Tane 35: 17-23 (1995)

FLORA OF KAREWA ISLAND, BAY OF PLENTY

by Alan J. Tennyson Threatened Species Unit, Department of Conservation, P O Box 10-420, Wellington

SUMMARY

Karewa Island is a relatively unmodified island with 33 species of vascular and nine species of lower plants currently recorded present. Only four species are adventive. Two tree species occur near or at their southern limit here. Ongoing monitoring of rare species and weed control is required and some active management may be needed to maintain some unusual plants.

INTRODUCTION

Karewa is a 5ha island (37°32'S 176°08'E, Figs. 1 and 2) which is best known for its tuatara (Sphenodon punctatus), lack of introduced mammals, its large burrowing petrel populations and the presence of some unusual plants (Sladden 1924). I visited Karewa from 27 April to 2 May 1995 primarily to assist Rachel McClellan with her MSc study on flesh-footed shearwaters (Puffinus carneipes). While there I took the opportunity to survey the flora. I carefully searched for vascular plants but did not survey lower plants thoroughly.

Sladden (1924) described the flora of Karewa Island, noting 22 species of vascular plant. L . C . Bell (in an unpublished 1948 Wildlife Service trip report) and Schmidt (1953) made some references to the vegetation but did not record further species. An unpublished Wildlife Service island survey form completed by L . Moran and J-C. Smuts-Kennedy (after a visit in 1972) lists species seen and notes the presence of the introduced brush wattle (Paraserianthes lophantha) for the first time. An unpublished Wildlife Service report (undated but more recent than 1972) summarises the plants present. An unpublished Wildlife Service report (dated 17 December 1985) by P. Jansen gives further information on wattle control. Beadel (1992) commented on threatened plants on the island.

FLORA

Voucher specimens of some plants have been deposited in the Auckland Institute and Museum (AK) and the Museum of New Zealand (WELT) herbaria.

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Vascular plants * denotes adventive species; f denotes species not recorded by Sladden (1924).

Paraserianthes lophantha brush wattle** I pulled out 72 seedlings and one 1.5m plant below the north-west end of the main ridge where Department of Conservation (DoC) staff had removed some large trees recently. In 1972, Moran and Smuts-Kennedy recorded that "a small grove of wattles exists above N . W . cliffs" and recommended "that these be removed and the situation checked annually". Jansen's report notes that the eradication of wattles was recommended again in 1985 after a visit by K. Cannell (Wildlife Service) who reported them at the same site. Jansen reports that he and J. Adams visited the island on 16 December 1985 and found the known wattle site plus a further site high on the northern face. A total of at least 100 trees were found and poisoned - the largest tree was 4m high with a trunk diameter of 20cm. Annual visits by DoC staff have been carried out since 1988 in an attempt to eradicate this weed (A. Jones pers. comm.). Large numbers of seedlings (e.g. 150 per m2) often grow but most die out in the following summer (A. Jones pers. comm.).

Arthropodium cirratum renga lily Only at one rocky outcrop near the centre of the island where it was frequent.

Asplenium oblongifolium shining spleenwort Common over the island.

Asplenium haurakiense Abundant on the ground and as an epiphyte. Sladden (1924) and Schmidt (1953) recorded this plant as A. flaccidum. There is a specimen of A. haurakiense from Karewa collected by B.C. Aston in 1911 in the Auckland Institute and Museum herbarium (E. Cameron pers. comm.). P.J. Brownsey (pers. comm.) identified hybrid A. haurakiense x A. oblongifolium fronds amongst material I brought back.

Collospermum hastatum' One clump on a western rocky outcrop.

Coprosma repens taupata The dominant tree on the island from sea level to the summit.

Corynocarpus laevigatus karaka Only eight trees were found, all on the south-western flat. Six of these were largely dead. A . Jones (pers. comm.) notes that the population is looking "more and more beaten up each year". Sladden (1924) and Moran and Smuts-Kennedy in 1972 recorded a "grove" of karaka in this area, so the population has declined. A severe storm, such as

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Fig. 1. Karewa Island from the north-west, November 1993. Photo: Anthony Wright.

Cyclone Bola in 1988, could have damaged this relatively exposed population but other factors must be preventing regeneration (I saw no young plants).

Crassula sieberiana* Occasional on rocky outcrops.

Cyperus ustulatus* A few plants on the north-west coast.

Dichondra repens^ One plant on the south-west coast.

Disphyma australe ice plant* Common in open sites, especially around the coastline.

Earina mucronata' A few clumps on a western rocky outcrop.

Einadia trigonos Frequent in exposed sites. Presumed to correspond with Sladden's (1924) record of Chenopodium triandrum.

Isolepis nodosa? Occasional, especially around the north-west coastline.

Lachnagrostis littoralis* A few dried plants with seed heads were found. Freshly sprouting grass was common at exposed sites but no other seed heads were found to allow identification to species. Sladden (1924) recorded three unidentified annual grasses.

Lepidium oleraceum Cook's scurvy grass Scattered plants (about 40 adults) were seen on the northern face on exposed sites and under forest, and along the south-east coast above the shoreline. This species has been recorded as densely covering about 60m2 in the northern area (Beadel 1992), so there appears to be considerable variation in the number of plants present over time.

Lobelia anceps shore lobelia* One clump on the south-eastern coast.

