Farthest North Strangest Things

Forest and Bird, Issue 300, 1 May 2001, Page 20

Farthest North Strangest Things

DEAN BAIGENT-MERCER

finds a strange region of

unique plants at the far northern tip of New Zealand.

any of the tourists who visit Cape Reinga, where the Tasman and Pacific Oceans mix, mistakenly believe they have reached the farthest north of New Zealand. Yet that point lies, generally inaccessible, 33 kilometres to the west, beyond Spirits Bay. Here above the giant Surville Cliffs is a 120-hectare plateau of botanical curiosities, protected from casual visitors by the North Cape Scientific Reserve. Until the last Ice Age melted, this place was a separate island, with its own strange plants. The major reason for its number of rarities, however, is the substance of the plateau itself — serpentine rock, which has its own peculiar vegetation.

The Surville Cliffs are thought to have been created when the Pacific and IndoAustralian tectonic plates collided, pinching a piece of oceanic crust and pushing it up. The crust was under such pressure that water molecules were squeezed out to create a ‘hydrated’ rock, somewhat similar to pounamu or jade, but which feels soapy to touch. The main rock type is serpentinite, which runs in a kilometre-wide strip for about three kilometres along the cliff tops. Serpentinite is an uncommon ‘ultramafic’ rock which is extremely rich in magnesium and iron, with lower levels of associated minerals such as nickel and chromium. The combination of these

The Surville Cliffs rise some 200 metres from the sea at North Cape. Rare plants grow in an area of serpentine on the cliff tops.

minerals forms a rock cocktail of toxic minerals which challenges normal plant growth. It is because of this rock that, over time, a unique vegetation has evolved, containing many plants found nowhere else. Among botanists, the Surville Cliffs serpentine area has the reputation of having the highest level of unique plants for its size in the whole country. Botanist Peter de Lange of the Department of Conservation, describes the ultramafic, heath-like vegetation as ‘utterly unique’ and estimates there are 15-20 forms of vascular plants found only on the Surville Cliffs. Mineral-rich ‘ultramafic’ areas occur elsewhere in New Zealand, including the Red Hill in the Richmond Range of Marlborough, the Cobb in northwest Nelson, and West Dome of the Red Hills in northern Fiordland. These have been glaciated, however, and so support fewer and mainly herbaceous localised plants. ‘The Surville Cliffs have never been glaciated, and occur within a warm, lowland setting; says Peter de Lange. "This

has enabled a shrubby, woody flora to develop, unlike other ultramafic areas. Approximately 7000 years ago, when sea levels were higher, the Surville Cliffs plateau was a separate island. Now it is joined to the mainland by a low-lying area clothed in manuka. Before the Te Paki area of the Far North was burned, however, kauri forest dominated the inland areas _ with pohutukawa forest in the coastal gullies and on the cliffs. These forests would have grown hard up to the ultramafic zone of the Surville Cliffs. It is from these forest plants that some of the Surville Cliff plants evolved. One of the most obvious and striking features of the vegetation is the number of plants which grow squat, sprawling, and trailing through other plants, with stems sometimes several metres long. These growth forms contrast strongly with neighbouring relatives from which they evolved. For example, tanekaha, a slender forest tree which grows up to 30 metres has become a different species growing only three metres high but spreading five metres wide here on the cliff tops. Tauhinu/cottonwood grows in nearby areas usually as an upright shrub of up to

three metres. On Surville Cliffs it has become a squat species up to one metre in height with larger, more yellow leaves. Pittosporum pimelioides, a rare shrub growing up to two metres high in the kauri forest, here has much larger leaves and grows horizontally with trailing branches. The serpentine influence has also shaped a local native jasmine Parsonsia praeruptis, which doesn’t climb at all but trails across rocks and amidst other plants. On the Surville Cliffs plateau, plants of 10 different families show these unusual characteristics. The special nature of the rock, and severe droughts, have placed strict selection criteria on those plants that survive. The Surville Cliffs is a place of evolution in action. Some plants are obviously different from their closest relatives; for example they may be smaller and have hairier leaves, but still aren't different enough to be considered a separate species. Some of these plants have instead been given the rank of ‘subspecies’ by botanists. Nine of the 15-20 endemic plants have already received formal botanical recognition, either as species or subspecies. A further three, a sedge, a coprosma and a kind of tanekaha, are in the process of being scientifically described. Further

Deciphering the past: fire and human habitation

he Surville Cliffs and OD area are dotted with historic pa sites and had been highly populated by Maori. This all changed in the 1800s with the introduction of muskets, when intertribal wars broke out. Large-scale massacres occurred around North Cape. The land has since been sparsely inhabited by Maori due to the tapu nature of the area. ‘This area has been protected through tragedy, says Dave Spicer, of the local Ngati Kuri people, who is also a biodiversity manager with the Department of Conservation. One of the earliest European naturalists to travel across this area was Ernst Dieffenbach in 1843. At this time, North Cape was obviously a landscape that had been changed by fire, with Dieffenbach noting burnt remains of large trees. For most of the first part of the 1900s, burning of the plant cover of the North Cape area was customary and frequent. Cattle, horses and sheep used to roam across the unfenced hills and wild pigs were numerous. By the 1970s very little forest remained sufficiently free of fire and animal damage to indicate the pre-human forest cover. Research into the localised tanekaha has shown burnt cores denoting numerous fires in the past. The most likely causes are lightning and fires lit accidentally or deliberately by people. The Surville Cliffs area is part of a Treaty of Waitangi land claim, lodged by Ngati Kuri. The tribe has also recently joined the "Wai 262’ claim which includes ownership of New Zealand’s flora and fauna, and related intellectual property rights.

research into the remaining 10 or so as yet ‘undescribed’ variants is underway. Biogeographically, the Surville Cliffs also have peculiar connections to Australia with some plant species having odd distributions between the countries. Surville Cliffs is home to an unnamed mingimingi (Leucopogon aff. parviflora). Its closest relatives live in coastal Australia from New South Wales to Tasmania and, even more surprisingly, the Chatham Islands. A relative of the common gumdiggers’ soap/kumarahou, Pomaderris paniculosa var. novaezelandica, reaches its greatest abundance at Surville Cliffs and Whangarei, with another close relative in Australia. Other unusual plant distributions

include Coprosma obconica, otherwise known only from near Taihape in the North Island, and in the South Island from Nelson, Canterbury, Otago and Southland. As might be expected, the Surville Cliffs form of Coprosma obconica is different in being a shorter, sprawling shrub, and it too is in the process of being formally described, possibly as a new subspecies, peculiar to the Surville Cliffs. Another bizarre occurrence is that of a small grass, Trisetum serpentinium, discovered on the Surville Cliffs in 1996. Till that time it was thought to be restricted to the ultramafic rocks of the Nelson region. To date it still has not been found in between, though it has recently been discovered on D’Urville Island in Cook Strait.

In recent years Peter de Lange, of DoC’s science and research division, and Dr Peter Heenan, of Landcare Research, have been studying the unnamed plants of the Surville Cliffs. ‘Everytime we visit the area another distinct and possibly new plant is discovered’ says Peter de _ Lange. Neither scientist believes that the Surville Cliffs has yielded up all its botanical treasures, and both stress the need for a more thorough and systematic botanical survey.

— The author acknowledges scientific advice from Peter de Lange.