Often the borer does not reach the center of the trunk, so the total number of years must be extrapolated from the radius of the trunk.
The radius (r) can be determined from the circumference of the trunk (C=2πr), or from special tape measures that give the diameter directly.
In this example, wood Sample D dates back to the year 1691.
According to Pascale Poussart, geochemist at Princeton University, tropical hardwoods have "invisible rings." She and her colleagues studied the apparently ringless tree (Miliusa velutina) of Thailand.
Their team used X-ray beams at the Brookhaven National Synchrotron Light Source to look at calcium taken up by cells during the growing season.
Close-up view of the increment borer, showing the slender wood core that is extracted from the trunk.
The core is sanded and treated with a wood oil to make the rings more distinct.
In addition, ring growth is not always annual, so a ring may be absent from a core sample. Chicago, IL: The University of Chicago Press, 1968.
These are some reasons why scientists can't rely solely on counting rings and must use crossdating from multiple samples to ensure accurate age determination. Republished by The University of Arizona Press, 1996. Web Sites NOVA Online—Methuselah Tree On this Web site, look at Methuselah and other bristlecone pines using Quick Time VR, learn how scientists date trees, discover the nature of longevity, and find out how photosynthesis occurs.
In the tropical rain forest, relatively few species of trees, such as teak, have visible annual rings.
The difference between wet and dry seasons for most trees is too subtle to make noticeable differences in the cell size and density between wet and dry seasonal growth.
A small core of the wood is removed and the rings are painstakingly counted.
This remarkable tree was approximately 1400 years old, and grew on this rugged mountain ridge during the time of Mohammed.
The rings are very close together and require magnification in order to count them.