The Curious Life of Rangitoto

Forest and Bird, Issue 311, 1 February 2004, Page 27

The Curious Life of Rangitoto

GORDON ELL

visits the volcano which

symbolises a city.

he volcanic island of Rangitoto is only about 600 years old but life there is primitive. Lying like an upturned platter across the approaches to Auckland, the island has become the symbol of the ‘city of volcanoes. Yet, when the first Maori settled on adjacent Motutapu Island, Rangitoto simply wasn’t there. The excavated footsteps of a family, buried in volcanic ash in a Maori garden on Motutapu, were among the clues to just how recent the volcano is. The volcano erupted from beneath the sea, building its bulk through an outpouring of scoria and

basalt from the still-active Auckland volcanic field. Rangitoto could have formed in just a year of eruptions; but possibly a few more. It may still have been steaming just 250 years ago. Rangitoto is simply the latest of some 48 or so volcanoes which have erupted across the Auckland isthmus, mostly in the past 10,000-50,000 years. Now Rangitoto is coloured a dun green when viewed from the city but its volcanic origin is strikingly clear when the visitor steps ashore onto the rugged basalt reefs and scoria fields of the island. When the first European settlers

picnicked here, in 1840, vast areas were still raw rock. Early photographs depict a rubblefield of broken basalt with only occasional trees. The more recent skin of spreading pohutukawa is still underlain with raw rock, and the closer view shows many bare areas between the trees. The lava cone of the island is still growing its first cloak of plants. Rangitoto is so young there hasn’t been time for much soil to form. Instead plants largely grow in the humus formed from leaves of the pioneer plants. These include the most primitive: blooms

of algae which appear purply-white on the open rockfields. The natural succession of plants is quicker than that suggests, however. Pohutukawa has established widely, thus creating shade under which more tender plants can grow. Botanists have identified the most successful of these pohutukawa as a local strain, a mix of pohutukawa and its cousin the northern rata. Gradually the adjacent colonies of trees are merging to create a broader forest. The pohutukawa have extremely long roots reaching far underground to tap into subterranean water. A fire can burn down

through these roots for weeks. There is no running water on the island but it is said to contain a miniscus of water underground — enough to provoke the suggestion at one stage that it should be tapped for a city supply. The trees and shrubs of the island, not surprisingly, have hard, hairy leaves or tiny needles to protect them from a harsh environment. The weather is often wet, with strong salty winds, or hot and dessicating. The common shrubs are kanuka and manuka, the pin-leaved mingimingi, and the shining-leaved robust coprosma. Plants that more usually grow in the crowns of forest trees grow here among the rocks; such as the shining broad-leaved griselinia or puka, the hairy Kirk’s tree daisy, northern rata vines, and narrow-leaved astelia which can form a luxuriant silver ground cover. Despite the rugged terrain, and daytime temperatures which may reach 50 degrees Celsius on the open rockfields, the most delicate plants can grow, but only in the shade. There are some 100 recorded species of mosses and liverworts, more usually lovers of damp places. There are more than 40 species of ferns; and some 20 different native orchids which find a niche in the shade, some on the trunks of trees, others growing from pockets of humus. A visit in late spring can provide a happy field of search for plant enthusiasts particularly in areas adjacent to the wharves. A less pleasant sight for the purists are ‘garden escapes’ and other weeds, more than

200 recorded, many of them about the wharves where holiday cottages were built in the 1920s and 1930s. Roosting gulls bring more, evidenced by the tomatoes and pumpkins which occasionally grow from the humus of abandoned nests. Another weed problem is pine trees which establish in remote rocky corners, wind-blown from plantations on the mainland. Removal is challenging because of the difficulties reaching them across untracked and broken lava reefs; sometimes, even, a helicopter has to be used to reach the dark green spires emerging above the native trees. For those who wish to explore the broader island, Rangitoto has a selection of tracks, some built to road standard by prison work parties. The climb to the summit from Rangitoto Wharf is most popular, following a ridge of lava with fine views back over the harbour and inner gulf. Near the summit, the track enters a softer world of older scoria cones where the forest includes emergent rewarewa, or New Zealand honeysuckle, which is one of the pioneer species of the warmer forests.

The summit is capped by a concrete bunker with a 360-degree view of the Hauraki Gulf and its islands. This was in wartime a forward command post of Auckland’s defences and an adjacent platform now provides a spectacular lookout. Directly in front is the forest-filled main crater. The softer scoria cones which surround it give to the familiar profile of the mountain top the form of a clenched fist — and its name as ‘the three knuckles of Peretu, in Maori. Rangitoto is the highest of Auckland’s volcanoes at 259 metres, a sprawling disc of volcanic rock about five kilometres across, and 2911 hectares in area. It abuts Motutapu, a farmed island reserve to which it is now attached by a causeway. When efforts were made to exterminate the possums gad the wallabies which were badly damaging the trees on Rangitoto, conservation management had to be applied to Motutapu too, to stop reinvasion. Possums were doing most damage, eating the growing shoots of pohutukawa. With no new growth surviving, the trees were collapsing when older leaves fell naturally

and there was nothing left to replace them. Taking the pests off the island, and the debate about poisons, was something new for conservation in the early 1990s. The consequence of success, however, has been the recovery of forest health on Rangitoto. Because of the reflected heat from the rock, Rangitoto is best visited in cooler seasons. When the mud is knee deep in the Auckland ranges, Rangitoto with its stone paths offers a firm, dry alternative for walking. From October into December, the blackbacked gulls are nesting in their thousands, usually on remote, untracked areas of bare rock to the northwest: but there is an easily accessible colony about 20 minutes’ walk west of Rangitoto Wharf, viewable from a track to Flax Point. (Birdlife on the island is otherwise restricted to common species.) Orchids are also easier to find in the spring, and of course the pohutukawa in flower is a major attraction just before Christmas. Rangitoto has enjoyed some form of reserve status since 1890 — prior to which it was a popular picnic spot for 35 years. It is now managed by the Department of Conservation.

— GORDON ELL

published a guidebook to Rangitoto

in 1980 and continues to enjoy occasional visits.