Here's an interesting new news story about the wood Stradivarius and the other 17th century makers had to work with:

Secret Ingredient in Stradivarius Violins May Be Heaven Sent

In brief, climatic history of Europe shows it was very cold from 1645 to 1720, so tree growth was slow at that time--producing dense, tight-grained wood which produces superior soundboards.

Since that's the same reason Sitka spruce is favoured for guitar tops, this makes sense. It is not presented as the whole reason for the magic of these instruments, but certainly, having a good supply of particularly high-grade wood to choose from would be a huge advantage for a luthier skilled enough to know the best.

W-O