"The study demonstrates that natural disturbances can convert forests from carbon sinks to carbon sources," Werner Kurz of Natural Resources Canada told environmentalresearchweb. "The outbreak of an unprecedented scale of the beetle was made possible (1) by very large areas of mature pines – the result of fire suppression and low rates of logging disturbances – and (2) by warmer summers and milder winters that no longer kill overwintering beetles."
Kurz says that these factors allowed the beetle population to explode. The beetles kill trees, reducing the uptake of carbon dioxode and increases emissions from the decay of dead trees. "These higher emissions, in turn, provide positive feedback to future climate change," he added.
The mountain pine beetle (Dendroctonus ponderosae Hopkins) is native to pine forests in western North America. Its population erupts periodically but the current outbreak in British Columbia is an order of magnitude larger in area and severity than all previous recorded outbreaks.
Kurz and colleagues revised their forest carbon dynamics model to take account of insect outbreaks for the period from 2000 to 2020. They estimate that the beetle will have a cumulative impact of 270 megatonnes of carbon over the period – or 36 g of carbon per square metre of forest per year, over 374,000 km2 of forest. This impact converted the forest from a small net-carbon sink to a large net-carbon source during and immediately after the outbreak.
"The focus of our research at present is to develop and assess the potential of forests and the forest sector to contribute to climate change mitigation options," said Kurz. "For example, can salvage logging and the use of the wood from the dead trees be used to provide biofuels that are not in competition with human food supply? And can we accelerate the regrowth of forests after disturbance so that they become sinks more quickly, through reforestation efforts including planting, tree species selection and silvicultural activities?"
The researchers reported their work in Nature.