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Kingdom: Plantae Division: Magnoliophyta Class: Magnoliopsida Order: Fagales Family: Fagaceae Genus: Quercus
The term oak can be used as part of the common name of any of several hundred species of trees and shrubs in the genus Quercus, and some related genera, notably Cyclobalanopsis and Lithocarpus. The genus is native to the northern hemisphere, and includes deciduous and evergreen species extending from cold latitudes to tropical Asia and the Americas.
Oaks have spirally arranged leaves, with a lobed margin in many species; some have serrated leaves or entire leaves with a smooth margin. The flowers are catkins, produced in spring. 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" (oaks with evergreen leaves) are not a distinct group.
The difference between the Common or Pedunculate oak (left) which has a peduncle or stalk between the parent twig and the base of the acorn and the Durmast or Sessile oak (right) which although it still has a stalk is very short, almost non existant, appears to grow from the parent twig. One of the acorns on the pedunculate oak has at the end of it a Knopper gall caused by the gall wasp Andricus quercuscalicis. If the acorns are not evident then the leaves hold the key. The Pedunculate oak has very short leaf stalks and at the leaf base there are two (one each side of the stalk) backward facing lobes. The Sessile oak has a longer leaf stalk and no lobes at the base. The two often hybridise in the wild, the hybrid being known as Quercus × rosacea.
Along with the naturally occurring Q. × rosacea, several hybrids with other white oak species have also been produced in cultivation;
The genus is divided into a number of sections:
A hybrid white oak, possibly Quercus stellata × Q. muhlenbergii. Hybrids are common in oaks but usually only between species within the same section; no verified inter-section hybrids are known, except between species of sections Quercus and Mesobalanus, where several occur.
The genus Cyclobalanopsis, here treated as a distinct genus following the Flora of China, is often included within Quercus as a distinct subgenus.
The life span of oaks typically ranges from 200 to 600 years, with a few species reaching 1,000 years.
Pedunculate Oak (Quercus robur) linnaeus
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Common Oak, English Oak, Irish Dair,is a large deciduous tree and probably our commonest tree. Usually found in mixed woodland on basic fertile soils with a ph 4.5 - 7.5 including heavy soils. Natural distribution throughout Britain and Ireland and most of Western Europe and Asia Minor with the exception of the far north and some areas of the Mediterranean, and also to parts of North Africa. It is the type species of the genus (the species by which the oak genus Quercus is defined), and a member of the white oak section, Quercus section Quercus. The populations in Italy, southeast Europe, and Asia Minor and the Caucasus are sometimes treated as separate species, Q. brutia Tenore, Q. pedunculiflora K. Koch and Q. haas Kotschy respectively. The pedunculate oak is the dominant tree of deciduous woods in Britain, it occurs in coppice woodland, high forest and ancient wood pastureland, and has often been planted in hedgerows. When growing in open areas it has a wide, rounded crown, but woodland specimens are usually tall and slender. It is able to grow in a range of soil types, but prefers those that are fertile and heavy but avoiding acid peat and shallow limestone soils. This oak, known as the 'king of trees' has a special place in the English psyche, and is a well-loved symbol of strength and duration. It is a magnificent tree, with a broad, irregular crown. The bark is grey-brown and fissured, becoming deeply fissured and developing burrs as it ages. The massive main branches often develop low on the trunk and become twisted and gnarled with age. The twigs are moderate, yellow-brown, smooth; brown buds are ovoid-conic, angled, short and round with each scale edged in light brown. The English oak is a deciduous tree, and in the autumn, usually around November, it sheds its leaves. Popularly supposed to be slow growing, really quite fast, up to 60cm in a year for a few years. Shoot expanded rapidly in a few weeks from late May. In good soil to 20 x 2m by 50 years. Girth increase slowing from 4cm to 2.5cm annually by 250 years, then decreasing. It is planted for forestry, and produces a long-lasting and durable heartwood, much in demand for interior and furniture work. Young oak trees are vulnerable to insect predation. They grow very quickly, but after reaching 100-200 years of age their rate of growth slows down. After this time, however they continue to increase in girth. It is a long-lived tree specimens typically live for up to 500 years, but some oaks are known to be 700 to 1200 years old. Indeed, Britain has more ancient oaks than any other country in western Europe. It can grow to a height of 30 - 40 m with a large widespreading head of rugged branches. While it may naturally live to an age of a few centuries, many of the oldest trees are pollarded or coppiced, both pruning techniques that extend the tree's potential lifespan, if not its health. A specimen of notable longevity is one in Stelmuþë, Lithuania which is believed to be approximately 1,500 years old, possibly making it the oldest oak in Europe; another specimen, called the Kongeegen (Kings Oak), estimated to be about 1,200 years old, grows in Jaegerspris, Denmark. Yet another can be found in Sweden, Kvilleken. It is over 1,000 years old and 14 meters around.