Lot of confusing information in this thread. White birch, which I have also heard called paper birch, Betula papyrifera, is a pretty solid fast-growing hardwood species here in the Northeast USA. It tends to be a pioneer species and dies when it becomes heavily shaded. In my experience, when the trees die, they fall within a year and rot to pulp within another year. The bark is waterproof and holds in moisture. I have pulled white birch out of a stack of dry and solid mixed hardwoods that were sitting for about six years, and the birch logs, unsplit, could literally be broken in half or crushed with one's hands. No structural integrity left. However, if properly split and dried, white birch will remain viable for several years and makes an excellent firewood, BTU content roughly that of red maple or black walnut, and slightly better than cherry. I like using white birch as firewood and harvest the trees as soon as I see a fair number of dead branches - it is a good sign they are not long for life. Anything larger than 4" gets split at least in half, the smaller stuff tends to season acceptably while unsplit.
Yellow birch and black birch behave much differently and are better species for firewood. They both have a distinct smell of wintergreen when freshly cut, black more than yellow, and are harder and heavier than white. Yellow birch has a distinct appearance, somewhat of a gold-colored shaggy bark that peels slightly. Black birch, especially when young, can be mistaken for cherry, but is obvious when cut.
I would be perfectly satisfied if I had nothing else to burn for firewood but the various species of birch.