Another interesting factor R2, which contributes to Don’s thoughts above about the true complexity of the situation.
I did a fair bit of reading this winter about fur trapping in this area (I live not far from Yellowstone as the crow flies) and from what I could gather, historically there weren’t many beaver within the current boundaries of the park. Most of the trapping seemed to happen at lower elevations outside of the present-day park – Teton Valley, the Madison and Yellowstone Valleys, etc. Trappers explored the plateau, and used it when it was passable to cross from one trapping area to another, but they didn’t seem to spend much time trapping within it, and I’m sure they would have had there been good populations of beaver. I could be wrong on this, but that was my impression from the sources I read.
So beaver impacts within Yellowstone could be a more recent phenomena as well, or at least more widespread in parts of the park that didn’t used to support them.
We tend to think of Yellowstone as a vision of primal, intact wilderness, and while it may be compared to much of the rest of the lower 48, the reality is obviously more complicated than a mere “vision of the way it used to be.”
