DOC's racing to cull predators before an expected beech mast in the South Island this summer

It expects trillions of beech tree seeds to drop from the top of the South Island to Fiordland, attracting rats, mice and stoats.

Predator Program Director Peter Morton says left unmonitored, the population in places like Arthur's Pass and Fiordland national parks will explode and acting now can make a difference.

He says between now and Christmas they need to knock down predator population in areas including Arthur's Pass and Fiordland National Parks.