The Effects of Introduced Wild Animals on New Zealand Forests

Abstract

Abstract Although New Zealand lacks native terrestrial mammals (except for two species of bats), more than 50 species of mammals have been introduced by human beings and have become established since the late eighteenth century. The impact of introduced browsing and grazing mammals on the vegetation of New Zealand is widely perceived as an ecological disaster involving severe depletion of the plant cover and widespread accelerated erosion. Although there is no doubt that introduced mammals have had profound and pervasive effects, determination of the magnitudes of these effects on the native forests is surprisingly difficult. For example, red deer (Cervus elaphus) are known to cause important shifts in understory species composition in beech (Nothofagus) forests but their long-term effects on the regeneration of the dominant tree species are not clear. Similarly, apparently excessive tree mortality in coniferbroadleaved forests has often been attributed to browsing by the Australian brush-tailed opossum (Trichosurus vulpecula), but natural stand dynamic processes also may contribute significantly to this mortality. Consideration of the effects of red deer and opossums on the native forests of New Zealand illustrates the difficulties in distinguishing animal-induced changes from other types of vegetation change. Key Words: deerdisturbanceforestherbivoreimpactintroduced animals Nothofagus opossum