Pigs: The Common of Mast
In the autumn commoners are allowed to let pigs roam the New Forest. The foraging domesticated pigs can then help sweep the forest for acorns in particular. Acorns can poison ponies or cattle. So the pigs help clear the acorns which helps keep the ponies and cattle from becoming ill.
Recently about 3 or 4 hundreds of pigs are depastured onto the Forest. Many years ago there would have been thousands.
The Wild Boar
The domesticated pigs ancestor the wild boar used to roam wild in the New Forest. These would have been hunted, like the deer by the royal hunting parties. Although much more dangerous.
One theory to explain the legend of the Burley Dragon was that it could have been a rogue wild boar. They can grow huge, and can be extremely vicious. The sight of one charging through the mist would have been terrifying.