It's important to keep in mind with very old wooden structures such as these that they are often rebuilt over the centuries, plank by plank, as it were.

From the Wikipedia entry you cited:

> A very important problem in dating the churches is that the solid ground sills are the construction elements most likely to have the outer parts of the log still preserved. Yet they are the most susceptible to humidity, and as people back then reused building parts, the church may have been rebuilt several times. If so, a dendrochronological dating may be based upon a log from a later reconstruction.

Boat builders reckon the answer is to build from Kauri or Huon Pine - both of which are extremely slow-growing, over logged in the past, and now on protected species lists. There's actually an industry in Tasmania of harvesting Kauri from swamps and riverbeds, and selling it as craft timber...