Poachers have been slaughtering deer grazing on lawns close to the caravan pitches in Tollymore Forest near Newcastle.
Warning signs have now been erected in the Co Down forest park to tell motorists that the vehicles will be excluded after 5pm on winter evenings due to "wildlife crime".
One landowner whose property lies close to the popular forest park told the Belfast Telegraph: "They were shooting there in the field beside me - they were in the park shooting out towards my house."
The British Deer Society said improved road access to the caravan park had been installed some time ago but in the winter months this allowed opportunistic poachers to drive in, shoot deer and remove the carcasses before the alert was raised.
Spokesman Martin Malone said: "Poaching was even easier than it had been. Once you go down in there, there are no caravans left at this time of year and the deer are coming out to feed first thing in the morning and last thing at night.
"They go in shooting at the deer, throw them in the back of the vehicle and go out without any bother."
Mr Malone said it is clear the fallow deer living in the forest are being disturbed as they are not being found in their normal areas.
"We know there is a significant amount of poaching going on there," he said.
"But with the vehicle access restricted, it means that anybody who does go in to poach will have to carry the carcass a long way."
This is the season when much of the poaching takes place, with the arrival of the legal deer stalking season, the dark nights, lack of walkers and arrival of deer down into the more popular areas.
To shoot deer legally, you need a licence issued by the PSNI and you need to abide by the conditions of that licence, including using the correct calibre of gun.
That includes taking part in a deer management course, which includes a background in ecology, a shooting test and tests of recognition - being able to identify different species, sexes and winter and summer coats.
A DARD spokesperson said: "Wider security arrangements for Forest Parks are continually reviewed. Restricting vehicular access to the car park at Tollymore Forest Park during evenings in the winter time is as a result of liaison with the PSNI to assist them in their efforts to reduce wildlife crime in the area."