While conducting a study that examined trees on a cellular level, scientists observed something that defied previous categorization: tiny structures marking a family of trees as neither softwood nor hardwood, but somewhere in between. What’s more, this newly identified type of wood, dubbed “midwood,” grows fast and stores a lot of carbon, making it highly effective for carbon sequestration, according to the researchers.
Tree categories are lumped into two types. While angiosperms are known colloquially as hardwood and gymnosperms are referred to as softwood, the names don’t have anything to do with the density of wood. Rather, they refer to how trees spread their seeds: hardwood trees disperse their seeds encased in fruit or shells (like oaks or maples), while softwoods have exposed seeds (such as conifers). The trees also differ in their microscopic makeups, with the cell walls in hardwoods having narrow macrofibrils—a structure in the cell wall that plays a role in giving the wood its stiffness and strength.
While conducting a study to better understand the microscopic makeup of both types of trees, researchers made a surprising discovery: Hardwood macrofibrils are around 15 nanometers in diameter, while those in softwood measure 25 nanometers.
As they documented in their paper, published in the journal New Phytologist, the researchers found that the macrofibrils of the only two surviving species from the Liriodendron genus—the Tulip Tree and Chinese Tulip Tree—measured 20 nanometers in diameter. This discovery was made while examining samples from a wide assortment of trees under an electron microscope.
The Tulip Tree is found in parts of Canada and the United States, growing up to 150 feet tall (45 meters). In contrast, the Chinese Tulip Tree can reach heights of 130 feet (40 meters) and is native to China and Vietnam. It is also cultivated as an ornamental tree in Europe and North America.
“We show Liriodendrons have an intermediate macrofibril structure that is significantly different from the structure of either softwood or hardwood,” Jan Lyczakowski, a scientist at Poland’s Jagiellonian University who worked on the study, explained in a statement. “Liriodendrons diverged from Magnolia Trees around 30-50 million years ago, which coincided with a rapid reduction in atmospheric CO2. This might help explain why Tulip Trees are highly effective at carbon storage.”
The tulip trees evolved to grow quickly, capturing and storing large amounts of carbon while doing so. That ability to pluck CO2 from the air could make midwood a valuable part of anti-climate change strategies, said Lyczakowski.
“Both Tulip Tree species are known to be exceptionally efficient at locking in carbon, and their enlarged macrofibril structure could be an adaptation to help them more readily capture and store larger quantities of carbon when the availability of atmospheric carbon was being reduced,” he said. “Tulip Trees may end up being useful for carbon capture plantations.”
Several east Asian countries are already using Liriodendron plantations for efficient carbon sequestration, which researchers now believe may be due to the unique structure of the wood, he added. Given the newly discovered type of wood’s potential utility, the next time somebody calls you “mid,” you might want to take it as a compliment.
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