FOCUS on………. Being a tree
Firstly it is important, when we talk about ‘trees’, to understand that they aren’t a distinct group of plants, it is simply a body form, in the same way that fish, dolphins and squid share some similar features, but they aren’t closely related. Secondly we need to realise that the ‘tree’ as a concept has been around for a very long time. The first ‘forests’ were around some 300- 400 million years ago, and consisted of plants similar to the ones above. Selaginella sp is what is called a ‘Club Moss’, and its relatives back then, grew over 100 feet in height. As you can see from the photo, it’s only a few centimetres in height today. Tree ferns, you will still find today, as components of many forests and still reaching reasonable heights.
So what is the point in being a tree? Basically it is simply to get you up above the other plants that can compete with you for light, and to get you out of the way of things that can eat you, or fires that can fry you. Seems pretty straightforward then, so why doesn’t everything grow like this, and why would things that had tree like relatives be tiny again today? Part of the answer is that it takes a lot of energy to make wood and become a tree. A tree builds its body one small piece at a time from carbon dioxide, water and sunlight. These three components create sugars which are then joined together to create larger molecules, which form the building blocks of wood. It is easier in some ways to be smaller, and not go to such immense effort, but if you can get it right, the rewards of being big can pay off.
There are two main components that make wood called lignin and cellulose. Most people will have heard of cellulose, it’s the stuff that lettuce and celery are made of. It’s soft, and in the case of lettuce bendy- celery tends to break into strings of bendy cellulose when you snap it! Lignin is a hard substance, very resistant to squashing. It’s these properties that allow us to use wood to build our own structures.
When you think about a giant redwood, there may be anywhere between about 2000- 4000 tons of wood above the base. The tree stem has to be able to cope with immense crushing forces, but also be able to flex in the wind, as we discussed last week. Trees have to make this amazing tough and flexible structure, using only what they can get from the soil around them, and the light of the sun. This means that they don’t waste energy, and only lay down wood where they want it.
Take a look at this ash tree:
Trees will incorporate other objects such as fences, gateposts and buildings into their structures, to save laying down wood.
Trees are very good at sensing what is going on around them. The living tissue in wood responds to stretching, squashing and irritation. Being able to incorporate other things into your body structure is a blessing and a curse., It saves energy, but at the same time, the old stone wall you are using to prop yourself up, may not be as strong as you think!
The picture below (from http://nowthatsnifty.blogspot.co.uk/2010/02/22-trees-growing-around-objects.html), pretty much sums it up…..