Location and General Description
The Kermadec Islands are an uninhabited group of 13 small islands formed by active and recently extinct volcanoes along the boundary of the Australian Plate between 29º to 31.5oS latitude and 178º to 179oW longitude (Sykes & West 1996). Raoul (29 km2) and Macauley Islands (3.1 km2) comprise more than 95 percent of the islands’ land area. Raoul and Curtis Islands remain active with almost-daily earthquakes, and small eruptions periodically destroy vegetation in the calderas (Mueller-Dombois & Fosberg 1998). The climate is subtropical with a maximum mean monthly temperature of 22.4oC in February and a minimum mean monthly temperature of 16.0oC in August (Parkes 1984). Annual rainfall is approximately 1,500 mm with a drier period from October through January (Parkes 1984). There are three warm volcanic lakes in the crater on Raoul Island but all streams are temporary, and most rainfall seeps quickly through the porous volcanic soil.
Forests are dominated by a canopy of 10 to 15 m Metrosideros kermadecensis, but have a different understory depending on elevation. Lower forests have an understory of Myrsine kermadecensis, Lobelia anceps, Poa polyphylla, Coprosma acutifolia, and Coriaria arborea. Higher areas up to the 516 m summit of Raoul Island are exposed to more cloud interception, and they support a mossy and dense M. kermadecensis forest with an understory dominated by Ascarina lucida, Melicytus ramiflorus, Pteris comans, and the endemic Nikau palm (Rhopalostylis baueriana) (Mueller-Dombois & Fosberg 1998). The introduced Alocasia macrorrhiza was formerly widespread in the understory, but is declining since goats were eradicated (Sykes &West 1996). Coastal vegetation is distinct and occurs in windswept, salt-sprayed areas. It is dominated by woody Myosporum obscurum and Coprosma petiolata and the herbaceous species Asplenium obtusatum, Cyperus ustulatus, Disphyma australe, and Scirpus nodosus (Mueller-Dombois & Fosberg 1998).
The flora includes 52 species of moss, 89 species of fungi, and 113 species of native vascular plants of which 23 are endemic. Most of the species are conspecific with flora in New Zealand with a small number originating in the tropical Pacific. Most of the 152 established introduced plants come from tropical areas (Sykes & West 1996). Included in the endemic species are two tree ferns, Cyathea milnei and the rare and declining Cyathea kermadecensis. Previously, only one plant of the endemic Hebe breviracemosa existed, but out-planted cuttings and seedling have increased the wild population (Sykes & West 1996).
Historically, the islands supported spectacular concentrations of millions of breeding seabirds. Still present are 14 species, including 10 that breed nowhere else in New Zealand and 3 that are breeding endemics to the Kermadecs and a few other Pacific island groups (Parkes 1984). Today, the world’s largest breeding populations of Kermadec petrel (Pterodroma neglecta), white-naped petrel (P. cervicalis), and black-winged petrel (P. nigripennis) are in the Kermadec Islands (Merton 1970). There are two passerines present, the tui (Prosthemadera novaeseelandiae) and the silver-eye (Zosterops lateralis), and 5 introduced passerines (Merton 1970).
The Kermadec Islands have experienced little direct human impact, with only limited settlement in the 1300s by Maoris and the 1800s and 1900s by European farmers and whalers (Merton 1970, Higham and Johnson 1997). The greatest impact of humans has been indirect: the introduction of mammals, especially Polynesian rats with the Maori, goats and cats (Felis catus) in the 1800s, and Norway rats (Rattus norvegicus) after a shipwreck in 1921 (Merton 1970). Rats and cats reduced the seabird population of Raoul and Macauley Islands from more than 1 million to a population of from 20,000 to 40,000 in less than 150 years. They also extirpated the Kermadec parakeet (Cyanoramphus novaezelandiae cyanurus), New Zealand pigeon (Hemiphaga novaeseelandiae), and spotless crake (Porzana tabuensis; Fitzgerald et al. 1991, Veitch 1998). Goats completely destroyed all forest that once covered Macauley Island and had major impacts on species composition and structure of Raoul Island’s forests.
Types and Severity of Threats
The New Zealand government has committed substantial resources to restoring the forests and seabirds of the Kermadec Islands. The islands have been protected since 1937, and in 1990 a 7,450 km2 marine reserve was established around them (Taylor 2000). Efforts to eradicate goats succeeded in 1970 on Macauley Island and 1984 on Raoul Island. Today Macauley Island remains covered in Cyperus ustulatus grassland, but forest species are beginning to return. The understories of Raoul Island’s forests are recovering rapidly (Sykes & West 1996). The New Zealand Department of Conservation is currently attempting to eradicate cats and rats in hopes that, once predators are removed, seabird colonies will expand from the small offshore islets they currently occupy to cover Raoul and Macauley Islands in numbers approaching their former profusion (Taylor 2000).
Justification of Ecoregion Delineation
This ecoregion comprises the Kermadec Islands of Raoul and Curtis, administered by New Zealand. Van Balgooy (1996) considers that the vegetation of the isolated Kermadec Islands is highly dissimilar from the surrounding Melanesian and Polynesian island groups, yet does lump them in the same category as the rest of New Zealand. Based on this evidence alone the Kermadecs were delineated as an ecoregional unit.
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Mueller-Dombois, D. and F.R. Fosberg. 1998. Vegetation of the Tropical Pacific Islands. Springer Press, New York.
Parkes, J.P. 1984. Feral goats on Raoul Island. 1. Effect of control methods on their density, distribution, and productivity. New Zealand Journal of Ecology 7:84-94.
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Taylor, G.A. 2000. Action plan for seabird conservation in New Zealand. Part A. Threatened Seabirds. Threatened Species Occasional Papers 16:1-234.
Van Balgooy, P.H. Hovenkamp, and P.C. Van Welzen. 1996. Phytogeography of the Pacific – floristic and historical distribution patterns in plants. Pages 191-213 in Keast, A. and S.E. Miller, editors. The origin and evolution of Pacific island biotas, New Guinea to Eastern Polynesia: Patterns and processes. SPB Academic Publishing, Amsterdam.
Veitch, C.R. 1998. Breeding season of Kermadec Petrels (Pterodroma neglecta neglecta) at Meyer Islands, Kermadec Group, New Zealand. Notornis 45:67-69.
Prepared by: Tim Male
Reviewed by: In process