The Mighty Oaks of Britain
Oak trees live longer than all other native trees and support a greater variety of wildlife than any other species in our islands. Even when they die, they still give food and protection.
From the top of its spreading crown to the ends of its roots, which can extend as far below the ground as its branches reach into the sky. The oak tree provides shelter and food for hundreds of different organisms. Like a crowded highrise block, the oak is inhabited at every level: birds and squirrels build nests in the crown, insects such as wasps, moths. Beetles and weevils devour the leaves; ivy, mistletoe, lichens, mosses, algae and fungi invade the branches and bark; birds, insects and mammals feed on the acorns. Even the roots of the young oak are sought out by such insects as weevils and, as the oak lets in quite a lot of light through its leaves, flowering plants grow underneath it.
You may think that the oak must be quickly overpowered by this invasion of wildlife, but once a sapling becomes established the oak can live for up to 800 years, continuing to act as host to this multitude of creatures. In fact the oak has adapted itself so successfully in temperate regions that there are over 450 different species of oak in the world. Several of these oaks grow in Britain and Ireland, but only two, the pedunculate (also known as the common or English oak) and the sessile (durmast) oak are native to our islands. It is not always easy to tell the difference between them.
When it is growing in the open, the pedunculate oak is gnarled and tends to have lower, more horizontal and wider-spreading branches, so that the main trunk is hidden beneath a mass of boughs and leaves. The sessile oak has a straighter, less gnarled trunk, with branches growing from higher up.
You are likely to come across woods where both species of oak are growing, often among other trees. The huge forests of Epping and the New Forest are typical of such mixed woods. Here it is more difficult to distinguish the two species. For example, when the pedunculate oak competes for light with other trees it may lose some of its broad shape. To make it even more confusing, one species is frequently fertilized by the other and the result is a hybrid with characteristics of both species.
If you get close to a true sessile or pedunculate oak, however, you should be able to tell them apart quite easily.
The leaves of the pedunculate oak are pale green and virtually hairless, with two obvious ‘ear-lobes’ (auricles) at the base. They have deep, rounded indentations all round. In autumn, acorns grow on long stalks called peduncles — hence its name.
The leaves of the sessile oak are dark green, have no auricles and the indentations are not so deep. Leaves grow on long stalks and have a few hairs on the midrib of the underside. Unlike the pedunculate, the sessile acorns sit on the twig.
Pedunculate oak woodlands are the most common, and are usually found on heavy clay soils throughout lowland Britain. The pedunculate oaks at Bagshot in Surrey and Hovingham, North Yorkshire, are well worth a visit. Sessile woodlands are found in the highland areas of Britain and usually occur on shallow acid soils. The Birkrigg and Keskadale oaks south west of Keswick in the Lake District are excellent examples of ‘pure’ sessile woodlands.
Trees are flowering plants but many of theirare not spectacular. Large or colourful and the oaks are no exception. Inconspicuous female catkins (flowers) are pollinated by the wind-carried pollen grains from male catkins (so large petals needed to attract insects for pollination are unnecessary). The oak’s acorn crop varies from year to year—in a bumper year each tree can produce as many as 50,000 acorns. But few of the hundreds of thousands that fall every year grow into full-sized trees. Acorns start to form in early summer (the warmer the summer the larger the acorns), and then during a few weeks of early autumn they fall to form a dense carpet. They do not stay long on the ground for they are seized by hordes of birds and animals, either to be eaten or stored away for the winter. Jays and squirrels in particular bury them (sometimes quite a distance from the wood) and then forget about them. This is one of the ways the oak is spread across the countryside.
Oak woods covered much of Britain in medieval times and our ancestors quickly discovered that oak made good fuel. The sessile oak was also valued for its acorns. From the Middle Ages until the 18th century people drove their pigs into the oak woods on common land to feed on the abundant acorns. Indeed, one way of assessing and comparing the size of each manor’s forest was to count the number of grazing pigs that could be supported. Such grazing rights still exist today in the New Forest in Hampshire.
Oak wood was used extensively for ship-building and many parks, such as Regents Park and Greenwich Park in London, were planted especially to supply the Royal and Merchant navies. Oak wood was used extensively for supporting beams in country cottages and is still used by builders today.