Tree

In most trees growing in a strongly seasonal climate, the vascular cambium produces wide, thin-walled cells in the spring, narrow thick-walled cells in the summer, and few or no cells in the autumn and winter. This seasonal regularity of cell production results in the formation of annual growth rings. The bristle-cone pine (Pinus aristata) is the world's longest-lived tree species, and one specimen of this species has about 5,000 growth rings, indicating it is at least 5,000 years old.

Within a given growth ring, the large cells of spring-wood and the small cells of summerwood are often readily discernible with the naked eye. Light, temperature, soil moisture and other environmental factors affect the growth of trees, and therefore the width of their growth rings.