Trees Respond to Climate Change by Producing More Carbon Dioxide

New study warns that climate models have overestimated the ability of trees to sequester carbon

 

While our planet's forests are a moderating force that can help counteract some of the effects of climate change, research concluded last year at Black Rock Forest creates a new understanding of what the limits may be for CO2  absorption by plants and trees. The study, led by Kevin Griffin, Ph.D., the outgoing president of the Black Rock Forest Consortium, shows that plants actually emit more carbon dioxide into the atmosphere than previously believed as temperatures rise.

Plants and trees store carbon dioxide during photosynthesis, but the new research — published last year in the prestigious Nature Communications journal — shows that when plants “exhale,” or respire, they emit around 30 percent more CO2 than scientists had previously predicted.

This means that as the planet warms, elevated respiration levels worldwide may reduce Earth’s ability to absorb the emissions created by burning fossil fuels, Griffin said.

“Plant respiration is an essential metabolic pathway that provides the energy and building blocks that plants need to grow and survive, but the process also releases CO2 to the atmosphere. For nearly 20 years my students, collaborators and I have been studying this process in Black Rock Forest and elsewhere, and we now have enough measurements to begin to identify global trends and make modeled predictions of future responses to climate change,” said Griffin, a professor at the Lamont-Doherty Earth Observatory of Columbia University.

Working with colleagues in the United Kingdom and Australia, Griffin’s findings were compared to more than 4,000 measurements of carbon dioxide respiration from plants across the globe.

What could the long-term impact be if plants and trees — among the planet’s greatest “carbon sinks” — don’t have the balancing effect that we believed they did?

“The study shows that as global temperatures increase, the amount of carbon dioxide released through plant respiration will increase significantly,” said Professor Owen Atkin from the Research School of Biology and the ARC Centre of Excellence in Plant Energy Biology at the Australian National University. “Currently, around 25 percent of carbon emissions from the use of fossil fuels is being taken up and stored by plants, which is good, as it helps reduce the concentration of greenhouse gases in the atmosphere. Our work suggests that this positive contribution of plants may decline in the future as they begin to respire more as the world warms.”

Griffin, Heskel and a team of Columbia students sampled leaves from the multiple deciduous tree species of Black Rock Forest, a site used frequently for critically important and well-respected research within the scientific community.  

“Black Rock Forest’s size, biological diversity and relatively undisturbed nature, along with its 90-plus year history as a research station, make it useful to represent the oak-dominated portion of North America’s eastern deciduous forest in global-scale studies,” said Bill Schuster, the executive director of the Black Rock Forest Consortium. “The work of Dr. Griffin and colleagues in Black Rock Forest has contributed to a more accurate understanding of our planet’s carbon cycle and a better ability to predict our future.”

In addition, Griffin’s study utilized plant respiration data from more than 100 other sites around the world, from hot deserts in Australia to the deciduous and boreal forests of North America and Europe, the arctic tundra in Alaska, and the tropical forests of South America, Asia, Africa and northern Australia.

The research now continues as scientists seek new data that will help them predict and respond to climate change. The next phase of the team’s work is to gather information on the growth respiration of leaves, which will provide two more important clues: how much additional energy is needed and how much CO2 is released when new leaves are added each year.

"We are now one step closer to more accurately modeling carbon exchange in ecosystems across the world,” said Dr. Mary Heskel, a postdoctoral scholar at the Ecosystems Center, Marine Biological Laboratory in Woods Hole, MA. “The study provides the most informed picture to date of current and future carbon release from plants in terrestrial systems."