Why does pottery become scarce during the Saxon/Anglian period...

[Marc Berger]

I thought Britain was heavily wooded until the time of Henry VIII who decimated the woods for timbers to build his ships.

this was heavily wooded Britain that had its own probably more important magna carter
http://info.sjc.ox.ac.uk/forests/Carta.htm
the woodlands seem to have been created out of an all mans no mans land principle post Norman top down with the rulers claiming ultimate right in times of need over designated areas. Most of medieval accounts though show payments for major construction timbers made sourced from individual estates/parishes the woodlands of which are less well defined.

This though is wood for construction rather than wood for firing roman military multinational civil engineering tile brick pot and keeping the underfloor heating on tickle over fed by the local Saxon slave who had an alternative choice trying to fathom lion feeding as a spectator sport for the first time.