In the Pleasure Grounds by the Lower Lake at Nostell, the bark of some of the old sweet chestnuts twists to the right while others twist to the left but on the majority of these old trees the fluting on the bark goes straight up, often dotted with knobbly swellings on the swollen bases of the trunks.
The two scars where the bark has been stripped from the lower trunk (above) might be the result of a lightning strike. The tree’s sap is instantly converted into steam, with explosive results.
The horse chestnut, which isn’t a close relation of the sweet chestnut, has scaly bark. This section of bark on the bough of an old horse chestnut, growing out towards the lake near the Cascade Bridge, has been worn and polished by generations of adventurous children so that it’s come to resemble the skin of a reptile.
I can’t draw a tree with twisting, carunculated bark without thinking of Arthur Rackham’s lively pen and watercolour drawings. No tree twists more than the hornbeam which always seems snakelike to me. This tree by the Lower Lake at Nostell is also dotted with pale lichens, echoing the cryptic colouring of a boa constrictor.
I’m going to add some colour to this, but I like it as a simple mapping pen drawing (Clip Studio Paint version on the iPad).
A cold front came in from the north during the night and today it’s noticeably cooler but mostly sunny.
Armed with secateurs, long-handled loppers, a step-ladder and a pruning saw, I trim back the golden hornet crab apple to a more manageable shape. It’s mainly a case of cutting back the whip-like vertical shoots that have grown since I last cut it back a year ago but I put in a bit of extra effort and use a pruning saw on one branch that’s managed to get its twiggy offshoots beyond my reach during the past few years.
Yes, it was a favourite look-out post for the resident blackbird, but it will soon find another perch. As I work at in the crown of a the tree, a long-tailed tit flits past my head and perches on a branch three feet in front of me. I don’t think it quite knows what to make of me.
Oak apples are at their freshest – spongy and sometimes rose-pink – around the time of Oak Apple Day, the 29 May. The day commemorates the Restoration of the Monarchy in Britain on 26 May 1660, when Charles II returned from exile.
The summer generation of the gall wasp Biorhiza pallida, has already emerged. As many as thirty of them live in separate larval chambers in the gall but they’re often joined by parasites and by inquilines: live-in lodgers that don’t attack the resident larvae. The variety of species sharing the gall probably explains the different sizes of the exit holes that they’ve made.
The fertilised females will go on to penetrate the ground and lay their eggs in the roots of oak trees. The larvae usually spend two winters developing underground, each in its own root gall, then emerge early in the year. This early spring generation will all be wingless and all female.
The unfertilised females climb into the branches of the oak and lay numerous eggs at the base of a bud. An oak apple forms from each bud and, as in my photograph, often several of them are clustered together. Males and females develop in separate galls.
These were on a small sessile oak growing by the towpath alongside the Calder & Hebble Navigation, downstream from Horbury Bridge.
These artichoke galls began to form earlier this summer when a female gall wasp Andricus fecundator laid a single egg in each of the terminal buds of this branch of a sessile oak.
Artichoke galls are also known as larch-cone galls or hop galls. The larva develops protected by the overlapping scales.
An adult female will emerge in the spring to lay her unfertilised eggs in the emerging catkins of the oak. The alternate summer generation of male and female gall wasps will emerge from the resulting hairy catkins galls in May or June.
This sessile oak was growing on the embankment of the disused colliery railway which formerly connected Hartley Bank to Addingford, crossing the canal and river en route.
Two species of lichens are thriving on the trunks of trees in the Asda supermarket car park in Dewsbury but nationally, as sulphur dioxide levels decrease, one of them appears to be gaining ground while the other is becoming rarer.
The yellow lichen with the pale-rimmed orange apothecia (the fruiting bodies of the lichen) is Xanthoriapolycarpa, which has spread as levels of sulphur dioxide in the atmosphere decrease.
It’s common on the coast but in urban settings you’ll often find it on twigs, fences and even on painted signs. It can tolerate high levels of nutrients and nitrogen, so it’s common around farms.
What is the source of nutrients or nitrogen here? Do these trees serve as starling roosts or, here in the middle of a car park, does the nitrogen come from vehicle exhausts?
The majority of lichens don’t have common names but the Latin name often includes a succinct description of the species. The genus name Xanthoria means ‘golden yellow’ while the species name polycarpa refers to its many fruiting bodies.
Acid Rain
Between the splodges of yellow, a grey-green lichen, Hypogymnia physodes, covers most of the bark. It grows in similar situations to the Xanthoria and tolerates acidic conditions but, nationally, this lichen has declined as air quality has improved. The introduction of smokeless zones and the phasing out of coal-fired power stations has resulted in less sulphur dioxide in the atmosphere and less acid rain.
It’s only in unpolluted sites that this lichen will produce fruiting bodies; there are three or four of them in my photograph above: red-brown discs on short stalks.
This lichen might be thriving here because it’s growing on the bark of a flowering cherry: cherry bark is highly acidic and in a dried, powdered form, has been used for medicinal purposes. The horizontal linear scar, visible amongst the lichens on my photograph, is characteristic of cherry.
