Mountain pine beetle and forest carbon feedback to climate change

Area of Science:

• Forestry science
• Ecology
• Climate change research

Background:

• Mountain pine beetle (Dendroctonus ponderosae) outbreaks are recurring events in western North American pine forests.
• These outbreaks cause significant tree mortality, impacting forest carbon uptake and increasing emissions from decomposition.
• Current large-scale modeling often overlooks insect impacts on forest carbon dynamics.

Purpose of the Study:

• To estimate the cumulative carbon impact of the mountain pine beetle outbreak in British Columbia from 2000-2020.
• To assess the shift in forest carbon balance from sink to source due to beetle-induced tree mortality.
• To compare the outbreak's carbon impact to other major emission sources like forest fires.

Main Methods:

• Estimation of cumulative carbon impact over a defined period (2000-2020) and area (374,000 km2).
• Calculation of average annual carbon emissions per unit area.
• Comparison of outbreak-related emissions to historical forest fire emissions and net primary production changes.

Main Results:

• The cumulative impact of the beetle outbreak is estimated at 270 megatonnes (Mt) of carbon.
• The affected forest shifted from a net carbon sink to a significant net carbon source.
• In peak years, outbreak impacts were equivalent to approximately 75% of Canada's average annual forest fire emissions (1959-1999).

Conclusions:

• Insect outbreaks, exacerbated by climate change, are a critical factor undermining the carbon sequestration capacity of northern forests.
• The significant carbon emissions from beetle outbreaks necessitate their inclusion in large-scale climate and forest management models.
• Climate change is a key driver of the unprecedented scale and severity of current insect outbreaks.