Every tree has a story to tell

The growth rings in the wood used to make the violin were beautifully visible, all 109 of them. Grissino-Mayer and his colleagues measured each one several times. Their conclusion? The wood is Norway spruce from the Italian Alps. It grew between 1577 and 1687. Stradivari lived from 1644 to 1737.

The violin, very possibly, is worth the money - but not necessarily. Knowing how old the wood is doesn't tell you when a wooden object was made. Tree-ring dating does not date the object, only the wood. All that Grissino-Mayer will say for sure is that the violin's wood dates from Stradivari's time.

In fact, "Very often [the] best violin copies were made with very old wood," says Roman Barnas, head of violinmaking and restoration at North Bennet Street School in Boston. Even today, the kind of wood the Italian masters used - wood of the right age and region - can be obtained from old buildings.

Ron Spronk of Harvard University in Cambridge, Mass., had a similar quest. A research curator at Harvard's Straus Center for Conservation, Mr. Spronk is investigating paintings on wood at three different museums in Belgium and the Netherlands. Spronk suspected that they were once a triptych - a three-paneled painting - done by a Renaissance Flemish painter. Dendrochronological tests told him that the panels were cut from the same tree. Spronk still needs more information to prove that the three paintings were once one, but the tree-ring evidence has strengthened his case.

Dendrochronology may not completely answer questions about the past, but it can make the past clearer. With historic houses, for example, tree-ring dating can stand tradition on its head.

Dendrochronology, used with documentary research (looking at old papers) and archaeology, can shed light on the lives of the people who lived in a particular building, according to Anne Grady. She's an architectural historian and preservation consultant. Over the years, she has done research and planning for more than 60 dendrochronological studies of old buildings in New England, including old homes.

In only one-quarter of the cases, the building studied was as old or older than its supposed date. The other 75 percent of the time, the building studied was more recent than it was thought to be, sometimes by 30 or 40 years.

"Some building owners were clearly disappointed," Ms. Grady says. "I understand how they feel. There is a cachet attached to having a very old building."

Take the Robert Pierce house in Dorchester, Mass., near Boston: "It had been recognized for generations as being built in the 1640s or 1650s," says Historic New England's Peter Gittleman, who organizes public tours of Colonial-era houses. When dendrochronology changed the date [to 1683], we lost Robert. He never set foot in the house; he'd died before construction. It's amazing how many signs we had to change."

When it comes to forest fires, there are good ones and bad ones.

Conventional wisdom once held that all forest fires were bad. Every forest fire - whether started by lightning or by human carelessness - was put out quickly. But it gradually dawned on forest managers that some fires were helpful. "Burns" are a natural part of a forest's life. Without periodic small fires, leaf litter and twigs build up on forest floors. All that fuel leads to hotter, more dangerous fires. Henri Grissino-Mayer calls them "forest killers."

Professor Grissino-Mayer specializes in forest fires: "Before the 19th century," he says, "fires cleaned the forest. Now they don't - there are more intense wildfires. We have changed the balance of nature."

The National Park Service and the USDA Forest Service have asked Grissino-Mayer and other dendrochronologists to research forest history. Fires leave scars in tree rings that can be dated and "read" to see how often naturally occurring fires happened. Using this information, scientists can figure out how frequently a forest should burn to keep it healthy.

"They want to condition the forests to burn the way they used to," explains Grissino-Mayer. "How often? You look at tree rings. When? Look at tree rings. How big should the fire be? You look at tree rings."

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