What do you count on a tree to tell how old it is?

You count the rings on a tree to tell how old it is. In many temperate trees, one visible growth ring represents one year of growth, so counting the rings can provide an age estimate.

The rings form in the vascular cambium, a layer of actively dividing cells near the bark. Early-season wood is usually lighter and less dense, while later-season wood is darker and denser; together, these bands create a yearly ring. Wide rings often indicate favorable moisture and growing conditions, while narrow rings can reflect drought or other stress.

The scientific study of tree rings is called dendrochronology. Scientists do not always rely on a simple count: drought can produce missing rings, and interrupted growing seasons can create false rings. By comparing ring patterns from several trees, researchers can identify these irregularities and reconstruct past climates. Ring studies can also date wooden buildings, archaeological objects, and works of art.