T A N E 25, 1979

VEGETATION AND FLORA OF PONUI ISLAND, HAURAKI GULF, NEW Z E A L A N D

by E . A . Brown Botany Department, University of Auckland, Private Bag, Auckland

S U M M A R Y

A total of 202 species of vascular plants (178 of which are indigenous to New Zealand) are recorded for Ponui Island. The major indigenous plant communities are discussed in detail. The composition of the flora is briefly discussed and compared with other areas.

Remnants of the island's probable former cover of kauri (Agathis australis) forest are present in the southern half of the island. However much of the kauri present is probably secondary forest that developed after milling in the early 1900's. Also present, both in coastal valleys and in valleys within the kauri forest, are remnants of taraire (Beilschmiedia tarairi) dominated broadleaf forests.

I N T R O D U C T I O N

If Ponui Island (1770 hectares) lies 30km east of Auckland (Fig. 1) and is the most eastern of the Inner Gulf island (latitude 36° 55' S, longitude 175 ° 11' E). The terrain is hilly for the most part and the southern half is dominated by a large ridge that runs roughly north south.

Most of the northern half of the island with the exception of one large valley (Fig. 1), several areas of teatree (Leptospermum) scrub and the steep coastal cliffs is in pasture. The survey was therefore concentrated on the southern end of the island where there are remnants of the kauri and broadleaf forests that probably once covered the island.

Studies on the vegetation of Ponui Island were carried out during the Auckland University Field Club scientific trip to the island, 26 August-2 September, 1978.

V E G E T A T I O N A L H I S T O R Y

Accounts of the vegetation of Ponui Island are extremely scarce (Cockayne 1904, 1905; Atkinson 1959) and virtually no material has been published. The extent of the forests in pre-European and even early-European times is unknown. There is abundant evidence of Maori occu­pation which suggests considerable areas of the natural vegetation may have been cleared or modified prior to European occupation. The diary of Frederick Chamberlin for 1853 tends to support this view as it mentions

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wild pigs being shot and scrub burned (Maddock and Whyte 1966). In the following eighty years the vegetation was further modified by the

introduction of gorse (Ulex europaeus), the actions of gumdiggers, the mill­ing of kauri in the Trig area and the periodic firing of the danthonia (Rytidosperma spp.) pastures.

At present two thirds of the island is in pasture and many bushed areas, particularly the coastal valleys, are grazed. The remaining kauri forest and regenerating areas nearby are largely kept clear of cattle and sheep (except during harsh winters). Efforts to control gorse and eradicate it from the pastures have been, to a large extent, successful and invasion of other habitats has remained at a minimum.

P L A N T C O M M U N I T I E S

Leptospermum (kanuka/manuka) scrub This occurs on dry, often quite steep slopes throughout the island. Most

of the areas observed are fairly heavily grazed and opened up by cattle. Kanuka (Leptospermum ericoides) and manuka (L. scoparium) up to 4m tall form the canopy. Where subcanopy and/or ground cover are present prickly heath (Cyathodes juniperina), mapou (Myrsine australis), Coprosma rhamnoides, Doodia media and Oplismenus imbecillus are occa­sional with introduced grasses forming the dominant ground cover.

Scrub is present in a number of areas adjoining the kauri forest. The youngest scrub lies just north of the trig and is dominated by manuka (l-2m). Common species include mingimingi, prickly heath, tauhinu (Pomaderris phylicifolia var. ericifolia), bracken (Pteridium aquilinum var. esculentum), heather (Erica lusitanica) and gorse. A few emergent tanekaha, towai, mapou, ponga and mamangi (Coprosma arborea) are present.

On the south-eastern reaches of the kauri forest the scrub is older and more open. Kanuka and Olearia spp. are the dominant trees with occasional stands of mamangi/mapou/kanuka. Ground cover is sparse but includes Gahnia, Morelotia affinis, comb fern (Schizaea fistulosa) and Lindsaea linearis. Kauri rickers are present in the older kanuka/Olearia scrub while podocarps are more common in mamangi dominated stands.

