Ontario's beech trees are slowly being consumed by a disease that's been on a steady march through the province for decades, experts say.

Beech bark disease comes as a two-part attack. First, a small insect burrows into the tree. Then a fungus takes over, slowly rotting the tree and causing it to die.

​"After the insect has moved through, then the fungus will follow and cause the cankers on the tree," said Sylvia Greifenhagen, a research forester with Ministry of Natural Resources and Forestry.

"When you get enough of these killing cankers in the bark, the tree will die."

Arrived in late 19th century

The disease has been relatively slow moving, arriving in Canada in the 1890s and gradually spreading through the Maritimes, Quebec and now Ontario.

Greifenhagen said the ministry has research plots across the province to track the disease's movement. In some cases, it's already taken a considerable number of trees.

"In some of the plots, the mortality [rate] is past 60 per cent of the large mature trees," she said.

That's particularly concerning, Greifenhagen said, since beech trees are a major part of Ontario's forests and an important component of the province's ecosystem.

She said the disease has done the most damage in eastern and southern Ontario, where it's existed the longest.

"The beech nuts are really high in nutrients and fat content for bears and deer, and the trees are used by all sorts of animals and birds for places to live," she said.

"There will be more and more mortality as the disease continues to work its way through the rest of forest."

Prevention measures

Unfortunately, there is no easy solution to stopping the disease, Greifenhagen said.

She advised anyone who owns a single tree to use a power washer to try and remove any small insects.

She also said people should generally not move firewood "from the area where they cut it or bought it," as that can lead to the disease-causing bugs being transported to different regions.

"They can potentially be moving the diseases if they move firewood," Greifenhagen said.