SILVER FIRS (Abies pectinata)
The silver fir sows itself very freely in places where the ground herbage is not so rank as to choke the young plants; but to allow natural reproduction a fair chance, ground game must be rigorously excluded, for deer, hares, and rabbits seem to regard this delicacy in much the same light as human beings do asparagus. This tree—Abies pectinata (I must resort to Latin to distinguish it from the other European, Asiatic, and American silvers) differs from every other member of the genus (so far as my observation goes) in being a shade-bearer; that is, it will grow under the shade and drip of deciduous trees, so dense as to be fatal to the health, and generally to the life, of every other conifer except the juniper. This renders it of almost unique utility for under-planting, the beech being its only rival for that purpose. It is true that the Douglas fir and the giant Thuja both stand a considerable amount of side shade, but the silver fir thrives under conditions of overhead drip which the others cannot suffer. One may read in books on forestry that the Norway spruce is patient of overhead shade; I can only say that, though I have sought diligently for an instance of its doing so, and have seen many thousands of spruce planted in faith of this misleading advice, I have never found a case where the attempt has succeeded.
In planting silver firs it is important to take advantage of their power of bearing shade, for the young trees are very susceptible of injury by late frost, from which older and taller woodland will protect them. It is remarkable how long and patiently the young silvers so treated will wait for head-room—marking time, as it were, till the older crop is cleared away, when they will go ahead and occupy the ground.
The silver fir is more exacting in the matter of climate than in that of soil. The great forest of the Vosges is chiefly on silicious ground; but that of the Jura, which is even finer, grows on limestone. The great silver firs at Rosneath, probably the oldest in the United Kingdom, stand near the sea level in deep sandy soil. They are certainly over 200 years old, the largest being about 110 feet high and 22 feet 7 inches in girth. These trees are very massive, and branch into great heads owing to their not having been grown under conditions of close forest. The only rival in bulk to them is to be found at Ardkinglass, on Loch Fyne, about 120 feet high, and estimated to contain over 1,000 cubic feet of timber.
In many places on the south and east coasts the silver fir does not thrive. It requires an abundant rainfall and a moist atmosphere, which probably accounts for its inability to stand the climate of the Eastern United States. There are, however, some fine specimens in Sussex (at Cowdray there is, or was a few years ago, a silver fir over 130 feet high, with a clean bole of 90 feet), and at Alnwick, in Northumberland; but at Novar, so famous for coniferous trees, Sir Ronald Munro Ferguson has given up planting it owing to its inability to resist the attacks of aphis. This seems to indicate a constitution impaired by climatic influence, for insect parasites, though they certainly hasten the death of a weakly subject, are not likely to prevail over a thoroughly vigorous one. In Western Scotland, where, as in Ireland, the silver fir makes grand growth, aphides swarm immediately upon any tree that has been debilitated by late frost or other injury. On the other hand, the Caucasian silver fir (Abies nordmanniana), which thrives splendidly in many parts of Britain where the common silver cannot be grown, frequently succumbs in the west to the attacks of aphis. At Benmore, on the Holy Loch, about 2,000 acres were planted about forty years ago with different kinds of conifers. I have examined the lists of the species planted, and find that by far the largest proportion consisted of this Caucasian fir. The forest remains, a splendid monument to its designer's enterprise; but hardly a Caucasian fir is to be found in it. The prevailing species are Douglas fir and giant Thuja.
Dr. Stewart M'Dougall has made some useful research, leading him to identify the silver fir aphis with Chermes abietis, the spruce louse which, as explained when treating of the larch, migrates to the larch and produces parthenogenic generations thereon. Dr. M'Dougall traces the silver fir louse to the same parentage. It follows from this that the spruce is a dangerous neighbour to silver firs.
Less serious, because not hurtful to the general health of the tree, is the "witch's broom" which forms upon the silver fir, sometimes greatly disfiguring it. This is caused, or at all events accompanied by, a fungus (Æcidium elatinum), which passes one phase of its existence upon certain humble herbs of the Pink family, such as the mouse-ear chickweed and sandwort.