Saproxylic Beetles

Dr Keith Alexander, an independent specialist in saproxylic beetles, claims that sub-fossil saproxylic beetle evidence has been interpreted – wrongly – to describe a landscape that was, in the past, predominantly closed canopy forest. In his view, however, the beetle evidence – when properly analysed – clearly shows the opposite:  a landscape characterised by open-grown trees. 

For example, species like Dryophthorus corticalis and Prostomis mandibularis, one of the commonest beetles of the Early Holocene, are highly specific and require large girth tree trunks containing volumes of decayed heartwood. Closed canopy conditions do not produce such trees. 

Overall, says Alexander, sub-fossil evidence for the early Holocene indicates that 28% of the sub-fossil beetle fauna were grassland and scrub species; 13% arboreal; and 47% wood decay. In the late Holocene, 44% were grassland & scrub species; 11% arboreal; and 34% wood decay. The composition shows very low levels of shade-demanding arboreal species – so while trees are well-represented, shade is clearly scarce. The Late Holocene records indicate increased open grassland and scrub, as well as the presence of early successional mosaic species, which would be expected as humans re-colonised the land and agriculture developed. For both the Early and Late Holocene, predominant open wood pasture is consistent with the data; closed canopy forest is not.