Originally, New Zealand’s conifer–broadleaf forests supported a rich mix of birds, bats, tuatara, lizards, frogs and giant invertebrates. The plant and animal species had evolved together and were interlinked in terms of feeding and plant regeneration. When people arrived, bringing mammals, they disrupted or destroyed many of these relationships.
The arrival of people and predators
When Polynesians first settled in New Zealand around 1250–1300 CE, they introduced dogs and kiore (the Polynesian rat). They also burnt forests. By the time Europeans arrived, some 35 bird species were extinct. So were three frog species and three lizard species. A number of other species disappeared from the mainland, surviving only on offshore islands. This was due to hunting by people and dogs, predation by kiore, and the loss of forests.
European settlers brought more predators. Ship rats, Norway rats, cats, stoats, ferrets, weasels and possums have all reduced native wildlife populations.
Impact on the forests
Some plants rely on a particular animal for pollination, and cannot regenerate without it. Tree fuchsia, rātā, kōwhai and some mistletoe species are pollinated by the nectar-feeding birds tūī, bellbird and hihi. The kiekie vine and the parasitic wood rose (Dactylanthus taylorii) are pollinated by the short-tailed bat.
Around 70% of New Zealand’s trees, including most species in the conifer–broadleaf forest, have fleshy fruits. The seeds are mainly dispersed by birds, although lizards and bats can also spread seed. Nowadays the main native birds carrying seed from small forest fruits are bellbirds, kererū (New Zealand pigeons), kōkako, silvereyes and tūī.
Kererū, kōkako and weka are the only native birds that can eat large fruits (more than 12 millimetres in diameter). Kōkako and weka now only live in small forest remnants. So only kererū can distribute the seed of the North Island’s large-fruited trees, such as tawa, taraire, karaka, kohekohe and pūriri. Kererū also spread the seeds of another 60 forest plants. Their numbers are decreasing around the country, so the long-term survival of many plants is not assured if kererū continue to decline.