NATURAL HEART OF A CITY
By Neville Peat
There are few cities on earth that are as well endowed naturally as the City of Dunedin. One reason for this is its far-flung extent. It is a city that embraces large areas of farmland, lonely hills, upland plateaux, rugged river gorges and, yes, even an alpine zone - all this for a human population of just 118,000.
It takes nearly two hours to drive from the city centre - the Octagon and its avenue of elegant plane trees - to the city's treeless, tussock-clad western boundary on the Old Dunstan Road.
Dunedin, all up, encompasses 3,350 square kilometres -just over 10 per cent of the area of Otago. So it is big, but why so big? The answer lies in the reorganisation of local government in 1989, when metropolitan Dunedin spread out to embrace several boroughs and the Taieri and Silver Peaks County Council areas. The old counties contained the city's most important catchments for water supply, in particular the Deep Stream catchment which has its origins in the Lammermoor Range. Thus water supply has had a major part to play in enlarging the city boundaries as far as mountain ranges to the west. These ranges form the eastern margin of Central Otago.
Of course, big does not necessarily mean better when it comes to natural history or anything else. But chances are that biological diversity (biodiversity) will increase in proportion to area, especially if, as in Dunedin's case, the area takes in a variety of rock types, landforms, waterways, altitudes and climates.
Dunedin's climate overall is temperate, with rainfall generally adequate across the bulk of the city area and measuring 785mm on average a year in the city centre, with somewhat more rain falling in the hill suburbs. Mean temperature is 11 degrees Celsius. At the coast, temperatures are moderated by the sea; inland, summers are hotter and drier than at the coast and winters bring more frosts and snow.
Onshore winds from the north-east quarter are often persistent, banking clouds on the Mt Cargill/Swampy Summit skyline and churning up harbour waters. But the most feared winds are from the south or south-west. These are the gales that cultivate wind-shear in exposed vegetation. A southerly front, approaching fast, can darken the sky in minutes and cause the air temperature to plummet by more than 10 degrees. The changeable nature of Dunedin's weather does have aesthetic compensations, though - the city is a spectacular place for cloud formations and variable lighting.
Weather is not the only changeable factor. Nothing in nature is fixed forever.
There are shifts in vegetation patterns going on in many places around Dunedin. Examples are the slow, successional, uphill movement of shrubland on Flagstaff,
and the wholesale takeover of the Green Island shrubland by Taupata Coprosma repens following the die-back of Hebe elliptica through, apparently, drought in the 1950s. Some changes are induced by burning off (after which native Hard tussock may overtake more palatable native grasses) or mass application of fertiliser, which can cause widespread regeneration of Matagouri in upland tussock grasslands. The Matagouri also responds to phosphate fertiliser by growing abnormally large.
Just as the plant life adjusts to changing conditions, fauna can make adjustments, too. Some moths and butterflies have adopted introduced plant species as hosts for their larvae. Red admiral butterflies, for example, have taken a shine to introduced nettles. The New Zealand falcon has probably extended its range thanks to an increase in prey species provided by introduced passerine birds. Fur seals and sea lions, virtually extinct on the mainland in the nineteenth century and for much of the twentieth century, are restaking claims on the rocky shores and beaches of Otago Peninsula.
Dunedin is best known for its Royal albatross and Yellow-eyed penguin, which have achieved icon status nationally - even internationally. But surprises are in store for anyone who cares to look beyond these icons in the fauna. Take the Royal spoonbill at Green Island, for example, or the South Island robin in the Flagstaff forest, South Island fernbird at the Waipori/Waihola wetlands, velvety Peripatus crawling about Caversham Valley bush, Clapping cicada in the Taieri Gorge, the Aoraia moth navigating through forest at night, and mountain weta confined to the harsh alpine zone of the Rock and Pillar Range, dependent on antifreeze in their blood to keep it from seizing up.
The diverse and pulsating parade of wildlife knows no bounds. It is joined from time to time by new players, occasionally vagrant birds or insects far from their known range. Moreover, ongoing research is making discoveries of new species of insects at a startling rate. Since 1980, more than 31 Dunedin species have been named. Many more have been discovered but await formal description and naming. Likewise, new records for existing plants are liable to show up - and sometimes even new species come to light.
Dunedin lays claim to 31 plants and animals that are endemic. Nowhere else on earth do they occur. It is a list that will no doubt be added to as time goes by. The city is a centre of biodiversity.
Because of its size and its range of habitats - from beaches of shining sand to frozen patterned ground in the alpine zone - Dunedin has more natural nooks left to be explored in depth than any New Zealand city. Moreover, it is much easier to find an alpine experience in Dunedin compared to North Island cities because the alpine zone is several hundred metres lower.
Although climate is important in determining the range of habitats and species present, a more fundamental factor is the tectonic history, which gives rise to the rocks in the first place, and the age and lie of the land surfaces.
Extract from Neville Peat’s guidebook
published by Otago University Press