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| 04/21/16

Global warming ‘fertilisation effect’ speeding up tree growth in BC


In a rare bit of positive climate change news, global warming and a rising concentration of carbon dioxide in the atmosphere is speeding up the growth of forests in British Columbia. This ‘fertilisation effect’ has been so pronounced, according to researchers, that the increased absorption of CO2 by the rapidly growing trees, will be enough to cancel out the boost in carbon emissions that resulted from the province’s devastating mountain pine beetle (MPB) outbreak.

This research was carried out by scientists with the Forestry Carbon Management Project, an initiative of the Pacific Institute for Climate Solutions, which investigates how forests can contribute to slowing global warming as well as adapt to the changing conditions. The findings were published in the scientific journal Geophysical Research Letters and announced by PICS last week, generating strong interest from the media.

Typically, as trees grow, they “breathe” in CO2 and store carbon in their leaves, trunks, branches and roots. But the MPB infestation that broke out in 1999 killed trees across some 18 million hectares in BC. Dead trees cannot draw down CO2 and worse still, as they rot, their stored carbon is released back into the atmosphere. As a result, during the peak years of the pine beetle disturbance BC’s forests are believed to have switched from being a carbon ‘sink’ to a carbon source. The study estimates that the net effect of the MPB disturbance has been reduced storage of around 300 megatonnes of carbon in province’s forests over the 1999-2020 period.

But while climate change will produce more such pest outbreaks, as well as make trees more vulnerable to drought and fire, in high latitudes such as Canada, Russia and northern Europe, the extra warmth, precipitation and carbon dioxide in the air also boosts tree growth, allowing forests to recover faster than normal from harvest, wildfires and insect disturbances. Tree growth in high-latitude forests is limited by temperature,in contrast to their counterparts in warmer tropical climes, so warmer temperatures help enhance growth rates.

This new PICS research, which was based on both computer models and historical observations, showed that by the end of this decade, the enhanced tree growth in BC will have outpaced the carbon losses due to the pine beetle outbreak, even taking into account forest fires—a rebound much earlier than had been expected, said lead researcher Vivek Arora of the Canadian Centre for Climate Modelling and Analysis.

In other words, climate change has increased the rate of growth and thus carbon storage in our forests so much that an additional 1000 megatonnes of carbon will be stored by trees between 1999 and 2020, or roughly three times what will have been lost due to the pine beetle.

“Ironically, while climate change can make insect outbreaks more likely, it can also help our forests recover more quickly from those outbreaks,” said Werner Kurz, the project’s team leader and senior research scientist at Natural Resources Canada.

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