North Carolina Bald Cypresses Are Among the World's Oldest Trees

Science
پنجشنبه 19 اردیبهشت 1398 ساعت 12:51
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Smith sonian mag
"There is no other place on Earth like this," Angie Carl says. Her voice carries across the swamp of North Carolina's Black River as we sit floating in kayaks at the knees of our elders, an ancient stand of bald cypress trees.
Following markers of neon-pink ribbons tied to branches, we've paddled to this remote stand to recreate a journey that Carl took eight years ago guiding David W. Stahle, a University of Arkansas scientist. Carl is the fire and coastal restoration manager for The Nature Conservancy’s Black River Preserve. Stahle is one of the deans of using dendrochronology (growth rings) and radiocarbon dating to study the climate hundreds or even thousands of years into the past.
On that hot, sunny summer day almost a decade ago, Stahle remembers coming on the stand of trees and immediately recognizing their importance. "They're ancient," he told Carl. "I can't prove it now, but we're going to find one in here to prove it."
The oldest known bald cypress in Black River Preserve, dated at 2,624 years old. (Charlie Peek)
The two conservationists had come upon the oldest living trees in the U.S. east of California and some of the oldest in the world. Testing would later reveal that one of them is at least 2,624 years old, making it alive when Nebuchadnezzar II built the Hanging Gardens in Babylon, when the Normans invaded England, and when Shakespeare first set quill to paper.
"It was like walking back into the Cretaceous," Stahle says. "It was essentially a virgin forest, an uncut old-growth forest of 1,000 to over 2,000-year-old trees cheek to jowl across this flooded land."
After examining the timber cores in the lab—measuring tree rings and taking radiocarbon readings—Stahle and his team today published a paper in IOP Science moving the bald cypress up the list of oldest living tree species to number five, behind the Sierra juniper of California and ahead of the Rocky Mountain bristlecone pine. The Great Basin bristlecone pine of California remains the oldest , non-clonal living tree in the world at 5,066 years. (These individual trees are distinct from a clonal colony, such as Pando in Utah , a group of trees that have all grown from the same root system.)
The value of the ancient bald cypresses in North Carolina goes beyond bragging rights at the old tree club. Tree rings offer a treasure trove of climate history going back thousands of years before the development of climate record keeping using science instruments (widespread use of rain gauges began in the late 19th century).
Bald cypresses are particularly adept at preserving the record of rainfall during the growing season. "It's an amazing coincidence that the oldest known living trees in eastern North America also have the strongest climate signal ever detected anywhere on Earth," Stahle says. "The best correlations we've ever seen are with these trees. Why that is I don't know. They're incredibly old and extremely sensitive to climate, especially rainfall."
Millenia-old bald cypress along Black River in North Carolina. (The Nature Conservatory Black River Preserve)
Dave Meko , a researcher at the University of Arizona's Laboratory of Tree-Ring Research who was not associated with Stahle's work, says it's rare to find trees old enough to frame the long view of climate. "We don't have many spots where we can sample tree rings to pick up variations over 2,000 years of climate," he says. "So where we can, we try to take advantage of them. Bald cypress is definitely a gold mine of climate information from the Southeast."
Tree-ring dating was invented by astronomer Andrew Ellicott Douglass in the early part of the 20th century. The stargazer was trying to determine if sunspots were linked to changes in the Earth’s climate (they’re not), and he founded the first tree ring laboratory at the University of Arizona in 1937.
The work of dendrochronologists has attracted the attention of a wide range of researchers in recent decades as they use the deep historical record found in trees to determine whether shifts in modern weather patterns are normal or signs of climate change.
Stahle’s career stretches back five decades to when he became the director of the Tree Ring Laboratory at the University of Arkansas. He began his career as an archaeologist, but a trip to northern Mexico to collect cores from churches while at the University of Arizona convinced him to go into dendrochronology. "It was the most fun I've ever had, and that sold me," he says.
Stahle started studying bald cypresses on the Black River in 1985 and discovered trees older than 1,000 years, including one named Methuselah that is more than 1,600 years old. But he'd never been to the remote region known as the Three Sisters where three braided channels converge.
Angie Carl, fire and coastal restoration manager for The Nature Conservancy’s Black River Preserve, among the ancient bald cypresses. (Jim Morrison)
After Stahle initially visited the region in 2011, he and his team returned a couple of times to drill cores the diameter of a child's pinkie using a long, hollow steel auger. The cores can be used to examine rings and date the trees. With bald cypress, however, it’s not always easy to find a cooperative core. Old bald cypresses often suffer from heart rot, or the hollowing out of the tree’s core. And getting into position to core an intact tree is not an easy task. The old trees have bulging buttresses that are part of the root system, so researchers carry ladders through the swamp to reach high enough on the trunk.
Once back in the lab, scientists examine the chronology—the width—of the rings. As trees grow, they form distinctive rings rippling out from the center. By examining the center ring, one can date the tree. "They have beautiful wood and the annual rings are exquisite," Stahle says.
The beautiful cypress wood is a library of stories found nowhere else. For example, Stahle has used bald cypress growth rings to pinpoint a drought beginning in 1587 and lasting two years—the worst in more than 1,000 years—that coincided with the Lost Colony of Roanoke disappearing from an island off the North Carolina coast. Another seven-year drought occurred during the early years of the also-doomed settlement at Jamestown, Virginia. Could these droughts have played a part in the communities’ fall?
One of Stahle's goals for dating the Black River trees was to document their age in hopes of contributing to their conservation. During his research, The Nature Conservancy had permission to visit the stand. Last year, it purchased the 319 acres including the Three Sisters area as part of 19,200 acres protected along the Black River.
The river, as black as its name, flows 66 miles through the state before emptying into the Cape Fear River. In the shallow-water maze of the Three Sisters, Carl leads me to the oldest tree. Time hasn't been kind to the bald cypress. Knobs and arthritic bulges protrude from the trunk, the top appears blown off, and fledgling limbs sprout from the top like the overgrown eyebrows of an old man.
We paddle downstream and back through time. The trees arise out of the water's mysterious gloom, highlighted against a white-grey morning sky. We weave our kayaks through the broken stumps of dead youngsters and the giant knees of ancients. Some of the larger trees are hollow, still alive thanks to pencil-thin limbs dotted with light green leaves. Later, when we return ashore, Carl says that 15 years after starting her job on the river, she still finds each visit magical.
The Conservancy doesn't plan to mark the oldest tree. After all, it's just the one that's been identified. "There are probably older trees out there,” Carl says. “They're all worth seeing. They all look different. They all have their own personalities. They're like grumpy old men and old women hanging out in this swamp looking down at you and saying, you are a blip in my existence."
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