodiversity, and forestry practices in Ontario. While this disease is posing a significant threat to beech stands in Ontario, not all trees are killed by the disease and some have shown resilience. Mature trees over 8 inches in diameter are most at risk of infection, small, more vigorous stems seem to be more resilient.


Recognizing beech bark disease in the forest and on your property is helpful in tracking the disease and in locating potentially resilient trees. Individual high-value ornamental beech trees can be treated with commercially available products. Mature and healthy beech trees within an area of high infection can provide an excellent seed source for the next generation of resistant beech trees.
For more information and to report beech bark disease in your area, contact the Ontario Invading Species Hotline at 1-800-563-7711 or report a sighting online.

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