Tree’s warning: Get ready for more dry spells By Taft Wireback
Staff Writer
Saturday, Mar. 22, 2008 3:00 am
Credit: News & Record
Evidence of wet and dry periods is in the growth rings.
GREENSBORO — The world's oldest living longleaf pine has spoken, and it has a disturbing message for residents of the Greensboro, Charlotte and Atlanta metros.
Research involving the ancient North Carolina longleaf suggests that if you think the current drought has been unsettling, just stick around a few decades.
Every century, the southeastern Piedmont from Georgia through the Triad averages one to two monster droughts lasting four years or more, according to the tree and the man who discovered it, UNCG graduate student Jason Ortegren.
That should come as sobering news to parts of the North Carolina Piedmont, including Greensboro, that have seen their water supplies severely tested in the past decade by droughts lasting a year or two.
"So you can imagine the impact a four-plus-year drought would have," said Ortegren, who found the ancient pine last year with UNCG geography professor Paul Knapp. They discovered the tree at Weymouth Woods Sandhills Nature Preserve near Southern Pines while Ortegren was doing research for his doctoral dissertation, which he is now wrapping up.
Ortegren's tree research did unearth a silver lining, however: The region seems to have a built-in brake that, so far, has protected it from ever reaching conditions like the Great Plains "Dust Bowl" of the 1930s.
Nature's drought brake? Hurricanes and tropical storms that sweep across the region periodically, bearing the gift of abundant rainfall.
"I call them drought busters," Ortegren said.
North Carolina's ancient longleaf dates to at least to 1548. Ortegren and Knapp "cored" the tree, harmlessly removing a small-bore plug from deep within the trunk to disclose the year-by-year weather conditions under which it has lived.
The evidence is displayed in the tree's structure of annual growth rings. In layman's terms, each wide ring represents a year with sufficient or abundant rainfall; a very narrow ring suggests a year of drought.
Ortegren detects a hurricane or powerful tropical storm when he finds a series of multiple, very narrow rings followed by an unusually wide band of yearly growth.
The region suffered one confirmed monster drought in the 20th century, from the early 1920s through 1927, and one borderline bad actor during the mid-'50s. According to Ortegren's tree-ring evidence, droughts of greater than four years also occurred during periods ending in 1699, 1750, 1801, 1819 and 1882.
He has combed the historical record and found reliable reports of tropical storms ending droughts in 1882 and 1927. Longtime Greensboro residents know the city was in bad shape in 1954 until Hurricane Hazel swept through and replenished its depleted water supply.
Ortegren spent weeks meticulously examining the core from the Weymouth Woods longleaf. Then, as part of his doctoral project in UNCG's geography program, he compared its data with that from other very old trees to develop a picture of rainfall and drought from 1690 through 1984.
Ortegren couldn't go back any further in time because not enough trees had lived as long as the Weymouth Woods specimen. He used trees cored and analyzed by other scientists across the Piedmont from Georgia through Virginia.
The number of trees spread across such a large area showed periods of broad-based regional drought in five-year snapshots. He eventually built his case on data from just one of those aged trees, in Georgia, because it best represented the entire group.
But North Carolina's 460-year-old longleaf and data from the other ancient trees gave him the basic information that revealed and verified the long-term trends, Ortegren said.
Tree-ring research is valuable because it can extend some amount of weather knowledge to periods earlier than 1900, when people began compiling records that can be relied upon with scientific precision.
Ortegren found it surprising that his work could be groundbreaking, that this type of research marrying tree data to long-term weather patterns apparently hasn't been done for such a populous region. The aim is to capture patterns that the climate repeats over cycles of decades and centuries so people can get a better idea what the future might bring.
"These are things we need to keep in mind when we're laying out our plans on how to further develop this region," Ortegren said. "We need to think about where our water resources are going to come from in the event one of these severe droughts occurs, which seems like something we can expect."
Ortegren's basic conclusions are valuable in driving home the point that Greensboro is vulnerable to periodic dry spells and must be vigilant about its water supplies, said Allan Williams, the city's director of water resources.
"Our reliable data only goes back to 1928," Williams said of the city's lake records. "We don't really know what happened before that. I think he's putting a scientific and statistically valid imprint on something we've been saying for a number of years."
Ortegren theorizes that through the centuries, the Piedmont's cycles of wet, dry and super dry have been driven by as-yet undefined variations in the El Niño and La Niña phenomena, alternate cycles of warming and cooling in the Pacific Ocean that influence how much rainfall the Southeast gets.
The Holy Grail for Ortegren is to reach a point where scientists can define that unknown wrinkle, some telltale event or alignment of stars that provides an early warning the region is about to experience a monster drought.
But just knowing what has happened repeatedly in the past is a start toward understanding the future, Ortegren said. So residents can take heart that El Niño and La Niña seem to insulate them from droughts of desert-making intensity.
"But we don't seem to be safe from the recurrence of the four-year-plus drought," he said. "And that still could have a devastating impact."
Contact Taft Wireback at 373-7100 or
taft.wireback@news-record.com 
