If a tree falls in a forest and no one is around to hear it, does it make a sound? This question has riddled scientists and philosophers for centuries. Some answer "no," citing a sound can't be created without the sensory organ of the ear.
But what if there is another type of observation beyond human sound? What if the trees themselves have a way of observing and storing memory about their own lives?
Using trees as witnesses to history is exactly what a biology team is doing at West Virginia University. Biology professor and chair Richard Thomas led a team into the Smoke Hole area of Grant County to examine eastern red cedar trees (Juniperus virginiana).
"Typically you don't think of trees recording history," Thomas said, "but in this case the trees have recorded the history of acid pollution in their tree rings.
"We looked at 100 years of tree growth," Thomas said. "In addition to just looking at how they were growing, we actually looked at the carbon atoms inside of the wood of those tree rings."
Analyzing carbon content in the tree was just one piece of the research that required a team of detectives.
"This research highlighted the role of collaboration among plant scientists to tackle complex ecological questions," said Jesse Nippert, professor of biology at Kansas State University, who was also on the team with the WVU members.
The group worked together using their mastery in isotopic dating of both carbon and sulfur to go back in time.
"What we found is that there is a clear signal that occurred about 10 years after the Clean Air Act," Thomas said.
The Clean Air Act was signed into law by Richard Nixon in 1970. One of its primary goals was to cut down on acid rain created by sulphur dioxide emissions at powerplants.
Thomas said for decades both forests and towns were subjected to acidic air pollution.
"We were kind of in the bullseye," he said. "We were downwind from the powerplants in the Ohio river valley."
By analyzing the trees, the scientists were able to tell when and how the trees transitioned.
"We found that the acid rain was closing the pores in the leaves, where the carbon dioxide is taken up for photosynthesis. These pores, called stomata, were getting smaller, smaller and smaller - closing more and more as the pollution continued for decades," Thomas said. "And then 10 years after the Clean Air Act of of 1970, the pores began to reopen, and they've been reopening ever since."
Another discovery by the team is that the cedar sensed and recorded the Great Depression.
The amount of energy needed during the Great Depression heavily decreased as production went down across the country.
"As the energy production went down, the amount of sulphur pollution went down. We can actually detect that in the tree rings," Thomas said.
"It's really interesting that these trees recorded two major events in U.S. history: the Great Depression and then the signing of the Clean Air Act," he said.
"Our research shows that the Clean Air Act has had a positive influence on forests and forest health in West Virginia," Thomas said.
"This is good news for all of the people who love being outdoors and it is good news for our economy as well," he said. "Two large parts of the West Virginia economy are tourism and forestry. Whether you are an outdoorsman, a hunter, a forest landowner, a hiker, a biker, a white water paddler, everyone in West Virginia is connected in some way to our forests."