The Urban Reality
As John Paul Sanborn stated, "...this is assuming a minimum average ring density of 8 per inch. In old growth trees with very tight grain this would not work."
One should really take to account the words 'this is assuming'. In an urban setting there are so many variables that could account for non-typical growth in plants, not to mention your oak tree.
An urban soil can be defined as a soil material having a non-agricultural, manmade surface layer more than 50 cm (approx. 1-2/3 feet for the American readers) thick, that has been produced by mixing, filling, or by contamination of land surfaces in urban and suburban areas. Therefore, a tree's ability to grow in a typical, natural fashion could be hindered by soil structure modification and compaction, restricted aeration and water drainage, interrupted organic matter and nutrient cycles, foreign contaminants, and increased soil temperatures. This is only a scrap in the surface of problems man has created in an urban environment.
Therefore, if a tree has been stress by any one or multiple numbers of the pre-described environmental alterations, false predictions could be made when attempting to accurately age a tree. Therefore, without actual removal of the tree and counting the annual growth rings or by turning to extracting a radial core of wood with an increment borer, one can honestly say that the prediction is simply that...............a prediction.
Urban Forests have made the jobs of arborists everywhere a trying and complicated science. This personally is what drives me to continually learn more. We, as the collective group of arborists, can look forward to an ever changing urban environment and thus more headaches down the road. Personally, I can't wait until the next challange knocks upon my door!
Shane Freeman