New Zealand’s natural forests can be divided into the following types:
Lowland forests
The lowland forests which extend from sea level to about 500 m above sea level in the north, and to about 300 m above sea level in the south, were the richest plant communities in New Zealand. Nearly all these lowland forests were destroyed as land was cleared for farming. They now occupy very restricted areas in the central North Island, Taranaki, Coromandel and Northland in the North Island and Westland and parts of Southland in the South Island. Extensive area of lowland forest only exist now in South Westland, Fiordland and parts of southland.
The illustration shows a typical lowland forest community. From outside the forest, you can see the variety of trees in the canopy, but the complexity of the community within the forest can only be observed from within the stand.
The taller trees showing above the canopy are emergent trees. Such trees are rimu, kahikatea, rata, kauri and pukatea and they have very diverse colours and textures. These trees are harvested for their timber.
The branches and foliage of large trees form the canopy, a close layer which screens out most direct sunlight. Typical canopy trees are tawa, taraire, hinau, mangaeao, kamahi and southern rata. Near the coast, kohekoe, karaka, pohutukawa, puriri and ngaio are more common and they form a tight wind-swept canopy.
Below the canopy are the understorey trees: young canopy trees and smaller, less light demanding trees, shrubs, tree ferns and climbing and perching plants. The lack of light and high humidity allows growth of plants with bold and rich or fine, delicate foliage. This is the most luxuriant tier of the forest.
Beneath the understorey branches is the shrub and litter layer. In dense lowland forests this can be very dark and shady. Small woody plants and ground ferns grow and fallen logs carry profusions of mosses, lichens, filmy ferns, fungi and seedlings.
Wetland Forests
A wetland or swamp is a plant community adapted to growing in conditions where the water table is close to or above the surface. It need not be large; an area of a few square metres can provide a good wetland habitat. Wetlands are dynamic habitats fringing large bodies of open water which are prone to seasonal drying. The water in swamps is seldom stagnant.
Flood plains, the ox-bows of rivers, or lakes are usual wetland environments. Plants growing in swamps face environmental hazards such as flooding, severe erosion and siltation. The nature of the plant community often encourages siltation, and wetlands can gradually ‘fill in’ to become normal lowland forests, shrubland or grassland environments.
The wildlife values add to the aesthetic appeal of wetlands. Many species are found nowhere else and they may even be found in very small wetlands.
Wetland Forest Zones:
Kahikatea Swamp Forest
A visually distinct type of lowland forest. Mature trees are notable for their tall, gaunt trunks and disproportionately small crowns. A lot of light reaches the understorey allowing a profusion of climbers, wet-tolerant small trees, shrubs and ground herbs. Cabbage trees are common. The most familiar stands are the densely-packed conical canopies of regenerating kahikatea trees.
Fringing Trees and Shrubs
These are more prone to periodic flooding than kahikatea swamp forest and its species must therefore be adaptable to marked variations in soil moisture. Manuka and mingimingi are most abundant and form a dense, neutral foreground to immature kahikatea stands and are in marked contrast to flaxes and toetoe in the foreground.
Shrubs, Toetoe, Flax, etc.
Flax forms a consistent fringe to most wetlands with the odd mingimingi or manuka nestled between its spikes. In small poorly-drained depressions it may achieve total dominance. The species which grow in this zone are able to cope with periodic flooding around the roots. They tend, therefore, to be restricted to a narrow zone fringing a body of water or the deepest depressions of wet areas.
Water Edge Vegetation
This vegetation fringes areas of still or slow-moving streams and tends to grow into areas of open water. Swamp sedge forms masses of thin brownish to green leaves arranged evenly around the crown. Its unique form and habitat have developed as it has adapted to fluctuating water levels. Raupo and rushes grow in even more open water and tend to die down in the winter, building up an organic layer which allows other species to invade.
Beech Forests
Beech forests cover vast tracts of the South Island and substantial parts of the North Island high country. They are the largest remaining indigenous forest type mainly because they grow on marginal agricultural land and have great importance as protected forests.
