1 minute, 21 seconds

Dr. Chris Fastie says:

The annual rings vary in width. So every year, these trees grow a little bit in diameter. But it's not the same amount every year. So there are narrow rings and wide rings. Those ring widths are determined by a lot of things, including what happens around the tree-- if a neighbor tree dies, there will be resources released that will allow the tree to grow a little bit faster-- but most of these trees respond to the climate here-- whether it's a wet year or a dry year or a cold year or a warm year-- So that all of these trees have a similar pattern from year to year of wide rings and narrow rings. So when we measure the ring widths of the increment cores we're taking from the live trees, and these cross sections we are taking from the dead trees, we will have a chronology of ring widths that probably goes back 2 or 300 years. And there will be distinct patterns of narrow and wide rings. This dead tree will have the same pattern which we'll be able to match up with the chronology of ring widths, and that will tell us which years this tree was alive.