Story: Southern beech forest
Page 1 – Southern beeches
The European botanists who first described plants in the southern hemisphere often named them after similar-looking northern hemisphere plants. New Zealand’s beech trees were first thought to resemble birches. Later they were described as true beech (Fagus). In 1850 a Dutch botanist recognised that southern-hemisphere beeches were distinct from northern species and named them Nothofagus, meaning false beech.
The term southern beech refers to beech species native to countries south of the equator – New Zealand, Australia, New Caledonia, New Guinea and South America.
New Zealand has two main types of native forest: conifer–broadleaf forest (including kauri forest) and beech forest. Most conifer–broadleaf forest grows at low altitudes, so has been logged and cleared for farming. Beech forest usually grows in hilly or mountainous areas, so has been left.
Pure beech forest now comprises almost half (about 3 million hectares) of New Zealand’s remaining native forest. Forests of beech and other tree species make up one quarter (about 1.3 million hectares).
Beech trees are found in 80–90% of native forest in the South Island, but in only 40% in the North Island. They do not grow naturally on Stewart Island.
Beech forest is typically less complex than other types of native forest:
- There are few other species in the canopy layer.
- There is a sparse, open understorey mostly made up of young beeches.
- There are few epiphytes (perching plants) or climbers.
New Zealand beeches
New Zealand has four beech species and one subspecies. All are evergreen, broadleaf trees. Most New Zealand trees and shrubs are pollinated by insects or birds, or have their seeds dispersed by birds, but beech’s dry, nut-like seeds are spread by the wind. All except silver beech will form hybrids wherever they grow together.
Red beech (Nothofagus fusca) is the largest beech species in New Zealand. Trees average 24–30 metres in height, with trunks 1.4–2.0 metres in diameter. When mature they have massive crowns, large flanges at the base of the trunk, and root buttresses. Of all the beeches, red beech is least resistant to unfavourable conditions. It grows on warm, lower- to mid-slopes, and deep, fertile, well-drained soils.
Hard beech (Nothofagus truncata) can grow as tall as red beech, but its trunk is more slender, at 0.6–1.2 metres in diameter. These trees develop basal flanges and buttressed roots. A low-altitude species, hard beech grows further north than other species, and is less tolerant of low temperatures. It can grow in poorer and more drought-prone soils than red beeches.
A good year
In mast years – years of exceptional flowering and seeding – the male flowers of mountain and black beech colour the entire forest canopy red. Masting may be a reproductive strategy, producing more seeds than can be eaten by birds and insects, or it may be a response to warm weather the previous summer.
Mountain beech (Nothofagus solandri var. cliffortioides) is the smallest New Zealand beech, reaching 12–15 metres high, with a trunk diameter of 0.5–0.75 metres. It grows at higher altitudes (from about 700 metres above sea level up to the treeline), on drier sites, and tolerates poorer drainage and soils than other beeches. Mountain beech on exposed or elevated sites sometimes grows as hummocks only 45 centimetres high. Snow drifts and avalanches can make its trunks grow horizontally for several metres before turning upright.
Black beech (Nothofagus solandri var. solandri) usually reaches 20–25 metres in height, with a trunk diameter similar to that of hard beech. Its trunks do not usually form flanges or buttresses. Black beech grows in poor and drought-prone soils.
Silver beech (Nothofagus menziesii) stands up to 20–25 metres high and has a trunk diameter of 0.6–1.5 metres. Its trunks can form heavy buttresses. Silver beech grows at similar altitudes to mountain beech, but needs wetter conditions and does not tolerate poor drainage or infertile soils. Like mountain beech, silver beech can grow as hummocks at high altitude, and can develop partly horizontal trunks in deep snow.