Arnhem local council is going back to the Middle Ages to stop the American oak tree from stifling native species, by letting loose a group of pigs to eat the acorns.

“This way of managing woods has completely disappeared,” a council spokesman told local paper De Gelderlander. In the Middle Ages feeding pigs for free and managing woodland went hand in hand, he said.

The American oak (quercus rubra) is slowly taking over the woods around Arnhem, endangering native oaks and firs. The thick foliage also stops plant growth on the ground, which in turn limits biodiversity as mosses and insects disappear.

While foraging for the acorns, the pigs disturb the soil which will then be seeded with herb mixtures.

“We are reintroducing this historical method because it is a wonderful way of managing our woods in a sustainable manner,” city biodiversity chief Marco van der Wel said.

Arnhem is putting nine Bonte Bentheimer pigs to work in the woodland at Groot Warnsborn along the A50 motorway to start with, and will then move them on to another part of the area, “much like a flock of sheep”, Van der Wel said.

The pigs will be around for a year at least and if the trial is successful, they will also be put to work in other woods around Arnhem.