I have been taking another look at the "progress report" written by Prof MPP for the Rust Family Foundation:
In the section on Waun Mawn some stress is placed on "the date of peat formation" as a guide to the age of the sockets and the speculations surrounding stone removal.
As far as the biggest recumbent stone in the putative "proto-Stonehenge" circle is concerned, MPP says this: Its former stone socket is lined with many packing stones, and the peat fills of this socket indicate that the stone fell after the onset of peat growth."
"We discovered two empty stone sockets on each end of the arc, suggesting that these stones may well be the remains of a dismantled stone circle (figs.5,6). Megaliths were removed from these sockets before the onset of peat growth on this site, indicating that the stone
circle was dismantled in the distant past."
PS. The only detailed work on the development of vegetation in the Preseli - North Pembrokeshire area is a thesis by Philip Seymour, completed in 1985. It can be seen here:
It's essentially a pollen analysis study based on a variety of upland and lowland suites, recording changes in pollen frequencies in sediment sequences. It makes the point that the development of blanket peat bogs was never very great in this area, partly because of the lack of extensive plateau surfaces where waterlogging could occur. So drainage -- mostly on gentle slopes -- was generally sufficient to prevent blanket peat development. This is borne out by the generally thin peat layers which we find across most of the landscape -- 10 cm is a rather typical thickness. Did all of the peat start to develop at about the same time? And was that time associated with the Neolithic / Bronze Age increase in land clearance associated with forest burning and increased grazing activity? Seymour suggests that this was the case, and that peat development before the Neolithic was not very marked, especially on fairly well-drained slopes. He takes a rather anthropogenic approach, suggesting that peat and soil development was very much influenced by settlement and land use practices. But there is a danger of circular reasoning -- was the environment causing man to make certain land-use decisions, or were cultural decisions shaping the environment? Walker and McCarroll (in the QRA Field Guide for West Wales, 2001) take a more nuanced approach, agreeing that periods of peat development are associated with periods of increased rainfall, leaching, iron pan creation and waterlogging -- while admitting that there is such a wide range of dates for the "onset of peat development" in West Wales that land use practices and settlement pressure must have some role to play.
It will be interesting to see what turns up when Waun Mawn is examined in greater detail.....