Pine needles evolved to help trees cope with rainfall

Sept. 29 (UPI) -- The needles of longleaf pine trees evolved to effectively shed water, according to a study published Tuesday in the journal Physics of Fluids, ensuring rain moistens the soil instead of clogging leaf pores.

"Our initial inspiration for this project was [to study] raindrop impact on pine trees," Andrew Dickerson, professor of engineering at University of Central Florida, told UPI in an email.

Dickerson and his research partners wanted to find whether or not rainfall has influenced the material properties of pine needles.

"We began impact drops onto cantilevered needles, but quickly realized the physics was very complicated and that the simpler problem of drop impact onto fixed, non-circular fibers had not yet been tackled," Dickerson said.

To tackle it, researchers set up high-speed cameras to capture high-resolution, slow-motion video of drops hitting the wedge-shaped needles of longleaf pines.

According to Dickerson, dozens of studies have looked at the interactions between fluid droplets and circular fibers, but this one is the first to consider water droplet impact onto non-circular fibers.

"We are able to draw contrasts in fluid behavior as compared to circular fibers and witness behaviors not yet documented," he said. "I was surprised how different the 'lobes' formed by impacting drops look when the fiber changes orientation."

In addition to more efficiently breaking apart water droplets, researchers showed wedge-shaped fibers also retained less water than circular fibers.

"From an evolutionary standpoint this is advantageous because water on the surface of pine needles arrests photosynthesis by blocking stomata -- gas exchange pores," Dickerson said.

Researchers are currently studying how pine needle shapes vary across different environments and different climates.

The new study suggests longleaf pines, found throughout the Southeastern United States, evolved their particular needle shape to contend with heavy rainfall.

Authors of the new study suggest their research could be used by material scientists to design fibers that are especially repellent to environmental moisture accumulation.