New Zealand’s native grasslands are dominated by tussocks – grasses that have a clumping growth form, with stems fanning up and outward from a central bunch.
This growth form helps grasses to survive. Much of the plant is protected in a bunch of basal stems, unlike woody plants, which have exposed and vulnerable growing stem tips. Tussocks tolerate fire better than most woody plants.
In the past, farmers burnt off large areas of tussock and tried to replace it with imported grasses, so they could graze more animals. But many people’s attitudes have changed, and grasslands are now valued as important native ecosystems. Tussocks are also popular with gardeners.
New Zealand has around 190 native grass species. Native tussocks belong to three genera: Chionochloa, Poa and Festuca. Most of the 24 species of Chionochloa have a tussock growth form – so do three important Poa species and three Festuca species.
Grasses favour open areas. Very few grow under a closed forest. A few grow on sand dunes or coastal cliffs, but they do not form extensive grasslands.
Most New Zealand grasslands are tussocklands. Before people arrived, there were also some low-growing sward (carpet-like) grasslands – around 2% of the total grassland area. These have been largely replaced by introduced grasses for farming.
Extent of grasslands
The extent of native grasslands has varied in response to the climate, and the frequency and intensity of fire. Over the last 10,000 years (the Holocene period), grasslands formed a mosaic with areas of woody vegetation in many parts of New Zealand. The pattern varied according to altitude, topography, slope, aspect and disturbance (including fire). Grasslands mainly grew in areas that were colder or drier than those which supported shrubland, woodland or forest.
Grasslands reached their greatest extent in the early 1800s, after Māori fires had burned much of the forest in the drier regions, and before Europeans settled in New Zealand and cleared land for farming. At that time, grasslands probably covered about 31% of the mainland (around 83,700 square kilometres).
What is a tussock?
‘Scientifically speaking, a tussock is not actually a single group of related plants but a growth habit – a particular arrangement of stems and leaves which forms a tuft of vegetation. The stems, or tillers from which the leaves sprout are unusually tightly clustered.’ 1
Grasslands and animals
New Zealand’s grassland ecosystems developed in the absence of grazing mammals. Birds and invertebrates were the main browsers until European settlers brought grazing mammals in the mid-1800s. Scientists still debate the extent to which introduced herbivores have taken the place of native browsing birds such as the now extinct moa.
Grasslands have a rich and diverse invertebrate fauna. As specific groups of life forms evolve over millions of years, this indicates the prolonged presence of grassland habitats at all altitudes in New Zealand’s past. They also supported many reptiles and birds.