English Oak – Quercus robur

Tree of the Week

24th April 2019 | Danny

Common Name: Pedunculate (English) Oak

Scientific Name: Quercus robur

English Oak is a large deciduous tree that can reach heights of up to 40m. It is one of the most famous trees in the UK and has earned the status as something of a national emblem. The English Oak is also associated with the Royal Navy. Up until the mid-19th century, the Royal Navy’s ships were constructed with oak timbers.

Identification

Leaves: Deeply lobed leaves with smooth edges and two auricles at the base. They grow up to 10cm in length. Leaves grow on very short stems of 5mm or less. The initial flush of leaves produced in mid-May are usually all quickly eaten by insects and are replaced in mid-summer by a second crop of leaves.

Buds: Terminal buds are brownish, ovate shaped and are clustered on the branching.

Bark: Greyish brown bark that is smooth for young trees and branches. In mature trees the bark forms deep fissures and is more blackish-brown in colour.

Form/growth habit: Young growth is rapid, and trunks branch out early. This causes the tree to form a large, broad treetop with a rounded shape. Oak trees are known for growing extremely large at the base, reaching circumferences of between 4 -12m. Growth usually slows down at around 120 years and interestingly, oaks are known to reduce in height in order to extend their lifetime.

Reproduction

Synoecious (flowers possess both male and female structures). Male and female catkins are produced along with the first flush of leaves in spring. After pollination, all male catkins die off. The fruit (acorn) ripens by mid autumn. Acorns are around 2-2.5cm long and are housed in a cup-shaped structure called ‘cupules’. As the acorn ripens, the colour changes from green to a more autumnal brown colour, before it detaches from it’s cupule and falls below the canopy.

Interesting facts

Tannin found in the bark of Oak trees has been used to tan leather since at least Roman times.

Ecological importance

Acorns are a rich food source for many wild animals such as birds, mice and squirrels and for this reason, many acorns never get the chance to germinate. The leaves, buds and acorns are also home to many insects. Q. robur supports the highest biodiversity of insect herbivores of any British plant.

Properties of English Oak and uses

Known for being the producer of one of the hardest and most durable timbers on the planet, Oak was the primary material for constructing ships until the mid-19th century. It is used now for furniture and architectural beams, as well as flooring, wine barrels and firewood. It can take up to 150 years for an oak tree to be ready for use in construction.

Associated Pests & Disorders

Oak Processionary Moth

The moth’s caterpillars feed off the leaves of Oak trees, causing serious leaf loss, weakening the tree, and leaving the tree susceptible to other pests and diseases. They also pose a threat to human health as the caterpillar’s tiny hairs contain a toxin that causes itchiness and respiratory problems if inhaled.

Sudden Oak Death (SOD)

Caused by the pathogen ‘Phytophthora Ramorum’, this disease kills oak trees. First reported in 1995, very few controls exist for the disease. Symptoms include Bleeding Cankers and dieback in the tree’s foliage, eventually leading to the death of the tree. The origins of this pathogen are still unclear.

Oak can also be affected by several fungi including: Honey Fungus, Beefsteak Fungus and a variety of Ganoderma species.

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