Purple heart partners DF mast. Recommend a species for the wedges?
Whatever you like......though some people will fit a softer species to act as a cushion and rather have the wedges take compression rather than a soft(spruce) mast. Cedar will probably be ok if you want something soft or just go with fir. Are you intending to leather or otherwise the mast around this point?
I have used douglas fir, western red cedar and cherry. The doug fir is too hard and mars a spruce mast , and sometimes even a doug fir mast. Western red cedar makes a lovely cushion for the stick, but can compress - even enough to fall out - when subjects to severe load. WRC also doesn't hold up well to the repeated insertions (with hammering) and removals of a small trailer-sailed boat. Not so much of an issue for a 'permanently' stepped mast. Cherry seems to me to be a nice compromise. Tough enough to hold up, yet smooth, soft, and resilient enough to be friendly to the mast.
"It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)
I used V.G. Redwood on my spruce mast (50' X 7 1/2" diameter at the partners). The mast has been pulled only once in five years. The wedges seemed to be holding up OK and didn't loosen in use, and there was no marring of the mast. YMMV.
I have yellow cedar for my 8 n a half inch fir tree mast. This is a place where sweet water may find entry and a bit of rot resistance is good.
Especially if , like mine,The mast does not come out .