Under the most favourable natural conditions, as around Puget Sound and on the western slopes of the Sierra Nevada, the Douglas Fir grows to a height of 300 feet, with a girth of 30 to 40 feet, but on the drier slopes of the Rocky Mountains it is not more than 100 feet high. In Colorado, forests of Douglas Fir are found at an elevation of 11,000 feet. The tree has not been sufficiently long established in this country to say what dimensions it will reach, though it appears to have taken kindly to Ireland and to Devon and Cornwall, where the rate of growth of young trees is about 30 inches per annum. There are plenty of trees in these islands, planted about the year 1834, which have reached or passed 100 feet, and there is no doubt that towards our western coasts this height will be greatly exceeded. Some of these trees have long since produced cones, and from their seeds many young trees have been raised.
[Illustration: Douglas Fir. A, female flower; B, male flower.]
The Douglas Fir is of pyramidal outline, with the lowest branches bending to the ground under their weight of branchlets and leaves; above, they spread horizontally, but the uppermost are more or less ascending. The branchlets are given off mostly in opposite pairs, densely clothed with slender, rich green leaves, ¾ to 1¼ inches in length, paler beneath. They endure for six or seven years, and are arranged in three or four ranks. The male flowers will be found clustered at intervals on the underside of the previous year's shoots, whilst the cones are formed at the tips of the lateral branchlets, and hang downwards. These cones are somewhat elliptical in outline, from 2½ to 4 inches long, with large scales, and from the back of each there extends a three-clawed bract, whereof the middle claw or awn is very long. Several well-marked varieties of the Douglas Fir are also to be met with occasionally in parks and gardens.
The Douglas Fir produces excellent timber, and is a most valuable forest tree, not only on that account, but because of its adaptability to varying conditions of soil and climate. It is the most widely distributed of all American forest trees, and the area of its distribution is spread over thirty-two degrees of latitude, and from end to end of this range it has, in the words of Sargent, "to endure the fierce gales and long winters of the north, and the nearly perpetual sunshine of the Mexican Cordilleras; to thrive in the rain and fog which sweep almost continuously along the Pacific coast range, and on the arid mountain slopes of the interior, where for months every year rain never falls." It appears to thrive best where the air is humid and the soil well drained. It begins to bear cones about its twenty-fifth year. The straight tapering trunk is largely used for the masts and spars of ships, its suitability for this purpose being evident to all visitors to Kew who have gazed at the flag-staff set up in the arboretum. This pole is 159 feet long, with a circumference of 6 feet at the base, tapering to 2 feet 2 inches at the top, and weighing about 3 tons. It was brought from Vancouver Island, and an examination of its rings before it was set up showed that it represented the growth of about 250 years. The full life of the Douglas Fir is estimated to be about 750 years.