DoC ranger Adrian Walker urged people to keep their pets out of Waitangi Forest, which stretches from the outskirts of Kerikeri to Waitangi.
It had the highest kiwi density of any plantation forest in the country but the birds were vulnerable to dogs being walked in the forest or allowed to wander, he said.
The forest had been the site of major predation events in the past - most notably in 1987 when a dumped dog is thought to have killed hundreds of kiwi over a six-week period - but kiwi numbers had bounced back since then, helped by pest control work carried out by hapu-led community group Iwi Kiwi and Northland Forest Managers.
The 2200ha Waitangi State Forest and the adjoining 570ha Waitangi Endowment Forest were a model of how plantation forestry and kiwi could coexist, Mr Walker said.
It was not known if the dog was being walked in the forest or had wandered in from a nearby property.
Since then, on September 1, an adult male kiwi was attacked by a dog as it was being walked along a road in Kaeo. The bird was still alive when it was taken to the DoC office in Kerikeri but its injuries were so severe it had to be put down.
Also this month a possum hunter was spoken to by DoC after a leg-hold trap left on the ground caught a kiwi near Russell, and a kiwi was run over at Dove's Bay near Kerikeri.
That bird survived and is being cared for at the Whangarei Bird Recovery Centre. It was one of 70 kiwi hit by cars in the Doves Bay/Rangitane area since 2000, Mr Walker said.
After the Wharau Rd deaths in 2015 DNA testing found a bull mastiff bitch was responsible for killing some of the birds. The dog owner was fined.
■ If you have information about the Waitangi Forest kiwi death, or you see a dog in the forest, call DoC on (09) 407 0300 or Northland Forest Managers on (09) 407 7115. After hours you can call the DoC hotline 0800 DOC HOT. Dogs are not permitted in the forest without a permit.