Gorse and broom could take over Christchurch's residential red zone and make it difficult to transform it into a reserve, an environmental scientist says.
The warning has been given at a forum organised by the Avon-Otakaro Network which wants to turn the red zone into a park for the whole city to share.
Demolition crews taking away houses are also ploughing up the land they used to sit on which a Lincoln University scientist says is activating long dormant gorse and broom seeds.
Glenn Stewart, from the department of environmental management, says this could make establishing native trees extremely difficult.
Mr Stewart says if gorse and broom take hold it could be 100 years before natives trees are able to grow through them.