Linked from
The 12 pages that link to Tree ring, each with the reason it gives.
TreeBroader topic: Seasonal changes in growth can leave dated layers in a tree’s wood.
PiceaRelated: Annual rings in spruce wood record changing growth conditions over time.
Western redcedarRelated: Its annual growth layers record age and changing growing conditions.
Petrified woodBroader topic: Petrified specimens can preserve growth rings as mineralized bands.
Pinus longaevaRelated: Annual rings allow the ages of bristlecone pines to be counted and compared.