'Fly grazing' ponies under threat in Monks Wood, Wick
Up to 40 horses, illegally abandoned in the Vale of Glamorgan, might be destroyed if new homes cannot be found for them.
The Welsh Gypsy Cobs were left on community land near the village of Wick.
The Woodland Trust, which owns the site, said so-called "fly-grazing" was a growing problem across south Wales.
South Wales Police said it was aware of the incident but could not intervene because it was a civil matter.
The ponies are on a piece of land known as Monks Wood.
Villagers, helped by the Woodland Trust, planted trees, some in the memory of loved ones, and they enjoyed the beauty spot as a community facility.
But just before Christmas the gates were broken and about 40 Welsh Gypsy Cobs were abandoned on the site.
The Woodland Trust said the area had taken a long time to establish, but the ponies were causing a lot of damage.
Before Christmas it posted a formal notice under the Animals Act 1971 warning the owner that it would have the right to remove and sell the horses if they were not removed within 14 days.
This deadline has now passed, but the owner is yet to come forward.
Jerry Langford, Wales director of the Woodland Trust, said: "The welfare of these horses is a major concern but we cannot guarantee their future.
"None of the animal sanctuaries have space for them and there are huge practical difficulties in moving potentially diseased animals around the country.
"We have a responsibility to the local community who worked hard to raise funds to buy this wood, to ensure that it is protected from damage, and is reopened to the public as soon as possible."
The trust said the animals were trampling the woodland floor, stripping bark off the trees, keeping out visitors, and they would eventually run out of food, causing a real animal welfare issue.
Lee Hackett, of the British Horse Society, said "fly-grazing" was a growing problem.
"There are many hundreds of these horses illegally abandoned on other people's land in south Wales," he added.
"This is a real animal welfare problem and puts an unfair burden on landowners who are faced with the unenviable problem of what to do with them."
The Woodland Trust has had hay delivered, but some of the ponies have died.