Research shows heightened CO2 boosts tree growth

By DAN SCHNEIDER, DMG Writer

HOUGHTON — Fall color may start later, but trees may grow faster, as the level of carbon dioxide in the atmosphere increases.

Results of a decade-long study on primarily aspen trees near Rhinelander, Wis., suggest that elevating carbon dioxide levels in the atmosphere may prolong the growing season for northern forests. Additionally, projected 2050 atmospheric carbon dioxide levels appear to speed trees’ rate of growth.

“We’re seeing about a 30 to 40 percent enhancement in growth and that’s been maintained pretty much throughout the 10 years of the experiment,” Michigan Technological University Forestry Professor David Karnosky said.

Karnosky is the director of the Aspen FACE (Free Air CO2 Enrichment) study. At a facility outside Rhinelander, Wis., he and other scientists have been simulating projected 2050 atmospheric CO2 levels by infusing the air at trees’ canopy level with the gas. The CO2 is added through rings of vertical vent pipes encircling stands of aspen, paper birch and sugar maple.

“We’ve noticed that basically all 10 years of the experiment, trees in those rings keep their leaves longer into the fall,” Karnosky said. “They also grow faster and photosynthesize at a greater rate than the control rings.”

He and 13 other researchers, including scientists doing research at a similar facility in Tuscania, Italy, published a paper documenting these findings in the current issue of the journal Global Change Biology. The title is “Future Atmospheric CO2 Leads to Delayed Autumnal Senescence.”

“Senescence” is the scientific term for the fall cessation of photosynthesis and color change in leaves. Karnosky said while the study shows increased CO2 concentration in the atmosphere will make the color change start later, it doesn’t appear it will affect the extent or duration of color change.

Increased CO2 in the atmosphere could be beneficial for the forestry industry. Stands of trees may grow to a harvestable stage at a greater rate.

“The rotation age may be reduced by a number of years,” Karnosky said, referring to the interval of time between harvests within a stand of trees.

But he cautioned the results of the experiment may not apply to more mature forest types.

“The work we report in this paper is done with very rapid-growing, early-forest-stage trees,” Karnosky said. “How that translates into a 30- or 40-year forest is much more difficult.”

He also said the increased rate of growth increases the forests’ nutrient demands, so the impact of boosted CO2 levels may vary regionally depending on local soil types.

[Who Funded this? Was any nutients added to the tree soil?]

The study will continue in Rhinelander. Karnosky said the final harvest of the trees there is slated to begin in 2009 and 2010. The harvest will allow scientists to assess the impact of heightened CO2 on the forest’s processes underground.

Dan Schneider can be reached at dschneider@mininggazette.com

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