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Tree parts

Figure 2: Tree cross section

For any species each passing year brings new growth rings in the tree trunk (refer Figure 2). The centre of the tree is often referred to as the 'pith' and is rarely used except in poles, piles and where very large sections are required, eg girders. The heartwood (or truewood) is usually darker in colour and extends from the centre (or pith) in the tree out to the sapwood. The sapwood is usually lighter in colour and extends from the heartwood to the cambium layer.

The sapwood is the living part of the wood and conducts water and nutrients upwards from the roots to the leaves and is a storage area for sugars and starches. As the tree grows the inner sapwood is converted to heartwood. Each has different properties relevant to construction applications.

• Sapwood has lower natural decay resistance than heartwood, but where necessary can be boosted by adding preservative treatments,
  
• Sapwood and heartwood have similar strength and dimensional stability,
  
• Both heartwood and sapwood may co-occur in timber used for appearance and structural purposes, but in some applications sapwood may be removed or limited in content.