This past weekend I discovered a couple more Yellow Birch. Each often begins life as a seedling germinating on a rotting stump.
As the seedling grows, the stump continues rotting into the forest floor. Meanwhile, the birch's roots are extending. At some point, the roots establish while the rest of the host rots away. What's left is a Yellow Birch that appears to be standing up out of the ground.
The first specimen we viewed some time ago did not exhibit this behavior and I'd been on the lookout since that first discovery. A very cool find indeed!