Introduced deer at low densities do not inhibit the regeneration of a dominant tree

Abstract

Deer have been introduced to forests worldwide as non-native invasive species. Red deer (Cervus elaphus scoticus) were introduced to New Zealand in 1851, became abundant throughout its forests, then their populations declined to current, typically low densities. It is uncertain whether browsing by red deer at low densities reduces growth and survival of seedlings of the dominant trees in New Zealand forests. We investigated this experimentally in a cool temperate rain forest dominated by mountain beech (Fuscospora cliffortioides, Nothofagaceae). Mountain beech regeneration depends on stand-level disturbances. Red deer are thought to exert strongest effects on regeneration in canopy gaps. Our factorial design was creation of canopy gaps, by felling trees, contrasted with intact canopies, and fencing to completely exclude deer, and unfenced treatments. We measured growth and mortality of mountain beech seedlings (initially 15-135 cm tall) in plots after 6. years. Seedling growth rates were much greater in canopy gaps than under intact canopies. They were greatest in gaps from which deer were excluded and the seedlings that were largest when gaps were created grew most rapidly. Mortality of seedlings was largely related to initial size and rates were greater in canopy gaps because of self-thinning. We conclude that red deer, at current low densities, affect the regeneration of the dominant canopy tree of these forests slightly, but at levels that are unlikely to prevent canopy replacement. Forest managers should focus efforts on managing deer and their effects on forest regeneration in the period that follows major canopy disturbance.