Structurally, these forests are rather simple, generally consisting of two layers: an overstory and understory. Some forests may support an intermediate layer of shrubs. Pine forests support an herbaceous understory that is generally dominated by grasses and herbaceous perennials, and are often subject to ecologically important wildfires.
Temperate rain forests occur only in seven regions around the world: the Pacific temperate rain forests of the Pacific Northwest, the Valdivian temperate rain forests of southwestern South America, the rain forests of New Zealand and Tasmania, northwest Europe (small pockets in Ireland, Scotland, Wales, Iceland and a somewhat larger area in Norway), southern Japan, and the eastern Black Sea-Caspian Sea region of Turkey and Georgia to northern Iran. The moist conditions of temperate rain forests generally support an understory of mosses, ecosystem and are notable for trees of massive proportions, including Giant Sequoia (Sequoiadendron gigantea), Coast Redwood (Sequoia sempervirens), Douglas-fir (Pseudotsuga menziesii), Sitka Spruce (Picea sitchensis), Alerce (Fitzroya cupressoides) and Kauri (Agathis australis). These forests are quite rare, occurring in small areas of North America, southwestern South America and northern New Zealand. The Klamath-Siskiyou forests of northwestern California and southwestern Oregon is known for its rich variety of plant and animal species, including many endemic species.