Saturday, April 11, 2009

Old Growth Timber

Old growth timber is one of those terms you run across on occasion but almost never hear defined. For the cabinet maker and timber frame carpenter old growth timber is the ideal medium for strong and stable furniture and framing. But what exactly is old growth timber?

Once upon a time in the forest primeval white pine and other trees grew close together in dense stands of timber. Since light was scarce under the thick canopy of leaves and pine boughs, young trees grew slowly but very straight as they strove to reach the sunlight far above them. Since there wasn’t much light near the ground, trees expended little energy growing branches and leaves low on their trunks. As a result the trunks of old growth trees were not covered with knots and produced clear lumber when milled.

The slow growth means growth rings were very thin, so the wood is very dense and stable. Another product of slow growth was a much higher percentage of fine heartwood. White pine was especially straight grained with little wane (i.e. the natural taper to a tree trunk) because the trees grew straight up to reach the sunlight of the canopy above.

In comparison to lumber sawn from true old growth timber, lumber today less dense, straight grained and much more liable to twist and warp. Below is a cross section of the sill from an 1882 depot from Chaksa, MN. This example has up to 20 growth rings per inch and is quite heavy and dense. Much pine harvested today has around 6 to 10 rings per inch and is far less dense in comparison. Anyone who has sorted through a pile of twisted, wracked and warped lumber at a lumberyard or supplier can appreciate the qualities of the old growth timber. It is little wonder that even some the most hastily built furniture from the 19th century survives with so little warping, splitting and decay.

Since virtually all of the old growth timber was harvested in the eastern U.S. and most of the remainder is now protected, old growth is now salvaged from building demolitions and remodels. A fair amount is also being recovered from lake and river bottoms where logs sank during the 19th century. Unlike the 19th century, when it was used for the most mundane purposes, old growth is scarce and expensive and used only for special projects.

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