Deep in the woods below Mount Saint Helens, a short boardwalk traverses a natural mosaic of green and black. As beautiful as it is, it might be hard at first glance to see both forests mentioned in the site’s name. The two forests of this trail are not separated by biome type or ecosystem, but instead by centuries of history. One is the forest you see today, verdant with Douglas fir and moss. The other is just a shadow of its former self—the remains of the previous environment, destroyed in…