New York Ag Connection - Forest Carbon Sink Neutralized by Growth-Lifespan Trade-Offs

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Forest Carbon Sink Neutralized by Growth-Lifespan Trade-Offs
New York Ag Connection - 09/16/2020

A study released in Nature Communications helps bust the myth that forests - and the trees within them - will increasingly compensate for increased human-induced carbon dioxide emissions.

In "Forest carbon sink neutralized by pervasive growth-lifespan trade-offs," more than a dozen researchers from around the world explored the relationship between tree growth, lifespan, and net carbon storage. They found that faster growth associated with higher temperatures causes trees to die sooner. Temperature did not directly shorten tree lifespan, rather it was the faster growth rates at warmer temperatures that increases mortality rates. Ultimately, these patterns will make forests less effective at absorbing carbon emissions from fossil fuels (coal, oil, and natural gas), potentially leading to a positive feedback on the warming of Earth's climate.

"Our findings confirm the need to stay the course on discovering ways or changing behaviors that can reduce emissions," said Steve Voelker, adjunct assistant professor at the SUNY College of Environmental Science and Forestry (ESF) and contributor to the study. "Planting trees is fantastic. Preserving forests or letting them grow to older ages are important parts of the solution. We can't do enough of this work. But in our new, warmer climate, trees grow faster, die sooner, and when they die, the carbon contained within them goes back into the atmosphere. We cannot continue to rely on forests to soak up carbon emissions and help us solve climate change concerns to the extent we have in recent decades."

Previous studies have experimentally exposed young forests to elevated concentrations of carbon dioxide, and most of these forests grow a bit faster, for at least a few years. Additionally, a study published in Nature earlier this year by John Drake, an ESF assistant professor, found that mature forests are unlikely to soak up additional carbon dioxide. Collectively, this work indicates that a growth stimulation by forests is not going to solve our climate crisis for us.

In the new study, researchers used tree-ring data compiled in global databases and collected raw data from 110 different tree species found around the world.

"Our data represents species from low tropical forests, the highest peaks, and across all latitudes, trees grow," said Voelker. "This trade-off of fast growth and decreased longevity has long been known across tree and animal species. However, it also occurs almost universally within single species, which is a really important finding for understanding how forests work. We project there to be less long-term carbon accrual in forests made up of trees that grow quickly, which means we need to find other ways to compensate for fossil fuel emissions."

Voelker focuses on forest health and forest responses to climate change. He primarily uses dendrochronology and stable isotope techniques, but also draws on a background in plant ecophysiology, disturbance ecology and paleoecology. His overarching goal is to determine how forests respond to environmental change that can support more accurate forecasts of climate change and other potential threats to forests and the ecosystem services they provide.

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