Giants in the landscape
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Oak trees dominate many rural and park landscapes in the county, having been a key species for timber for centuries. Liz Hamilton of Herts Campaign to Protect Rural England looks at its history and how it remains a giant in Hertfordshire
The oak is frequently the species of choice for anyone planning to plant a new area of woodland, and with good reason. The oak is the most common tree in Britain, its wood the most widely used, and mature oaks grace many landscapes and support more wildlife species than any other native tree.
The pioneering ecologist Arthur Tansley (1871-1955) argued that Britain’s ancient woodland was dominated by oak, based on his observations of woods in the early 20th century. It took meticulous research by Oliver Rackham, the Cambridge botanist who died last year aged 75, to reveal that in lowland Britain lime was the commonest tree in ‘wildwood’ (woodland largely uninfluenced by man), in particular small-leaved lime Tilia cordata. Recent archaeological excavations at Must Farm quarry in the Cambridgeshire fens found 3,000 year old Bronze Age houses together with remarkably-preserved textiles made of lime bark fibres.
Rackham’s book Ancient Woodland, published in 1980, remains a classic for anyone wanting to find out more about our woods and their history. He concluded that the apparent dominance of oak in modern woods is due to its exceptional qualities as timber, which made it the first choice for buildings, ships and furniture. Oak also excels as firewood and its bark is used to tan leather. As a result oak was favoured by woodsmen for centuries, who often felled trees when they were relatively small, and ensured they were replaced by a new generation.
Often talked about as a single type of tree, there are in fact two species of oak native to Britain: Quercus petraea (sessile oak) and Quercus robur (English oak, sometimes called pedunculate oak). Sessile oak tends to grow on poorer soils, but the two species often grow together and also hybridise. They both produce acorns – those on sessile oak are stalkless (the definition of sessile), whereas robur holds its flowers, and the acorns which follow, in bunches on long stalks called peduncles. Like other woodland trees, especially ash, oak is late coming into leaf, it can be well into May before bright green leaves appear that gradually darken in colour.
Oaks are renowned for their longevity. They can grow quite rapidly when young, exceptionally reaching 40 metres in height. The two-kilometre Oak Trail at Panshanger Park, opened in 2015, takes in the Panshanger Oak which according to local legend was planted by Elizabeth I. It is the largest unpollarded or ‘maiden oak’ in the country and has a girth of 7.6 metres.
Pollarded oaks, which have had their trunks cut off typically two to five metres above the ground so that crops of wood could be taken in areas grazed by stock or deer, tend to grow broader trunks and live longer. The oldest of these in Britain measure 12-13 metres around the boles (the lower, uncut trunks) and may be 800 years old. The parkland of Hatfield House is still managed as wood pasture and here you can see many fine ancient pollarded oaks, as well as beech and hornbeam pollards.
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Oak, together with hornbeam, is the main tree species in many ancient woodland sites in the centre of the county. Ancient woods are those thought to have been in existence since at least 1600 - predating any major woodland planting and so likely to be natural in origin and of considerable wildlife value. This combination of species is a Hertfordshire speciality, although in the far west of the county they give way to beech-dominated woods (the dominance of beech is at least in part man-made) and in the north-east ancient woods of ash with field maple are common on this area’s heavy boulder clay. Ecologists also recognise other ancient woodland types in the county, often with distinctive associations of ground and shrub flora.
The county’s most extensive area of oak and hornbeam woodland is Broxbourne Woods National Nature Reserve, a Special Area of Conservation of European importance, and open to the public under the ownership of the county council and Woodland Trust. Hoddesdon Park Wood at the northern end of the area is an especially fine example of mature oak and hornbeam woodland. Here the oaks are mainly sessile but English oak is also present.
Although planting young trees is the most obvious way to create new woodland, trees will also regenerate naturally in many places. Jays and squirrels bury acorns and other tree and shrub fruits, especially hazelnuts in grassland, where they germinate and grow if left undamaged by grazing animals or mowing. The tendency of unmanaged open land to ‘tumble down to woodland’ (a phrase used by Oliver Rackham) is typically seen on Hertfordshire’s many commons, where grazing stopped early in the 20th century allowing woodland of oak, birch and hawthorn to establish.
An important postscript in this brief account of oaks and oak woodland is the conservation of ancient and especially pollarded oaks found in large numbers in old parkland, on commons and in hedges, and marking features such as parish boundaries. Many of the species supported by oaks, including invertebrates, birds, lichens, mosses and fungi, are associated with decaying timber, so it is vital that ancient oaks are protected and neither tidied away nor over-shadowed by younger trees.
Visit cpreherts.org.uk to find out about how CPRE works to protect our county’s countryside.