Novel forest decline triggered by multiple interactions among climate, an introduced pathogen and bark beetles

Area of Science:

• Ecology
• Forestry
• Environmental Science

Background:

• Novel forest decline is a growing concern linked to global environmental change.
• Understanding the complex interactions between climate and biotic factors driving forest decline is crucial.

Purpose of the Study:

• To investigate the causal factors and their interactions leading to whitebark pine (Pinus albicaulis) decline in the southern Canadian Rockies.
• To analyze long-term climate-growth relationships and their divergence between healthy and declining tree populations.

Main Methods:

• Utilized tree ring analysis across 16 whitebark pine stands.
• Examined climate-growth relationships over time, considering factors like temperature, drought, and the Pacific Decadal Oscillation (PDO).
• Assessed the roles of blister rust (Cronartium ribicola) and bark beetles (Dendroctonus ponderosae, Ips spp.) in tree mortality.

Main Results:

• 72% of whitebark pines in the study area were dead, with significant growth decline starting decades before mortality.
• Climate-growth relationships varied, with drought limiting growth during cool PDO phases and warming temperatures impacting snowpack.
• Divergent climate-growth trends in declining trees, influenced by blister rust and climatic stress, predisposed them to bark beetle infestation and death.

Conclusions:

• Multiple interacting factors over decades, including climate variation, drought stress, blister rust, and bark beetles, caused unprecedented whitebark pine mortality.
• Forest decline is a complex process requiring consideration of multi-faceted drought-disease-insect interactions across various timescales.
• Findings highlight the need for integrated approaches to understand and manage forest decline in the face of environmental change.