For many, the very mention of tree climbing conjures up nostalgic memories of youth and this month’s tree species is the perfect apparatus for this favoured past time! The English oak is a tree of extremes, not only is it the largest and most common of our native, broad-leaves (along with sessile oak), it is also one of the most long-lived. In fact, their longevity means that the trees you played upon were probably equally cherished by previous generations and will continue to be enjoyed by many to come. For us long-life may be crowned with the arrival of great-grand children or reaching our 100th birthday. Comparatively, a newly emerged oak sapling standing a mere 20cm from the ground today has the capacity to live over 1000 years, produce over 25 million acorns and may well welcome in the next millennia as one of our gentle giants – a humbling thought indeed.
Typically measuring around 10cm in length, the oak’s 4-5 deeply lobed leaves (1) with smooth edges is one of its most distinguishable features. Leaf-burst occurs mid-May and, unlike it’s close relative the sessile oak, Quercus petraea, the leaves have almost no stem (2) and grow in bunches. Its fruit, commonly known as the acorn, are 2 – 2.5cm long, borne on lengthy stalks and held tightly by cupules (the cup-shaped base of the acorn). As it ripens, the initially green acorn takes on a more autumnal, browner colouration, loosens from the cupule and falls to the canopy below. At the same time these deciduous trees begin to litter the ground with their leaves. Most acorns will never get the chance to germinate, they are a starch-rich food source, utilised by many wild creatures including jays, mice and squirrels. Acorns need to germinate and root quickly to prevent drying out or becoming victims of the harvest. Following successful germination, a new sapling will appear the following spring.
Interesting Fact: Acorns are not produced until the tree is at least 40 years old. Peak acorn fecundity usually occurs around 80 – 120 years.
As English oaks mature they have a tendency to form a broad and spreading crown with sturdy, inviting branches beneath. Like the Ash, their open canopy enables light to penetrate through to the woodland floor, allowing magnificent floral displays of bluebells and primroses below. Their smooth and silvery brown bark transforms with age and becomes rugged and deeply fissured. Oak tree growth is particularly rapid in youth but gradually slows around 120 years. Oaks even shorten with age, retrenching their energy heavy canopy in order to extend their lifespan.
Oak forests provide a habitat rich in biodiversity; they support a larger number of different life forms than any other native trees. They play host to over 280 species of insect and over 300 species/sub-species of lichens can be found on any one tree.
The diverse array of insects form part of a fascinating food chain and supply many British birds with a crucial food source. In autumn mammals such as badgers, boars and deer take advantage of the falling acorns. Historically humans also collected acorns and processed them into flour for bread making. These culinary techniques have mostly died out following the domestication of wheat production 10,000 years ago, leaving the harvest for wild birds and mammals.
The soft leaves of English oaks breakdown with ease in autumn and form a rich leaf mould beneath the tree. Search carefully among the decaying leaves and you may find invertebrates, such as the stag beetle, and numerous fungi, like the oakbug milkcap.
Take a few moments to identify any holes or crevices in the tree bark, these could belong to a nesting pied flycatcher or marsh tit. Several British bat species may also roost in old woodpecker holes or under loose bark, as well as feeding on the rich supply of insects in the tree canopy.
The oak is held in high esteem across most major cultures in Europe. The oak was sacred to many gods including Zeus (Greek), Jupiter (Roman) and Dagda (Celtic). Each of these gods ruled over thunder and lightening, and oak trees are prone to lightening strikes as they are often the tallest living feature in the landscape. Druids frequently practised and worshipped their rituals in oak groves and cherished the mistletoe that frequents oak tree branches. Royalty has had a long association with oak trees too; ancient kings adorned themselves with crowns of oak leaves, King Charles II hid from his pursuers in an oak tree at Boscobel House and Roman Emperors were presented with crowns of oak leaves during victory parades.
In England the oak has for centuries been a national symbol of strength and survival. It has played an important part in our culture – couples were wed under ancient oaks in Oliver Cromwell’s time, the festive Yule Log was traditionally cut from oak, it features on the 1987 pound coin and is the inspiration for the emblem of many environmentally focused organisations, including the Woodland Trust.
Oaks produce one of the hardest and most durable timbers on the planet, even its Latin name, Quercus robur, means strength. However, it takes up to 150 years before an oak is ready to use in construction. It has been a prized hardwood timber for thousands of years, was the primary ship building material until the mid 19th century and remains a popular wood for architectural beams. Traditionally the leaves, bark and acorns were believed to heal many medical ailments including diarrhoea, inflammation and kidney stones. Tannin, found in the bark has been used as a leather tanner since Roman times. Nowadays Britain’s only remaining oak-bark tannery is based in Colyton, Devon. Modern uses of English oak include flooring, wine barrels and firewood.
Despite their high numbers in Britain and protection from over-harvest, our oak trees are threatened by a number of pests and pathogens. The oak processionary moth is a non-native pest that has been found in London and Berkshire. Not only does it damage the foliage of the trees and increase the oak’s susceptibility to other diseases, it is actually a risk to human health. The moth’s hairs are toxic and can lead to itching and/or respiratory problems if breathed in.
Acute Oak Decline (AOD) and chronic oak decline (COD) are serious conditions affecting Britain’s oaks, several contributing factors are linked to the diseases. Decline of mature oaks first aroused concern in the 1920s, today most cases are in central, southern and eastern England. Key symptoms include canopy thinning, branch dieback and black weeping patches on stems and lesions underlying the bleed spots.
Read more about oak processionary moth, AOD and COD in our tree pests and diseases issue of Wood Wise.
Quick oak facts…
Click here to see other blogs in this series on tree species.
Hannah Cole, Conservation Communications Intern