Annual Rings
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State
An annual ring forms from the contrast between spring wood's wide, thin-walled cells and denser, thick-walled autumn wood produced later the same year.
Show
Counting a cross-sectioned trunk's rings estimates a tree's age; ring width and density also vary with that season's climate.
Watch for
A ring records one season's growing conditions, not a fixed clock — width varies with rainfall and temperature, not age.