From what I understood "old growth" to mean is that the maple tree that the wood was taken from had a long time to mature and grow before it was harvested for lumber at least 150+ years old.
As a tree grows, they have those concentric circles that form. This makes them wider (and hopefully taller depending on enviromental factors)and as they grow. Now as a tree gets wider, the space arround these rings gets smaller and smaller. This is what creates shafts with more rings per inch. The wood taken from the outer side of the tree will have more rings than the wood taken from closer to the center. They are both still "old growth" and may be from the same tree but have less rings. If you ever seen a cut tree stump you will see these rings and how they grow. Old growth maple is denser than newly formed maple.
Now counting only rings does not always work. And here is why, if a tree is starved of nutrition or growing in harsh conditions, it will not grow as quickly or as big as a tree with proper nutrition. These trees will have smaller spaces between the growth rings also (more rings per inch) but gre in harsher conditions. This is similar to bonsia trees. The wood here may not be as good even though it has many growth rings. It may not be as dense.
Wood that has been underwater for a century certainly can be "old growth" because they were harvested when the trees had a long time to grow. But so can the tree that is still alive in Georgia that has had centuries of good light and nutrition.
Now I do not want to take credit for all of this information, Qbilder provided an excelent post about it at EPT http://www.easypooltutor.com/modules.php?name=Forums&file=viewtopic&t=8819
As a tree grows, they have those concentric circles that form. This makes them wider (and hopefully taller depending on enviromental factors)and as they grow. Now as a tree gets wider, the space arround these rings gets smaller and smaller. This is what creates shafts with more rings per inch. The wood taken from the outer side of the tree will have more rings than the wood taken from closer to the center. They are both still "old growth" and may be from the same tree but have less rings. If you ever seen a cut tree stump you will see these rings and how they grow. Old growth maple is denser than newly formed maple.
Now counting only rings does not always work. And here is why, if a tree is starved of nutrition or growing in harsh conditions, it will not grow as quickly or as big as a tree with proper nutrition. These trees will have smaller spaces between the growth rings also (more rings per inch) but gre in harsher conditions. This is similar to bonsia trees. The wood here may not be as good even though it has many growth rings. It may not be as dense.
Wood that has been underwater for a century certainly can be "old growth" because they were harvested when the trees had a long time to grow. But so can the tree that is still alive in Georgia that has had centuries of good light and nutrition.
Now I do not want to take credit for all of this information, Qbilder provided an excelent post about it at EPT http://www.easypooltutor.com/modules.php?name=Forums&file=viewtopic&t=8819