Protesters have called for a halt to council plans to sell the freehold of four farms in East Sussex.
The rally and walk in protest at the plans for part of the Eastbourne Downland Estate was held by Friends of the Earth on Saturday.
Campaigners fear the sale could reverse decades of restoration, wildlife protection and improved public access.
But Eastbourne council said the land's use cannot change and is protected by covenants and its national park status.
Eastbourne Friends of the Earth has collected more than 2,500 signatures on a petition to stop the sale.
It said the estate is of local, national, and international importance because of its rare wildlife habitats and beauty.
Once the council has sold the freeholds, it fears the way it is managed could damage it - a concern backed by other countryside action groups including the CPRE and the South Downs Society.
But Eastbourne Borough Council said it had been leasing the land on the Eastbourne Downland Estate to tenant farmers for many years.
Councillor David Tutt said if the freehold was sold the land would continue to be farmed and all existing rights of way would remain in place.
He added: "A vast majority of downland farms are already in private ownership and have been for generations.
"The only noticeable difference selling the freehold will make will be improvements to the open downland which is accessible to the public as the council plans to spend around £1m to improve paths, signage and visitor facilities.
"The remainder of the proceeds from the sale will go towards supporting the ambitious capital programme the council has.
"This aims at providing jobs, housing, improved public realm, recreation and town centre improvements."