Old-growth forests have a complex structure, meaning that there are components important to wildlife at every level from the forest floor to the tops of the tallest trees. This multi-storied environment can be seen here with groundcover, logs, understory plants, small trees, mid-sized trees, tall trees, and branches at all levels in the canopy. This is different from a structurally simple managed forest that consists primarily of tree trunks and an upper canopy, because the trees are of uniform age, densely spaced, and don't allow sunlight to penetrate. This makes a huge difference to forest-dwelling animals. Photo © copyright by Stephen Penland.