Thus, over centuries, western hemlock and western redcedar will come to dominate the canopy. Douglas-fir is a seral species in the wet forests of western British Columbia, Washington, Oregon, and California. In these areas it requires a large disturbance, such as fire or a large landslide, to open the forest and expose mineral soil where its seedlings prefer to establish. It has a faster growth rate than most other trees, giving the Douglas-fir a competitive advantage when it overtops slower growing species during re-establishment of the canopy. The tree ring ages of dominant Douglas-fir trees can indicate the date of the last stand-replacing fire. Because Douglas-fir is long-lived, it can remain dominant in the forest for more than 300-years following the last fire. A history of fluctuating climate resulted in synchronous fire episodes across western Washington and Oregon, thus many Douglas-fir stands date to a warm-dry periods in the late 1400s and early 1500s, while few date to a cool-wet period from 1650 to 1800. Douglas-fir is also particularly well adapted to fires: once they reach around 100 years in age they have thick enough bark that protects the cambium layer of the tree from heat damage. Large Douglas-fir often survive low intensity forest fires. Such sites, common in western Oregon, have two or three cohorts of Douglas-fir, adding to the complexity of the old-growth forest. Fire is increasingly rare northward towards the central coast of British Columbia where Douglas-fir is a minor component of the forest. The logging practices of the last 200 years created artificial disturbances that allowed Douglas-fir to thrive. The Douglas-fir's useful wood and its quick growth make it the crop of choice for many timber companies, which typically replant a clear-cut area with Douglas-fir seedlings. The high-light conditions that exist within a clear-cut also naturally favor the regeneration of Douglas-fir, though in wet coastal climates alders and shrubs compete with Douglas-fir seedlings. Because of clear-cut logging, almost all of the forests west of the Cascade Range not strictly set aside for protection are today dominated by Douglas-fir, while the normally dominant climax species, such as western hemlock and western redcedar are less common. On drier sites in California, where Douglas-fir behaves as a climax species in the absence of fire, Douglas-fir has become somewhat invasive following fire suppression practices of the twentieth and twenty-first centuries; it is becoming a dominant species in many oak woodlands, in which it was previously a minor component.