Nonstructural carbohydrate dynamics of lodgepole pine dying from mountain pine beetle attack

Area of Science:

• Forestry
• Plant Physiology
• Ecology

Background:

• Bark beetle outbreaks cause significant tree mortality globally.
• The physiological mechanisms of tree death during bark beetle attacks are not fully understood.
• Nonstructural carbohydrate (NSC) dynamics are crucial for plant defense and survival but their role in beetle-induced tree death is unclear.

Purpose of the Study:

• To investigate the whole-tree NSC dynamics in lodgepole pines attacked by mountain pine beetles.
• To determine the sequence of NSC depletion across different tree organs following bark beetle infestation.
• To elucidate the physiological mechanisms leading to tree mortality during bark beetle outbreaks.

Main Methods:

• Monitoring of NSC concentrations in all organs (bole, needles, branches, roots) of attacked and protected lodgepole pines (Pinus contorta).
• Study conducted during a mountain pine beetle (Dendroctonus ponderosae) outbreak in British Columbia from June 2011 to October 2012.
• Correlation analysis between beetle damage, initial NSC concentrations, and tree survival.

Main Results:

• NSC concentrations initially decreased in the bole region attacked by beetles.
• Needle NSC declined by late 2011, followed by branch and root NSC decline in 2012.
• Lower beetle damage and higher initial bark NSC concentrations in attacked trees correlated with survival.
• NSC dynamics suggest tree death resulted from impaired water conduction rather than girdling.

Conclusions:

• Locally reduced carbohydrate availability exacerbates tree susceptibility to bark beetle attacks, especially under drought stress.
• Water conduction loss, not girdling, is the primary cause of tree death during mountain pine beetle outbreaks.
• Understanding NSC dynamics is critical for predicting tree mortality and managing forest ecosystems under climate change and pest pressure.