Although New Zealand has a temperate climate, its lowland conifer–broadleaf forests have the layered structure of subtropical rainforests, with many small trees and shrubs growing below the main canopy. Even southern beech forests, which grow at higher altitudes and have a less complex structure, often have a dense understorey.
Several hundred species of small trees and shrubs grow in these forests. Although many belong to genera that are spread widely around the world, about 80% of them are endemic – they are found naturally only in New Zealand.
In general, small forest trees and shrubs become less varied and dense with increasing latitude and altitude. Larger-leaved, more tropical-looking species are gradually replaced by smaller-leaved species that are adapted to the cold. However, many small trees and shrubs are also among the first to grow in open ground or gaps in the forest, and can be found in abundance in young regenerating forest.
Peculiar growth forms
Some forest understorey species have growth forms that are unique to New Zealand: twiggy, small-leaved shrubs that look alike but are not related. About 14% of these lookalikes are actually juveniles, which grow into adult trees that look quite different – from the young version, and from each other.
The origins and purposes of these features have aroused much interest.