The lower elevations of the Olympic mountains, from roughly up to - , feature the western hemlock zone, so-called because in most of the zone, the climax tree species would be western hemlock, even though much of the area is dominated by Douglas-fir. The reason for this is that Douglas-fir is an early seral species, and reproduces primarily after disturbances such as fire, logging, landslides, and windstorms. Western hemlock does not reproduce well on disturbed, exposed soil but germinates under the canopy of Douglas-fir, eventually overtaking the forest by shading out the Douglas-fir, which cannot reproduce in shade. In this zone, despite the high annual precipitation, drought stress in summer is sufficiently severe to limit growth of many species, such as Sitka spruce. Hardwoods such as bigleaf maple, willows, and red alder are limited to disturbed sites and riparian areas. red-cedar grows in the wettest sites. A very small area of the northeastern rain shadow contains the limited Douglas-fir zone, where it is too dry for western hemlock.