Douglas fir, Douglas-fir, Douglas tree – Pseudotsuga

Trees & Shrubs – Pseudotsuga /ˌsjdˈtsɡə/ is a genus of evergreen coniferous trees in the family Pinaceae. Common names include Douglas fir, Douglas-fir, Douglas tree, and Oregon pine. Pseudotsuga menziesii is widespread in western North America and is an important source of timber. The number of species has long been debated, but two in western North America and two to four in eastern Asia are commonly acknowledged. Nineteenth-century botanists had problems in classifying Douglas-firs, due to the species’ similarity to various other conifers better known at the time; they have at times been classified in Pinus, Picea, Abies, Tsuga, and even Sequoia. Because of their distinctive cones, Douglas-firs were finally placed in the new genus Pseudotsuga (meaning “false hemlock”) by the French botanist Carrière in 1867. The genus name has also been hyphenated as Pseudo-tsuga.

The common name Douglas-fir honours David Douglas, the Scottish botanist who first introduced Pseudotsuga menziesii into cultivation at Scone Palace in 1827. Douglas is known for introducing many North American native conifers to Europe. The hyphen in the name indicates that Douglas-firs are not true firs, not being members of the genus Abies.

By far the best-known is the very widespread and abundant North American species Pseudotsuga menziesii, a taxonomically complex species divided into two major varieties (treated as distinct species or subspecies by some botanists): coast Douglas-fir or “green Douglas-fir”, on the Pacific coast; and Rocky Mountain Douglas-fir or “interior Douglas-fir”, in the interior west of the continent.

Edward Step on Douglas Fir (classification has changed since his days)

Douglas-fir-Pseudotsuga Douglas fir, Douglas-fir, Douglas tree - Pseudotsuga
Douglas fir – Pseudotsuga –

A, female flower; B, male flower.

The Douglas Fir (Pseudotsuga douglasii).

Although the name of this tree in English and Latin might reasonably lead one to suppose that David Douglas, the intrepid botanical explorer, was the discoverer of it, that is not really so. It was Archibald Menzies who first made it known to science, by means of herbarium specimens collected in 1792, when, as the companion of Vancouver, he visited the western coasts of North America. But Douglas, in his capacity of collector to the Royal Horticultural Society, landed at Fort Vancouver on the Columbia River in 1825, and not only sent home herbarium specimens, but seeds also, of this and several previously unknown Conifers. It was by means of these seeds that the Douglas Fir was introduced to Britain. It was already known by Lambert’s name of Abies taxifolia, but Dr. Lindley, a short time previous to Douglas’ untimely death, selected the tree as a suitable and enduring memorial of the enormous services Douglas had rendered, and named it Abies douglasii. Since then Carrière has split up the old genus Abies and placed douglasii in the new genus Pseudotsuga.

Douglas-fir-Pseudotsuga-trunk Douglas fir, Douglas-fir, Douglas tree - Pseudotsuga
Douglas fir – Pseudotsuga – trunk

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.

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 mostlyin 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.

Douglas-fir-Pseudotsuga-in-summer Douglas fir, Douglas-fir, Douglas tree - Pseudotsuga
Douglas fir – Pseudotsuga in summer

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.