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Bald Cypress tree rings reveal 2,000-year history of climate disruption
The bald cypress tree (Taxodium distichum) has been quietly standing sentinel to centuries of ecological change in the murky wetlands of the American Southeast. These towering trees are some of the oldest living organisms in Eastern North America, their gnarled "knees" that tower above the water as a defining feature.
However, even long-lived specimens such as these are beginning to show the worrying signs of enormous global change. New research has found that while these trees do not die of old age, external stressors such as a changing climate, rising sea levels, pests, and erratic weather drastically shorten their lifespans.
In collaboration with partner institutions, a team of scientists from Florida Atlantic University investigated 95 specimens of ancient bald cypress preserved in subfossil form near the Altamaha River, Georgia. The researchers used radiocarbon dating and tree ring analysis to reconstruct over two millennia's worth of growth patterns of these trees and found how environmental changes impacted the cypress specimens.
"The rings of the bald cypress are like nature's journal entries, written year by year and season by season, showing how even slow changes can shape the course of life," said Katharine G. Napora, the study's senior author.
The team's findings highlight a dramatic shift that began around 500 A.D. Before that point, bald cypress trees in the region regularly lived for more than 470 years. But after this period, their average lifespan fell sharply to 186 years.
This drop corresponds with the beginning of a sixth-century climatic disruption known as the Vandal Minimum, which marked the start of a worldwide cooling period believed to be the result of extreme volcanic activity combined with the possible impact of a comet.
"This shift wasn't a brief disruption. Even centuries later, the trees never regained their former longevity. Their lifespans continued to decline over time," said Napora.
"The last of the long-lived trees in the deposit died during another major climatic event, the Little Ice Age. Our findings underscore how long-lasting the localized effects of major climate shifts can be, especially for coastal forests that are already vulnerable to wind damage, saltwater intrusion, and rising seas."
Researchers found no evidence that human activities such as fire or logging contributed to the trees' demise. Dry spells may have encouraged the spread of mites and other pests, further stressing these trees.
"These ancient giants not only inspire awe but also serve as natural archives, helping scientists understand how trees have weathered past climate events – and how they might fare in the face of modern climate change," said Napora.
Despite the grim trend, hope endures. Isolated pockets of old-growth swamps still shelter bald cypress trees up to 2,600 years old.
"In their quiet persistence, these trees offer both a warning and a lesson: that the world is more interconnected than we often realize, and that the story of the Earth isn't only told through written history – it's etched into wood, embedded in landscapes and carried forward by living organisms," said Napora.
"The past lives on in the trunks of these ancient trees, reminding us that environmental shifts – whether natural or human-caused – reverberate through time in ways we are only beginning to understand," she concluded.
The study has been published in the Proceedings of the National Academy of Sciences.
