Deer in the headlights: sleepwalking our way to a native forest catastrophe

A slowly unfolding native forest crisis is currently occurring in Aotearoa | New Zealand (hereafter New Zealand) because the numbers of deer in many native forests have risen rapidly to unsustainable levels. The natural forests of New Zealand are critical for many reasons: as habitat for native biodiversity, for providing resilience to catchments, as vast stores of carbon, and for their cultural values to Māori (indigenous people of New Zealand) and Pākehā (non-Māori people of New Zealand) alike. These critical values are being compromised by high deer numbers. Deer are causing irreversible harm to both old-growth and regenerating native forests through browsing and impacts on forest floor soil and litter. The flow-on effects from these include changes in understorey and eventually canopy composition, reduced habitat quality for fauna, and the retarding of regeneration caused by deer browsing of disturbed areas, such as on landslides, causing reduced water retention and enhanced sediment loss. Introduced mammalian herbivores, especially deer, and climate change stress natural forests. Their combined impacts are likely to be far worse than their effects individually. While the effects of climate change on old-growth forests cannot be directly mitigated, their vulnerability can be reduced by reducing the impacts of feral deer. Regenerating forests can also be protected so that they stand the best chance of being resilient to climate change as they age and mature. Control of deer is complex, especially because of the social values these animals have. Ecologically, the case for reducing deer to effectively zero densities is clear, but this cannot be undertaken in isolation from other values. We propose a national deer strategy and control programme that prioritises native biodiversity and climate change resilience over any other values that deer might have. This will require that in many places, deer numbers are reduced to zero, while in other places deer are managed for their social values. Ignoring the deer problem any longer will result in a catastrophic outcome for our native forests and for all people in New Zealand.