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A field after a stand of trees is cut.

Doing the math: Equations for calculating trees’ carbon amount

Note: This story is part of a special issue of The Warnell Log focused on carbon

If you want to calculate the amount of carbon stored in a tree or in forests, Warnell researcher Dehai Zhao has you covered.

For more than a decade, Zhao, a senior research scientist who specializes in statistics and forest biometrics, has developed a series of equations to more accurately determine the green weight, dry weight, and carbon amount in southern pine species.

The result is a more accurate depiction of what landowners have in stock, and what they can predict for the future.

“Carbon concentration is different depending on which part of the tree. For example, the stem, the bark, the branch and the foliage,” said Zhao. “Because these carbon concentrations are different, we’ve developed biomass equations for different components. The multiplication of the biomass and carbon concentration of a component gets the amount carbon in that component. Put them together, we get the total carbon.”

Zhao’s work is part of the ongoing research conducted by the Plantation Management Research Cooperative (PMRC), a collaborative effort between Warnell and landowners across the Southeast. The PMRC and its crew of field researchers works to improve forest management practices, and calculating carbon is just one part of the suite of studies they pursue.

Bronson Bullock, director of the PMRC, said Dehai’s work on biomass equations dovetails with work he’s done on taper and weight.

“And not just on the carbon side but on the biomass side, this work has been very collaborative with the U.S. Forest Service and other institutions because we work with extensive databases and the data we collected is very intensive,” said Bullock. “To get enough samples to really do this you need a network; many years ago we got federal funding from the Forest Inventory and Analysis program to focus on biomass sampling and to improving the estimates for pine in the southeast U.S.; we also sampled a subset of hardwood trees to improve the sampling distribution.”

The PMRC and Warnell are plugged into this network, primarily focusing on southern pine species—loblolly and slash pines in particular. That analysis focuses more on biomass, but Bullock added that carbon is a component of that.

Water is about 50% of a tree’s green weight, and carbon is roughly about half of the dry weight, he said. “If we have weight and volume, we can use conversion factors to get at the carbon,” he added.

But as management practices shift due to changing climates and landowners look to carbon as another possible revenue source, calculating that carbon becomes crucial.

Zhao has been refining his equations for years and regularly presents new data, including more recent work on forecasting carbon into the future.

It’s one more tool for landowners to better manage their timber.

“Over time, we can know how the biomass and carbon is changing,” added Zhao. He pointed to graphs that showed the potential change for carbon capture and release in sample plots, depending on management practices. “As forests develop, the live trees continue to capture carbon from the atmosphere, while mortality increases. Some carbon in dead trees and other materials will release back to the atmosphere. All this shows how the carbon capture, release and storage in forests are changing over time—and this is what we need to understand to help forest managers enhance carbon storage while sustain their timber productions.”



Professor, Forest Biometrics & Quantitative Timber Management, Director, Plantation Management Research Cooperative (PMRC)
Senior Research Scientist/Graduate Faculty, (Statistics, Forest Biometrics), Plantation Management Research Cooperative (PMRC)

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