How to Tell a Tree's Age

Trees perform a wide variety of vital functions on earth, contributing to a habitable biosphere for all other living things. Among other functions, trees are vital for:

1. Contributing significantly to the earth's oxygen supply.
2. They have the ability to absorb, and therefore remove from wider circulation, a number of toxins and pollutants.
3. Trees can be blockades for unwanted noise and thus reduce noise pollution when planted strategically around your home or neighborhood.
4. They can slow down storm water runoff, encouraging the recharging of ground water aquifers.
5. Because they are carbon sinks, absorbing vast amounts of carbon dioxide during photosynthesis, they contribute to the removal of this green house gas from the atmosphere.
6. Trees cleanse the air of particulates, shade and cool even on a global scale and provide windbreaks.

Understanding the age of individual trees is important for a number of reasons. Foresters use tree age data to determine:

• age of a stand of trees
• how quickly the trees are growing (can be extrapolated by width of individual rings)
• the health of individual trees which is also important for urban areas where unhealthy trees suffering from internal rot could pose dangers during storms or high wind periods.
• a site index which provides a relative measurement of the quality of that particular forest site based on the average height of dominant tree species taken at a specified age;
• this site index helps predict future returns from this site with respect to tree harvesting and also provides a means of predicting the land productivity for both trees and wildlife
• core samples from trees can also be used to reconstruct past climate and events
• trees used in historically significant structures and art can be dated using techniques employed by dendrologists

Only 1% of a tree is actually living tissue. Just under the bark is a thin layer of living cells called the cambium. Other living cells are found in the roots, the growing tip, buds and leaves. In terms of determining tree age, the tree trunk is the key.

• The cambium produces phloem cells, which transport food from leaves down to the roots, closest to the bark on its outside layer
• The cambium also produces xylem cells, which transport water and nutrients from roots to leaves, on its inside layer.
• Phloem continues to live for the life of the plant while xylem in trees lives only one season.
• The dead xylem forms the woody support structure of a tree.

Each year's growth of xylem provides:

• one light ring representing early spring growth with thin-walled large cells adapted for transport of large water quantities
• and one dark ring in the summer composed of thicker walled cells adapted for strength for supporting the abundant new growth from the spring and summer.

1. You can tell how old a tree is by counting the pattern of dark and light rings in the tree trunk. One light ring plus the neighboring dark ring constitute one year of growth for the tree.

• This method works well for dead trees.
• It can also be accomplished by the utilization of an increment borer. This borer needs to be longer than the radius of the tree. The borer takes a core sample to the pith in the middle of the trunk. Tree rings can be counted in this core sample and the tree is not permanently damaged.

2. It is still possible to closely estimate the age of a tree without counting rings. Knowing the species of tree and the tree's circumference will allow for a fairly accurate determination of age.

• Determine the correct species of tree.
• Wrap a tape measure around the tree trunk about 4½ feet above the ground, measuring the circumference of the trunk in inches.
• Multiply the tree's circumference by 3.14 to determine the tree's diameter in inches.
• In the chart below, find your tree's growth factor and multiply it by the tree's diameter.

For a sugar maple:

Step 1: circumference=5 feet 4 inches

Step 2: its diameter=64 inches / 3.14 = 20.4 inches

Step 3: 5.0 (growth factor)x 20.4 inches (diameter) = 102

Therefore, this sugar maple is about 102 years old.

Nix, Steve. About.com Forestry. Using the Annual Tree Ring to Determine Tree Age, 2012.

Journey North. Signs of the Seasons. How Old is Your Tree?. 2012

Royal Forestry Society. Tree Biology. How Trees Grow. 2012