South Island high country stands usually comprise any one or more of the five native beech species (red, silver, black, hard and mountain). The distribution of each of these species is often zoned according to altitude or influenced by aspect. One, the hard beech, has a different distribution however. It is found on dry ridges from Mangonui in Northland through East Cape to Nelson and Marlborough, whereas the other species are found from the north Waikato southwards and throughout the South Island.
There is much regional variation in the character of beech forests. They can merge into mixed rainforests from more or less pure stands and can form coastal forests in the South Island.
In pure beech forests, poor soils and often harsh climate dictate a simple vegetative character compared with podocarp/hardwood rain forests. Beech saplings in many cases make up the mid-canopy as well.
In forests where mountain or silver beech trees are dominant, there is a strong visual emphasis on the horizontal line caused by the trees’ layering branching habit.
Structure of a Beech Forest:
Upper Canopy
The upper canopy has a strong influence on lighting and shadow patterns. Light is generally more uniform than is the case in rain forests. In cases of severe noxious animal damage the upper canopy is often all that remains.
Mid Canopy
The mid canopy is often very sparse, allowing quite extensive views within the forest – especially where noxious animals have had an impact. Often the tiered/layered branching habit of mature beech trees extends into the mid canopy. Apart from young beech trees there may be very hardy shrubs and trees and climbers capable of growing in poor soils. The mountain cabbage tree and the grass trees (Dracophyllum spp) often provide spectacular focal points.
Forest Floor
Before the impact of noxious animals, the floor was a wealth of mosses and ferns, and other species often of subalpine origin. Mosses often develop spectacularly to form thick spongy and continuous layers which help absorb water and moderate run-off.
Coastal Forests
Little native coastal vegetation is left – much of it has been cleared for new land uses – farming, urban settlements, ports and industrial facilities. The extensive planting of introduced species such as marram grass, lupins or pine trees has further threatened indigenous pingao, sand coprosma and other once common sand species.
New Zealand has over 10,000 kilometres of coastline with a wide range of landforms and habitats – vast dunes, sheer cliffs, sheltered coves, salt marshes, estuaries, mangrove swamps and rocky shrublands. The coastal landscapes were once very diverse and rich. There was regional variety too – for example, pohutukawas are characteristic of northern coastal landscapes but are not found in the south.
All these distinct plant communities have aesthetic, physical, environmental and economic value. What remains needs to be preserved and wherever possible, they should be restored where they have been modified or removed.
Coastal Forest Zones:
Coastal Forest
Windshear and a dense, uniform canopy height are typical of coastal forests. Tree trunks are often distorted and may be massive. In the north, and especially on off-shore islands, the tropical lushness of many species is uncharacteristic of a temperate climate and is a remnant of the pre-glacial flora that was once widespread.
Coastal Shrublands
Where coastal conditions are too harsh or in dry climates which cannot support a coastal forest, shrublands were once a common coastal feature. Sand coprosma, sand daphne, pohuehue, tauhinau and taupata were common, and lowland and mountain flaxes dominated some coasts. Such plants are most abundant today on rocky shorelines where they have a competitive advantage over marram grass and other exotic species which have overwhelmed them elsewhere.
Shoreline Communities
These are adapted to very harsh and unstable conditions either on sand dunes or by the sea. The vegetation has to resist shifting sand, wind and drenching salt spray. Sand convolvulus, Maori ice plant, sand spinifex and dwarf sand sedge add diversity and are still quite common in many areas. Pingoa, once a distinctive dune feature, is now rare.
Estuaries and Salt Marshes
North of the Bay of Plenty and Kawhia Harbour, many estuarine communities are dominated by mangroves. Mangroves grow in pure stands that are uniformly olive green. A characteristic feature are the pneumatophores which stick up vertically from the roots and allow the trees to breathe. Elsewhere, other estuarine species such as salt tolerant rushes and sedges were once common but are now rare in many areas.