[1] Of maiden (not pollarded) specimens, one of the oldest is the great oak of Ivenack, Germany. Tree-ring research of this tree and other oaks nearby gives an estimated age of 700 to 800 years old. Mature trees can tolerate flooding even by sea-water. A close relative is the Sessile Oak (Quercus petraea), which shares much of its range. Pedunculate Oak is distinguished from this species by its leaves having only a very short stalk 3–8 mm long, and by its pendunculate acorns. Much more prone to gall-infestation than Sessile Oak. The Sessile oak has been adopted as the National tree of Wales and is sometimes reffered to as the Welsh oak. The two often hybridise in the wild, the hybrid being known as Quercus × rosacea. Oak catkins are Monoecious and made up of small, yellowish-green flowers. The males are slender yellow-green catkins 2 to 3 inches long, in clusters of 2 to 4 in leaf axils. The male flowers hang down on bright green catkins. Near the tip of each twig, on the end of long stalks, are the very small reddish-brown coloured female flowers. The flowers of an oak tree usually emerge in March or April with the leaves following in April with lobed and nearly sessile (very short-stalked) leaves 7–14 cm long. The leaves are alternate, simple, obovate to oblong, 3 to 7 pairs of rounded lobes with sinuses going halfway to midvein, very small ear-lobes at leaf base forming a typical 'wavy-edged' outline, very short petiole, the upper surface is a dark shiny green, the underside is a paler blue-green and by authumn often covered in small discs of spangle-gall. Varying shades of yellow and coppery brown during fisrt growth from May, then red young leaves during second growth in July. Young leaves are often covered in a layer of fine downy hairs. Their fruit, called acorns, appear after the female flowers are fertilized in spring and ripen by October of the same year. The acorns occur in clusters on long stalks known as peduncles, 3–7 cm long (hence the common name of this species) and are 2–2.5 cm long, pedunculate (having a peduncle or acorn-stalk) with one to four acorns on each peduncle. The egg-shaped acorns sit in scaly cups that measure up to 18mm across and covering approximatly one third of the acorn. They are typically brown, tan, yellow, light green, deep green or grayish green. Oaks grow slowly and usually do not bear acorns until they are about 20 years old. Acorns require stratification to stimulate sprouting. Most white oaks need immediate stratification. The acorns are rich in starch and tannins, and are eaten by small mammals and a number of birds. Jays Garrulus glandarius and squirrels are extremely important in dispersing acorns away from the parent trees; they bury them for later consumption, and many of these acorns germinate. Acorns were once widely used to feed pigs; they were also ground down to make a substitute for coffee and even a type of bread. A good crop of acorns was used to predict a good harvest, and a heavy fall of acorns was thought to signal an impending harsh winter. Within its native range it is valued for its importance to insects and other wildlife. Numerous insects live on the leaves, buds, and in the acorns. The oak tree can be home to more than 300 species of invertebrates. The acorns form a valuable food resource for several small mammals and some birds. Upland oak woodlands have declined by 30-40% over the last 60 years as a result of re-planting with conifers, conversion to grazing land, overgrazing by sheep and deer, and unsuitable management. The decline in the ancient technique of coppicing has resulted in oak woodlands becoming more shaded; acorns do not germinate as well in these conditions. Many oak forests have a skewed age structure, as young trees are not able to regenerate. This may cause problems for many of the rare species that are dependent on ancient oaks; as the old trees die there will not be trees in the vicinity of a suitable age, so entire communities are at risk. Upland oak woodland is a priority habitat under the UK Biodiversity Action Plan (UK BAP). An action plan has been produced to guide the conservation of this habitat. Not only is the English oak of important cultural significance, it is a beautiful, majestic species. Furthermore, the communities of plants, animals and fungi that are associated with oak trees are often unique, and internationally significant. Conserving this 'king of trees' is therefore of utmost importance. |
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Sudden Oak Death (Phytophthora ramorum) is a water mould infection which afflicts some oak species and some other trees and shrubs, causing them to die rapidly, it can kill oaks within just a few weeks. It also causes a non-fatal leaf disease in many other plants such as rhododendrons. There is no known cure but new studies show that periodic wildfires help protect against the mould.
