What science studies the patterns formed by annual tree rings?

Dendrochronology is the science that studies patterns formed by annual tree rings.

In many temperate trees, a ring records one year of growth. Light-colored earlywood forms during rapid spring growth, while darker latewood develops later in the season. Scientists measure ring widths and compare patterns among living trees, dead wood, and historical timbers.

This technique can date wooden objects and reconstruct past climate conditions, including droughts, floods, and unusually cold periods. Cross-dating is essential: a sequence from one sample is matched against overlapping sequences from other trees.

Dendrochronology is related to dendrology, the broader study of trees, but the terms are not interchangeable. Tree rings do not always represent exactly one calendar year in every environment, especially where growth is irregular or multiple rings form during a single season.