Canopy Tree Project
The Real Lord of the Rings: Tales Beneath the Bark
November 13, 2025
Tree rings are the visible concentric rings inside a tree trunk. Each year, trees grow a new ring, tracking its age, health and logging environmental conditions along the way. In this way, trees act as living archives: their growth patterns are woven into ecological history, preserving a record of droughts, floods, and other climate changes over time. By studying these rings, scientists can uncover insights into past climates and how ecosystems responded—acting as a natural memory etched in wood.
If Trees Could Talk…
Tree rings vary in color and size, indicating each seasonal growth. The growth of trees is attributed to the cambium cell layer, which produces new bark and wood as hormones, such as auxins and cytokinins, pass through the tree. Yes, trees have hormones too!
When temperatures warm up in the spring, the cambium layer is activated, and a new, light-colored band is formed. Darker, denser bands form in the late summer and fall, when growth slows down and eventually completely stops. Both bands make up one ring.
Trees do not grow in winter, so as soon as spring comes around, a new ring is formed. Tree ring width varies from year to year: wider rings indicate wetter seasons, when the tree has more water for growth, while thinner rings correspond to drier seasons. Year after year, these tree rings represent a tree’s growth pattern.
The Real Lord of the Rings
How do scientists learn about trees without cutting them down?
In the early 1900s, Andrew E. Douglass founded the study of dendrochronology, the science of dating past events, environmental or archaeological, by examining tree rings. For example, archaeologists can study timber from ancient buildings or ships to determine exactly when the wood was cut.
At the Aztec Ruins, researchers discovered that the Ancestral Puebloans carefully harvested wood in early spring, before the sap began to flow, ensuring their beams were strong and durable. The rings are not just telling us when the trees were cut. They reveal how people lived, worked, and interacted with their environment, offering a glimpse into daily life and the resourcefulness of civilizations long past.
To collect the samples, scientists use a tool called an increment borer, a long hollow steel stick with a sharp end. After inserting the tool into the side of a tree, they extract a small core, about the size of a pencil.
Because tree ring patterns are influenced by the weather and climate, two trees that grow in the same area, under similar conditions will exhibit similar tree ring growth patterns. Scientists compare cores from multiple trees, looking for overlapping sequences of wide and narrow rings. When these patterns align, they can build a chronological timeline, accurately dating the trees and reconstructing environmental conditions in that region over time.
Stories Beneath the Bark
As trees grow, they take in carbon dioxide from the air, and at the same time store a record of atmospheric conditions in their rings. Scientists can study what the Earth may have looked and felt like, up to two thousand years into the past. The tree rings can reveal how the climate has varied over decades. Recent research shows that the carbon isotope ratios in tree rings have steadily shifted over the past few decades, mirroring the rapid rise of carbon dioxide in the atmosphere.
Scientists also use tree ring data to study past insect outbreaks. When insects attack trees and eat their leaves or needles, a process called defoliation, tree growth can be impacted because leaves play a major role converting sunlight into food, a process known as photosynthesis. This suppression of growth is shown as a thinner ring. In 2003, researchers studying conifer forests in southern Colorado observed at least 14 major insect outbreaks over the past 350 years.
In 2022, researchers studying trees in North America found a sample that dated from 1370 to 1710, with scars from nineteen separate fires. When a fire damages a tree’s cambium layer, it leaves a permanent fire scar in the ring record. By examining these scars, scientists can reconstruct the history of past fires, including their frequency, their intensity and spread direction. Revealing how the landscape and ecosystems responded over centuries
Researchers at the University of Arizona and ETH Zurich were able to create a record of solar activity from 1000 BCE to 2 BCE, using tree ring samples. This gives new insight into how the sun has behaved over thousands of years, and how we can predict and understand future solar outbursts, such as solar flares. When solar flares erupt, carbon-14 levels spike which are then absorbed by trees during photosynthesis; the more flares, the more carbon-14, the more it shows up in the tree ring record.
Tree Rings in Action
In 2018, a preserved Neolithic wooden water well was uncovered during highway construction in the Czech Republic. Using dendrochronology, the wood used for the well was dated back to 5256 BCE, making it over 7,000 years old!
Centuries after that well was buried, tree rings continued to tell stories about European life. Tree rings reveal that between 300 BCE and 200 CE, Europe experienced ideal agricultural conditions, supporting the rise of the Roman Empire. Around 364 CE, the rings show a sharp drop in rainfall, signaling drought and crop failures. This environmental stress is theorized to have contributed to Rome’s weakening control over Europe.
Thousands of miles away, evidence from the American Southwest, revealed a similar drought taking place hundreds of years later in the late 1200s. Scientists observed thin tree rings in wood used for building homes and theorized this drought contributed to the Ancestral Pueblo People abandoning their dwellings at Mesa Verde.
Dendrochronology has also helped uncover stories in our contemporary world. In 2010, during another construction project, this time at the World Trade Center in New York City, the remains of a large wooden ship were discovered. After analyzing the rings, it was found to be a Revolutionary War-era ship, with the wood likely coming from Pennsylvania in the 1770s.
Trees Are More Than Just Breathing the Air
Human memory may be fallible, and important historical documents or artifacts may be lost, but the elemental composition of trees can fill in those gaps. Trees are valuable for their spiritual significance, underground interconnectedness, and contribution to healthy ecosystems. That’s why EARTHDAY.org is working to plant 60 million trees by 2030. If you would like to support this mission, please consider donating to the Canopy Tree Project today.
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