It was first discovered in California in 1995 when large numbers of Tanoaks (Lithocarpus densiflorus) died mysteriously, and was described as a new species of Phytophthora in 2000. It has subsequently been found in many other areas including Britain, Germany, and some other American states, either accidentally introduced on nursery stock, or already present undetected. The origin of the disease remains unknown, although it was reported infecting European nursery rhododendrons and viburnum in 1993. In tan oaks, the disease may be recognized by wilting new shoots, older leaves becoming pale green, and after a period of two to three weeks, foliage turns brown while clinging to the branches. Dark brown sap may stain the lower trunk's bark. Bark may split and exude gum, with visible discoloration. After the tree dies, suckers will sprout next year, but their tips soon bend and die. Ambrosia beetles (Monarthrum scutellare) will most likely infest a dying tree during midsummer, producing piles of fine white dust near tiny holes. Later, bark beetles (Pseudopityophthorus pubipennis) produce fine red boring dust. Small black domes, the fruiting bodies of the Hypoxylon fungus, may also be present on the bark. Leaf death may occur more than a year after the initial infection and months after the tree has been girdled by beetles.
Promoting tree health may help prevent disease and insect infestations. Make certain roots and soil remain undisturbed, prune dead and dying branches out, and landscape below oaks with mulch or drought-tolerant plants. When a tree dies, experts recommend cutting it down and grinding down the stump. Firewood should be covered with 6 mil plastic, sealed at the edges with dirt or rocks, for six months to prevent beetle emergence.
In addition to oaks, many other forest species may be host for the disease, including rhododendron, Douglas Fir (Pseudotsuga menziesii), Honeysuckle (Lonicera hispidula) and Shreve's Oak (Quercus parvula v. shrevei). Disease progression on these species is not well documented but hikers have observed dead Douglas Firs with massive quantities of red frass surrounding their base. Redwoods exhibit needle discoloration and cankers on small branches, with purple lesions on sprouts that may lead to sprout mortality.
is a lethal disease of some oaks, particularly the red oaks (the white oaks can be infected but generally live longer), caused by a fungal disease, Ceratocystis fagacearum (a fungus closely related to Dutch Elm Disease), which can quickly kill an oak tree. The fungus originated in eastern Russia. The tree reacts to the presence of the fungus by plugging its own cambial tissue in an attempt to block the fungus from spreading further. As the area around cambium (the vascular tissue) is crucial for delivering nutrients and water to the rest of the plant, this plug prevents them from travelling up the trunk of the tree, eventually killing it.
Oak wilt spreads in two basic ways. A transmission via root graft is the most common source of infection, as trees within as much as 15 m (50 feet) of an infected tree can be infected. The second method of infection is via sap beetles. These beetles are attracted to the bleeding sap of the oak tree, as well as the fungus in an infected or dead tree, and so can transfer the disease to healthy but injured trees. This is less common as trees are rarely infected this way unless injured, but it is the only way to jump barriers (rivers, for example) and infect trees in new areas.
Oak wilt is identifiable by the rapid pattern of wilting starting from the top of the tree and progressively dying down to the bottom, and on specific leaves, wilting from the edges to the base. Oak with oak wilt stand out with their dead crown compared to a green canopy in the summer, so much so that oak wilt infections can be spotted from the air. A new infection via beetles instead of root grafts can kill a tree somewhat more slowly, if a branch is infected instead of the trunk.
Oak wilt affects all oak species, but has somewhat different effects on different groups. Red Oaks such as the Northern red oak are particularly susceptible, and when infected, generally die over the course of a single summer. White oaks are more resistant, and can live for several years after infection, losing a few branches each season (from the top down). White oaks in particular are resistant. Some types of white oak, such as bur oak are more susceptible, although still not as much as red oaks.
Although possible, it is rare for oak wilt to jump between oaks of different species via root grafting. Different species do not graft often, and so contaminate each other less frequently.
