Tiritiri Matangi is a 220 ha offshore island in the Hauraki Gulf, 3.5km east of Whangaparaoa Peninsula and 28 km north of Auckland. It is most commonly referred to as "Tiri". Tiri is highly modified, having had a long history of human use and habitation. Restoration began in 1983, and has so far involved revegetation, bird translocations, and eradication of kiore. Tiri is part of the Department of Conservation estate, and there are three DoC staff based on the island. However, a lot of the restoration work had been initiated and undertaken by the Supporters of Tiritiri Matangi, a volunteer organisation. See below for information on the restoration programme and/or contact Tiri@clear.net.nz.
European settlers had begun running sheep and pigs on Tiri in about 1854, and the last maori occupation ended at about the same time. The island continued to be leased for farming until 1971, when most of it was left to return to bush. In 1970, 142 ha were gazetted as part of the new Hauraki Gulf Maritime Park, with 64 more ha added in 1975. The remaining 14ha were classified as a lighthouse reserve, and includes the lighthouse erected in 1864. The park portion was initially classified as a reserve for recreation purposes, but was later classified as a reserve for scientific purposes and called the "Tiritiri Matangi Island Scientific Reserve".
Tiri would have originally been covered in coastal broadleaf forest (Esler 1978), although there are no records. Maori would have cleared some land for cultivation, as shown by the terraces, and the wild onion which is still found on the island. It's known that most of Tiri was cleared by the end of last century, and that the island was mostly grass and scrub with some remnant forest by that time. This remnant forest consists of several small patches in gullies, which were saved for "fuel purposes" following the orders of a crown lands ranger sent to review grazing leases. He also ordered that all the remaining pohutakawas should be preserved, and pohutakawa are still found on the cliffs all around the island as well as in the forest remnants.
Farming by the leaseholders mostly consisted of burning off, sowing grass seed, running sheep, and destroying the rabbits which were abundant last century. Weeds would have arrived in grass seed and by wind, and now account for 45% of plant species on Tiri. Surprisingly, no mice or European rats seem to have been accidentally introduced, and the only rodent on Tiri was the kiore earlier introduced by maori. Tiri also never had possums. There were wild cats and goats on the island in the early 1960s, but these were eradicated by lighthouse keepers. Rabbits, while plentiful last century, were eradicated by 1908. Tiri continued to be stocked by sheep and cattle until the last lease ended in 1971. Sheep are still farmed in the lighthouse reserve, but are scheduled for removal in the next 5 years.
In 1972, Tiri was mostly covered with grass, and the forest remnants had no understorey. Stock had been eating any seedlings establishing, and had also trampled the soil. Seedlings were initially slow to establish after stock removal, probably due to soil compaction, but by 1982 there were tree seedlings all over the ground and many new shoots from trunks. However, the forest didn't expand at all in those 10 years. While there was good dispersal of wind-borne seeds, there was no establishment in the open areas covered with grass and bracken (West 1980). The biggest change was that much of the grassland had been taken over by bracken.
In 1979, John Craig and Neil Mitchell from Auckland University put a proposal to the Hauraki Gulf Maritime Parks Board to revegetate Tiri and transfer native fauna. Their proposal was subsequently developed into the Tiritiri Matangi Island Working Plan (Drey et al. 1982). The overall goal proposed by the plan was to manage Tiritiri Matangi as a suitable habitat for some of our endangered flora and fauna, where people, particularly Aucklanders, could ultimately view these species in their natural environment. Restoration of Tiri could relieve the pressure for people to visit more pristine islands such as Little Barrier (Hauturu), Cuvier, and the Hen and Chickens group.
