Absolutely Barking!

These posters are available as downloads and as prints in my online shop microscosmic.shop

Leaves of British -  Trees Buds of British Trees -  Bark of British Trees

Absolutely Barking!

Examples of different bark types trees which I've photographed on the patch

Bark is like almost everything in nature – the more you look the more you see. If you walk through a wood you will, of course, be aware of the trees, but only have a vague sense of the variety of bark. Once you stop to look you’ll see that every tree species has its own kind of bark, and even amongst trees of the same species – no two are alike.

My latest patch project has been to photograph an example of the bark of each of the tree species on the patch – the result being the photos on this page. A quick glance through these is enough to show the range of bark types, colours and textures to be found - as well as their beauty . Some are rough, others smooth, some have vertical fissures others horizontal. Still others are patterned with ridges, sploges or square-shaped markings.

That no two trees are alike is well demonstrated by these examples of sycamores I've found on the patch. These are roughly ordered by age of tree which also gives an indication of how bark can vary throughout the tree's lifetime

Layers of the cross section of a tree

Tree bark and human skin, have a lot in common. They are both outer layers with a role in protecting the tissues beneath, and both are unique to the individual. Each fingerprint is famously unlike any other and no two trees have exactly identical bark.

There are a whole host of organisms, which share the tree's habitat and would like to 'get their hands on' the nutritious tree tissues. For this reason the tree has to invest a lot of resources on protection - hence bark. 

The outermost layer of the tree is made up of dead cork cells - this is the part we can see and touch. Cork protects the tree by helping to prevent water loss and insect / pathogen attack.  These cells are air-filled which helps insulate the tree and also accounts for the lightness of bark.

Why is tree bark so variable?

Different tree species occupy different ecological niches and each one has its own way of ‘going about things’ - this effects the kind of bark it has.

Beech, for example, has smooth bark which helps the tree avoid ‘hangers on’ -  ivy, mosses, insects etc find it difficult to gain a foothold. This smoothness has a cost, however – the bark must be produced slowly so the growth rate of the tree is limited and injuries are slow to heal.

Oak bark grows much faster than that of Beech, helping the tree repair injury sites and retain moisture. Again this comes at a cost – rapid growth causes the bark to crack, so harbouring insects and other pests. The Oak, therefore, has to counter these threats by making the bark less palatable and so produces protective chemicals such as tannins (which comes at metabolic cost).

Birch trees grow in damp environments and so are prone to lichen and moss infestation.  Therefore, to help shed these plants birches, have thin bark which peels easily.

Only a few species are like the Beech, in maintaining smooth, unbroken bark for their entire lifespan. The outer bark continues to grow at the same rate  as the increasing circumference of the tree. Most species reach a point where their wood is growing faster than the bark — and so the wood pushes outward against the bark - causing cracks, fissures etc. The specific characteristics of the specie's bark are partly a result of the way the it responds to this pressure.

Patch bark gallery

Alder

Ash

Aspen

Beech

Blackthorn

Cherry

Common Lime

Downy Birch

English Oak

Goat Willow

Hawthorn

Hazel

Holly

Hornbean

Horse Chestnut

Larch

Leyland cypress

Lombardy poplar

Juniper

Magnolia

Mountain ash

Norway spruce

Rhododendron

Rose (Dog Rose)

Scots pine

Sequoia

Silver birch

Sycamore

Turkey oak

Weeping willow

White poplar

Wych elm

Yew

So I’m looking at the bark of a tree – can I say why the bark like it is? Is it possible to say what has determined why this particular tree has this particular pattern. Well, it’s almost certainly, not possible, to account for every minute detail of the bark, some of it will probably be entirely random.

In a previous post on moth camouflage I found it a fascinating exercise to try to consider what might be the factors at play in determining the markings on a moths wing. A similarly interesting question concerns tree bark. 

This won’t be a complete list of factors  (and some of these factors may overlap, amount to same thing as other factors, or indeed not be relevant)

Species factors                     

Those that are common to all individuals of a given species and so have determined the way the tree has evolved

Environmental factors - influenced by the tree's distribution, habitat and the ecological niche it occupies

Climate -  how wet, dry, windy, sunny etc
Tree structure - size, shape

Interaction with other species -  protection from epiphytes, parasites,  herbivores, pathogens

Interaction with other species - non-protection  mycorrhizal fungi for example

Protection, physical - from extremes of temperature, resistance to fire, against water loss, impacts etc

Protection, chemical – chemicals protecting against insects, fungi bacteria etc

Bark chemical composition – may influence bark colour for example

Bark physical composition  – e.g how much air in the cells, this may also effect colour

Response to injury or infection 

How is bark shed by the tree

Bark layer composition – 3 layers of outer bark phellem, phellogen, phelloderm – and 2 of the inner, phloem, vascular cambium – how much of each is present and in what form

Other parts of the tree -  leaves, flowers, seeds may well have an influence

‘Lifestyle’ – e.g. is it deciduous, when does it come into leaf

Speed of growth – see the examples of beech and oak above

Photosynthesis – how much bark photosynthesis takes place – which will effect presence or absence 
of Lenticles (the pores which allow gas exchange through the bark)

How Long lived

Which part of the tree – are we looking at  - the lower trunk, a branch or a twig
Feedbacks – for example,  the overall weight of the bark will affect the structural properties of the tree which may be a factor which feeds back to influence the properties of the bark

Individual factors   

No two trees of the same species are exactly alike, so overlaying the species factors  will be factors effecting the bark of the individual                        

Location – in which part of the species' range is the tree growing and in which habitat within the  species' habitat range.

Neighbours – what other individuals of other species and the same are growing / living nearby

History – what has happened during the tree’s lifetime

• Weather
• Lighting strike
• Herbivore / pest attack
• Woodpecker holes, etc, etc

Age
Genetics

As we saw with the examples of Oak and Beech, and with moth camouflage, there are competing factors which are traded of against each other and there will, in fact be a whole network of interactions in constant flux.

To take a step back for a moment - tree bark and moth's wing aren't particularly special in this respect. It's probably true to say that most things are the way they are due to a large web of interacting factors.

 ...or to put it more simply - things are the way they for lots of reasons (which is a statement so blindingly obvious it calls for a "no sh*t Sherlock!")

This tree on the patch was probably struck by lightning. It is burned out and almost completely hollow inside.
The fact that it continues to grow, seemingly healthily, is testament to the fact that most of the life of the tree is in the inner bark

As an experiment I was interested to see if I could distill bark patterns down to something more simple as a kind of identification guide -  I don't think it's particularly successful - but I rather like the design!
Sycamore, Aspen, Silver birch, Alder, Oak, Cherry

 

Recent Patch Sightings
4/2 - 110 Pink footed Geese - north
6/2 - Song thrush, Starling, Great tit, Coal tit, Dunnock now in song
6/2 - First spring flowers - Opposite Leaved Golden Saxifrage
7/2 - 2 Willow tit, 3 Roe Deer
8/2 - Scarlet Elf Cup

Scarlet Elf Cup

Get this