The eastern South Island and Central Otago lie in the ‘rain shadow’ of the central mountain ranges – they have low rainfalls and dry soils. Before humans arrived in New Zealand, these areas were clothed in forests and tall scrub. They have been frequently burnt and heavily grazed, which few native woody plants can survive, so grasslands and shrublands now dominate. All but the most fire-tolerant and unpalatable plant species are gone from the slopes and valleys.
Kānuka (Kunzea ericoides) is found in the drier areas of the eastern South Island. Like mānuka, it is a pioneer plant (able to grow on cleared land). In some areas, it is replaced by broad-leaved forest trees after 100 years or so. However, in the driest locations of Central Otago, kānuka is a permanent part of the vegetation, and has formed open woodlands along with kōwhai (Sophora microphylla) and Hall’s tōtara (Podocarpus hallii).
Matagouri (Discaria toumatou), also known as wild Irishman and tūmatakuru, is widespread in semi-arid and moderate rainfall regions of the South Island below 1,000 metres.
The only native plant with thorns, it forms sparse to dense shrublands among short-tussock grasslands. Common associates include other small-leaved, highly branched shrubs such as mingimingi (Coprosma propinqua), porcupine shrub (Melicytus alpinus), native brooms (Carmichaelia species) and sweet briar (Rosa rubiginosa). Although plentiful now, matagouri was even more so in the mid-1800s when it grew up to 6 metres high among tall tussock. Matagouri can resprout after a fire, but frequent burning, heavy sheep grazing and rabbit browsing have reduced its spread.
The introduced sweet briar rose (Rosa rubiginosa) is the other common prickly shrub on the South Island’s east coast. With matagouri, it occupied about 1 million hectares of dry South Island country in the 1970s (when the area was last measured).
Sweet briar has been in New Zealand since the early days of European settlement. By 1900 it had spread through much of the South Island sheep country, and was declared a noxious weed. It favours fertile sites and quickly colonises disturbed open ground. It sprouts numerous, thorny stems, forming impenetrable thickets 2–3 metres tall.
Grey scrub – a mix of small-leaved, dark twiggy plants – is widespread in dry areas, frosty river terraces and exposed hill country. Although it always includes mingimingi, the other species vary around the country. At least 25 different coprosma species could be present, along with a number of small-leaved pittosporum and olearia species. Grey scrub always includes climbing plants such as pōhuehue (Muehlenbeckia complexa), native jasmine (Parsonsia heterophylla) and clematis, their stems winding through the twiggy shrubs.