A neighbour 2 doors down from my Dad had to cut down one of his giant maple trees a few years back. It had died. I was checking out the stump afterwards, counting the rings. I estimated that the tree had been around 200 years old. Amazingly enough, the width of the rings were fairly even in size.
Last weekend I was at a friend's house. He had trimmed up his neighbour's Mulberry trees last year and I had asked him to give me the trimmings as I wanted to use them for the base of my small Hugelkulturs (no dig garden beds). Mulberry's are leguminous trees and give nitrogen back to the soul. I was looking at the trunks of these Mulberry's and I said to my friend, "I estimate those trees are anywhere from 10 to 20 years old."
He looked at me with a rather surprised look on his face. He said "Yes. Actually, they are 16 years old." Once you know roughly how big a tree ring is for each year, you get to know the age of a tree just by sizing up the circumference of it's trunk.
What is truly amazing about trees is that what you see above ground is just a fraction of what is actually going on. Their roots are part of a massive underground network. Nutrients from one tree do transfer to nearby trees. They are also an integral part of our air and water systems on Earth.
To paraphrase Bill Mollison about forest systems:
"We don't think of this as being stable in the sense of a conrete building or concrete road. It's stable in the sense of constant adjustments like when you ride a bicycle. It has a dynamic stability. It's not like a machine where we can screw on fittings or put wires between part of the system. Here we rely on a fungus to do its job to make the connection. Therefore, if we lose the forests, we lose our only instructors. There are 100s of thousands of things to learn in here. And people must see these forests and wilderness as the greatest education system we have on this planet.
We could lose all the universities, and we would lose nothing. But If we lose the forests, we lose everything."