The diversity of age classes in an old-growth forest provides a rich understory and canopy of vegetation. The different levels of canopy allow sunlight to touch the forest floor in places. Eventually, the snags and logs decompose and become new soil. Some of the last extensive stands of old-growth forest left in the United States are the lowland forests of the Cascade Mountains. The greatest concentration of old-growth western red cedar in the North Cascades is found along the lower reaches of Big Beaver Creek below 2,000 feet.
Red cedars grow in moist habitats.
Thus, they are ideally suited to the North Cascades, where summers are cloudy and winters are mild. Tapering from heavily buttressed bases often over 10 feet in diameter, they rise 200 feet above the forest floor, balanced on a shallow, wide-spreading root system that provides stability in the wet valley soils. They are distinguished by their stringy, fibrous bark, which peels away in thin strips. Lacy sprays of flat needles give western red cedars a delicate appearance despite their great size. Another dominant tree of the river valleys is western hemlock .