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Natural History of Rangitoto IslandNatural History of Rangitoto Island:
Hauraki Gulf, Auckland, New Zealand

Edited by Mike D. Wilcox
Published by Auckland Botanical Society Inc. 2007
Paperback, 192 pages, 185 × 250mm, NZ, 2007
ISBN 978-0-9583447-3-9
Auckland Botanical Society Bulletin No. 27
$NZ39.99

Reviewed by Bruce Clarkson

This extremely attractive 14 chapter natural history covers everything from vertebrates and invertebrates to vegetation patterns, plants, and fungi found on the Hauraki Gulf’s most iconic island, Rangitoto. An impressive line-up of authors has been brought together by the Auckland Botanical Society to achieve this task; the book has been ably edited by Mike Wilcox and dedicated to society pioneers Crookes, Cranwell, and Millener. A brief introduction by Wilcox covers the vital background information including geology, history, and previous botanical studies. This chapter is preceded by a fine series of location maps including a particularly stunning aerial photograph of the whole island. I would have liked to have seen here an introductory section on the nutrient status of the parent material (basalt lava), its weathering characteristics, and consequences for soil fertility so crucial for plant succession discussed later in Chapter 4.

Chapters 2 ‘Vertebrate fauna’ and 3 ‘Invertebrate fauna’ begin the trend apparent throughout the book of comprehensively documenting all that is known about the biota of the island. Needless to say, different groups have been subject to different levels of survey and inventory, and reliance on published information varies. The general approach though of trying to canvas the range of species found and to include where possible information on ecology and habitat or pointers for identification is successful, albeit demanding on retaining interest levels throughout each chapter.

Chapter 4 ‘Vegetation patterns’ (pp. 41–58) is understandably, because of Rangitoto’s importance as a succession study site, the longest chapter in the book. The importance of crevice colonisation and the establishment of the ubiquitous vegetation patches and their coalescence into continuous forest are well covered, based on the research of Whiting and Julian, in MSc and PhD theses, respectively, undertaken at the University of Auckland. Variations in vegetation across the island are discussed and depicted in a vegetation map, but the text and map are not well connected. The lack of explicit height definitions for short and tall pohutukawa patches is problematic both for understanding the sequence of species enrichment of patches (patches expand radially as well as in height with a highly predictable assemblage of species relating to patch size) and in practical use of the map provided. The suggestion by Atkinson (1960) that ash distributed over the lava flow flanks accounts in part for the pattern of vegetation is not addressed, and Millener’s opinion on the age of
the oldest trees remains, as noted, untested by adequate tree ring data.

Comments about species which are ‘normally’ epiphytic growing on the lava somewhat over-represent the view that species have a single lifestyle or strategy. In the case of northern rata (Metrosideros robusta) in particular, the lifestyle varies considerably.

Taking a broader successional view, northern rata is an earlier coloniser of debris flows, slip faces and, in this instance, lava flows; later in a succession it establishes epiphytically although it is best described as a hemi-epiphyte. While the abundance of terrestrial northern rata is a feature of Rangitoto, it is also characteristic in other volcanic landscapes, probably the most spectacular example being found in the Hangatahua (Stony River) catchment of Egmont National Park. Similarly, the common albeit localised rupestral occurrence of puka (Griselinia lucida) in other parts of the North Island is not admitted. Differences between the lava flow vegetation and the scoria cone and crater habitat are well elucidated, and the chapter concludes with a detailed account of the vegetation and species of the island’s 16 km shoreline.

Chapters 5–14 deal with the plants (vascular plants 5–8; non-vascular plants 10 and 11), lichens (12), fungi (13), and algae/seaweeds (14) systematically by way of taxonomic and/or life form grouping. A list of vascular plants complete with authorities and relevant statistics is presented as Chapter 9, while lists of non-vascular species, lichens, fungi and algae (seaweeds), are contained within their relevant chapter. Each of these chapters provides an overview of the group to varying detail and then focuses on particular species selected by the author because of their prominence on Rangitoto or for other reasons such as a special adaptation or feature of interest. Obviously, it is impossible to describe every organism, but the selection offered whets the appetite and encourages the reader to take a greater interest in being able to identify or understand a wider range of the biota present on the island.

