trees

You can only use growth rings to count the age of a tree in areas with the distinct four seasons (for example, in most of the US). In tropical areas, trees may lay down multiple growth rings in a year, since a new growth ring occurs whenever the weather changes from dry to wet.

In the United States, you can also tell the difference between wood grown in the spring and the summer when looking at slices of woody plants in a microscope; in the spring, the cells the tree creates are larger, and summer cells tend to be more compact. This is due to the greater amount of water that is usually available during the spring, which fuels faster and more growth.