Human impact on the environment and biota of New
Zealand was both late and severe. Not only did
Polynesians burn the forests and and reduce the
avifauna in variety and numbers, but their
introduction of the rat and heavy exploitation of the
larger birds virtually eliminated the only indigenous
browsing vertebrates. Thus, even that vegetation
which survived unscathed is likely to have differed
from its pre-human condition. These islands are
therefore still in a ferment of biological change that
began with Polynesian settlement shortly before 1000
yr B.P. However, anthropogenic modification is just
one of many environmental factors: large-scale
erosion, earthquakes, volcanic eruptions, fire, extreme
climatic events and long-term climatic trends are all
part of the natural background of change. It is
difficult to distinguish the effects of these natural
changes from those caused by humans.