Slide 1
A growth ring records a season’s wood
In many seasonal climates, a tree adds a growth ring during a year. The ring records wood produced under that season's conditions.
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A tree grows thicker through a living layer near its outer edge. The centre is not repeatedly expanding outward, which is why old wood can preserve a long sequence.
Slide 2
Early and late wood reveal the ring boundary
Wood formed early and late in a growing season can differ in cell structure. That contrast makes ring boundaries visible.
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The exact pattern depends on species and environment. A clear annual ring is common in suitable seasonal trees, but should not be assumed for every tree in every climate.
Slide 3
A narrow ring can have several causes
A small growth ring can indicate a difficult year. Water supply, temperature, competition and damage can all influence growth.
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Researchers compare many trees to separate a shared environmental signal from an individual tree's history. One thin ring alone cannot identify a particular drought or temperature with confidence.
Slide 4
Matching ring patterns links different wood samples
Overlapping sequences of wide and narrow rings can link different wood samples. This matching is called cross-dating.
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Timber from an old building can overlap a living tree's record. Linking suitable samples extends a chronology farther back than the lifespan of a single tree available today.
Slide 5
A narrow core reveals rings without felling the tree
A narrow core can reveal a sequence of rings. Researchers can study growth history without cutting down the whole tree.
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The measurements become more useful when archived with species, location and methods. Those details allow later researchers to compare records and judge what environmental question each sample can answer.
Sources
- Tree Rings and the Tales They Tell
National Park Service
- Tree Ring
NOAA NCEI