The American beech tree is found in the Eastern regions of the United States; it once flourished as far west as California. Beech trees are susceptible to 70 varieties of fungus, flooding and temperature fluctuations. Temperatures below minus-40 degrees Fahrenheit can kill a tree. Despite the many damaging agents, beech trees have been recorded as old as 300 to 400 years of age, according to the USDA forest service. One of the oldest know beech trees in the U.S. is a 366-year-old Pennsylvania tree. Research into the tree girth and age of many beech trees reveals a standardised way to tell a beech tree's age.

Measure the height of the beech tree from the base to 50 inches up from the ground.

Make a small mark at the 50-inch height with your chalk.

At the 50-inch height mark you measured in Step 2, measure around the girth of the tree with your measuring tape. The girth of the tree is the measurement all the way around.

Calculate the age of the tree. If the girth of the tree is less than 157.5 inches, multiply the girth by 0.45. If the girth is more than157.5 inches, multiply by 0.5. For example, if your tree is 321 inches around, 321 x 0.5 = 160.5 years old.