Trees – Oak – English Oak – Quercus robur and other Quercus

Trees & Shrubs – Oak Trees – quercus including Quercus robur (English oak or Pedunculate oak or common oak).

London Tree Surgeons are experienced in pruning oak trees, and in care and tree surgery on oak trees. Single oak trees are cared for and planting and woodland restoration involve work with oaks. We can also diagnose pests and diseases associated with oak trees, including the oak processionary (Thaumetopoea processionea) a moth whose caterpillars can be found in oak trees in London.

To shop for Quercus for your garden visit the UK’s largest gardening website.

An oak is a tree or shrub in the genus Quercus (/ˈkwɜrkəs/; Latin “oak tree”) of the beech family, Fagaceae, having approximately 600 extant species.

The common name “oak” may also appear in the names of species in related genera, notably Lithocarpus. The genus is native to the Northern Hemisphere, and includes deciduous and evergreen species extending from cool temperate to tropical latitudes in Asia and the Americas.

Oak trees are common in London in larger gardens and parks,

The two native “English oaks”

Quercus petraea AGM (sessile oak): 30m, good specimen tree, lime-tolerant
Quercus robur AGM (English oak or Pedunculate oak or Common oak or just oak in the UK): 35m, good specimen tree, lime-tolerant

and the two naturalized (i.e. introduced into the wild where they now flourish): species as listed by the RHS.

Quercus ilex (holm oak)
Quercus cerris (Turkey oak)

Most other species exist somewhere in London planted over the centuries by gardeners and horticulturalists.

Even though the Oak is the most English of trees with links in pre-Roman Celtic Briton folklore and the more recent Oak walls of the British Royal Navy, North America actually contains the largest number of oak species, with approximately 90 occurring in the United States. Mexico has 160 species, of which 109 are endemic. The second greatest centre of oak diversity is China, which contains approximately 100 species.

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Oak.
A, female flower; B, male flowers.

Oaks have spirally arranged leaves, with lobate margins in many species; some have serrated leaves or entire leaves with smooth margins. Many deciduous species are marcescent, not dropping dead leaves until spring. In spring, a single oak tree produces both male flowers (in the form of catkins) and small female flowers.

The fruit is a nut called an acorn, borne in a cup-like structure known as a cupule; each acorn contains one seed (rarely two or three) and takes 6–18 months to mature, depending on species. The live oaks are distinguished for being evergreen, but are not actually a distinct group and instead are dispersed across the genus.

Below are extracts from the previous centuries from great horticulturalists’ in the field of Sylva such as Edward Step and John Evelyn on the English Oak.

The Oak (Quercus robur).

When good John Evelyn wrote his “Sylva, or a Discourse of Forest Trees,” he was greatly concerned lest our “wooden walls” should diminish in strength for want of a succession of stout Oaks in our woodlands, and therefore he put the Oak in the forefront of his discourse. To-day steel and teak have largely supplanted oak in the building of our navy, and our walls of defence are no longer of wood. Yet in spite of these changes, and the consequent reduction of the Oak’s importance, we must still look upon it as the typical British tree, and, regardless of its place in botanical classifications, we shall follow the lead of our master and place it first on our list.
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There is no necessity for entering upon a minute description of the botanical characters of so well known a tree. The sturdy, massive trunk, firm as a rock; the broad, rounded outline of its head, caused by the downward sweeping extremities of the wide-spreading lower limbs; the wavy outline of the lobed leaves, and the equally distinct egg-and-cup-shaped fruit—these are characters that cannot be confused with those of any other tree, and are the most familiar objects in the landscape in most parts of our islands. To my mind, no wood is so awe-inspiring as one filled with old oaks, all so much alike, yet each with a distinct individuality. We regard with reverence a human centenarian, who may have nothing beyond his great age to commend him to us; but we think of the long period of history of which he has been a spectator, possibly an active maker of history. The huge Oak has probably lived through ten or twenty such periods. Compared with the Oak, man is but of mushroom growth. It does not produce an acorn until sixty or seventy years old, and even then it is not mature. Not till a century and a half have passed over its head is its timber fit for use, and as a rule it is not felled under the age of two hundred years. Many trees are left to a much greater age, or we should not have still with us so many venerable specimens, and where they have not been left until partially decayed, the timber is found to be still very valuable when finally cut down. Of one of these patriarchs of the forest, cut down in the year 1810, we have figures of quantity and value from a contemporary record. It was known as the Gelenos Oak, and stood about four miles from Newport, Monmouthshire. When felled, it yielded 2426 cubic feet of sound timber, and six tons of bark. It was bought just as it stood for £405, and the purchaser had to pay £82 for labour for stripping, felling, and converting into timber. Five men were employed for twenty days in stripping the bark and felling the tree, and after that a pair of sawyers, working six days a week, were five months cutting it up. But the bark realized £200, and the timber about £400. The timber and bark from this one tree were about equal to the average produce of three acres of oak coppice after fifteen years growth.

