Forests Not Solution to Offsetting Carbon Emissions, Study Finds

October 27, 2010 - News Release

Don't look to forests to soak up increasing amounts of global-warming gases being pumped into the atmosphere, says a new study by University of Guelph scientists.

The study by Guelph geography professors Ze'ev Gedalof and Aaron Berg appeared recently in the journal Global Biogeochemical Cycles.

The results will surprise people on both sides of the carbon-sequestration debate who have called for tree planting to help offset CO2 emissions, said Gedalof.

“Trees will play a role in assimilating atmospheric CO2, but it’s much smaller than most people expect.”

Referring to the Kyoto Protocol on greenhouse-gas emissions, he said: “Canada has options under Kyoto to use forest regrowth to offset emissions. Our results suggest that looking to forests to grow more quickly and thereby offset emissions is not going to work.”

Studying archived tree-ring measurements held by the National Oceanic and Atmospheric Administration in the United States, they found CO2 fertilization spurred faster tree growth at only about 20 per cent of sites worldwide, despite the fact that the gas typically accelerates growth in plants.

“Eighty per cent of the world’s forests don’t care,” said Gedalof.

The researchers found that those faster growth rates could not be traced to climatic change, nitrogen deposition, changing sensitivity to climate, elevation or latitude, all of which may influence growth rates of trees.

They also found no evidence that higher atmospheric CO2 enables trees to use water more efficiently, contrary to claims that climate change will allow forests to extend into dry areas.

Gedalof and Berg analyzed data from about 2,300 forest sites on six continents and covered 86 species of trees.

Another study published this past summer by researchers in Guelph’s School of Environmental Sciences led by Prof. Madhur Anand found that tree growth in Ontario has declined over the past century despite rising amounts of CO2 in the atmosphere.

Gedalof plans to investigate forests in western North America more closely to learn why CO2 fertilization helped increase growth in only a few places.

He said there are other environmental reasons to plant trees but not necessarily to mitigate carbon emissions.

“Long-term, the only solution is to reduce emissions and look for non-fossil-fuel energy sources,” he said.

Prof. Ze'ev Gedalof
Department of Geography
519-824-4120 x58083

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