What are tall broadleaf trees?
New Zealand’s tall broadleaf trees are evergreen flowering trees, normally more than 15 metres in height. The term broadleaf distinguishes flowering trees from conifers, which have narrow or scale leaves.
Broadleaf trees grow in conifer–broadleaf forests throughout New Zealand – mostly in the forest canopy, or occasionally emerging through it.
Southern beech (Nothofagus) trees are also broadleaf trees, but grow mainly in beech forests, and are usually distinguished from other broadleaf species.
Broadleaf is also the common name for one tree species, Griselinia littoralis.
Origins
All of New Zealand’s native tall broadleaf tree species are endemic (naturally found nowhere else). However, they have close relatives (in the same genus) in other countries. Plant scientists believe that some New Zealand trees are descended from the ancient forests of the supercontinent Gondwana. Others were more recent immigrants, from tropical forests north of New Zealand.
Reproduction
Most of the tall broadleaf trees have inconspicuous green or white flowers, which are pollinated by insects. The exceptions are rātā, pōhutukawa, pūriri and rewarewa, whose showy red or pink flowers are pollinated by birds and insects.
Native birds are important seed dispersers for most of the tall broadleaf trees. After they have fed on the trees' fleshy fruits, they expel the seeds at a new location.
Life expectancy
New Zealand’s tall broadleaf trees do not live as long as the conifers they share the forests with. Most live 200–400 years, while conifers can live 600–1,200 years.
Threats to trees
After Māori arrived in New Zealand, they burnt large areas of forest. Later, European settlers cleared much of the remaining lowland forest for farming. Many tall broadleaf trees disappeared from areas where they formerly grew. Forests were also logged for timber from the 19th century.
Browsing by introduced mammals such as possums, deer and goats has harmed trees. Mammal predators have stopped trees regenerating, by killing the birds that disperse seed. Rodents also eat flowers, fruits and seeds.