This is an odd way of timing things. I love the term "dendrochronology". Apparently there is more growth in the spring so the wood is less dense and lighter. Later in the year, the opposite is true and a darker section is formed. I believe that you can tell what kind of a year it has been by the relative amounts of growth. I forgot to see if these photographs were of the same species. I suspect not because I think that the rings are wider in the bottom picture which might represent a faster growing tree. These sorts of ideas are useful in analysing things like climate change.
