The closure will affect the section between Binderton Bridge and West Dean Tunnel for four months from Friday, May 21 until October 2021.
The South Downs National Park Authority said it is 'necessary to remove diseased ash trees' that have suffered Ash Dieback to ensure public safety on the route.
Two alternative routes will be available for cyclists and walkers that link Binderton Bridge with West Dean – via bridleway 455 and bridleway 457 – or by using the paved shared-path along the A286. Temporary signage and diversions will be put in place to help people take the alternative routes.
Allison Thorpe, access and recreation lead for the National Park Authority, said: “Our absolute priority is the safety of the public using the Centurion Way and, in liaison with the West Dean Estate, we’ve had to take the difficult decision of temporarily closing a section of the route.
“There are alternative off-road routes in place for cyclists and walkers and so people will still be able to access the heart of the National Park and enjoy some wonderful views. We’re committed to keeping disruption to a minimum while this essential Ash Dieback work takes place.”
The work to remove the diseased trees will be carried out in stages by arboriculturalists and professional ecologists, with the first phase including habitat surveys to ensure compliance and good practice.
The National Park Authority will provide updates on the re-opening of the section via its website www.southdowns.gov.uk and social media channels.
The Centurion Way is an 11km cycling and walking path between Chichester, Lavant and West Dean and follows the old dismantled Chichester to Midhurst railway line, which closed in 1991. Following the latest path upgrade in 2015 as part of a project led by the National Park Authority, plans are now being developed to extend the Centurion Way from West Dean to connect with the South Downs Way at Cocking.