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Oak tree in summer

Pl. 2. Oak—summer.


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Oak tree in winter

Pl. 3. Oak—winter.

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Oak tree in winter – LondonTreeSurgeons

Full-grown oaks vary in height from sixty to one hundred and thirty feet, the difference depending upon situation; the tallest, of course, being those that have been drawn up in forests, at the expense of their branches. Trees growing freely in the open are of less height, and are made to appear comparative dwarfs by the huge proportions of the bole. In the forest this may be no more than ten feet in girth, but in isolated specimens may be as much as fifty-four feet (Cowthorpe Oak), with a much broader base. The thick rough bark is deeply furrowed in a large network pattern, which affords temporary hiding-places for insects. The branches are much given to turn and zig-zag from side to side—a character that makes them very useful in boat-building, as “knees” of various angles may be cut from them without having recourse to bending. The best knees are to be obtained from Oaks grown in the hedgerow.

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flowers of the oak tree

 

The Oak flowers in April or May, and the blossoms are of two distinct forms—male and female. The males are in little clusters, which are borne at intervals along a hanging stalk, two or three inches in length. They are green, and therefore inconspicuous; but examined separately, they will be found to have a definite calyx, whose margin is cut into an uncertain number (4-7) of lobes. There are no petals, but attached to the sides of the calyx there are ten stamens. The female flowers are fewer, and will be found on short erect stalks above the male catkins. Each female flower consists of a calyx, invested by a number of overlapping scales, and enclosing an ovary with three styles. The ovary is divided into three cells, each containing two seed-eggs. An acorn should therefore contain six kernels, but, as a rule, only one of the seed-eggs develops, though occasionally an acorn contains two kernels. The overlapping scales at the base of the female flower become the rough cup that holds the acorn.

The Oak is subject to a considerable amount of variation, probably due to differences of situation, soil, etc., and some authors have sought to elevate certain of the varieties into species by giving them distinctive names. It does not appear to be certain, however, that these forms are at all constant, and they are connected by intermediate forms that make the identification of many individuals a matter of difficulty. In one of these forms (sessiliflora) the stalk of the acorns connecting them with the branch is very short, but the leaves have a distinct footstalk, from half an inch to an inch long. This form is more plentiful in the north and west, and is conspicuous in the Forest of Dean. A second form, known as pedunculata, has the leaf-stalk short or absent, the base of the leaf broad and somewhat heart-shaped, and the stalk upon which the acorns are borne very long. A third form (intermedia), commonly known as Durmast, has short leaf-stalks, short stalks to the acorns, and the under side of the leaf downy. Pedunculata is found more on the lower hills and the sides of valleys, whilst sessiliflora prefers higher ground, with a southern or western aspect.

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oak tree trunk or bole of oak

Pl. 4. Bole of Oak.

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Trunk of Oak tree – LondonTreeSurgeons
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The distinctive bark of the Oak tree – London Tree Surgeons

 

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Oak tree bark – LondonTreeSurgeons

 


 

The Oak is most abundant on clay soils, but is at its best when growing in deep sandy loam, where there is also plenty of humus. Its roots in such soil strike down to a depth of five feet, and therefore it thrives in association with Beech, whose roots are much nearer the surface, and whose fallen leaves supply it with humus.

The Oak is more persistently attacked by insects than any other tree. One authority (Leunis) has tabulated the species that get their living mainly or entirely from their attacks on the foliage, timber, or bark, and they number about five hundred. With some species this warfare is waged on so extensive a scale, that in some years by early summer the Oaks are almost divested of their foliage, and a new crop of leaves becomes a necessity. But the reserve forces of the Oak are quite equal to this drain, and the tree does not appear to suffer, though a much less thorough attack would be serious to a Conifer. One of the worst of these Oak-spoilers—though it by no means restricts its energies to attacks on this tree—is the Mottled Umber Moth (Hibernia defoliaria), whose pretty caterpillars may be seen hanging by silken threads from the leafless twigs.

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stag beetle

A striking Oak insect is the Stag Beetle

(Lucanus cervus), which, in warm evenings in the south of England, may be seen flying round the Oaks, the size and antler-like jaws of the male arousing feelings of respect in the minds of those who are not acquainted with its habits. The formidable looking “horns” are usually harmless. The beetle spends its larval stage in the wood of unhealthy Oaks, and, when mature, seeks his hornless mate among its foliage.