The plan considered the merits of allowing natural revegetation versus active restoration. Natural revegetation was considered to have the advantages of being low cost and having no interference to natural ecosystems. However, it was clear that natural revegetation would be very slow. Once bracken occupies a site, it takes several decades before it loses "vigour" and is invaded by trees (Mitchell 1985). This natural revegetation was not likely to be attractive to visitors, would be fire prone, and might not create habitat for the desired fauna. The authors suggested that costs could be minimised by having volunteers do the planting, and that this public involvement would facilitate the island's role as an open sanctuary for the public. They also argued that careful planning, and accompanying research, could ensure that revegetation was not unnatural (as noted in the introduction, the idea that any type of succession is the natural one, particularly following human disturbance, is not supported by recent ecological research).
The plan strongly advocated active restoration, and identified three components to the programme: (1) revegetation, to provide habitat for selected native fauna and flora; (2) reintroduction/introduction of fauna and flora; (3) provision for a controlled level of natural outdoor recreation activity. The project was supported by a grant from the World Wide Fund for Nature, which allowed it to get underway.
The overall aim of the revegetation programme was to short-cut the natural revegetation process by planting the "climax forest" directly (Mitchell 1985). The main limitation was competition for light from grass and bracken, and this could be overcome by growing seedlings to a size where they could compete. The programme needed to be low cost and low maintenance. It therefore needed to take into account the ecology of existing species on Tiri, along with the climate and soil. Tiri has free-draining soil with high natural fertility. The climate is mild with moderate rainfall, but there tend to be summer droughts in which the soil dries and cracks. Therefore, seedlings needed to withstand this summer dryness, and well as the exposure they would experience planted in open areas.
Of the plants on Tiri, the species that would ultimately be the climax species were pohutakawa, taraire, and kohekohe. Pohutakawa seedlings are the hardiest of these with respect to exposure and drought, so was used as the main species with the other two interspersed. A total of 20 tree species were planted, to encompass the variety of canopy and sub-canopy species found in the forest remnants on Tiri. These were strategically planted according to their tolerance of exposure. Ten shrub species were also planted, mostly to meet predicted bird requirements. Most species were grown from seed collected on the island. However, a few species were translocated from Little Barrier Island because of poor viability of seed from Tiri, or becuase the species were not found on Tiri and were viewed as particularly valuable to birds.
All plants were grown in nursery facilities built on Tiri, starting in 1983. The requirements were a propagation house, glasshouse (for seed raising), shade house, standing out area for hardening off, and soil mix bins. The shade house is 2/3 covered with 30% shade cloth (for pohutakawa), and 1/3 with 50% shade cloth (for other species). The standing out area has 70% shade cloth (for taraire, tawaroa, kohekohe), 30% shade cloth (pohutakawa), and 50% shade cloth (everything else). Production was based on estimates of the number of plants that could be planted with volunteer labour, taking into account the number of likely boat trips during the planting season. On Tiri, this was about 30,000 plants per year. There were initially two full time staff running the nursery: park ranger (later DoC officer) Ray Walter and landscape architect Mike Cole. Mike Cole left after the project after 14 months, and Ray Walter continues to run the nursery.
Seeds were planted in root trainers (Tinus RT-40 or RT-45) with commercial peat-pumice seed raising mix (with 'Osmacote' and 'Terazole'). Root trainers were used to minimise the amount of soil used, and maximise ease of transport. Some species (taraire, whau, puriri) needed more soil, hence were grown in potting bags. The small soil volume in root trainers meant that plants needed to be watered every 2-3 days, hence they needed a guaranteed water supply. Consequently, the dam in the adjacent valley was raised, and a pumphouse built to pump water to the nursery. Water tanks with 40,000 litres storage were built at the nursery. Plants were sprayed for pests and diseases every fortnight, a Benlate/Lanate mix alternating with other mixes such as Orthene/Ronilan or Ridomil. Most plants were grown for one year before planting. Planting took place every winter from 1984-1994. Groups doing the planting included schools, Forest and Bird, tramping clubs, scouts, etc., with 15-150 people per group. They usually planted 1000-1400 trees per trip. There was no site preparation in grass, whereas bracken was mowed 1-2 weeks before planting. Plants were put straight into the ground, about 2m apart, with a teaspoon of Osmacote at the bottom of each hole.