Kauri forest South of the Trig (Fig. 1) there is an area of healthy, relatively young

kauri (Agathis australis) forest. Mill ing in the early 1900s removed many of the larger specimens; most of the remaining trees have a diameter at breast height of 0.7-1.0m. Many species commonly associated with kauri are pres­ent: Gahnia spp., Kirk 's tree daisy (Senecio kirkii), hoihoi (Alseuosmia macrophylla), ponga (Cyathea dealbata) and hangehange (Geniostoma ligustrifolium). However kauri grass (Astelia trinerva) is absent and the miniature tree fern Blechnum fraseri was found in only one place (covering

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an area of some 3m 2). Young towai (Weinmannia silvicola), rimu (Dacrydium cupressinum), miro (Podocarpus ferrugineus), matai (Podocarpus spicatus) and tanekaha (Phyllocladus trichomanoides) are present in varying quantities. With the exception of tanekaha few specimens of these species are larger than striplings. Common understorey species include lancewood (Pseudopanax crassifolius), mingimingi (Cyathodes fasciculata), white maire (Nestegis lanceolata) and clinging rata (Metrosideros perforata); while ground cover is provided by the orchids Acianthus reniformis, Pterostylis brumalis and Bulbophyllum pygmaeum and a number of ferns; mangemange (Lygodium articulatum), hound's tongue (Phymatodes diversifolium), Lindsaea spp. and filmy ferns (Trichomanes spp., Hymenophyllum spp.).

In many areas the kauri forest grades into gumland scrub while numerous valleys within the forest are clad in broadleaf species. Three hard beech (Nothofagus truncata) saplings were found on one ridge (immediately SE of the trig).

Coastal cliffs Pohutukawa (Metrosideros excelsa) is the most common tree on the

unstable greywacke cliffs. Houpara (Pseudopanax lessonii), karo (Pittosporum crassifolium), akepiro (Olearia furfuracea), mahoe (Melicytus ramiflorus) and mapou most frequently form the sparse subcanopy. Wharawhara (Astelia banksii) is a prominent ground dweller; renga lily (Arthropodium cirratum), N . Z . flax (Phormium tenax), Coprosma rhamnoides and Mercury Bay weed (Dichondra repens) are also present in vary­ing quantities.

Younger scrub (2-3m) consists of dense stands of manuka, wharawhara, houpara, karo, mapou, hangehange, taupata (Coprosma repens), koromiko (Hebe stricta var. sticta), bracken and gorse. In several places pohutukawa and houpara form a more important part of the cover. Near Motunau Bay radiata pine (Pinus radiata) and macrocarpa (Cupressus macrocarpa) form self sown colonies. South of Shell Bay boxthorn (Lycium ferocissimum) has similarly escaped from cultivation.

Broadleaf forest Broadleaf forest is present in many coastal valleys and also in some of the

wetter valleys associated with the kauri forest. Taraire (Beilschmiedia tarairi) and karaka (Corynocarpus laevigatus) are the most common members of the canopy. Puriri (Vitex lucens) and kohekohe (Dysoxylum spectabile) are present in smaller amounts, as are tawa (Beilschmiedia tawa), white maire and mamangi.

Most of the broadleaf forest is heavily grazed thus a subcanopy is rarely present. Ponga and mamaku (Cyathea medullaris) are occasional. Several ferns are commonly present near the small seasonal streams: Blechnum filiforme, B. membranaceum, heruheru (Todea hymenophylloides) and

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Doodia media. Epiphytes include kokaha (Collospermum hastatum), iwituna (Lycopodium billardieri), Earina mucronata, makawe (Asplenium flaccidum subsp. flaccidum) and Pyrrosia serpens.

Kauri and rewarewa (Knightia excelsa) are frequently found in the well drained headwaters of the larger valleys.

Raupo/Cyperus swamp Two swampy areas on Ponui Island were incompletely surveyed. The

largest area lies inland from Motunau Bay (Fig. 1). Cyperus ustulatus is the main species present with cabbage tree (Cordyline australis), wheki (Dicksonia squarrosa) and ponga also occurring. The absence of raupo (Typha orientalis) suggests that during the summer months the water level in the swamp becomes quite low.

The second, very small swamp is situated behind Rabbit Bay. Raupo is dominant in the swamp with Cyperus ustulatus occuring on the drier margins. Several herbs e.g. a native willow herb Epilobium pallidiflorum, celery leaved buttercup (Ranunculus sceleratus) and starwort (Callitriche stagnalis) are abundant on the swamp margins.

