People have been urged to refrain from picking mushrooms in Epping Forest to preserve the woodland's delicate ecological balance.
The forest in Essex is home to 440 endangered fungi species and the agency conserving it has warned picking them "damages the valuable" forest biodiversity developed in the area over the past 10,000 years.
Nine people have been prosecuted by the City of London Corporation, which oversees the ancient woodland, for breaching the forest's byelaws since 2022, with offenders receiving criminal records.
One person was caught with a substantial 49kg haul.
Fungi are vital to the health of the woodland's one million trees - 55,000 of which are ancient, reaching up to 1,000 years of age.
The City Corporation says mushrooms play a key role in protecting these trees' roots, providing them with water and vital minerals.
Deer and rare insects also feed on them, it added.
Chairman of the City of London Corporation's Epping Forest and Commons Committee, Ben Murphy, said fungi play a "remarkably important role" in maintaining the balance of biodiversity in the forest.
"Picking mushrooms can seem harmless, but it actually damages our wildlife habitats and threatens rare species," he said.
"We want people to come and enjoy our ancient woodland and experience these natural wonders for themselves, but I hope by explaining why Epping Forest's fungi is so unique, we can change behaviours and discourage foragers from this location.
"If not, as conservators, we are duty bound to take enforcement action."
Epping Forest, which spans over 6,000 acres, is designated as a Site of Special Scientific Interest and a Special Area of Conservation.
It is one of the few remaining extensive natural woodlands in southern England.