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Tuesday, April 23, 2024

Where and how trees are used affects greenhouse gas emissions

The volume of greenhouse gas released when a forest is cleared depends on the part of the world where the trees are grown and how they will be used, according to a new study by UC Davis researchers.

In the study, lead author and doctoral student with the UC Davis Institute of Transportation Studies Jeffrey Mason Earles, along with Sonia Yeh and Kenneth E. Skog, found that when trees are felled to create solid wood products such as furniture or lumber for housing, the wood stores carbon for a longer period of time.

However, when the trees are used for bioenergy or paper, almost all of their stored carbon is released into the atmosphere, contributing to greenhouse gases.

“If the wood is put into products like lumber (e.g. 2-by-4s) and wood panels (e.g. plywood), the carbon is stored until they are sent to the landfill where decay begins or they are burned,” Earles said. “As wood decomposes, or when it’s burned, carbon is released to the atmosphere as a greenhouse gas, typically carbon dioxide or methane.”

The researchers looked specifically at comparing the amounts and endurance of carbon in trees that are burned on-site versus those that are removed and used as wood products.

“We tried to follow the lifecycle of the wood once they left the forest and the fate of these products that they are turned into,” said Yeh, research scientist with the UC Davis Institute of Transportation Studies.

The results of their study could hold implications for biofuel incentives in different regions. The researchers found that wood products in tropical countries stored very little carbon in comparison to temperate forests.

“In countries with predominantly temperate forests, such as the U.S., Canada, and many European countries, we found that between 30 and 40 percent of carbon is still stored as wood products 30 years after deforestation,” Earles said.

What this means for the global environment is that the American biofuel industry may change its methods of outsourcing. For example, if the U.S. decides to provide an incentive for corn ethanol, less-profitable crops like soybeans may go to other countries. In the process, the new country will have to clear out forests to provide room for the new crops.

“The biofuel policies [of the U.S. and E.U.] greatly expand the demands for biofuel feedstock, sometimes by displacing forest land or existing agricultural land, which in turn lead to more conversion of forest land for the displaced agricultural production,” Yeh said.

According to Skog, the supervisory research forester of the U.S. Department of Agriculture Forest Service, greenhouse gas emissions have been decreasing since 2005.

“Scientific research is continuing to better identify what the smarter choices are concerning use of natural resources to mitigate greenhouse gas emissions,” Skog said.

The destination of the displaced agricultural production and the way the wood from that forest land is used would impact how much carbon would be emitted into the atmosphere. This information could help reduce the overall possible emission of greenhouse gases from these global crops.

RACHEL KUBICA can be reached at science@theaggie.org.

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