The response of New Zealand forest diversity to Quaternary climates

Abstract

The New Zealand archipelago lies at mid-latitudes in the south-west Pacific Ocean and has an oceanic, mainly moist, warm-temperate to cool-temperate climate. Evergreen forest forms the natural cover of ca. 85% of the landmass. The forests are not species rich; only some 420 species characteristically occur in them (Wardle 1991), ca. 210 of tree size. Approximately 70% of trees, 40% of shrubs and 30% of vines have bird-dispersed fruit, including all the podocarps; the remainder have wind-or gravity-dispersed fruits (Wardle 1991, Burrows 1994). Most terrestrial birds in New Zealand will eat fruit, but only 5 are regular consumers and effective dispersers, most important being the New Zealand pigeon Hemiphaga novaeseelandiae (Lee et al. 1991a). Seed of most forest species appears to be well dispersed over short distances of up to several kilometres. A recent study (Bray et al. 1994) found that gaps in lowland podocarp/angiosperm forest are colonised rapidly, most species arriving within 2 years. Although birds migrate to and from New Zealand, there are no migratory movements within the country. However, many fruit- and seed-eating birds move seasonally within a district, often between mountain and coast.