Small trees and shrubs shoot upwards to create multiple layers of plants beneath the remaining large trees.
Large dead trees, both as snags and logs, are another important characteristic of old-growth forests. Decaying wood is a major source of food energy in these forests and provides homes for many animals.
Constant winter rains leach away nutrients, leaving poor, acidic soils behind. This forces trees to get most of their nutrients directly from the thin layer of organic material at the top of the soil. To do this, they enlist the help of some fungi. The food-gathering part of the fungus is a wide-spreading mat of fine hairs called the mycelium. When these fine hairs encounter tree roots and if the species combination is right, the fungus and root form a remarkable partnership. These partnerships are called mycorrhizae — literally "fungus root." The fungal side of the deal provides the tree with nutrients that the mycelium can extract from the soil much more efficiently than the roots. The tree in return gives the fungus sugars produced by its leaves. Without this partnership, most trees can barely stay alive, let alone grow to towering heights.