How are tree rings formed? Why do trees have rings?

1, the annual rings are between bark and wood, and there is a layer of cells called cambium.

2. Formation principle of annual rings: When the weather is dry in winter, cambium cells are dormant; In spring and summer, the temperature is high, the water is abundant, the cambium cells are active, the differentiated vessel molecules are many, the diameter is large, the tube wall is thin and the wood texture is loose, so it is called' early wood' or' spring wood'; In autumn, the temperature gradually gets colder, the activity of cambium cells gradually weakens, and the differentiated vessel molecules decrease correspondingly, with small diameter, thick wall, more wood fibers and dense wood texture. The early and late trees of that year combined to form annual rings, which are called annual rings.

3. The annual ring refers to the growth layer of wood and bark seen on the cross section of the stem within one year. Vascular cambium or cambium is a kind of secondary meristem with infinite meristem developed from procambium. In the life of a plant, secondary phloem is produced outward and secondary xylem is produced inward.