How will boreal forests respond to global warming?

New satellite data helps track photosynthesis in evergreens

How will forests respond to global warming? @bberwyn photo.
An aerial photo of forests in western Colorado. New satellite data will help show how evergreen forests are responding to climate change. @bberwyn photo.

Staff Report

Despite the huge importance of forests in the global carbon cycle, researchers still aren’t exactly certain how they will respond to climate change. But that could soon change thanks to satellite sensors that can track photosynthesis in evergreen forests by monitoring slight color shifts.

The new information could help assess the health of northern forests over time, showing how they are responding to global warming. Photosynthesis is easy to track in deciduous trees — when leaves bud or turn yellow and fall off. But until recently, it had been impossible to detect in evergreen conifers on a large scale.

“Photosynthesis is arguably the most important process on the planet, without which life as we know it would not exist,” said John Gamon, lead researcher and a professor of biological sciences at the University of Alberta. “As the climate changes, plants respond — their photosynthesis changes, their growing season changes. And if photosynthesis changes, that in turn further affects the atmosphere and climate.”

For scientists, the big question is whether forests will be able to maintain their role as carbon sinks as the planet continues to warm due to human activity. Some researchers speculated that a longer growing season will result in plants sucking up even more CO2, further slowing climate change. Others predict that drought stress could slow photosynthetic activity, resulting in higher releases of CO2 into the atmosphere through a process called respiration — which would accelerate global warming.

“If it’s hypothesis one, that’s helping us. If it’s hypothesis two, that’s pretty scary,” said Gamon.

The research team combined two different satellite bands — one of which was used to study oceans and only recently made public by NASA — to track seasonal changes in green (pigment created by chlorophyll) and yellow (created by carotenoid) needle color. The index they developed provides a new tool to monitor changes in northern forests, which cover 14 per cent of all the land on Earth.

Gamon has taken a leave of absence from the U of A to further the research, now funded by NASA, at the University of Nebraska-Lincoln. His lab in the U.S. is reviewing 15 years’ worth of satellite data on forests in Canada and Alaska to ultimately determine whether photosynthetic cycles are happening earlier because of climate change and whether forests are becoming more or less productive at converting CO2.

“Those are key questions we haven’t been able to answer for the boreal forest as a whole,” he said.

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