Oak

The oak tree is a tree or shrub in the genus Quercus. There are about 500 living species. They are divided into subgenera. The common name “oak” may also appear in the names of species in related genera, such as Lithocarpus.

Oaks have spirally arranged leaves, with rounded edges in many species; some have leaves with jagged edges or entire leaves with smooth margins. Many deciduous species do not drop dead leaves until the next Spring. In Spring, a single oak tree produces both male flowers (as catkins) and small female flowers. The fruit is a nut called an acorn, carried in a cup-like structure. Each acorn has one seed (rarely two or three) and takes 6–18 months to mature, depending on species. The so-called “live oaks” are evergreen. They are not a taxonomic group, just a life style which occurs in the genus.

The oak is a kind of hardwood forest tree. They are well known as a climax vegetation in the temperate zone of the northern hemisphere. That means, left untouched by humans, it would be the dominant tree. Much of England was covered by oak forests before modern farming took over the land. The last extensive oak woodlands were cut down to build ships for the Royal Navy in the 18th century.

Some kinds of oak wood are very hard. That is why people in past centuries cut them down to make ships, furniture and other things. The wood is now scarce and expensive and only used to make a few things anymore. Much cheaper are softwoods like pine.

Oak trees grow slowly and can live up to 1000 years.

Quercus robur or English oak

Quercus robur, the pedunculate oak or English oak,[3][4] is a species of flowering plant in the beech and oak family, Fagaceae. It is a large tree, native to most of Europe and western Asia, and is widely cultivated in other temperate regions. It grows on soils of near neutral acidity in the lowlands and is notable for its value to natural ecosystems, supporting a very wide diversity of herbivorous insects and other pests, predators and pathogens.

Oak – Description

Quercus robur is a deciduous tree up to 40 metres (130 ft) tall, with a single stout trunk that can be as much as 11 m (36 ft) in girth (circumference at breast height) or even 14 m (46 ft) in pollarded specimens. Older trees tend to be pollarded, with boles (the main trunk) 2–3 m (6+1⁄2–10 ft) long. These live longer and become more stout than unpollarded trees. The crown is spreading and unevenly domed, and trees often have massive lower branches. The bark is greyish-brown and closely grooved, with vertical plates. There are often large burrs on the trunk, which typically produce many small shoots. Oaks do not produce suckers but do recover well from pruning or lightning damage. The twigs are hairless and the buds are rounded (ovoid), brownish and pointed.

The leaves are arranged alternately along the twigs and are broadly oblong or ovate, 10–12 centimetres (4–4+1⁄2 in) long by 7–8 cm (2+3⁄4–3+1⁄4 in) wide, with a short (typically 2–3 millimetres or 1⁄16–1⁄8 inch) petiole. They have a cordate (auricled) base and 3–6 rounded lobes, divided no further than halfway to the midrib. The leaves are usually glabrous or have just a few simple hairs on the lower surface. They are dark green above, paler below, and are often covered in small disks of spangle gall by autumn.

Flowering takes place in spring (early May in England). It is wind-pollinated. The male flowers occur in narrow catkins some 2–4 cm (3⁄4–1+1⁄2 in) long and arranged in small bunches; the female flowers are small, brown with dark red stigmas, about 2 mm in diameter and are found at the tips of new shoots on peduncles 2–5 cm long.

The fruits (acorns) are borne in clusters of 2–3 on a long peduncle (stalk) 4–8 cm long. Each acorn is 1.5–4 cm long, ovoid with a pointed tip, starting whitish-green and becoming brown, then black. As with all oaks, the acorns are carried in a shallow cup which can be distinctive in identifying the species.[6] It is an “alternate bearing” species, its large crops produced every other year.

Ecology

Within its native range, Q. robur is valued for its importance to insects and other wildlife, supporting the highest biodiversity of insect herbivores of any British plant (at least 400 species). The most well-known of these are the ones that form galls, which number about 35. In Britain, the knopper gall is very common, and Andricus grossulariae produces somewhat similar spiky galls on the acorn cups. Also common in Britain are two types of spherical galls on the twigs: the oak marble gall and the cola nut gall. The latter are smaller and rougher than the former. A single, large exit hole indicates that the wasp inside has escaped, whereas several smaller holes show that it was parasitised by another insect, and these emerged instead. The undersides of oak leaves are often covered in spangle galls, which persist after the leaves fall.

One of the most distinctive galls is the oak apple, a 4.5 cm diameter spongy ball created from the buds by the wasp Biorhiza pallida. The pineapple gall, while less common, is also easily recognised.

The quantity of caterpillar species on an oak tree increases with the age of the tree, with blue tits and great tits timing their egg hatching to the leaves opening. The most common caterpillar species include the winter moth, the green tortrix and the mottled umber, all of which can become extremely abundant on the first flush of leaves in May, but the oak trees do recover their foliage later in the year.

The acorns are typically produced in large quantities every other year (unlike Q. petraea, which produces large crops only every 4-10 years) and form a valuable food resource for several small mammals and some birds, notably Eurasian jays Garrulus glandarius. Jays were overwhelmingly the primary propagators of oaks before humans began planting them commercially (and remain the principal propagators for wild oaks), because of their habit of taking acorns from the umbra of its parent tree and burying them undamaged elsewhere.

Sources:
WIKIPEDIA 1

WIKIPEDIA 2