Minor plant communities There are several microhabitats on Ponui Island. On the headland south

of Rabbit Bay gorse has invaded the pasture. In one place (Fig. 1) mamangi has established itself on a cleared slope.

The young stand is extremely dense and at present no other species occurs in significant numbers within this community.

Associated with the kauri forest there is a swampy valley. Kiekie (Freycinetia banksii) grows abundantly around the edges with kotukutuku (Fuchsia excorticata), nikau (Rhopalostylis sapida) and hangehange grow­ing in the wetter areas. Kiokio (Blechnum capense), wheki, heruheru, A thy Hum australe, A. japonicum, Carex dissita and C. virgata are also present in great profusion. Further down this valley the king fern (Marattia salicina) grows in and beside the small stream. This fern may have originally been planted by the Maori (A. Wright pers. comm.) and has survived only because the valley sides are too steep to permit the entry of cattle and sheep.

V A S C U L A R P L A N T SPECIES LIST

Both native and adventive species are listed. As no attempt has been made to include pasture and garden species the adventive flora is incomplete.

Nomenclature of indigenous plants follows Allan (1961) and Moore and Edgar (1970) except where otherwise referenced. Adventive plants are named according to various sources e.g. Clapham et al. (1962). Well known common names are given, and where applicable follow "Standard Com­mon Names for Weeds in N . Z . " .

Families are ordered according to V o l . I & II of the "F lora of N . Z . " .

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Those families not native to N . Z . are listed at the end of each section. Genera are listed alphabetically within families, as are species within genera. * denotes adventive species ** denotes adventive family t collected by G . P . Adams t t recorded during visits by the Auckland Botanical Society (Hastings

1956)

PSILOPSIDA Psilotaceae

LYCOPSIDA Lycopodiaceae

FILICOPSIDA Marattiaceae Osmundaceae Schizaeaceae

Hymenophyllaceae

Dicksoniaceae Cyatheaceae

Polypodiaceae

Grammitidaceae

Thelypteridaceae Lindsaeaceae

Davalliaceae Pteridaceae

Aspleniaceae

Tmesipteris elongata subsp. elongata T. elongata subsp. robusta T. tannensis

Lycopodium billardieri I. deuterodensum I. volubile

Marattia salicina Todea hymenophylloides Lygodium articulation Schizaea fistulosa

Hymenophyllum demissum H. flabellatum H. multifidum H. rarum H. revolutum H. sanguinolentum Trichomonas elongation T. reniforme T. venosum Dicksonia squarrosa Cyathea dealbata C. medullaris Phymatodes diversifolium P. scandens Pyrrosia serpens Grammitis billardieri G. ciliata G. heterophylla Thelypteris pennigera Lindsaea linearis L. trichomanoides var. lessonii Arthropteris tenella Pteridium aquilinum var. esculentum Pteris conians^ P. macilenta P. tremula Asplenium bulbiferum var. bulbiferum A. flaccidum subsp. flaccidum

Chinnock (1975)

