The Texas cedar elm is the most widespread native elm in Texas, growing virtually everywhere except in the extreme southeastern corner of the state. These trees can thrive in most soil types and are extremely drought-tolerant. They can grow 90 feet tall and have a canopy spread of up to 80 feet. Unless you know for certain when a Texas cedar elm was planted, determining the age of one of these trees isn't an exact science; however, your results may be close to the actual age. Some methods of determining age are more damaging to the tree than others. The method you choose depends on how accurate you need your measurement to be, the location of the tree and the tree's overall health.
Locate a similar-sized tree that has been cut or fallen, and count the rings from the center of the trunk to the outer edge of the trunk. Each ring equals one year of growth. Because of the widespread growth of the Texas cedar elm, finding a fallen tree of a similar size might not be too difficult. The accuracy of this method is determined by how similar in size the fallen tree is to the tree you wish to know the age of.
Measure the circumference (the distance around the outside) of the tree whose age you wish to know at a height of 4.5 feet from the ground, if you do not have access to a fallen tree of a similar size. Divide the circumference by 3.14 (pi) to determine the diameter (the distance straight through the center of your Texas cedar elm). Then divide the diameter by 2 to get the radius (the distance from the outer edge of the tree to the center). Finally, subtract 1/2 inch from the radius to account for the thickness of the tree's bark to give you the true radius.
Find another Texas cedar elm that has fallen or been cut and measure how thick 10 growth rings are. Divide this measurement by 10 to get the average width of a growth ring for a Texas cedar elm in your area.
Multiply the average width of a growth ring by the true radius of your tree. The answer is a relatively accurate estimate of the age of the tree.
Use an incremental borer when a very accurate measurement of a tree's age is required. Follow the instructions that came with the incremental borer and bore into the tree the distance of the tree's radius as determined in Step 2 above. Carefully remove the core, which contains the growth rings.
Use a magnifying glass to physically count every growth ring from the center of the tree to the edge of the bark. This is the most accurate way to tell the age of the Texas cedar elm tree.