Although similar to Dutch Elm Disease, Oak wilt is more controllable. Prevention is key, as there is no permanent cure. To prevent beetle transmission, oaks should never be pruned in the spring months. Late autumn and early winter are preferable. Also, care should be taken to prevent injury during this period, particularly during construction. If a tree is injured through a storm or accident in the spring, tree paint to cover the wound is advised, although it is not a good idea in general. Reducing the source of infection is also helpful. Dead oaks should be checked for fungal mats in the spring, and if present, all wood should be chipped, burned, or covered in plastic. Logs from wilted trees should never be moved to unaffected areas, even for firewood.
If a tree is discovered to be infected, a trench (or better yet, two at different distances) should be dug between the it and any other trees of its species to prevent root graft disease transmission. This will sever any root grafts that could carry the disease to neighboring trees. The placement of these root cuts depends on size of trees, soil type, timing, topography, etc., and usually needs professional experience, but in general should be about 40 feet and one healthy tree away from the sick tree to be effective. Root cutting is most efficiently done in most cases with a machine called a vibratory cable plow that uses a solid steel blade cutting to a depth of 5 feet. Injections of propiconazole can help to prevent transmission as well. Injections every other year can also be used to treat a white oak, if it is not yet greatly affected, although this is expensive. An infected tree should not be immediately cut down, as this can force the oak wilt down into the roots to affect other trees, and can also injure nearby trees and make them more susceptible to beetle transmission. The tree should be cut down the following autumn, and debarked, chipped, burned, or covered in plastic by the next spring to prevent contamination by fungal mats.
Other dangers include wood-boring beetles, as well as root rot in older trees which may not be apparent on the outside, often only being discovered when the trees come down in a strong gale.
Feeding and other inter-species relationships associated with Quercus robur:
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The name Turkey Oak is also commonly used in this form for the American Turkey Oak (Quercus laevis). The Turkey Oak (Quercus cerris) which is often alternatively called Turkish Oak, is an oak native to southern Europe and Asia Minor. It is the type species of Quercus sect. Cerris, a section of the genus characterised by shoot buds surrounded by soft bristles, bristle-tipped leaf lobes, and acorns that usually mature in 18 months. The species' range extended to northern Europe and the British Isles before the previous ice age, about 120,000 years ago. Reintroduced in the United Kingdom and in Ireland in the eighteenth century, its gall wasps now provide early food for birds.
It is a large deciduous tree with a broad, rounded outline, growing to 25-40 m tall with a trunk up to 2 m diameter. The bark is dark grey and deeply furrowed more fissured and rough than native oaks. The alternate glossy leaves are 7-14 cm long and 3-5 cm wide, with 6-12 various sizes of triangular lobes on each side; the regularity of the lobing varies greatly, with some trees having very regular lobes, others much less regular. The leaves are paler below and hairy on both surfaces when they are young. They have no 'ears' at the base and narrow to a leaf stalk 10-25 mm long, at the base of which are pale, narrow stipules. The leaves hang on well into the winter and some stay until the following spring.
Turkey Oak is widely planted and is naturalised in much of Europe. This is partly for its relatively fast growth. It is used as an ornamental, and as a coastal windbreak. The wood has many of the characteristics of other oaks, but is very prone to crack and split and hence is relegated to such uses as fencing. The timber is of little value as it warps and splits during seasoning. Several cultivars have been selected, including 'Variegata', a variegated cultivar, and 'Woden', with large, deeply-lobed leaves.
Turkey Oak readily hybridises with Cork Oak (Q. suber), the resulting hybrid being named Q. × hispanica Lam. (Spanish Oak). This hybrid occurs both naturally where its parents ranges overlap in the wild, and has also arisen in cultivation. It is a very variable medium to large tree, usually semi-evergreen, sometimes nearly completely so, and often with marked hybrid vigour; its bark is thick and fissured but never as thick as that of the Cork Oak. Numerous cultivars are available, often grafted onto Turkey Oak root stock. These include 'Ambrozyana', evergreen except in severe winters, originating from the Mlyňany Arboretum in Slovakia, home of the late Count Ambrozy; 'Diversifolia', with the leaves are extremely deeply cut leaving a narrow strip down the centre, and very corky bark; 'Fulhamensis' (Fulham Oak), raised at Osborne's nursery in Fulham c.1760; and 'Lucombeana' (Lucombe Oak), raised by William Lucombe at his nursery in Exeter c.1762. An early specimen raised by Lucombe is at the Royal Botanic Gardens, Kew
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