The Secret Life of Trees
by Leslie Lytle, Messenger Staff Writer
Observing a large old tree often prompts the sentiment, “If only trees could talk.” Well, they can. At the Aug. 26 program sponsored by the Beersheba Springs Historical Society, Scott Torreano, University Professor of Forestry, shared some of the secrets hidden in the Plateau trees, secrets as much history as science.
In 1774, Thomas Jefferson’s complained in his diary about a late spring freeze followed by two years of catastrophic drought. How bad was it? The worst drought most people alive today remember is the drought of 2007. Based on the story trees tell, compared to Jefferson’s drought, the 2007 drought “was a cakewalk, Torreano said.
Dendrochronology, tree-time data obtained by analyzing tree growth rings, reveals not only the tree’s age, but information about the environmental conditions occurring throughout the tree’s life, forest fires, earthquakes, tsunamis, tornadoes and drought. The width of the ring reveals how a tree grew. Moisture has the greatest impact on a tree’s growth, Torreano said, with tiny rings indicating drought years.
The pioneering work using trees as a historical document was done by archeologist Andrew Douglass. In the pre-computer era of the early 1900s, Douglass painstakingly graphed tree ring growth patterns from trees in the southwest and compared the patterns to core samples from a ceiling joist to determine the age of ancient Pueblo structures. The growth pattern data offered answers to long enigmatic questions. Why did the ancient Chaco Canyon people suddenly disappear? Tree ring growth data suggests they left during the worst drought in 1200 years. Similarly, the mid-1500s disappearance of a once thriving culture in eastern North America coincided with the worst drought in 800 years.
Torreano stressed taking core samples did not harm trees and could be done without damage to buildings. Core samples taken from timber at Rebel’s Rest showed the samples matched trees within eight miles of Sewanee, except for the flooring which matched with core samples from buildings in the Beersheba Springs area. Even more intriguing, the Rebel’s Rest core samples show the same 1774 spring freeze and drought on the Plateau which Jefferson described occurring in Virginia.
In 1838, a military officer escorting Cherokee along the Trail of Tears removal to Oklahoma wrote to his superiors begging to halt the march temporarily, arguing, “I cannot as a Christian man make these people move any more.” The travelers had no water and no food and local people had none to share. Dendrochronology shows a severe drought in 1838.
Davy Crockett wrote about damage to trees characteristic of what is now known to be the Southern Pine Beetle, Torreano said. Forest fire frequently follows beetle devastation, with the dead trees easily ignited by a lightning strike. A large stand of short-leaf pine suggests severe fire occurred. Unlike other pines, the short-leaf pine seedling can withstand extreme heat and regenerate from a node on the trunk. The seedlings of the normally hardier Virginia pine die, giving the short-leaf pine an opportunity to be established.
Asked if it was safe to let pine trees stand after a pine-beetle scourge, Torreano replied, “Not if fire is an issue.” He praised the Tennessee Department of Environment and Conservation for being responsive to the importance of and need for prescribed burns, unlike forestry management agencies in most states.
Among the questions Torreano hopes to answer is whether the Cherokee conducted prescribed burns on the Plateau, which they are known to have done in the valley. Data harvested from trees can determine what season of the year drought occurred, the temperature of a fire, if severe wind events occurred, how long a glacier lasted, and much more not only about the past, but the future. In California plagued with recent devastation from forest fires, insurance companies use trees to determine risk profiles, Torreano said. Among the secrets researchers have learned from analyzing tree ring data: in the east, droughts typically last two or three years, while in the western United States a drought usually settles in for a 20-year stay.