My answer in How Did They Warm Baths Before Electricity? mainly employ the sources from Medieval Iceland.

I can't answer this, but wanted to share something I noticed in Iceland when I visited in the end of May.

While travelling out of the West Fjords (I don't remember the precise area), we noticed that beaches where littered with logs and wood. I'm guessing the ocean current brought it there, but noticed that locals used this same kind of wood to build fences and what not. Wouldn't suprise me that some also use it as firewood. Now this would be specific to this area, but I thought it was an interesting tidbit.