Dendrochronology and the Fenno House

I’ve been hoping to write about dendrochronology, simply because I like the word “dendrochronology.” And now the Old Sturbridge Visitor (the magazine for Old Sturbridge Village members) has published an article about dendrochronology. So today I’m going to write about dendrochronology.

Some of you might be wondering what dendrochronology is. (Some of you might already be sick of hearing about it.) Here’s a description for a presentation on the subject by William Flynt and Anne A. Grady:

Tree-ring dating (dendrochronology) is a scientifically accurate means of dating historic buildings by the tree-ring patterns in construction timbers. Dendrochronology was developed in the 1920’s and refined in succeeding decades but only recently has the technique become available for studying the early buildings in the northeast.

The scientific basis of dendrochronology is that all the trees in an area experienced the same weather over the course of a year. And, as we know, for each year a tree trunk grows another ring. Thus, all trees in a single region underwent, say, three lean years in which they didn’t grow much, then a year with lots of water which created a fat tree ring, then two medium years, another fat year, and so on. Those variations create a pattern that appears in all the nearby trees growing at that time. And that pattern is unique enough to that span of years in that place that a dendrochronologist looking at a piece of wood from a known region could say, “This part was growing from 1814 to 1832,” or whatever. (Just like a readout from a mass spectrometer, okay?)

Before dendrochronology was refined, many of New England’s historic houses were dated based on local traditions, spotty real estate records, and architectural features. One example was the Fenno House from Canton, Massachusetts (formerly part of Stoughton), which was moved to Old Sturbridge Village in the 20th century. At least as early as 1893, it was said to have been built in 1704, though there was no documentary evidence one way or the other.

Last fall, Old Sturbridge asked William Flynt, Building Conservator at Historic Deerfield, to examine the Fenno House. He

took samples from 13 different locations within the Fenno House, from timbers that appeared to have their outermost edges still intact (that is, the wood with the last annual growth ring still in place).

It turned out all the samples Flynt could date came from trees chopped down in 1724. That means the Fenno House must have been built after that year, probably soon after. Those logs certainly couldn’t have been assembled into a house in 1704 since they were still growing after that time.

Old Sturbridge Village depicts New England life in 1837, so it presents the Fenno House as the antique home of an antique widow, a householder who still spins her own yarn and dyes it with plants rather than buying machine-made materials. Therefore, losing twenty years from the life of the building doesn’t affect the interpretation one way or another. And now we have a solid scientific basis for stating that house is over 280 years old.

And what is that science? Dendrochronology, dendrochronology, dendrochronology!