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 gives 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 1,000 years.
The Ontario white cedars are remarkable, but we have at least five longer-lived species growing near here. Recorded ages are 1,824 years for yellow-cedar (aged from a stump near Sechelt), 1,400 years for red cedar, 1,350 years for Sitka spruce, 1,300+ years for Douglas-fir, 1,238 years for western hemlock, and over 1,000 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 learn of the incredible longevity of bristlecones.
In 1964, a Ph.D. student studying glaciation in a Nevada park set out to core a bristlecone pine. Unfortunately for the tree, the coring tool got stuck, and the student got permission to cut the tree down to retrieve his tool. Once back in his lab with sections of the newly-deceased tree, the student counted 4,846 rings -- enough to make it the oldest known organism on earth, and the silvicidal student about as popular as an overcooked broccoli.
Written by: Bob Brett