The ‘Naked-below Bellows-like’ Lichen
The genus name of this lichen, Hypogymnia, means ‘naked below’ and refers to this lichen having no rootlike growths – rhizinae – on its undersurface.
Bellows from ‘Theatrum instrumentorum et machinarum’, 1582
The species name, physodes, means ‘bellows-like’ and I guess this refers to the lobes along the fringes of the lichen which are shaped like a pair of bellows.
In places the fan-like margins appear to be sprinkled with flour. These are described as farinose soredia. Farinose means ‘flour-like’. The soredia produce powdery granules which contain the fungal and algal cells of the lichen; these become detached and can grow into new lichens.
Leaf-like Lichens
Both these lichens are foliose, which means they can easily be detached from the surface they are growing on. Other lichens can be crustose and can’t easily be detached or fruticose: bushy.
Lichens, an Illustrated Guide
Coming across these in the Asda car park in Dewsbury gives me a chance to test out my new lichen field guides.
The first one that I reach for is the Field Studies Council’s Guide to common urban lichens 1 (on trees and wood). There aren’t many yellow lichens to choose from, so I soon narrow it down to Xanthoria polycarpa, then, taking a good look at my macro photographs of the grey-green lichen, I immediately pick out Hypogymnia physodes from the chart. I need illustrations; I’m not methodical enough to work my way through a key to identify a species.
There’s a brief summary of key features and habitat in the symbols and the tables included in the FSC guide, but it’s useful, now that I’ve got a name to look it up in an index and to go for the more detailed description and notes on distribution in Lichens, An Illustrated Guide to the British and Irish Species, by Frank S. Dobson, which has just been republished in a revised and updated edition.
There are six FSC guides to lichens in particular habitats – such as churchyards, rocky shores and moorland – so if you’re in one of those habitats it’s easier to have the few dozen of the species you’re most likely to come across to choose from, rather than trying to find it amongst the one thousand plus lichens in Frank Dobson’s book. The two publications work well together.
I already had five field guides on my bookshelves which include a selection of lichens but only one of them, The Observer’s Book of Lichens, briefly mentions the particular Xanthoria that I’ve photographed, but it isn’t illustrated and there isn’t enough of a description to enable me to identify it.
If you’re interested in lichens, I’d say it’s worth investing in these two publications (below). I went for the hardback and I’m pleased to say that it’s been given a binding that stays open when you put it down on the desk, which is so useful when you’re looking something up!
Flaky bark and even flakier tree recognition: I take a closer look at the tree that I photographed on Friday and, although the bark is flaky, it isn’t as flaky as that of London Plane: it’s Horse Chestnut, which probably explains why the bark is so polished; it’s been climbed by generations of conker collectors.
At this time of year, the swelling buds are almost as distinctive at the autumn conker fruits. The bud scales are red-brown and sticky and beneath them are the shield-shaped scars where last year’s leaves were attached.
The lenticels that dot the twigs are raised pores which allow for gaseous exchange.
These boughs of a Horse Chestnut*, snaking out over the Middle Lake at Nostell Priory have been polished by generations of young explorers so that the scaly bark resembles the skin of a serpent.
*Not London Plane, as I’d said in the original version of this post. I went back and checked the buds and they’re big, brown and sticky.
There’s often a carrion crow on the old felled sweet chestnut trunk near the Lower Lake bridge, feeding on grain that’s been left there and frequently being photographed. You can see in my photograph that it’s stuffed its crop with grain.
A few rooks feeding alongside jackdaws on the turf in Obelisk Park also have full crops, but they are more likely to be feeding on earthworms and insect larvae, such as leather-jackets: the caterpillar-like larvae of the crane fly.
Under a yew near the Menagerie seven grey squirrels have gathered. They’re turning over the leaf litter and stopping to nibble at frequent intervals. One appears to have found half a nut, probably an acorn that it – or another of the squirrels – had hidden during the autumn.
We disturb the adult grey heron yet again. This time it was hoping to be left in peace at the top end of the lake beneath the Cascade Bridge. It takes off, clearing the clapper stones of the Druid’s Bridge with inches to spare.
The flock of fieldfares are still around. Wigeon have left the now completely ice-covered field pool. There’s a pair on the Middle Lake, along with two pairs of gadwall, tufted, the usual mallards and swans and an increasing number of goosanders, some swimming in pairs.
There are more wigeon on the ice-free Upper Lake, which isn’t accessible from the Park.
As we walk along the edge of Top Park Wood, a kestrel wheels from tree to tree ahead of us.
On the northern half of the trunk of an oak by the Lower Lake a coating of powdery green algae shows up in the morning sunlight. It is absent from the sunny south side of the tree so, if you’re trying to do a bit of natural navigating and you’re lost deep in the forest this could help you to orientate yourself.
This is probably Pleurococcus or a very similar-looking species of green algae. Seen through a microscope, Pleurcoccus is a globular single-celled alga with a thick cell wall to help it resist desiccation. The individual cells are slimy and stick together to form the powdery coating.
Green algae contains two kinds of chlorophyll: Chlorophyll A and Chlorophyll B. The two molecules work together; Chlorophyll A absorbs blue-violet and orange-red light while B extends the spectrum by absorbing blue light. The green that we see is the light that doesn’t get absorbed.
