Pine Beetle Attacks: Infant Pines Targeted Too

In a disturbing fungal connection, pine beetle attacks are not only leading to the death of adult trees, but can also weaken the next generation of pine trees, leaving them vulnerable to future insect attack, say researchers at the University of Alberta in this recent report.

Already, the beetles have damaged or killed more than 116 million acres of mainly lodgepole pine forests in western North America in the last ten years.

"The next pine forest is at risk," said Justine Karst, an assistant professor in restoration ecology in the University of Alberta's Department of Renewable Resources, according to Phys.org.

Karst is the co-lead author of that new study with Nadir Erbilgin, Canada Research Chair and associate professor in forest entomology and chemical ecology.

Until now, there was no reason to think that mature trees' deaths would affect the resistance of young trees to insect attack too, Karst said, according to Phys.org. Pine beetles, that is, are known to attack only mature trees, those with tissue and sugars to provide for hatched juvenile beetles.

In the normal chain of events, sugars in live trees move from the tree into beneficial fungi on the roots, creating a mutually positive relationships. When trees die, sugars no longer flow, and many of the "good" fungi disappear.

When those fungi are gone, different fungi move in. For reasons not entirely understood, according to the report, this affects the defenses of the new pine seedlings.

Without the established population of positive fungi, pine seedlings populate in fewer numbers, grow more slowly and have fewer defense chemicals. In the forests of western Alberta that were studied, seedling survival was sharply reduced. The survival rate in beetle-killed stands was one percent, compared with 25 percent for those in healthy areas, according to the report.

Karst and fellow researchers at University of Alberta, and in the Faculty of Forestry at University of British Columbia, will continue focusing on what could be happening underground and in the ecosystem of western forests.