Well, I dunno. I have had to make fires on several occasions when it was really critical, and I have always gone with small stuff - usually something I could break by hand, by stomping, or by dropping a large rock. Worked every time. In my youth, I routinely cooked over open fires, employing the same techniques. The best use for a saw in my experience has been to clear out a helispot.

Even then on one memorable operation, as I was dutifully setting about to fell a nice healthy pinon (8" diam.) my companions persuaded me to try and just push it over. Moral of the story: A motivated rescuer is better than any tool.

Of course, it is true what is said about sawing - it warms you twice - once when you are cutting, and again when you burn it.