Trees can be aged by counting their annual growth rings. This process of is called dendrochronology from the Greek words dendron (tree limb), khronos (time), and logia (study). In temperate climates, most trees will produce an annual growth ring each year. Annual growth usually consists of a wide light-colored ring (spring growth) and a narrow dark-colored ring (summer growth).
An individual tree does not grow at the same rate each year, but instead grow at rates that depend on the temperature and availability of water. A year with little precipitation may be marked by a very narrow growth ring, while a year with abundant precipitation will be marked by a wide growth ring. These pattern can be used to determine climate patterns for a region even when precipitation records do not exist.
Here are photos of six different species showing different patterns of growth. Each photograph was taken a 2X magnification with a digital microscope. Each photograph shows an area of the same size on the sample of tree trunk.
The first sample is of an American Beech. American Beech is a slow-growing hardwood species. The rings on this sample are running from left to right. Counting from the top of the photograph over one dozen closely-packed rings are visible in this small sample. Each ring is approximately the same size.
|American Beech (Fagus grandifolia)|
|Green Ash (Fraxinus pennsylvanica)|
|Red Pine (Pinus resinosa)|
|Silver Maple (Acer saccharinum)|
|Sycamore (Platanus spp.) - petrified|
|Willow (Salix spp.) - petrified|