paul:
how the piles are so well preserved at Fiavè
As I understand it wood can be preserved when, and as long as it stays fully waterlogged but cannot stand being dried after being wet - thus special actions had to be taken for ships like the Vasa and Mary Rose when they were raised.
The excavations at Fiave took place between 1969 -76 and, presumably, nothing was visible before that? The Nomination File does indicate some issues -
"spontaneous vegataton growing on the upper parts of the piles emerging from the water of the old trenches is a serious threat ...... it is being monitored and risk assessment is under way" - Well that's ok then!! Certainly, given the way in which the piles in Els's photos are being allowed to stand proud of the water and are presumably, depending on weather and water level, both regularly drying and then getting wet again is surprising! Such wood contains potential valuable archaeological information in its dendrochronology, chemistry and biology - and no doubt in ways of which we are currently unaware. Normal good archaeological practice is to do everything possible to preserve such evidence for the future - hence the "back covering" of the site I visited and reported on near Ulm in Germany.
See
http://www.sha.org/documents/Technical_briefs_articles/vol1article_05.pdf