Why is the forest always so loud?
Because there is so much bark(ing)!
A Tree in the Woods
Look at a tree and you will notice three things: there is a top, filled with greenery; there is a cacophonous network of branches; there is the main trunk. The top – the “crown” – is where photosynthesis happens and flowering (usually*) happens. The branches hold the crown up and in place, and “branch out” to increase the amount of sunlight the tree can capture. The trunk holds them both high above the ground, into the sky. The trunk also provides strength against wind and physical damage, such as other falling trees. In the end, the structure, or “architecture” of various species of trees will be different – trunks thin to fat, crowns patchy to dense, branches growing upright or at right angles to the tree, for example – but the general plan of a tree is just that. Grow up and compete with other trees for valuable sunlight by making branches that grow smaller branches that grow leaves and flowers, and hopefully, you will make enough energy to survive and reproduce. Nature at its finest.
Let us look at that trunk. Find a tree in the forest or in your mind, and look closely at the trunk and only the trunk. That trunk is made up of many parts that help keep the tree alive – a tree is a complex living organism. Leaves, roots, flowers, buds, bark, vascular tissue, … it is a biologically amazing thing to have evolved!
Back to the trunk itself. Within that trunk are the conduits for nutrients and water from the roots in the soil to move up and feed and hydrate the leaves; within that trunk are also the conduits for nutrients and gases and a whole assortment of goodies made in the leaves to move down through the plant and to the roots.
Other things move along the trunk, too. Chemicals – exudates – that are there to protect or feed the tree that we have found a secondary use for. Rubber comes from the trunks of trees. Maple syrup comes from the trunks of trees. To get these, we need to puncture the tree somehow to make the inner liquids or latex leak out – no different than you cutting your arm and your inner blood leaking out. We need, somehow, to access the inner part of the tree.
Why? Because the inner part of the tree is still alive. The outer part, the bark, is dead. Stone cold dead. Mostly. The term “bark” is what ecologists call a non-technical term, meaning that it is a general description of a general part of the tree that surrounds the trunk and is generally dead. Generally.
Every species will have bark with different characteristics, and it is hard to give a complete and reasonably concise definition. But here goes: it is three layers of the dead to dead-ish material that surrounds the living wood in the trunk. The layers are (again, “generally”!) cork, secondary phloem (flow-um) and bark.
Above: Bark can share a common character, but present in different ways. Look for the size of gaps, the depth of ridges, the pattern – do the ridges go straight or wander around. There will be many things that stick out to you the more you look and the more you compare trees to each other.
One of those words should sound familiar to you. Well, maybe two! Cork is used to plug up the tops of wine bottles and is good for wine preservation for the same reason that it is good for trees – it is an exceptionally good barrier that does not allow moisture or even gases to pass through. If you left a wine bottle open all night (I’m thinking of a nice Malbec or a Syrah…) you would potentially wake to something edging closer to cooking wine or vinegar than that which the grapes of Argentina had in mind when they were plucked, stomped, fermented and bottled. Cork (now being replaced by plastic “cork”; the real cork will break and chip off with a fingernail dig if you try) is a natural layer within the bark of trees that, when jammed into a bottle, stops the ageing process (or the fouling process). The cork used in wine bottles comes from an oak tree that makes peculiarly thick cork layers that are easily peeled off, causing little harm to the tree (“little harm” is a contentious phrase here, but it paints the right picture. Anything you do to a tree that requires it to spend energy fixing or rebuilding tissue or chemicals will impact the tree growth or health. It may not kill it, but it does take energy away from other necessary deeds, such as growth. So, harvesting sap to make maple syrup is sustainable – it will not kill the tree – but it does have a measurable impact on tree growth).
Cork layers in bark protect the tree. Then there is a secondary phloem layer, which transports some liquid goodies through the tree. This gets complicated but is a vital part of the tree’s system.
Then there is the bark we are all familiar with – the outermost layer.
If you get a chance to see a cut tree or even branch (branches have bark, too!), look closely at the “bark” and you will see some distinct layering. That layering is all part of the tree’s bark system!
Above: Some bark is flaky and will almost shatter off the tree when touched (left; Bischofia javanica), some is like low-grade sandpaper (middle; Ficus species with “cauloflory” figs growing off the trunk), or patterned like a map of a distant planet (right; Fraxinus grifithii)
Why do Trees Have Bark?
The bark of a tree is its protection. The stuff inside is vital – keeping the tree standing upright (there is strong dead wood at the centre of most trees) and keeping the tree fed and hydrated and filled with necessary chemicals and nutrients (the living tissues inside) keeps the tree alive. The bark, as an outside layer, protects this. Bark is the tree’s bodyguard. One of them, at least.
Some of the main things that bark protects the tree from are fire, insects, fungi, physical damage, and water loss. All these and many more will severely hurt the tree, and an outer bark layer has evolved as a way to protect the tree’s vital organs.
Trees can also adapt as infections or infestations happen, and be noticeable in the bark appearance. Not quickly, but quick enough. Some severe damage is unavoidable – woodpecker holes, for example. They peck and pluck too hard and too fast for a tree to compete by mending its wounds. But trees have other ways to protect themselves in these cases. For example, trees can simply close off the living tissue around these wounds, so insects and fungi that can invade afterwards have nothing to keep them alive.
Have you ever seen a tree with a weird, sometimes grotesque bulge on its trunk? This is a tree response to an infection of some sort, where the tree grows new wood quicker than normal around and infected area and cuts it off. The result is a healthy tree, but with bulges.
Bark is there to protect the tree, in many ways, from the many assaults encountered daily. And bark is very species-specific, making it a very useful tool to identify or recognize trees.
Above: Some bark is bumpy (left; these are lenticels, places where the bark allows gas exchange – yes, trunks (and branches) breathe, too!), some bark is remarkably smooth (middle; this is Lagerstroemia subcostata, sometimes referred to as ‘monkey-no-climb’ tree as it is too smooth and hard to climb), or kind of a mix of rough and cracked (right).
See the forest for the bark
Do you still have that tree in your mind? Look at its bark. What does it look like? Colour, texture, everything.
Bark is a good way to get to know various trees. I must warn though that many trees have similar types of bark; however, within a given species the bark type will be very consistent. So if you learn to recognize what Bischofia javanica (Autumn Maple) bark looks like, it will look like that on every individual of Bischofia javanica.
The best way to learn your barks is to get close and touch a tree. Does the bark peel off or is it tough? Smooth or rough? Brown or grey? You may find trees that have wildly patterned bark, with green and yellow and white kaleidoscopic patterns up and down the trunk. This is not the bark colouration itself; this is lichen growing on the tree. Lichen will often grow on trees with smooth bark.
In places where many trees have smooth bark, for example, many aseasonal tropical forests, you may have five species around you that all have the same pattern of bark and all look alike. However, if you find a lichen-free section, you will notice differences.
So go look and look hard. Try to find differences and patterns, and try to combine this with leaf patterns and soon some more trees will start to make more sense. And always remember that when you are checking out a tree’s bark, you are communicating with an aged and evolved natural bodyguard that has allowed trees to grow and survive amidst a chaotic world.