The most destructive pest to North America’s mature pine forests, the mountain pine beetle, is threatening the next generation.

A study conducted by a University of Alberta researcher shows that the pine beetle not only kills adult trees, but can also leave the next generation of pine vulnerable.

“The next pine forest is at risk,” said Justine Karst, an assistant professor in restoration ecology at the U of A, and co-lead author of the study with Nadir Erbilgin, Canada research chair and associate professor in forest entomology and chemical ecology.

The insect’s population exploded in B.C. in the early 2000s, then moving across the Rockies into Alberta. The beetles are now established in northern and western Alberta and have been reported in the Northwest Territories.

Mountain pine beetles kill pine trees by clogging and destroying their conductive tissue.

Mature trees contain enough of the tissue and sugars needed for the survival of the next generation of pine trees. But those sugars also sustain fungi, which provide nutrients necessary for trees to make defence chemicals to protect themselves against insect attacks, that live at a tree’s roots.

When the trees die, many of these fungi disappear.

But according to Karst, the forest gets “a different suite of fungi,” and this affects the defences of the new pine seedlings. As a result, the seedlings establish in fewer numbers, grow more slowly and contain fewer defence chemicals.

The research team found that seedling survival in the forests studied in western Alberta was dramatically reduced. In beetle-killed stands the survival rate was one per cent, compared to 25 per cent for those in healthy stands.

The study by Karst, and researchers at the U of A and the University of British Columbia, has been published in New Phytologist.

Alberta has six million hectares of pine forest, and the provincial government has warned the tiny bugs could threaten watersheds, tourism, fish and wildlife habitats, and Alberta’s $4-billion forestry industry.