The important point to appreciate is that Vitruvius believes he has a rational perspective; today we would call it scientific. But that would be inappropriate in this context, and with the benefit of technical hindsight, we know just how wrong he turned out to be.
It is worth noting that a great deal of less valuable timber would be used in temporary scaffolding and the formwork required for the creation of masonry and concrete structures.
Alder: Alder is another familiar tree, which Vitruvius tells us was grown, then as now, close to riverbanks. He notes that it is of little value for buildings, but is exceptionally durable wood when used under water, and was widely used in his time for piles, notably in Ravenna.
Throughout, Vitruvius is fulsome of his praise of the larch.[left] Perhaps significantly, Vitruvius chooses this point in the narrative to push the idea of importing larch into Rome, to be used for fire resistant eaves to protect buildings and prevent fires from spreading. We will likely never know if this civic-minded innovation was in someone’s pecuniary interest, or if it was adopted.
Hornbeam is not a timber traditionally associated with building, but because of its toughness, was traditionally used for things like woodwork in machinery and pulley-blocks. This reminds us of Vitruvius background in military engineering and the wider field that ‘architecture’ embraced.