iwituna clubmoss waewaekoukou, clubmoss

para, king tern heruheru mangemange

filmy ferns

.•limbing

wheki ponga mamaku hound's tongue

bracken

turawera hen and chickens makawe

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Blechnaceae

Dryopteridaceae

Athyriaceae

Adiantiaceae

SPERMATOPSIDA Podocarpaceae

Araucariaceae Cupressaceae Pinaceae

Lauraceae

Monimiaceae Ranunculaceae

Piperaceae

Violaceae Droseraceae Aizoaceae Polygonaceae

Chenopodiaceae

Geraniaceae Oxalidaceae Haloragaceae Onagraceae

Callitrichaceae Thymelaeaceae Proteaceae Coriariaceae Pittosporaceae Myrtaceae

A. lucidum A. obtusatum subsp. obtusatum A. polyodon Blechnum capense B. filiforme B. fraseri B. lanceolatum B. membranaceum B. norfolkianum Doodia media Ctenitis decomposita C. glabella Polystichum richardii Rumohra hispida Athyrium australe A. japonicum Adiantum cunning/iamb A. fulvum G Y M N O S P E R M A E Dacrydium cupressinum Phyllocladus trichomanoides Podocarpus dacrydioides P. ferrugineus P. spicatus A gal his australis Cupressus macrocarpa* Pinus radial a" ANGIOSPERMAE: DICOTYLEDONES Beilschmiedia tarairi B. tawa Hedycarya arborea Clematis paniculata Ranunculus hirtus R. sceleratus* Macropiper excelsum Peperomia urvilleana Melicytus ramiflorus Drosera auriculata Disphyma australe Muehlenbeckia complexa Rumex brownii* A triplex has la la * Salicornia australis Geranium sp. Oxalis corniculata Haloragis erecta Epilobium pallidiflorum Fuchsia excorticata Callitriche stagnalis Pimelea tomentosa Knightia excelsa Coriaria arborea Pittosporum crassifolium Leptospermum ericoides

(Brownsey 1977) kiokio

maidenhair maidenhair

rimu tanekaha kahikatea miro matai kauri macrocarpa radiata pine i taraire large-leaved tawa pigeonwood clematis

celery leaved buttercup kawakawa

mahoe sundew NZ iceplant pohuehue, wirevine hooked dock orache glasswort

oxalis shrubby haloragis

kotukutuku starwort

rewarewa tutu karo kanuka

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Elaeocarpaceae Tiliaceae Cunoniaceae Escalloniaceae Rosaceae

Papilionaceae

Fagaceae Corynocarpaceae Santalaceae

Rhamnaceae

Meliaceae Sapindaceae Araliaceae

Umbelliferae

Ericaceae Epacridaceae

Myrsinaceae Oleaceae

Loganiaceae Apocynaceae Caprifoliaceae

Rubiaceae

Compositae

Primulaceae

Plantaginaceae Solanaceae

L. scoparium Metrosideros diffusa M. excelsa M. perforata Elaeocarpus dentatus Entelea arborescens Weinmannia silvicola Quintinia serrata Acaena anserinifolia Rubus cissoides Carmichaelia aligera Sophora microphylla Ulex europaeus* Nothofagus truncata Corynocarpus laevigatus Mida salicifolia M. salicifolia var. myrtifolia Pomaderris phylicifolia var. ericifolia P. rugosa Dysoxylum spectabile Dodonaea viscosa Pseudopanax crassifolius P. crassifolius x lessonii t P. lessonii Schefflera digitata Apium australe Centella uniflora Erica lusitanica* Cyathodes fasciculata C. juniperina Myrsine australis Nestegis cunninghamii^^ N. lanceolata Geniostoma ligustrifolium Parsonsia heterophylla AIseuosmia macrophylla Alseuosmia x quercifolia Coprosma arborea C. australis C. macrocarpa C. repens C. rhamnoides Brachyglottis repanda Erigeron floribundus* Gnaphalium sp. Olearia furfuracea O. rani

Senecio hispidulus Sonchus oleraceus* Anagallis arvensis* Samolus repens Plantago lanceolata* Lycium ferocissimum* Solanum aviculare S. nigrum*

manuka

pohutukawa clinging rata hinau whau towai tawheowheo piripiri bush lawyer NZ broom kowhai gorse hard beech karaka maire

tauhinu

kohekohe akeake

horoeka, lancewood

houpara pate, sevenfinger NZ celery heather mingimingi prickly heath mapou

white maire hangehange kaiwhiria, NZ jasmine hoihoi

mamangi raurekau coastal karamu taupata

rangiora broad-leaved fleabane

akepiro heketara

sowthistle scarlet pimpernel

narrow-leaved plantain boxthorn poroporo black nightshade

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Convolvulaceae Scrophulariaceae

Myoporaceae Verbenaceae Avicenniaceae Labiatae Papaveraceae** Phytolaccaceae*'

