Douglas-fir is currently the most prevalent forest type in Idaho. It can be found in extensive pure stands, either even- or uneven-aged, or in mixture with a wide range of other species.
Statewide, the amount of Douglas-fir cover type has increased modestly over past decades. Rather large increases have occurred in some areas, however, such as in the Northern and parts of the central Rockies where it has replaced western larch and western white pine on many sites. It also has become the predominant species in locations throughout the state where ponderosa pine has decreased.
Successful fire control during the 20th century has increased stand densities in some warm, dry Douglas-fir types and created fuel ladders where large intense fires may result. In addition, successful fire control has increased the area occupied by Douglas-fir by allowing it to invade dry sites that were formerly grasslands maintained by fire.
These changes in forest composition have favored a number of native insects and diseases, defoliating insects, dwarf mistletoes and root rots. These are discussed further in the “issues” section of the report.
Widely distributed throughout the western United States and Canada, Douglas-fir is not a true fir at all, but, instead, a close relative of the hemlock.
The Douglas-fir is distinguished by its compact, conical crown with sloping side branches. The species features needles of about 1.5 inches in length sticking out in all directions from its branches, and “shaggy” looking seed cones which are 3 to 4 inches long. The bark of young Douglas-firs is smooth and gray. When the trees mature, the bark becomes dark, thick, and furrowed.
This species grows rapidly, attaining a height in the Idaho forest of from 100 to 130 feet and a diameter of up to 3 feet. (Douglas-firs found in moister Pacific Coast forests grow to heights of 250 feet and diameters of 8 feet.) Prized for its strength, Douglas-fir has long been preferred for use in structural framing lumber.