Q.A timber merchant bought 2 logs of wood from a forest & named them A & B, The log A was 50 year old & B was 20 years old. Which log of wood will last longer for the merchant? Why?

Step 1. Recall the difference between sapwood and heartwood. Sapwood (alburnum) is young, pale, actively water-conducting wood, while heartwood (duramen) is older, dark wood whose vessels are blocked by tyloses and infiltrated with tannins, resins and gums - infiltration that makes heartwood markedly more resistant to decay, fungal attack and insect damage than sapwood.

Step 2. Connect tree age to the sapwood/heartwood ratio. As a tree ages, the vascular cambium keeps adding new sapwood at the periphery every year, while older sapwood layers progressively convert into heartwood further in. The net effect is that an older tree accumulates a much larger core of heartwood relative to its thin remaining ring of sapwood, whereas a younger tree - having had fewer years for this conversion to occur - is still mostly sapwood.

Step 3. Apply this to logs A and B. Log A, from a 50-year-old tree, has had five decades of cambial activity converting sapwood to heartwood, so it will contain a substantial proportion of durable heartwood. Log B, from a 20-year-old tree, has had far less time for this conversion, so it will still be mostly sapwood. …

Connect tree age to a higher heartwood-to-sapwood ratio, then explain that heartwood's decay resista …

• Assuming a younger log is automatically 'fresher' and therefore better, without considering the durability difference between sapwood and heartwood. …