Zosteraceae Liliaceae

Smilacaceae Agavaceae

Juncaceae Restionaceae Typhaceae Palmae Pandanaceae Orchidaceae

Cyperaceae

Gramineae

S. nodiflorum Dichondra repens Hebe stricta var. stricta Veronica arvensis* V. plebeja* Myoporum laetum Vitex lucens Avicennia resinifera Mentha sp.* Fumaria muralis* Phytolacca octandra* M O N O C O T Y L E D O N E S Zostera capricorni Arthropodium cirratum Astelia banksii Collospermum hastatum Dianella nigra Ripogonum scandens Cordyline australis Phormium tenax Juncus gregiflorus Leptocarpus similis Typha orientalis Rhopalostylis sapida Freycinetia banksii Acianthus fornicatus var. sinclairii A. reniformis Bulbophyllum pygmaeum Corybas sp. Dendrobium cunninghamii Drymoanthus adversus Earina mucronata Microtis unifolia Pterostylis brumalis Thelymitra intermedia T. longifolia Baumea juncea Carex dissita C. virgata Cyperus ustulatus Gahnia lacera G. setifolia Lepidosperma australe Morelotia affinis Schoenus tendo Scirpus nodosus Uncinia banksii Agrostis tenuis* Anthoxanthum odoratum* Cortaderia jubata* Dactylis glomerata* Deyeuxia billardieri Echinopogon ovatus Oplismenus imbecillus Poa anceps

small-flowered nightshade Mercury Bay weed koromiko

Australian speedwell ngaio puriri manawa, mangrove

scrambling fumitory inkweed

seagrass renga lily wharawhara kokaha turutu supplejack cabbage tree NZ flax

oioi, jointed rush raupo nikau kiekie

spider orchid

microtis greenhood

square stemmed sedge

hooked sedge browntop sweet vernal purple pampas grass cocksfoot sand wind grass hedgehog grass

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Sporobolus africanus * Stenotaphrum secundatum * Stipa teretifolia

ratstail buffalo grass needle grass

DISCUSSION

Past vegetation cover Large kauris were removed from the Trig area earlier this century. This

together with the presence of a flourishing, relatively young kauri forest (possibly the result of secondary forest development (Atkinson 1959) after milling) suggests that, in the past, kauri forest clad the higher ground. Broadleaf forests would have dominated the inland valleys (taraire-tawa-kohekohe-puriri) and coastal valleys (taraire-karaka-kohekohe). The absence of mature podocarps, if natural rather than man induced, would suggest that the kauri/podocarp mixtures found in several areas are a recent (0-150 years) occurrence.

Composition of the flora The native flora of Ponui Island is not large and varied. The floras of

similar sized, and even much smaller islands, are larger by up to 30 % (Table 1). In this respect Ponui is floristically more similar to the mainland kauri forest of Waipoua.

The ferns and fern allies (pteridophytes) make up 32% of Ponui's indigenous flora; the island is also well represented by filmy ferns. It has been suggested (Wright 1976) that the latter, together with a high propor­tion of ferns, is indicative of a flora formerly more diverse and extensive. This would appear to be true on Ponui, where many ferns are present only in small isolated pockets within the kauri forest.

Comparison of the number of indigenous species with those from other areas (Table 1) reveals a high ratio of monocotyledons to dicotyledons. Both Tiritiri Matangi (Esler 1978) and Great Mercury (Wright 1976), where vegetation has been extensively modified, have similarly high ratios. It can perhaps be concluded (Wright 1976) that the dicotyledonous element of the flora is less tolerant of changes than its counterparts; susceptibility to habitat changes, diaspore motility and seed dispersal mechanisms are but a few of the possible barriers to survival and/or re-establishment that may exist.

Atkinson (1959) mentions that a single stand, and some scattered trees of hard beech are present on the southern slopes of Ponui. Although several saplings were found in the kauri forest no other sightings were made during our visit. It would be interesting to know if these specimens are still present, as hard beech is not commonly found in the Auckland region.

A n unusual feature of the kauri forest is the almost complete absence of the two more notable kauri associates, kauri grass and Blechnum fraseri. The apparent absence of kauri grass, a bird dispersed species which occurs

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Table I. The distribution and percentage (in brackets) of the indigenous vascular floras of Tiritiri Matangi I. (Esler 19781. Little Bar­rier I. Hamilton and Atkinson i w . l i . Waipoua Forest {Cockayne 1*081. Kapiti I. (Cockayne 1907). Great Mercury I. (Wright 1976) and Ponui I. according to plant groups.

