The rings of a tree are more than just markers of age; they are a historical record of environmental conditions. The University of Arizona has long been a leader in this field, known as dendroecology, which involves studying tree rings to understand past climates and ecosystems.
The science of dendroecology, which was developed in Tucson, is based on the fact that trees grow one ring per year. The width of each ring reflects the environmental conditions of that year: wider rings indicate wet, favorable conditions, while narrow rings suggest drought or stress. By matching ring sequences from different trees in the same region, scientists can build long-term timelines that extend far beyond the lifespan of individual trees.
Historic Origins
Founded in 1937 by astronomer Andrew Ellicott Douglass, the Laboratory of Tree-Ring Research (LTRR) is the oldest dendrochronology laboratory in the world. Douglass realized that tree growth patterns could be synchronized across regions and historical timelines could be established. This groundbreaking method provided archaeologists, climate scientists, and historians with an invaluable year-by-year record of the natural world.
Unparalleled Collection
The LTRR boasts the largest collection of tree-ring specimens globally, including cores, cross-sections, and ancient beams sourced from around the world. This collection supports research in dating artifacts, reconstructing past droughts and floods, and understanding ecosystem responses to climate changes. By cross-referencing samples from living trees, ancient stumps, and archaeological timber, the lab has created continuous chronologies dating back over 12,000 years.
This work has had ramifications beyond tree science. In the 1950s, chemist Willard Libby used precisely dated wood from the LTRR to calibrate his radiocarbon dating method, which later earned him a Nobel Prize. Learn more about this achievement.
Broad Applications and Innovations
Today, the lab’s research spans archaeology, paleoclimatology, fire ecology, and isotope geochemistry. Researchers have used tree rings to date the ancient Thera volcanic eruption and investigate ancient solar storms using radiocarbon signals preserved in wood. Closer to home, studies on fire history aim to improve land management practices.
“One of the things we can study with tree rings is the history of forest fires. We are working on a project to extract information from that fire history to inform prescribed burning and fire management in American forests, specifically by looking at the seasonality of fires and when is the best time to burn,” said Valerie Trouet, a Distinguished Scholar and professor at LTTR.
Advancing the Field
New technologies are extending the capabilities of dendroecology. Collaborating with Ghent University in Belgium, LTRR researchers are using an X-ray scanning technique to measure ring density in broadleaf trees for the first time. According to Trouet, “Density is really important because it is the part of the tree ring that is most responsive to changes in temperature.”
The LTRR has been instrumental in establishing dendrochronology programs worldwide, training researchers and setting methodologies that have been adopted globally. Nearly 90 years after its inception, the lab continues to be a leader in a science that is now practiced around the world.
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