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 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.
Some experts questioned the study's conclusions, saying the interplay between forests and carbon emissions is more complex than the data suggests.
Werner Kurz, senior research scientist with Natural Resources Canada, said tree growth is not the only way forests absorb carbon from the atmosphere, adding biomass from dead wood and other organic matter also contribute to the process.
"You don't need, necessarily, higher growth rates as observed in tree rings to get a bigger carbon sink," Kurz said. "So what I'm saying is that the study in itself is not necessarily conclusive that forests have not increased their sink strength."
Kurz said Canada has not made forest management a central piece of its carbon reduction strategy, adding policy-makers opted not to make use of it when deciding how to comply with the Kyoto protocol.
The decision was made based on a number of scientific analyses as well as complicated international regulations, he said.
"Canada elected not to include forest management, not because we don't think that there might be some opportunities, but because the rules were just not working for many countries."
Gedalof praised Canada for resisting the temptation to rely heavily on forest management strategies, calling the stance "wise."
Forests have a role to play in the fight to reduce carbon levels, Gedalof said, but urged caution as countries draft future policies.
"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."
