Tree silhouettes in winter

Every autumn, as the last leaf falls, I've had good intentions of recording a set of images of the characteristic silhouettes of different tree species in winter. They are all distinctive and beautiful in their various ways.

This winter I finally made a start but I hadn't bargained on how difficult it would be to find good isolated examples of trees silhouetted again a clear sky background, so progress has been slow. Anyway, here are a few, that I hope to add to before bud burst begins in a few weeks' time.  

Sycamore Acer pseudoplatanus. Only the tree on the left has had enough space to develop symmetrical growth; the two on the right have got in each other's way.

Horse chestnut Aesculus hippocastanum. Those almost horizontal heavy lower limbs are characteristic; in the rare absence of grazing animals they'll sweep almost down to the ground and are usually the first to be shed from old trees in gales.

Ash Fraxinus excelsior. The upward sweep of the rather thick twigs is characteristic.

Durmast oak Quercus petraea

Nature Tables..

Today's Guardian Country Diary is about nature tables in primary schools. After half a century, I can still remember the one in my village school, run by a kindly teacher called Miss Waghorn and stocked with various treasures that her pupils brought into school from the surrounding countryside.

At this time of year Miss Waghorn's contribution to the table was a jam jar full of horse chestnut twigs that she brought in for the class to draw over the days and weeks as they gradually opened. Her influence lingers on because, at this time every year, I like to have a horse chestnut twig with its glossy 'sticky buds' on my desk so that I can enjoy a preview of what is to come in spring. There's a one week difference between the first and second images below - as the buds swell and change shape they also produce more sticky resin.

I realise when I look around my desk and along the bookshelves in the room where I work that there are other manifestations of Miss Waghorn's influence lying around. Over the years, I've accumulated a nature table of my own - specimens and artefacts that I've picked up at various times and kept as natural mementoes. 

Looking around, I can see a fossil sea urchin that I've had since I was a kid, a piece of Whitby jet, a dead convolvulus hawk-moth, a guillemot's skull, the skeletonised fruits of bellflower, the exuvium of a dragonfly nymph that has hatched, a Faroe sunset shell and a painted topshell, various pine cones, a jay's feather, part of a tree wasp's nest, an ammonite, some granite pebbles from a beach in Dumfries and a tube full of preserved gammarid shrimps that I collected 1000 feet underground just before Wearmouth colliery closed and entombed their fellow shrimps forever. Every specimen has a story attached - or at least that's what I tell my very tolerant wife.

I blame it all on Miss Waghorn and her nature table.....

A Tree-Spotter's Guide to Bark: Part 4

The success of London plane Planatus x hispanica as a street tree owes a lot to its propensity to slough off flakes of bark frequently, shedding pollutants along with it - and leaving an attractive abstract pattern of pastel coloured patches.

Marooned in a sea of of concrete and asphalt and assailed by exhaust fumes; it's a small miracle that plane trees like this not only survive but thrive in the urban jungle.

On a sunny day, it's pretty obvious how redwoods got their name. This is the giant sequoia Sequoiadendron giganteum, a species that was introduced into Britain in 1853. The bark is incredibly thick, soft and fibrous and, it is said, has been adopted as a roosting site by treecreepers that hollow out small depressions where they spend the night. Where did treecreepers roost before 1853, I wonder? The tree is sometimes known as Wellingtonia, named after the Duke of Wellington who died the year before it was introduced, but attempts to formalise this name as Wellingtonia gigantea - an act of imperialistic arrogance - upset the Americans. It was, after all, their tree so they countered with the name Washingtonia, to commemorate their national hero.... but there was already a palm species with the same name. Thankfully, it turned out that it was a cousin of the coast redwood Sequoia sempervirens and so could also be called Sequoia, circumventing any further taxonomic squabbling. It became Sequoiadendron in 1939, when detailed examination revealed that it was sufficiently distinct to be placed in a genus of its own. 

Horse chestnut Aesculus hippocastanum becomes flaky with age but isn't easily shed - so it often acquires a veneer of green algae on the northern, shady side of the trunk.

Elder Sambucus nigra rarely lives long enough to develop tree proportions but when it does the deeply fissured corky bark can be very attractive.

When common hawthorn Crataegus monogyna grows as a tree, rather than as a regularly cut hedgerow shrub, it tends to branch from low down from an early age and this produces a trunk that resembles vertical branches welded together - which is what they are, I suppose.

For more information on tree identification click here

The Alien that Conquered Britain

The conker season is here again – amply celebrated today in an article in the Times newspaper (see http://www.timesonline.co.uk/tol/news/uk/article6860922.ece). Horse chestnut Aesculus hippocastanum is our best-loved alien species which, during the 400 years since it was first introduced into Britain from the Balkans, has graced our parklands and become the focus of a traditional sport that has left generations of school-kids nursing aching knuckles after misjudged swings of an opponent’s conker.

The seeds of horse chestnut are truly exquisite objects. Their deep umber hue has given its name to a colour and their glossy texture contrasts wonderfully with the spiky husk that they are enclosed within. Sadly, it’s a beauty that doesn’t last – after a day or two those glossy seeds become leathery and lose their rippled patterns. In the USA Aesculus species are known as buckeyes, on account of the resemblance between those glossy brown orbs and the eyes of deer.

I may be wrong, but I suspect the horse chestnut seed is the largest amongst trees in Britain. They invest a lot of resources in giving their germinating seeds the best possible start in life, by providing them with a very large food store.... but at the expense of long-distance dispersal (take a look at http://beyondthehumaneye.blogspot.com/2009/10/travelling-light.html for a completely different plant seed dispersal strategy).

One of the perils of producing seeds with a large food store is that they simply become food for hungry animals (think of all the acorns that are guzzled by squirrels, jays and wood pigeons) - which may be why conkers contain high levels of toxic substances called saponins which are natural detergents and generally damaging to animal digestive systems. Ground-up conker flesh can provide a deterrent against slugs, which have a strong aversion for saponins and tend not to cross a barrier of conker meal. This might be the basis for a natural method of slug control, but for the fact that saponins are water soluble, so that any attempt to use them as slug deterrents would be washed away in the first shower of rain.

Horse Chestnut Traffic Signals

Newly-opened horse chestnut flowers have a yellow spot on the petals, that turns red once the flower is pollinated. More than half the flowers in this photograph seem to have been pollinated, probably by bees seeking nectar that apparently contains a high concentration of sugar in horse chestnut. I recall reading somewhere that this floral colour change is the tree’s way of telling bees not to waste their time visiting flowers that have already been visited and pollinated. The theory was that this works because bee eyes can see yellow but are well known to be relatively insensitive to the longer-wavelength red end of the spectrum. So this is horse chestnut’s traffic light signalling system – conspicuous yellow for ‘proceed’ and inconspicuous red for ‘don’t bother’. I’ve never see any published scientific evidence to back up this plausible but possibly apocryphal story, but with the aid of a decent pair of binoculars it shouldn’t be difficult to see whether the bees do visit the red flowers......