By: Bob Brett
Date: August 19, 2004
A tree grows pretty much like a big broccoli – both grow best with just the right combination of sun and rain. Unlike broccoli, a tree is long-lived and each year it’s alive it adds one growth ring. In good years, the ring is wide; in poor years, the ring is narrow.
Each ring is composed of rows of cells that look a bit like balloons squished like so: 00000000. Fast growth in spring and early summer causes individual cells in each row to stretch so much they lose some of their colour – the same way an uninflated balloon appears red, but turns pink when it’s blown up. Later in the year, when growth slows, cells are stretched less and are therefore darker.
Whether you’re looking at the wood grain on a salad bowl or a Scrabble piece, you’re looking at a history of tree growth. This same concept allows scientists to accurately count tree ages or determine when fires occurred. The width of rings also give a great deal of information about past growing conditions which has helped piece together climate patterns over many centuries.
Tree rings have proved that old trees aren’t necessarily big, a fact re-confirmed last decade by rock-climbing Ontario scientists. They noticed spindly little white cedars growing out of limestone cliffs on the Niagara Escarpment and decided to find out how old they were. After rappelling down, they bored the trees to remove knitting needle-sized samples, then counted the rings under a microscope. These tiny trees, most smaller than a 10 year-old Douglas-fir, were closing in on 1000 years.
The Ontario white cedars are remarkable, but we have at least 5 longer-lived species growing near here. Record ages are 1824 years for yellow-cedar (aged from a stump near Sechelt), 1400 years for redcedar, 1350 years for Sitka spruce, 1300+ years for Douglas-fir, 1238 years for western hemlock, and over 1000 years for mountain hemlock. But B.C. trees are teenagers compared to the oldest known trees in the world, the bristlecone pines of the southwestern U.S.
Here’s the sad tale of how the world came to know how long bristlecones can live. In 1964, a Ph.D. student studying glaciation in a Nevada park partially cored a bristlecone and found it was over 4,000 years-old. Unfortunately for the tree, the coring tool got stuck, the student got permission from the U.S. Park Service to cut the tree down so he could retrieve the tool, and that’s how the oldest tree ever found was aged – 4862 rings in all. Among tree ring scientists, as you can imagine, that silvicidal student is less popular than an overcooked broccoli.