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Don’t count on forests to offset emissions: study

The trees and forests long thought to be a key weapon in the fight against rising carbon emissions may not be effective in long-term efforts to combat global warming, researchers suggested Tuesday.

TORONTO — The trees and forests long thought to be a key weapon in the fight against rising carbon emissions may not be effective in long-term efforts to combat global warming, researchers suggested Tuesday.

A new study from the University of Guelph in southern Ontario found rising carbon levels failed to stimulate faster growth in 80 per cent of the world’s trees, despite the fact that the gas typically accelerates growth in most plants.

Only 20 per cent of trees appeared to respond positively to higher carbon levels, prompting researchers to urge countries to rethink their long-term environmental policies.

Ze’ev Gedalof, Associate Professor of Geography at the University of Guelph and co-author of the study, said the results challenge long-held assumptions about forests’ role in the fight to curb carbon emissions.

Many forecast models are based on the principle that higher carbon levels will allow trees to thrive, he said, adding the findings expose a potential flaw in popular environmental policy.

“Our research suggests that in fact is not going to happen, that we can’t look to forests to achieve our Kyoto obligations, that we can’t look to forests to offset emissions from burning fossil fuels,” Gedalof said in a telephone interview.

“There might be a very slight increase in the total rate of growth in trees, but they’re not going to be these vacuum cleaners that will magically suck up the CO2 that we’re emitting.”

Gedalof and study co-author Aaron Berg gathered their data by examining tree rings, or distinctive marks left on individual trees that allow researchers to see how much growth took place from year to year.

Despite studying 86 types of trees over more than 2,300 sites on six continents, Gedalof said no clear patterns emerged.

Most trees failed to respond to higher carbon dioxide levels regardless of their species or geographical location, he said, adding there were “positive responders” on all continents except Australia.

Gedalof said Canada had the opportunity to make forest growth a central piece of its carbon-reduction policy after signing the Kyoto Protocol, but has so far resisted the temptation to do so.

He called Canada’s stance “wise” and urged further caution, adding the only way to truly reduce carbon levels is to cut back on man-made emissions.

“Many of the growth models that are used to forecast how (forests) grow in the future might be over-estimating the growth rate of the forest, so we should be very cautious about using them as a management tool for balancing emissions elsewhere,” he said.

“Undoubtedly, forest management is going to be an important part of reducing carbon emissions in the short-term, but in the long-term, they’re going to be relatively unimportant. And probably more critically, they’re not going to be as powerful a tool as we might hope that they would be.”