Larry, you've received good advice so far. As you can see, one way of playing in G is to tune DGD.
I don't do that, but I don't have as much experience with different tunings as Robin and Rob do. I mostly tune to DAd for 90 percent of what I play. But that does allow me--with the aid of a capo--to play in most common keys.
I play semi-regularly in a multi-instrument jam. At most bluegrass, folk, and old-timey jams, the most common keys are C, D, G, and A.
To get the key of C, I just tune to CGc.
To get D, I tune DAd. And then in that tuning I use a capo at the 3rd fret for the key of G and a capo at the 4th fret for the key of A.
You can play in G and A out of a DAd tuning, but it takes a better understanding of the fretboard than I have. But using a capo enables me to play everything I know and forget about what key we're in.
My experience is that there are a huge number of variables which affect the sound of a dulcimer, and that the kind of wood is pretty far down the list. A competent luthier can make almost any wood (or even cardboard, plastic or Legos) sound the way you want by adjusting any of a number of variables such as bracing, cubic sound box area, VSL, break angle of strings, details of fretboard construction, etc., etc.
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