On the first day of college we were instructed that the only book we would need at this stage was The Hillier Manual of Trees and Shrubs. We were pretty horrified to see that it didn’t have any pictures. But can you imagine how huge a tome it would have to be with the section on the Quercus (oak) genus alone describing just a small proportion of the 500 species of oak?
However, we’ve only two native species in the UK: Quercus robur, the English Oak, which is surely the most easily recognised native tree we have, a national emblem if you like, and the sessile oak, Quercus petraea.
They’re easy to tell apart in that the acorns of Q. robur are held on a long stalk whilst those of the sessile grow straight from the stem. The other way to identify them is that the leaves of the English oak are far smaller than those of the sessile – about four inches compared to the sessile leaf which is a good six or seven inches or so. And sessile oaks, which do well in damp conditions, are mainly found in the wetter west of the UK.
However, wandering down the lane by my house recently, I found sessile oak leaves in the hedge and near a pond, but the plant itself definitely hadn’t reached the dizzy heights of a mature tree.
The oak is a massive feat of engineering in itself. Given some space and a lot of it, it can grow up to forty metres tall and live for hundreds of years. When young it has a growth spurt which slows down when it reaches 120 years old. This the tree does in order to extend its own lifespan.
Wandering through the woods, you’re likely to see a lot of pretty lanky ‘young’ oaks looking a bit sorry for themselves and without the fissured bark of a mature tree. This is because they’ve been fighting for light and resources all their lives and it shows, but somewhere in that same wood will be their ‘free range’ parent, so recognisable by its thick squat trunk and its lower branches growing sideways and its upper branches growing in a very distinct matrix of sturdy limbs.
A large tree will compete more successfully for said resources if it rearranges itself over the years. It has to be able to cope with prevailing environmental conditions, usually high winds, and to do this it spreads its weight equally around its ‘body’ which tends to become as wide as it is high.
This of course is in an ideal world and it’s rare to see an oak in a perfect ‘cloud’ shape, but the ones which have had optimum conditions and the time to create their own core strength create a very distinctive silhouette – as beloved by designers of corporate logos – in the winter months after their leaves have fallen.
Oak woods create an incredible haven for numerous species of insects, animals and birdlife. The flowers, produced in early spring at the same time as the leaves, provide food for caterpillars of various butterflies including the little native purple hairstreak.
The purple hairstreak’s larvae burrow into young oak flower buds and can be found in crevices of oak branches. They’re seldom seen as they tend to live high up in a tree’s canopy unless feeding off honeydew provided by aphids nearer the ground.
Oak leaves are soft and break down into a hugely rich leaf mould which is home for both invertebrates and fungi. Bats roost in any loose bark they might find as well as in old woodpecker holes; all manner of creatures eat the acorns.
It is an interesting fact that the acorns of Q. robur are not produced until the tree is at least forty years old with peak acorn production at twice that age. Acorns, even produced in huge numbers, are such a good food source – eaten by squirrels, mice, pigeons, woodpeckers, ponies and pigs when they get the chance – that many hundreds of thousands fail to germinate each season. They are too busy being useful.
I know that there are wild boar in the local woods and maybe they are helping germination by trampling some of the acorns into the ground as they forage. It has been found that in European woods oaks tend to have a higher germination rate than here due to the number of wild boar being sustained there. And in the days when a commoner had the right (pannage) to graze his pigs in local woodland, doubtless there would have been a higher acorn germination rate.
Either way, acorns are pretty miraculous if you think about their individual size in relation to that of their parent. However, I’m sure that squirrels and the odd jay that stores a supply here and there before the winter must forget some of their stashes enabling some to sprout in the shelter of a hedge bottom or bank.
Bluebell Nursery and Arboretum have a particularly wonderful selection of different oaks in their catalogue. One of the trees they sell is an absolute winner – if you have the space. Not native to here but one of the North American oaks, the Northern Pin Oak or Q. ellipsoidalis ‘Hemelrijk’ is really to be recommended.
It tends to come into leaf later than our natives but the new, deeply lobed leaves start off with a pink tinge, turning bright green until the autumn when they have brilliant red tones finally ending up a cinnamon brown and remaining on the tree for ages. The other nice things about it are the drooping branches and fast growth.
This is definitely one oak you’ll be able to see reach a decent size in your lifetime with a bit of luck. I love Quercus palustris, too, to which the Northern Pin Oak is related. This is another good elegant tree with a very distinctive habit. The leaves are very distinctly lobed and a shiny, shiny green. This one is good for autumn colour too, turning a rich red as the weather cools down.
Oak woods create an incredible haven for numerous species of insects, animals and birdlife
- words: Sue Whigham
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