ONE RING A YEAR
Light, then dark
In conifers, earlywood has thin-walled, wide cells and looks light; latewood has thick-walled, narrow cells and looks dark. Together they make one year's ring.
Read the history
NATURE'S OLDEST LIFE TRACKER
A diary
written in wood.
Every year, a tree adds a ring.
Light spring wood and dark late wood make one band a year, wide in good years and narrow in hard ones. Read carefully and matched across many trees, those bands date ancient buildings and old climates to the exact year.
ONE RING for every year
Age an oak- Light band, dark band, one year
- Match patterns, don't just count
- A tape measure ages an oak
- How trees keep time
THE SHORT ANSWER
Rings record years,
patterns record history.
Three ideas behind tree-ring dating.
The third one you can try in a park this weekend.
CROSSDATING
Counting is not enough
Some rings are missing from part of a trunk and some years leave a false ring. So scientists match the pattern of wide and narrow rings across many samples.
See the numbers
NO SAW NEEDED
Age an oak with a tape
For an open-grown oak, measure the girth at about 1.5 metres from the ground and look it up on the Woodland Trust's ready reckoner.
Try the reckoner
TRY IT ON A LOCAL OAK
A tape measure,
five minutes.
The Woodland Trust's method needs a soft tape measure, a piece of string, your arms or a few friends. It works best for oaks growing in the open.
Measure at about 1.5 metres
Wrap the tape round the trunk at roughly chest height and mark where you started.
Skip any bulge
If the trunk is very bulbous there, measure where it returns to its usual 'waist' size.
Read the ready reckoner
Look up the girth to get an approximate age, remembering it is based on open-grown oaks in south-east England.
Look at character, not just size
Hollowing, decay holes and dead wood in the crown are signs of age. Woodland or pollarded oaks can be ancient at only 3.5 metres round.
TWO NUMBERS WORTH KNOWING
Long lives,
long records.
One figure for the UK's oldest tree,
one for how many places tree rings have been measured.
2,000–3,000 years
Estimated age of the Fortingall Yew, Perthshire
The oldest individual tree in the world is thought to be a Great Basin bristlecone pine in California, at almost 5,000 years old.
OLDEST UK TREE · WOODLAND TRUST
5,000+ sites
Sites in the International Tree-Ring Data Bank
The archive holds ring widths, wood density and isotope measurements from sites on six continents, used to reconstruct past climate.
TREE-RING DATA · NOAA
Ring width varies with the conditions in the year it formed, which is why studying the variation tells scientists about past environments, according to the University of Arizona's Laboratory of Tree-Ring Research.
HOW OLD IS THAT OAK?
Measure the girth,
read the age.
Pick a girth, measured round the trunk at about 1.5 metres. The bar shows how close the estimated age is to the 400 years at which an oak counts as ancient.
Estimates for oaks in open ground in south-east England; woodland or pollarded oaks grow differently.
HOW TREE-RING DATING BEGAN
An astronomer
and a beam.
In 1904 the astronomer Andrew Ellicott Douglass collected his first tree-ring specimens from lumber yards in Flagstaff, Arizona, measuring the rings with a steel ruler and a magnifying lens. His first tree-ring paper appeared in 1909.
For 15 years his team searched for an old beam that would join their living-tree record to timbers from ancient Puebloan ruins. On 22 June 1929, a beam numbered HH-39 bridged the gap, and that evening Douglass called out construction dates of ruin after ruin.
Questions
Questions people ask
Does a tree add exactly one ring every year?
Usually one band of light earlywood and dark latewood forms each year. But a ring can be locally absent from part of a trunk, and a false band can appear, so scientists crossdate rather than simply count.
What is crossdating?
Matching the pattern of ring growth across many samples from the same area so each ring can be given its exact year of formation. One method is the skeleton plot, which marks the variation on graph strips.
Can I tell a tree's age without cutting it down?
For an oak, yes, roughly. Measure the girth at about 1.5 metres and use the Woodland Trust's ready reckoner. It is based on open-grown oaks in south-east England, so ages vary elsewhere.
How old is the UK's oldest tree?
The Woodland Trust says the Fortingall Yew in Perthshire is believed to be the oldest, with an estimated age of 2,000 to 3,000 years.
When is an oak tree ancient?
The Ancient Tree Inventory classes all oaks as chronologically ancient from 400 years, though many show ancient characteristics from around 300 years.
Sources
- Laboratory of Tree-Ring Research, University of Arizona: Dendrochronology (earlywood, latewood, crossdating)
- Laboratory of Tree-Ring Research: Brief history of the LTRR (A.E. Douglass, beam HH-39)
- Woodland Trust: How to estimate the age of an oak, ready reckoner (leaflet, hosted by WBRC)
- Woodland Trust Ancient Tree Inventory: Oak species guide
- Woodland Trust: The oldest tree in the UK, how long do trees live?
- NOAA NCEI: Tree Ring data (International Tree-Ring Data Bank)
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