Tir i t ir i L i n k Barrier W a i p o u a Kapit i Great Mercury Ponui

Area (in hectares) 220 3 020 9 310 2 000 1 850 1 770

Species/hectare 0.85 0.12 0.11 0.14 0.10

Pteridophytes 31(16.5) 90 (24.5) 63 (26.0) 43 (19.5) 63 (25.0) 56 (31.5)

Gymnosperms 1(0.5) 9(2 .5) 11(4.5) 2(1.0) 2(1.0) 6(3 .0)

Dicotyledons 92 (49.0) 187 (51.0) 122 (50 5) 126(58 0) 113 (44,5) 76(43.0)

Monocoty ledons 64 (34.0) 82 (22.0) 45(19.0) 4 7 ( 2 1 5 ) 75 (29.5) 40(22.51

T O T A L 188 368 241 218 253 178

on nearby Waiheke Island, is particularly hard to explain, unless ii is palatable and has been exterminated by stock.

On Ponui Island the relatively low topography and few permanent streams with the consequent lack of habitat diversity delimits the potential flora. Although indirect evidence such as the monocotyledon/dicotyledon ratio suggests that the flora may have been larger it probably never has had the diversity of nearby Waiheke (Kirk 1878) or Waipoua.

A D D E N D A

Mr A . E . Wright has supplied 9 additional taxa which are recorded in the collecting notebook of Mrs P. Hynes.

Hymenophyllaceae

Cyatheaceae Dennstaedtiaceae Pteridaceae Aspleniaceae

Adiantaceae

Hymenophyllum scabrum Trichomonas endlicherianum Cyathea smithii ?? Hypolepis distans Paesia scaberula Asplenium flabellifolium A. hookerianum A. lamprophyllum Adiantum hispidulum

scented fern

rosy maidenhair

ACKNOWLEDGEMENTS

There are many people I would like lo thank; all the members of A . U . F . C . involved in the planning and preparation for the trip, the Chamberlin family for their hospitality and help, Mr Arthur Calvert for the use of his boat, A . E . Wright for his help in identifying a number of specimens and Associate Professor J.A. Rattenbury for critically reading this manuscript.

REFERENCES

Allan. H . H . 1961; "Flora of New Zealand". Volume I. Government Printer, Wellington. 1085pp.

Atkinson, l .A .F . 1959: Forest vegetation of the inner islands of the Hauraki Gulf. Proceedings of the New Zealand Ecological Society 7: 29-33.

Brownsey, P.J. 1977: Asplenium hybrids in the New Zealand flora. New Zealand Journal of Botany 15: 601-637.

Cheeseman, T.F. 1925: "Manual of the New Zealand Flora". Second Edition. Government Printer, Wellington.

Chinnock, R.J. 1975: The New Zealand species of Tmesipteris (Psilotaceae). New Zealand Journal of Botany 13: 743-768.

Clapham, A.R., Tutin, T . G . & Warburg, E.F. 1962: "Flora of the British Isles". Second Edition. Cambridge University Press. 1269pp.

Cockayne, L. 1905: Notebook 21, In Leonard Cockayne manuscript collections (Ms 74), Auckland Institute and Museum Library, Auckland.

Cockayne, L. 1907: Report on a botanical survey of Kapiti Island. Appendix to the Journal of the House of Representatives of New Zealand C8. 23pp.

Cockayne, L. 1908: Report on a botanical survey of the Waipoua Kauri Forest. Appendix to the House of Representatives of New Zealand CI4, 44pp.

Edgar, E. 1973: Names in Pseudopanax . Koch (Araliaceae). New Zealand Journal of Botany II: 171-172. 354pp.

Esler, A . E . 1978: Botanical features of Tiritiri Island, Hauraki Gulf, New Zealand. New Zea­land Journal of Botany 16: 207-226.

Hamilton, W . M . & Atkinson, I.A. 1961: Vegetation. In Hamilton, W . M . (Ed.): Little Barrier Island (Hauturu). New Zealand Department of Scientific and Industrial Research Bul­letin 137. Government Printer, Wellington. 198pp.

Maddock, S. & Whyte, D. 1966: "Islands of the Gulf". Collins, Auckland and London. 286pp.

Moore, L.B. & Edgar, E. 1970: "Flora of New Zealand". Volume II. Government Printer, Wellington.

New Zealand Weed and Pest Control Society 1969: Standard common names for weeds in New Zealand. Editorial Services, Wellington. 141pp.

Wright, A . E . 1976: The vegetation of Great Mercury Island. Tone 22: 23-49.

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