[Spruce]

Too many moose can produce a spruce forest. When aspens, birches, and willows are eaten away by hungry moose, young spruce thrive without competition. Once a spruce forest has taken hold, both beaver and moose must move on.

[RightWhale]

When aspens, birches, and willows are eaten away by hungry moose

Moose don't eat aspen. It's rabbits that eat aspen. Moose eat willow, and they do this because of the analgesic properties of the bark. Moose have really big headaches. Nobody eats birch except by accident and they don't make that mistake again.