Sapwood
Also called: alburnum
One page. Other spellings and regional names stay on this URL.
Sapwood is the younger outer wood around a tree's heartwood, and its proportion affects durability and how readily preservative can enter.
Recognise the band
Sapwood surrounds the heartwood, the older inner wood, but the boundary and width vary with species and growing conditions. Some trees have a narrow band, while others carry much more sapwood. A pale outer strip is therefore a clue, not a fixed measurement or a guarantee of one timber's performance.
Two views of strength
Hasluck (1907) and Rivington (1875) describe heartwood as stronger and more lasting than sapwood, and recommend it for good work. Hoadley (1980) records no basic-strength increase attributable simply to the change from sapwood to heartwood. Treat those as separate questions: a board's resistance to load and its resistance to decay need not change in the same way.
Treatment and selection
The proportion of sapwood matters when preservative penetration is required. Pine species with a large amount of treatable sapwood supply many treated products. Young or immature trees can contain an unusually large sapwood proportion and may be less durable, so inspect the stock and intended exposure before choosing it.
A qualified exception
Creosote treatment can make sapwood last longer, but treated sapwood still differs from heartwood in strength. Treatment changes how the wood performs in service; it does not turn every sapwood board into heartwood or remove the need to check the species and load.