Once you have determined a forest stands overstory dominant
species and their mean average diameter, you can then ascertain
the stands approximate age.
There is a positive correlation between tree girth and tree age.
Growth rate however, varies considerably between species. Tree
health, soil, climatic and site conditions also have a significant
effect on the rate of growth.
Annual rings afford the best method of determining tree age
1 Trees grow in diameter by adding a new layer of wood
each year between the old wood and bark. The formation of this
layer continues throughout the growing season. The woody tissue
formed in the spring (springwood) is more porous and lighter in
color than the woody tissue formed through the summer (
summerwood). Thus, the annual growth of a tree appears on a cross
section of the stem as a series of concentric rings. A count of
the number of rings on a given cross section gives the age of a
tree.
On standing trees an increment borer may be used. This consists
of a hollow auger bit that is screwed into the tree. The radial
core of wood that is forced into the hollow center of the bit is
removed with the extraction. The number of annual rings on the
core gives the age of the tree.
Another less exacting method to determine a stands age is using a
simple formula published by the International Society of
Arboriculture.2
First, determine tree diameter in inches measured at 4 1/2 feet
above ground level. Remember that diameter equals circumference
divided by 3.14. The following table assigns a factor number to
various species. Multiply the diameter in inches by the
appropriate factor to determine the estimated tree age.
Determining Tree Age
( Factor x Diameter = Tree Age )
| Tree Species |
|
Factor |
| Acer rubrum |
Red Maple |
3.0 |
| Acer saccharinum |
Silver Maple |
2.0 |
| Betula nigra |
River Birch |
3.0 |
| Carya ovata |
Shagbark Hickory |
7.0 |
| Fagus grandifolia |
American Beech |
6.0 |
| Fraxinus americana |
White Ash |
4.0 |
| Fraxinus pennsylvanica |
Green Ash |
3.5 |
| Juglans nigra |
Black Walnut |
3.5 |
| Liquidambar styraciflua |
Sweetgum |
4.0 |
| Liriodendron tulipifera |
Tulip Poplar |
2.5 |
| Pinus strobus |
White Pine |
4.5 |
| Platanus occidentalis |
Sycamore |
3.5 |
| Prunus serotina |
Black Cherry |
4.0 |
| Quercus alba |
White Oak |
5.0 |
| Quercus coccinea |
Scarlet Oak |
4.0 |
| Quercus palustris |
Pin Oak |
3.5 |
| Quercus rubra |
Northern Red Oak |
3.5 |
| Ulmus americana |
American Elm |
3.0 |
Example
White oak is the overstory dominant species in a hypothetical
stand, with a mean average diameter of 18" d.b.h.
white oak factor 5.0 x 18"d.b.h. = 90 yrs. old
The forest stand is estimated to be 90 years old.
Everything growing beneath the overstory is
performing in response to the dominance of the oaks,
in that, the overstory often drives, directs and
dictates forest community structure below itıs canopy.
Forest Measurements, Avery and Burkhart, 1983, Pages 86-87
2 Valuation of Landscape Trees, Shrubs and Other Plants, International Society of Arboriculture, 1988, Pages 33-34
