Lewis will be regional manager for the South, based in Withyham, East Sussex. He will co-ordinate the UPM Tilhill teams in the Midlands, West Country, East Anglia and the South East.
Liddon and Johnson have become regional managers for the North and central UK respectively.
Robert Herbert steps into Liddon's former role as district manager for south-west Scotland; Rory Chisholm takes over from Johnson as district manager for North Wales; and Rick Vallis has been promoted from deputy to district manager of the south-east England district.
In addition, Iain Sutherland, formerly timber operations manager for the North, takes on a new role as biomass business manager, and Richard Baker is promoted to regional harvesting manager for the South.