Saturday, 20 July 2013

Mighty Oaks

Tony Leech, NWT Trustee and County Fungus Recorder

Oak at NWT Thursford Wood, photo by Tony Leech
A few weeks ago I hugged a tree. I didn’t fall in love with it, and I don’t think it was too bothered either, but I wanted to measure its girth - which turned out to be about 27 feet. The tree in question (pictured) is an oak in Thursford Wood, roughly half-way between Holt and Fakenham. It is a small wood but an ancient one. Owned by Norfolk Wildlife Trust it is a mere strip adjacent to the A148, so nowhere in the wood is out of sound of traffic. But the trees are very special because some of them have been there for a long time. It is said that oak trees grow for 300 years, rest for 300 years and decline for 300 years. By this reckoning, the one I was measuring is well over 600 years old.

The decline manifests itself in two main ways; first by ‘stag-heading’. When the tree is no longer increasing in size, and is unable even to replace and replenish what it has achieved, it undergoes a controlled reduction. Twigs and small branches die but the thicker branches in the canopy persist as pointed and skeletal antlers. Such trees have been felled by the ignorant under the misapprehension that they are dying; perhaps they are but are likely to take a very long time doing so. In good years (wet ones) new growth will burst out to maintain a green head from which the dead branches project.
The second indication of decline is hollowing, the removal of heartwood through the activity of specialised fungi. It used to be thought that this was an indication of disease but it is now appreciated that this removal of dead tissue might even be beneficial as it reduces weight but not strength. In gales, hollow trees are more likely to remain standing when similar-sized solid stems fall.

Coppiced oak stool at Holt Hall, Tony Leech
The hugged tree at Thursford, the largest of a number of giants, has been pollarded, that is, cut repeatedly in the past about eight to ten feet from the ground to promote the growth of thinner branches for harvesting. Repeated cutting down to the base (coppicing) produced straighter branches but the new growth would have been more easily eaten by browsing animals. When coppicing has been carried out for centuries and then neglected, a coppice ring may have formed, as in the woods at Holt Hall; all these stems have sprouted from the same stool. Both coppicing and pollarding prolong the active growth phase of a tree.

There are two rather similar species of (assumed) native oak in Britain, The English (or Pedunculate) Oak (as at Thursford) and the Sessile Oak (named because its acorns are sessile, i.e.unstalked). The latter is predominantly a northern and western species in Britain, quite scarce in Norfolk, although distribution is much influenced by planting. A magnificent (and relatively young) Sessile Oak, a tree which is often more slender than the English Oak, can be seen in front of Holt Hall (below). In nature, the two species hybridise to produce trees of intermediate character.

Sessile Oak at Holt Hall, photo by Tony Leech
An enormous amount of folklore is associated with oaks; each acorn, for example, possesses its own fairy. The Thursford oak is closely surrounded by a well-worn path. I have visited the tree at night but have always gone cautiously, wary of surprising witches enjoying their pagan rites.

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