Comparison of forest structure and regeneration on Bench and Stewart Islands, New Zealand

Bench Island, located 5 km E. of Stewart Island, has similar vegetation to the latter but lacks any introduced browsing animals. The population structures of the main canopy tree species, Metrosideros umbellata, Weinmannia racemosa and Dacrydium cupressinum, are similar on both islands. However, on Stewart Island, browsing animals, mainly American white-tailed deer (Odocoileus virginianus) and the Australian brush-tailed possum (Trichosurus vulpecula), have drastically reduced the abundance of sub-canopy trees and shrubs, ferns and herbs. The regeneration of the tree fern Dicksonia squarrosa is also severely impeded by browsing, and the generally sparse character of the understorey vegetation on Stewart Island contrasts sharply with the nearly continuous cover on Bench Island. On Stewart Island, the more open main tree canopy and greatly reduced abundance of plants in the 15-140 cm tier results in greater species frequencies in the 0-15 cm tier, but browsing pressure i!