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Essen tial Woodcarying Techniques

softwoods are evergreen and hardwoods are dcciduous. You only havc to look at larch (Larix decidua) and holly {Ilex aquifolium) in wintcr to realize that this łs wrong.

WATER IN WOOD

Sapwood AND Hf. ART WOOD: COLOUR AND CONTENTS To use wood effectively it is essential to know the role of water in the life of the trec. A cross-scction of a maturę tree trunk usually shows a band of lighter-coloured wood next to the bark (Fig 2.12). Tliis is the sapwood, and it is through this that the water moves from the ground to the Jeave$. As the tree grows in diameter not all the wood is nceded for conducting sap, so the core or hcartwood bccomcs inert. As this would lcave it without means of combating disease or repairing itself the tree deposits waste products (the sorts of by-products of food that animals expel from their bodies as poisonous or useless) into the wood next to the sapwood to provide a natural preservative. Trecs which producc the darkest heartwood are gcncrally the most resisrant to decay and woodworm. Timbers with light-coloured heartwood such as sycamore (Acer pseudoplatanus), limę, holly and birch (Betula spp.) rot very quickly if not carcd for (Fig 2.13). Any sapwood, being light, also rots fast. Sapwood also contains starch and nitrogen which are readily consumcd by moulds and other fungi, bacteria and woodworm.

Poisons in Wood

Because of the so-called extractives which give wood its colour and natural preservatives, many woods are regarded as poisonous, especially in dust form, occasionally causing an allergic response and, in sonie cases, cancer. The list is

Fig 2.12 The ctit end ofa smaliyew tree. The dark area is heartwood; the light band is sapwood. The Y-shapedfissnre is where the buttresses have begiin to separate into three stems and is lined with bark. Had the tree continued growing for many years this fault would have been unpredictable from the outside of the tree.

FIG 2.13 A piece of spalted beecb showing the zonę lines where rival fungi have met. The wood is likely to crumble when carved.

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