New research shows that there is a serious ripple effect when pine beetles kill mature pine trees, weakening seedlings and greatly affecting their survivability

New research shows that there is a serious ripple effect when pine beetles kill mature pine trees, the symbiotic root fungi in the soil, and so weakening seedlings and greatly affecting their survivability
Photo Credit: Justine Karst - U Ab

Pine beetles: unsuspected additional threat to boreal forest

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Canada’s vast boreal forests are under attack. The enemy is the pine beetle which is destroying many millions of trees in British Columbia and Alberta and spreading eastward.

A new study has found that young pines are not surviving even though they haven’t been infected.

Justine Karst (PhD) is co-lead author of new research into this phenomenon. She is an assistant professor in the Department of Renewable Resources at the University of Alberta.

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The new research from the Faculty of Agricultural, Life and Environmental Sciences (ALES) shows that when pine beetles kill off mature trees, it has a ripple effect which dramatically reduces the survivability of seedlings.

Justine Karst (PhD) assistant professor Dept of Renewable Resources, ALES, University of Alberta, and co-lead author of a new study showing how pine beetle death also kills off fungi the trees need, compromising survival of seedling trees, thereby killing off the older trees directly, and the seedlings indirectly
Justine Karst (PhD) assistant professor Dept of Renewable Resources, ALES, University of Alberta, and co-lead author of a new study showing how pine beetle death also kills off fungi the trees need, compromising survival of seedling trees, thereby killing off the older trees directly, and the seedlings indirectly © ALES- U Ab

The study, co-lead authored with Nadir Erbilgin, Canada Research Chair and associate professor in forest entomology and chemical ecology, was published in the journal New Phytologist.

The research found that when the trees are killed, the soil fungi along their roots also dies.  That same soil fungi helps new seedlings, the next generation in the forest, to survive and grow.  The fungi feed on sugars from the fine tree roots and in turn process nutrients and minerals which the tree needs to grow and to produce chemicals which provide some defences against insects and pathogens.

Pine seedling growing in the understory of a pine forest.  Survival rates of seedling diminish greatly when beetles kill off mature trees along with the fungi in their roots and the soil
Pine seedling growing in the understory of a pine forest. Survival rates of seedling diminish greatly when beetles kill off mature trees along which also kills the fungi in their roots and the soil © J Karst- U Ab

Karst says research shows that while all trees have this relationship, pines are particularly sensitive to the type of fungi colonizing their roots.

When the trees are killed and that soil fungi dies or is depleted, the research shows it changes the ability of seedlings to survive and their defence chemistry is changed.

A healthy forest exists in symbiosis with fungi in the soil. Pine mortality caused by mountain pine beetle attack causes changes in soil fungi to occur, which can have negative effects on pine seedlings and their survivability
A healthy forest exists in symbiosis with fungi in the soil. Pine mortality caused by mountain pine beetle attack causes changes in soil fungi to occur, which can have negative effects on pine seedlings and their survivability © J Karst- U Ab

In fact, Karst says their research showed in a healthy stand of trees, seedlings have a 25 percent survival rate, whereas in a severely affected beetle-killed stand, seedling survival was almost zero.

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Karst says that their study provides even more insight into the interconnectedness of nature and the ripple effects of removal of any particular element from an ecosystem.

“Red forest”- the healthy green pines, once attacked and killed by the pine beetle first turn a red-orange-yellowish colour- then grey as needles fall off. Harvested logs to the right The pine beetle is causing massive destruction to the boreal forest, and will change its structure and composotion over time © J Karst-U Ab

It also shows a possible solution to enabling survival of replanted pines into a stand that has been killed off. She says adding the correct fungi to the seedlings might increase their ability to survive.

However she says, given the massive destruction caused  by the pine beetle, the make-up of the boreal forest is almost certain to change in the near future.

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