Planting has now taken place over most of the island. The exception is the lighthouse reserve area, and several archaeological areas (which could be destroyed by tree roots). There have been big differences between plant species in growth rates, and the fast-growing species have also tended to have higher survival rates (Cashmore 1995). In general, the early successional species (shrubs) have have high growth rates and survival than the canopy species. Growth and survival rates have also varied according to conditions at the planting sites (Cashmore 1995).
The fauna translocations in the original management plan included 7 birds, plus pekapeka (short-tailed bats), tuatara, and pupu (Placostylus) snails. Translocations since 1983 have involved 8 bird species (saddleback, brown teal, whitehead, takahe, New Zealand robin, little spotted kiwi, stitchbird, kokako) and one plant species (Dactylanthus taylorii). For details, click on each of these species under New Zealand translocations in the 1990s, and look for the Tiri translocation. All of the birds were listed on the original management plan except for brown teal. The bird species differ in their habitat use, and this is reflected in the degree to which they've made use of the planted areas. At one extreme, robins don't use the planted areas at all, except to move from patch to patch. This makes them an interested case study. Was it sensible to translocate robins when the planted bush was still quite young, or should the translocation have been delayed until the bush was more mature (as recommended in the working plan)? There is currently a carrying capacity of about 60 individuals in the old bush. Demographic PVA (population viability analysis) suggests that this is a viable population, and that they are unlikely to go extinct before the planted forest forms a canopy (D. Armstrong et al., in prep.). This suggests that it was OK to release the robins fairly early. At the other extreme, takahe avoid the old areas, and will probably stop using the planted areas once the grass is shaded out (Baber 1996). This means that the carrying capacity of Tiri for takahe will probably decline. Other species have wider use of habitat (e.g., kakariki, saddlebacks, whiteheads), and may be less affected by the maturation of the planted areas (although note that the use of planted areas by tieke has been facilitated by articial roost and nest boxes). However, the revegetation project was aimed at enhancement of habitat quality as well as creating habitat. This enhancement was aimed at nectar-feeding birds, especially the endangered hihi. Research following the recent hihi translocation in 1995 has partly evaluated whether Tiri has sufficient nectar and fruit resourcees to support a viable population (Wilson 1997; Ewen & Armstrong, in prep.).
The poison drop received criticism on several fronts. (1) Kiore have cultural value to maori (Roberts 1995), were being progressively eradicated from offshore islands, and there was no plan indicating where kiore would be conserved. (2) The poison would have impact on existing fauna, including the birds that had been released there. The timing was such that several species had started nesting, meaning the eggs or young could be abandoned when parents were killed. The time had been selected to maximise bait intake by kiore. (3) The bait could have been laid by hand in bait tunnels, given that Tiri is small and easy to walk about. This could have been done with volunteers, hence no labour costs, and would facilitate public involvement. The aerial drop was selected because the cost of the helicopter was less than the projected cost of bait tunnels. (4) The fact that the drop was not part of a plan, and done with little notice, meant that opportunities were lost to obtain good data on the ecological effects of eradicating kiore. Fortuitously, Neil Mitchell already had plots in place to study regeneration, and these can be used to assess the effect of kiore removal. Chris Green (DoC, Auckland) installed pitfall traps a few months before the drop, and is using these to monitor invertebrates. .
The three takahe on Tiri at the time were enclosed to protect them from the poison, and two pairs of brown teal were also taken into captivity. Seven native species are known to have suffered some mortality (pukeko, brown teal, spotless crake, paradise duck, saddleback, robin and kakariki).
There are insufficient data for most species to accurately assess the mortality due to the drop, the effect on population dynamics, or the effects of removing kiore. Three native species seem to have suffered high impacts. About 90% of pukeko were killed, and morepork and harriers were obviously reduced. No obvious effects occurred in other species, and the disappearance of morepork and harriers could have been due to a drop in food supply (the kiore) rather than direct poisoning. Moko skinks seemed to become more visible after the drop, even before their breeding season. This suggests that the eradication caused a behavioural change, but increases over subsequent years suggests a population increase as well. There is also an apparent increase in the number of seedlings of some plant species.