I particularly liked the brief but effective accounts of mosses, liverworts and hornworts, fungi, lichens, and algae (seaweeds) which were self-contained to the extent that they could be read without having to scan the whole book and also because the writing style was lively enough to maintain the reader’s interest. Some chapters may have been improved if the approach taken in Chapter 11 (liverworts and hornworts) was followed with the size of flora indicated early without having to check this out in the accompanying species list. Although most lists do give a total (e.g., lichens), or subtotal by major group (e.g., fungi and algae), the moss and lichen and hornwort lists do not provide summary data.

All chapters in the book are extremely well illustrated with a good selection of high quality colour photographs of species, growth forms, and habitats.

As is the usual case, vascular plants take the greater proportion of the book with four chapters devoted to ferns (Chapter 5), conifers and dicots (Chapter 6), orchids and other monocots (Chapter 7), exotics (Chapter 8) and, as already noted, a comprehensive vascular species list (Chapter 9). The ferns are particularly well illustrated, and native conifers and dicots have a valuable table giving flowering times which will help the reader wishing to see the spectacular flowering of kohurangi (Brachyglottis kirkii) among other species. The native orchids and monocots chapter notes that of eight species of epiphytic orchids found in New Zealand, four grow on Rangitoto, but the Chapter 9 species list includes five such species. Astelia, such an important ground cover, is rightfully given prominence in text and photographs, enabling the reader to discern the difference between A. banksii and A. solandri. However, given the close intermingling of species, I suspect that hybridism is more common than realised and may (rarely) even include intergeneric crosses with Collospermum.

The exotic vascular flora is numerically dominant (354 exotic species versus 228 native species) and therefore deserves its full chapter treatment (Chapter 8). The history of weeds is covered first then the focus shifts to environmental weeds and their control, followed by other introduced plants. The question of how the exotic plants arrived is superficially dealt with, given the comprehensive species list available, for example, what is the proportion of wind dispersed versus bird dispersed or human assisted species. The discussion for the species list (Chapter 9) necessarily duplicates some information already presented but also adds additional material strongly pertinent to earlier chapters; for example, the origin of the introduced plants not addressed in the previous chapter.

The book ends with an epilogue clarifying and summarising the features that make Rangitoto so special (16 bullet points are listed). While a few of the points could be debated, as an example of a restored rare (sensu Williams et al., 2007) coastal recent lava ecosystem, it is unmatched elsewhere in New Zealand and seems to me more closely akin to ecosystems of the island of Hawaii (Clarkson and Juvik, 1991). This book greatly assists the process of helping New Zealanders truly appreciate Rangitoto’s ecology and biodiversity and will hopefully encourage botanical groups elsewhere to complete similarly comprehensive natural history guides for their own sites of special interest.

References
Atkinson, I.A.E. (1960). Forest vegetation of the inner islands of the Hauraki Gulf. Proceedings of the New Zealand Ecological Society 7: 29–33.

Clarkson, B.D. and Juvik, J.O. (1991). A comparative study of Metrosideros dominated primary succession on recent a’a lava flows at Rangitoto Island, New Zealand and Mauna Loa, Hawai’i. Abstract. New Zealand Botanical Society Newsletter 26: 22.

Williams, P.A.; Wiser, S.; Clarkson, B.; Stanley, M.C. (2007). New Zealand’s historically rare terrestrial ecosystems set in a physical and physiognomic framework. New Zealand Journal of Ecology 31: 119–128.

Reproduced with permission from the New Zealand Journal of Botany, 2008, Vol. 46: 101–102.

 


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