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Since New Zealand
became isolated from Gondwanaland approximately 80 - 90 million years ago, it
has many archaic plants and animals, all of which have evolved in the absence of
mammals. Many of New Zealand's forests are unique, such as the kauri and
podocarp forests which date back 200 million years. Below we present a brief
overview of New Zealand's prominent native vegetative cover.
Kauri Forest | Podocarp Forest | Beech Forest | Mountain Cedar | Alpine Plants
The leaves of the mangrove are typical of xerophytes, they are
sclerified with a shiny upper surface and white tomentum underneath to
reflect the intense light coming off the water. Its root system is very
strong, and forms a horizontal network, just under the mud surface. The
vertical pencil-like aerial breathing roots, ‘pneumatophores’ stick
out of the mud for some 10 cm. These have a water-resistant bark and a
spongy aerenchyma, stiffened by an axis of vascular tissue. These
pneumatophores are often coated with the estuarine barnacle, and black
mussel. Rock oysters can also encrust the pneumatophores and trunk of the
mangrove, so much so, that their weight can bend the pneumatophore over.
This sheltered area of water underneath the mangrove canopy also provides
an important and protective breeding ground for crustaceans and fishes.
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The beech species are adapted to growing on low fertility and poorly drained soils, dry sites such as ridge crests, and areas of recent disturbance. They often form extensive, relatively uniform forests in the montane region, but at lower altitudes give way to the more competitive hardwoods and softwoods. The beech species tend to form discrete pure stands rather than occur in intricate mixtures with other tree genera. This may be related to mycorrhizal symbionts.
Beech forest occurs almost throughout the full latitudinal range of the North and South Islands, though its distribution in the north-west tends to be local. It does not occur naturally on the neighbouring Stewart Island, nor does it occur on the subantarctic islands south of New Zealand such as the Aucklands, Campbell and Snares, even though these fall well within the latitudinal range of the genus in South America.
The altitude of the beech timberline varies depending on latitude, from
600-1400 m a.s.l.. Hard beech has a more northerly distribution and is
associated with lower altitudes than the other beeches, whereas mountain
beech has the highest altitudinal range of any beech species. At lower
altitudes, beech is associated with the podocarp species, particularly
rimu, and the broad-leaved hardwoods, kamahi, and in the
North Island, tawa. Within their altitudinal range, beech
generally form pure forest stands. In montane and subalpine regions on
shallow and poorly drained soils, beech is sometimes associated with cedar
and shrub Dacrydium species. At their upper altitudinal range, on
exposed ridges, beech tend to become dwarfed with wind-shorn canopies. On
the most exposed sites, silver beech can be reduced to flattened cushions
with slender layering branches, sometimes less than 50-100 cm high and 15
cm diameter. In such sites, beech can develop specialised growth forms as
a result of drifting and avalanching snow.
The North Island volcanic mountains supporting alpine communities are: Egmont 2,518 m (8,260 ft) on the west coast; Ruapehu, 2,796 m (9,175 ft), Tongariro 1,986 m (6,517 ft), and Ngauruhoe 2,290 m (7,515 ft) on the central plateau. These volcanoes reached their present height during the last glaciation in the Pleistocene, except Ngauruhoe which is younger. Their relatively early evolution has meant that alpine community diversity is relatively low compared with other alpine areas. The highly erodible porous larva and loose scoria makes it difficult for plants to become established.
About 93% of the alpine plant species are endemic to New Zealand; these are considered to have originated either here or on the Antarctic continent. New Zealand’s alpine flora has probably evolved within the last two million years or so during the last glaciations, from pre-existing nonalpine flora, together with chance immigrants from other areas that supported alpine plants, such as Antarctica, or Australia. This theory of the recent evolution of alpine flora, is supported by the widespread occurrence of hybridism and the variation or polymorphism in many of the alpine plant groups.
In the 1000 m altitudinal range between the tree line and snow line, there is a greater range of alpine vegetation than occurs in most other parts of the world. Because of the great plant diversity in this area, two zones are recognised. The low-alpine zone is dominated by tussocks, Chionochloa spp., Coprosma, Dracophyllum, Hebe, Celmisia, Ranunculus, Gentiana, Aciphylla, Anisotome, and Astelia. Some of these are represented in the high-alpine zone where there is less complete plant cover. The transition between the low and high-alpine zones is generally too subtle to detect, however, it mostly occurs half way between the tree and snow lines. Plants in the high-alpine zone tend to grow in a compact creeping form (cushion) close to the ground, such as the Raoulia (vegetable sheep). The ground in this zone can be very mobile in areas of scree, sloping 30 - 35 degrees. However, it is generally only the top 10 - 20 cm layer that is mobile. Beneath is a compact, permanently moist soil, where highly adapted plants with large taproots or rhizomes can persist. The leaves these plants do not persist over winter, and are delicately attached to the stem so that they break off easily without damaging.
If you find any information above that is incorrect or misleading, please feel free to contact us.
