Skip to main content

Helping landowners calculate their worth

UGA researcher’s equations give foresters a global competitive edge


Looking out over a stand of tall pine trees, you can use some math equations to calculate the amount of wood you have.

But what about the parts of the trees not included in that arithmetic? The bark, needles or leaves and small branches have typically been left out of that equation—until now.

Thanks to the work of forestry biometrics researcher Dehai Zhao, a faculty member in the University of Georgia Warnell School of Forestry and Natural Resources, landowners now have a new set of equations to help calculate more than just wood volume. This helps give American foresters a competitive edge among landowners around the world, where information on carbon sequestration and woody biomass are part of the business of growing trees.

“The market is changing. In addition to traditional forest products, such as pulpwood, chip-n-saw and sawtimber, forest landowners recognize that managing forests for biomass biofuel feedstocks and forest carbon stock may strengthen their financial returns. The woody utilization standard is also changing,” said Zhao, a senior research scientist whose work is funded by a U.S. Department of Agriculture grant. “So, for the industry, they need some flexibility to accurately estimate any mixture of their forest products or potential products.”

The last time these equations were updated was the 1980s, said Zhao. At the time, tree growers only required one number: The volume of wood derived from each tree trunk in a stand. But since then, global markets for wood products have shifted to include much more. Today, metrics such as volume, green and dry weight, and carbon capture are just as important, and allow landowners to make better-informed decisions about land management and market conditions.

For example, there is a growing global demand for biomass to produce bioenergy and bioproducts—offering potential new markets for leaves, branches, small trees and other leftover materials that otherwise might become mulch. It’s important for landowners to be able to calculate that value along with other traditional wood products. And by being able to more accurately estimate the volume and weight of a tree’s trunk and the weight of other tree parts, growers can better respond to alternative forest management practices, such as fertilizing or thinning.

With the help of a field crew, Zhao collected samples from 800 pine trees across the Southeast. Samples included “cookies,” or pieces cut across the width of the tree, as well as subsamples of branches and leaves.

At the laboratory, samples were used for dry weight determination and energy and nutrient analyses. The new data was added to existing tree data to assist Zhao in developing new systems of equations.

The new equations address several problems that persisted among previous methods, Zhao said: They use specific model structures to guarantee the compatibility among a tree’s taper, they account for merchantable and total volume, and the additivity of tree biomass equations; using appropriate model estimation methods to address the heteroscedasticity and correlations among the equations. Thus, the new equations give more accurate and consistent values.

As a result, the new equations go beyond what the 1980s versions did. And new options that include taper, volume, weight and carbon information help landowners become more competitive on a global scale.

It’s as if you updated your car’s stereo from a tape deck to a Bluetooth-enabled system. Suddenly, you have a lot more options.

“My new system of taper and volume equations has been used for loblolly and slash pine plantations in the United States and five pine species in mixed-species forests in Mexico. The new system of volume and biomass equations can be used to accurately estimate the volume and weight of any portion of tree bole, and biomass of foliage, branches and even stem bark,” added Zhao. “For the next step, we will use the new model systems and modeling methodologies for other species of hardwoods in the U.S.”

Zhao’s work is part of a national effort by the USDA to develop equations to determine volume, biomass and carbon content of trees and tree components for more than 25 major tree species. Now that Zhao has completed work on Southeastern pine equations, he’s assisting with research in other parts of the country. He said he expects the project to continue another two years.

The work is essential for forest owners, said Zhao, and is an essential upgrade from previous modeling tools.

“This is very fundamental work for forest management,” he said. “Because the market is changing, forest managers need more flexible equations to estimate their products.”

Associated Personnel:
Article Type: