Almost half of the cover of the Isabella Plantation in Richmond Park will be removed over the next five years.
About 40 per cent of the Isabella Plantation is covered with rhododendron ponticum, a non-native and invasive variety of rhododendron introduced by the Victorians.
This cover has expanded over the years, blocking light out and trapping air, creating a warm and humid environment in which pests and diseases can breed.
A significant fear is that the Isabella Plantation will become infected by fungal pathogen known as sudden oak death.
If it does it could quickly spread through its valuable plant collection.
Removal has already begun, and is being carried out partly by machine and partly with the help of volunteers from Friends of Richmond Park and the local community.
These include young people from local schools and youth groups, as part of the Challenge Network, who have been helping with the clearing process.
Hannah Pritchard, partnership and community engagement officer for the Royal Parks, said: “It is great to have so many young people here helping and learning about how the parks are maintained.”
The areas that are cleared will be replanted with mixed planting, mainly deciduous trees and shrubs. This will break up the cover, safeguarding against the spread of pests and disease, as well as providing food and shelter for birds and insects.