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Sunday, 6 May 2012

Tree rings and climate measures

This was a puzzler box that I planned to include in one of the plants chapters in Australian Backyard Explorer, before we decided to drop the whole plants side. Oh well, here it is in the blog instead.

By the way, you can now have a good look at the book for free, courtesy of Google Books.

Part of one of the earliest descriptions of tracking
old weather by looking at tree rings, from Scientific
American, 10 September, 1859, page 178. You can
click on the image to enlarge it a bit (or use the link
below to view it online).
You can measure the age of trees by looking at the growth rings laid down each year. Tree rings form because the cells of wood formed in winter are smaller, which makes the wood look darker. In a bad season, the ring will not be as wide.

Professional scientists have tools that drill into trees to take core samples, but making holes isn't good for the tree, so you need to find a tree stump or a section of a log that you can cut. You may need to sand or smooth the surface with a plane or a sander, and the rings are clearer if you varnish the wood or rub grease into it.

Count the rings carefully, from the outside in. How old is the tree, if there is one ring each year? If you can get a second log from another tree, cut a few years earlier, see if you can match up the patterns of rings between the two trees. Matching rings is the basis of a clever branch of science called dendrochronology. Look it up, one rainy day.

As you can see from the article above, the idea isn't new. Here is a link to the complete article in Scientific American. The interface isn't the easiest I have ever used, and one of my friends even calls it user-ferocious, but I recommend it as one that is well worth persevering with.
A neat use of tree rings.
When a new painting by a famous painter suddenly appears from nowhere, everybody wonders if it might be a forgery, so the tests begin. Are the clothing fashions in the painting correct for the period, do the brush strokes go the right way for that artist? If they are correct, is the paint what it should be, or are there modern pigments? Is the canvas or wood under the paint right for the date of the picture? What do X-rays show us about how the layers were put in place?
A few years ago, a major problem arose with early English and Dutch paintings on panels of oak wood. Using what we know about tree rings, the wood in many well-documented Rembrandt works did not match the standard patterns of oak trees in western Europe, but the paintings were definitely Rembrandts, known and recorded since his time.
We now know that timber merchants in the Netherlands imported oak from somewhere around Poland or Lithuania, where the annual climate patterns were different, so the tree ring patterns were different as well.
If you plan to forge Rembrandts, you have to get oak from the right place and it has to be the right age. Then you must make up the right pigments, learn how to do the brush strokes, learn how to do the base coats, know about styles of dress from those times, and quite a lot more. It might pay less, but how about digging ditches as a career? It would certainly be easier!
There is an Australian aspect to this story as well.

The Dutch ship Batavia was wrecked off the West Australian coast in 1629, and some of the oak planks from the wreck have been tested by scientists from the Netherlands. The patterns show that these planks also came from Poland from oak trees that were acorns in about 1325!

But can you do some detective work like that in your garden?

A footnote added  May 17: I came across a mention today of alleged Stradivarius violins being declared a fake, based on tree-ring analysis, somewhere in Germany.  I couldn't find a link to that, but I did find this story from the University of Arkansas: Summary: "We can’t confirm that this is a Stradivarius, but we can say that it’s in the right time frame."

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