Perhaps the most interesting of the Oak’s pensioners to the woodland rambler will be the varied forms of gall on different parts of the tree. There is the so-called Oak-apple, of uneven surface and spongy to the touch, which certain people still wear on May 29th, in honour of Charles II.; the well-rounded hard Bullet-gall of Cynips kollari, the Artichoke-gall of Cynips gemmæ, the Spangle-galls of Neuroterus lenticularis, so plentiful on the back of the leaf, and the Root-gall of Biorhiza aptera. All these galls are abnormal growths, due to the irritation set up by the Gall-wasps named, when they pierced the young tissues in order to lay their eggs in them. Where any of these galls are perforated it may be known that the Gall-wasp whose grub fed within has flown, but where there is no such perforation the grub is still within, feeding upon the flesh of the gall, or in the chrysalis stage, awaiting translation to the winged condition.

Several Oaks of foreign origin are also grown in our parks and open spaces; among them the Holm Oak (Quercus ilex) whose evergreen leathery leaves have toothed or plain edges, and occasionally the lower ones develop marginal spines, whence its name of Holm or Holly Oak. It is notable for retaining its lower branches, so that its appearance, as Loudon remarks, “even when fully grown, is that of an immense bush, rather than that of a timber tree.” It is a native of Southern Europe and North Africa, and appears to have been introduced about the middle of the sixteenth century. It usually attains a height of from twenty to thirty feet, but occasionally specimens are seen up to sixty feet. It has a much thinner, more even bark than that of our native Oak, and of a black colour. The long brown acorns do not ripen until the second year.

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holm oak tree

Pl. 6. Holm Oak.


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Acorns of the Turkey Oak tree

Pl. 7. Acorns of Turkey Oak.

The Turkey Oak (Quercus cerris) is a much larger tree, attaining to similar heights to our British Oak, but easily distinguishable by its more pyramidal outline, and its attenuated leaves. The lance-shaped lobes of these are unequal, sharp, and angular; and the footless acorn-cups are covered with bristly or mossy-looking scales. The acorns, which are small and exceedingly bitter, rarely ripen till their second autumn. The whole tree—trunk, branches, and twigs—is of straighter growth than Quercus robur. It is a native of Southern Europe and the Levant, and was introduced in the 18th century.

The spring rambler in the woods may come upon a party of woodmen stripping young Oaks of their bark, or felling them, whilst cylinders of separated bark rest across poles in the process of drying. This is the industry of barking for the purpose of the tanner. When the Oaks in a coppice are about sixteen years old they are most suitable for this purpose, the bark then containing a larger percentage of tannin than at any other period. The operation is best performed in May, when the sap is in flow, and should be completed between the first swelling of the leaf-buds and the unrolling of the leaves. If the weather is cold and damp the bark will peel the better, provided there is an absence of north or east winds. Before the tree is cut down the bole is stripped, the first ring being taken from just above the roots to a height of two and a half feet above. When the tree is felled, it is cut into lengths and the bark stripped from them; then all branches that are an inch or more in diameter are peeled. The bark is piled to dry for a couple of weeks, and is then broken into small pieces and sent away in sacks.

It is not alone in the use of the bark that the tannic acid of the Oak is made evident; it is to the presence of this that the austerity of the acorn is due, and also the ink-producing properties of certain Oak-galls. Everything connected with the tree gets a roughness of flavour from this same principle. Even that remarkable fungus, the Vegetable Beef-steak, that may be found on old Oaks in autumn, is impregnated with it.

Prior regards the name Oak (Anglo-Saxon ac) as originally belonging to the fruit, and only later transferred to the tree that produces it. The more obvious explanation (though we know that in etymological and other matters the obvious is not always the true interpretation) is, that acorn (ac-corn) signified the corn or fruit of the ac. Selby tells us that “During the Anglo-Saxon rule, and even for some time after the Conquest, Oak-forests were chiefly valued for the fattening of swine. Laws relating to pannage, or the fattening of hogs in the forest, were enacted during the Heptarchy; and by Ina’s statutes, any person wantonly injuring or destroying an Oak-tree was mulcted in a fine varying according to size, or the quantity of mast it produced.”

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Acorns of Pedunculate Oak.

Quercus robur (English oak or Pedunculate oak or common oak) is best distinguished from Quercus petraea or sessile oak with the long stem of the acorn, sessile oak having a short acorn stem. The opposite is generally true of the leaf stem, but it is not so reliable when identifying the species.

Also see American oaks

London Tree Surgeons – Oak pdfS