Police are looking out for shooters who are illegally using the Dome Valley forest north of Auckland as a range.
Police in Wellsford said almost every road sign and safety marker in the Conical Peak and Waiwhiu Road area had been shot at.
Sergeant Kellie Bissett said the ground was littered with shells and broken glass.
She said the behaviour posed a significant risk to the safety of visitors and forestry workers.
Ms Bissett said the police were working with the forest owners to clean up the damage.