TANE 25, 1979 VEGETATION AND FLORA OF PONUI ISLAND, HAURAKI GULF, NEW ZEALAND by E.A. Brown Botany Department, University of Auckland, Private Bag, Auckland SUMMARY 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. INTRODUCTION 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. VEGETATIONAL HISTORY 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 occu• pation 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 5 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 mill• ing 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. PLANT COMMUNITIES 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 occa• sional 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. Milling 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 pres• ent: 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 7 an area of some 3m2). 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 vary• ing 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 8 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 grow• ing 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. VASCULAR PLANT SPECIES LIST Both native and