CHANGING COLOURS OF TREE SYMBOLIC OF BRITAIN'S COUNTRYSIDE
As autumn approaches, the mighty oak takes on its new seasonal colours. As the sap subsides, these iconic trees put on a fine show. The exhausted summer greens turn to buttery yellows, burnished with gold. Finally, only the brown, crisped memories of the past year’s leaves still cling to the mother tree.
From its acorns nestled in their cross-hatched cups, to the distinctive lobed leaves and the bold, billowing form of its mighty frame, the oak is one of the most recognisable of British trees. It is the commonest large broadleaf tree, Britain’s dominant woodland species. There are estimated to be more than 200 million mature trees growing around the country.
As useful as it is beautiful, oaks have been planted and nurtured for hundreds of years. Its acorns fed pigs, tannin from its bark was used to produce leather and its excellent quality timber went into buildings, ships and furniture.
There are 600 species of oak in the genus Quercus. Only two are native to Britain, the common, English or pedunculate oak, Quercus robur, and the sessile oak, Quercus petrel. The terms pedunculate and sessile refer to whether the acorns have stalks – peduncles – or not. Sessile is from the Latin sessilis, meaning fit for sitting on. The sessile oak’s acorns sit on the stems, with no stalks.
The native oak is often regarded as a single generic tree, but there are several ways to disseminate the two species. From a distance they can often look remarkably similar. However, in general, the English oak tends to be a more rugged, spreading tree with a zigzag pattern to its branches. These were once keenly sought by shipbuilders for the L-shaped wooden brackets known as knees and crooks.
In profile the sessile oak tends to have much straighter, more upswept boughs.
Both species may still adopt forms that confuse. Differentiation can be further complicated by the fact that there are a plethora of intermediate forms and hybrids. This is inevitable with both species sharing the same territory.
Moving in a little closer is useful to discover which species is which. Acorns that clearly have short stems (peduncles) an inch or two long on to the twig and leaves with little or no stem are definitely English oak. Acorns with no stems that sit snugly on the twig, usually in little clusters, and leaves with short stems will be sessile oak. Even so, it is common to find oaks with both very short-stemmed acorns as well as leaves.
Every three or four years oaks produce a huge crop of acorns in autumn, up to 50,000. This is called a ‘mast year’. With so many acorns on the ground, it is likely that more will survive predation.
Both male and female flowers are found on the same tree. Male flowers are long, green pendulous catkins (up to 1¾in/4cm). The tiny female flowers comprise a cluster of bracts surrounding a bud-like structure with three styles. Both appear with the leaves in spring. They are pollinated by the wind.
Growth and extreme age
Oaks flourish in all manner of soils and aspects, but English oak is essentially the lowland species. It excels in the deep loams and boulder clays of the south and east. The sessile oak is most commonly associated with lighter sandy soils and gravels, usually more acidic in character. Its dominant range is the west coast, northwest England and Scotland. However, extensive species overlap for thousands of years has lead to a blurring of these natural ranges.
British oaks have the capacity to grow to approximately 130ft (40m) in height, although that is exceptional. In 2012 a 200-year-old sessile oak was discovered in woodland on the National Trust’s Stourhead Estate in Wiltshire. It had forged upwards seeking sunlight from the dense woodland. It finally reached a height verified by the Tree Register at 132½ ft (40.4m) and has now been recognised as the tallest oak in Britain.
Oak trees can attain extreme old age, up to 900 years and beyond. This particularly applies to oaks that have been pollarded. This is done by trimming boughs at around 8ft to 10ft (2.4-3m) above ground on a regular rotation. It ‘fools’ the tree into believing that it has yet to fully mature, so it keeps producing new growth. A pollarded tree frequently thrives for 1,000 years. Some of the most ancient oaks have survived to 1,200 or 1,300 years. However, the oaks that have reached these mighty spans are invariably hollow. This makes an annual ring count impossible to do. Dendrochronolgy, or tree-ring dating, is the scientific method of ageing trees. It dates the time at which a tree’s annual growth rings were formed, often to the exact calendar year. The lack of rings on the ancient hollow trees means their age can only be gauged by extrapolating outwards from younger trees of known ages. If a sequence of oaks are found to be 300, 500, or 700 years old, then their measurements can be used to estimate the age of a much larger tree.
For a maiden oak – a tree that has not been pollarded – reaching 900 years would be remarkable. There are a handful of trees, such as “Majesty” at Fredville in Kent, that might easily surpass this span. Most maiden oaks in perfect situations should certainly make at least 600 years.
The most ancient oaks are recognisable by their stupendous girths and enchanting, knobbly, burry, contorted forms. Anything much over 38ft (11.5m) around at chest height can claim to be 1,000 years old. The record breakers at 42ft (12.8m) could be more than 1,300 years old.
A long legacy of coppicing oak trees in woodland has created many impressive coppice stools. At first glance, these appear to be massive stumps with relatively small oak trunks emerging from them, their size depending on how recently they have been harvested. The truth is that these stools can be cropped and allowed to regenerate indefinitely. Some of them may be many hundreds, perhaps even 1,000 years old. It is impossible to tell.
Native British oaks have enormous benefits for wildlife. The English oak supports a greater variety of species than any other tree in the British Isles, making it an important habitat in its own right. The oaks provide a habitat for many hundreds of species from moth larvae which rely on them for food, to owls that nest in cavities. Many birds, such as blue tits and chaffinches, are attracted to the insects that live on the leaves, buds and bark, and even inside the acorns. The acorns provide food for jays, wood pigeons and squirrels.
The decaying wood of veteran oaks supports wood-boring insects such as stag and long horn beetles.
Place in the landscape
The stature and longevity of oaks and their place in the landscape never cease to inspire awe. To this is added their contribution to British culture, history and economy, plus their immense value as wildlife habitat. It is no wonder the oak is a most treasured tree.
Words: Archie Miles Photography: Alamy
The feature about the oak originally appeared in the Sept / Oct 2014 issue of LandScape.
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