An important byproduct of inspiring visitors is that the public has ultimately done most of the work on Tiri. We've already mentioned the role of volunteers in revegetation, but the role of volunteers extends to all aspects of Tiri's management. This was formalised in 1988 with the formation of Supporters of Tiritiri Matangi. Public involvement on Tiri is discussed in detail by Galbraith (1990), Galbraith (1991), and Galbraith and Hayson (1994). Education has been strongly promoted by this involvement, particularly the involvement of many groups of primary and secondary school students.
The revegetation is finished except for some planting around ponds created for takahe, in the lighthouse reserve to provide cover for takahe, and to obscure one location where trees were planted in rows. While the revegetation is stopping, several more plant species are listed for translocation. The emphasis with these plantings will be conservation of the individual species, and not creation of habitat. There are also several species of lizards listed, and a few more birds, and bats are still listed as a possibility. The species were selected according to their status and whether they are likely to have inhabited Tiri. Invertebrates will also be reintroduced, but planning of invertebrate introductions will begin after the existing invertebrate fauna are surveyed.
Armstrong, D. P., Lovegrove, T. G., Allen, D. G., & Craig, J. L. (1994). Composition of founder groups for bird translocations: does familiarity matter? In M. Serena (Eds.), Reintroduction biology of Australian and New Zealand fauna (pp. 105-111). Chipping Norton: Surrey Beatty & Sons.
Barraclough, R. (1995) An evaluation of aspects of the development of Tiritiri Matangi Island. MSc thesis, University of Auckland.
Cashmore, P. (1995) Revegetation ecology in Tiritiri Matangi Island and its application to Motutapu Island. MSc thesis, University of Auckland.
Drey, R., Connel, P. J., Craig, J. L., Mitchell, N. D., & Spring-Rice, W. (1982). Tiritiri Matangi Island Working Plan. Auckland: Department of Lands and Survey for the Hauraki Gulf Maritime Park Board.
Esler, A. E. (1978). Botanical features of Tiritiri Matangi Island, Hauraki Gulf, New Zealand. New Zealand Journal of Botany, 16, 207-226.
Ewen, J. G. (1998) A genetic and behavioural investigation of extra-pair copulation in stitchbirds (Notiomystis cincta) breeding on Tiritiri Matangi Island. MSc thesis, Massey University, Palmerston North
Galbraith, M. P. (1990). Volunteers' view of the ecological restoration of an offshore island. In D. R. Towns, C. H. Daugherty, & I. A. E. Atkinson (Eds.), Ecological restoration of New Zealand islands (pp. 170-174). Wellington.: Department of Conservation.
Galbraith, M. P. (1991). Tiritiri Matangi Island: environmental education through involvement. In D. Springett & C. M. Hall (Eds.), Our common future: the way forward (pp. 158-162). Palmerston North: New Zealand Natural Heritage Foundation.
Galbraith, M. P., & Hayson, C. R. (1994). Tiritiri Matangi Island, New Zealand: public participation in species translocation to an open sanctuary. In M. Serena (Eds.), Reintroduction biology of Australian and New Zealand fauna (pp. 149-154). Chipping Norton: Surrey Beatty & Sons.
Hawley, J. (1995). Tiritiri Matangi draft working plan. Department of Conservation, Auckland Conservancy.
Hoyle, S.D. (1993). North Island saddlebakcs on Tiritiri Matangi Island: a computer model of population dynamics. MSc thesis, University of Auckland.
Mitchell, N. D. (1985). The revegetation of Tiritiri Matangi Island: the creation of an open sanctuary. Royal New Zealand Horticultural Scoeity Annual Journal, 13, 36-41.
West, C. J. (1980) Aspects of regeneration on Tiritiri Matangi Island. MSc thesis, University of Auckland.
Wilson, L.R. (1997). The ecology and management of honeyeaters in northern New Zealand. MSc thesis, University of Auckland.