At https://www.researchgate.net/publication/296060902 …. European oak tree chronologies archaeologically anchored in Roman times are all separated from early medieval chronologies by a severe timber depletion in late antiquity. Late antiquity here signifies the immediate post-Roman period. It embraces the 6th century low growth tree ring events in 536 and 540AD. Was something going on around this time that caused oak trees to cease reproduction? One other way to look at lack of timbers across the period is to think there is a hole in chronology. This appears to be the driving force behind the article – the AD revision of Heribert Illig and others.
According to the authors the dendrochronology gap is probably unnecessarily wide. They also suggest the Roman dendro complex as a whole is dated too old by 218 year. They also say the Christian era has been inflated by 232 years – by back dating western Roman and related history, by using astronomical retrocalculation (following the collapse of the western empire). This means a difference of 14 years between western dendrochronology and astronomical dating – which is very close to the figure hypothesized by Steve Mitchell in his various SIS articles on Bede and the Bickerman Gap. They bring into the equation Ptolemy's Almagest where astronomical events do not seem to match modern data (such as retrocalculated eclipse data). By moving Ptolemy forwards by 218 years they claim to be able to square the data – or some of it. Others have suggested a slight change in the axis of rotation to account for the discrepancies – but most professional scientists have assumed Ptolemy was at fault (and even Hipparchus).
This is a brief look at what follows. Do read – there are 49 pages.