The Leaf

The leaf is the most iconic, most important part of the tree. In fact it is the lifeline for the tree. Without the leaf the tree would be dead and we would struggle to breath.

The leaf is the first port of call for identifying a tree.

Generally speaking if the tree loses its leaves, it is a broadleaf tree, if not it is a conifer. Once we know this we can then go on further to identify the tree. Even if the tree has lost its leaves you can generally find fallen ones by the tree and begin to look further at the leaf.

• What shape is the leaf?

• How is the leaf structured?

Most people would probably be able to identify an oak tree as it has a very iconic leaf shape. Even if you cannot tell a red oak from a turkey oak you would probably be able to look at its leaf and recognise the distinctive oak shape.

An ash leaf is structured very differently from an oak but has an equally distinctive shape (a compound of many leaflets) and therefore is relatively easy to identify. Most people would also be able to tell the difference between an ash tree and a yew tree. In fact the conifers may be a harder group to differentiate the different species but there are a few general rules which make the process a little easier. For example, the pine needle will feel like a pin when you touch the end of it.

But apart from helping us to identify the tree the leaf has a much more important function.

Without the leaf the tree would simply not function as a tree. It would be simply standing wood – great for insects, wildlife and for firewood but it would no longer be a tree. The leaf is the heart, the lungs, the life blood of the tree.

Using a process called evapotranspiration the leaf draws water up from the water table, through the roots and stem of the tree and out into the atmosphere via the leaf. A large oak tree can transpire 40,000 gallons of water a year. This process, in turn, brings up the nutrients (nitrogen, phosphorous and potassium) the tree needs to nourish itself. As well as this vital function the leaf has a molecule in it called chlorophyll. This molecule absorbs sunlight and combines the water from the evapotranspiration and carbon dioxide (CO2) to make sugar (carbohydrates). The sugars are the energy that the tree needs to grow, repair and reproduce. After this process oxygen is released back into the atmosphere as a waste product.

Simply put the leaf is integral to humans as well as the tree for without the process of photosynthesis (for which the tree is a major contributor) we would not be able to breathe.

As well as all these important factors the leaf is also used for many things:

• gardeners use it for feeding their plants;
• cooks use it for flavouring;
• herbalists for healing;
• poisoners for poisoning (!);
• artists for decorating and inspiration and
• tree huggers like me just like to look at them and study them!

Have a great new year and I hope you all get to turn over a new leaf!

Simon Zec - www.treedomsussex.co.uk

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