Lycium ferocissimum boxthorn** Three medium-sized trees and two seedlings were seen on the northern rocky faces. I pulled out the seedlings. The size of the trees (up to 2m tall) indicates that the species must have been present for several years.

Melicytus novae-zelandiae Common over the island.

Muehlenbeckia complexa wire vine Frequent in open sites. Sladden's

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(1924) reference to the "scrambling Muehlenbeckia" and Schmidt's (1953) reference to "pohuehue Muelenbeckia [sic]" are clearly this species.

Peperomia urvilleana Occasional around rocky outcrops.

Phytolacca octandra inkweed* Occasional in exposed sites.

Pisonia brunoniana parapara Only six stunted trees were found, all on the south-western flat. Beadel (1992) noted one large and seven smaller trees and additional seedlings. However, the large tree died in 1983 (A. Jones pers. comm.). Three 0.5m tall plants were found by A . Jones but these disappeared during a dry period in 1991 (A. Jones pers. comm.).

Pittosporum crassifolium karo1 One medium-sized tree was found near the north-western shore.

Pouteria costata tawapou Four shrubby trees were seen at the north-west end of the main ridge and one further tree on the south side of the summit. Sladden (1924) recorded this species as "not a scarce plant" which suggests it could have declined.

Pseudopanax lessonii houpara Common over the island. In 1948 Bell noted "fivefingers" which I've assumed to be a reference to this species.

Pyrrosia eleagnifolia Frequent on rocky outcrops.

Sarcocornia quinqueflora glasswort Common around the coastline.

Senecio lautus shore groundsel Frequent above the shoreline.

Solanum americanum small-flowered nightshadet Present in exposed sites.

Solanum nigrum black nightshade* Frequent in exposed sites.

Stellaria parviflora chickweed t Frequent above the shoreline.

Streblus banksii large-leaved milk tree Only one 3.5m tall tree was found growing near tawapou at the north-west end of the main ridge. Sladden (1924) recorded this species apparently at the same site but did not indicate how many plants he saw. The undated Wildlife Service summary notes that the "odd" plant

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occurs toward the western extremity of the island near karaka and parapara trees but I found none in this area. Given other inaccuracies in this report, I suspect that their locality or species identification is an error.

Bryophytes Bryum I capillare Campylopus I pyriformis Fissidens linearis subsp. linearis Frullania I solanderiana Lophocolea semiteres Sematophyllum contiguum

Lichens Pseudocyphellaria sp. Ramalina celastri Xanthoparmelia sp.

DISCUSSION

The current floral list of Karewa Island includes 33 vascular and nine lower plants. Four species are adventive (inkweed, black nightshade, brush wattle, boxthorn), the latter two being invasive trees. Of the 22 vascular species recorded by Sladden (1924) there were only two species that I did not see - ngaio {Myoporum laetum) and cabbage tree (Cordyline australis) - but he only saw immatures so these plants may not have established, and he noted two further annual grasses (not identified to species). Moran and Smuts-Kennedy in 1972 recorded Pittosporum ellipticum "at higher levels" and Tetragonia trigyna as common (repeated in the unpublished Wildlife Service report), but I found no sign of these species. It is unlikely P. ellipticum would have been present as it is not normally found on small islands (G. Taylor pers. comm.). This record is probably based on a misidentification of tawapou as this species occurs relatively high up the island and was not noted by Moran and Smuts-Kennedy. I suspect that records of Tetragonia may also be in error because the observers did not record Einadia (a plant bearing superficial resemblance to Tetragonia) as present.

Beadel (1992) noted the significance of the parapara population which is the southernmost known for the species. The tawapou population is near the southernmost limit of the species also. These populations show no recent signs of regeneration despite seed germination occurring regularly (A. Jones pers. comm.). A combination of dry conditions and disturbance by petrels is thought to be the main reason for this lack of regeneration (A. Jones pers. comm.). The

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demise of the karaka "grove" demonstrates that small populations of tree species on Karewa are vulnerable to decline. The milk tree population seems doomed unless other plants are present but undetected. The nationally threatened (Molloy & Davis 1994) Cook's scurvy grass is in smaller numbers than reported earlier.

Annual checks of the parapara, tawapou and Cook's scurvey grass are made by DoC and seed is collected but no planting has occurred on the island. As recommended by Beadel (1992), annual checks should continue. Active management may be needed to maintain some of the rarer tree species. The annual DoC wattle control should also continue and boxthorn should be controlled at the same time. Unfortunately these weeds will probably continue to reach Karewa. Boxthorn, with its fleshy fruit, is presumed to be transported by starlings (Sturnus vulgaris) which come from the mainland to roost at night. Brush wattle seeds sometimes float (pers. obs.) and I suspect these have been carried to the island by one or more of the petrel species present as such birds often swallow floating objects at sea (e.g. I have seen kowhai (Sophora sp.) seeds in the guts of white-faced storm petrels (Pelagodroma marina) on the Chatham Islands).

ACKNOWLEDGEMENTS

Thanks to Rachel McClellan for organising the trip; the DoC Tauranga Field Centre staff who supported us in many ways, especially Alan Jones, Bob Mankelow, and Christine Browne on the boat; Carole Long for organising to get our gear sent back to Wellington after we had to leave it behind on Karewa due to bad weather; the National Archives and Kira Karena for providing access to the Bell and Jansen reports; and Paul Jansen and John Adams for help regarding the history of weeds on the island. Thanks also to Graeme Taylor, Ewen Cameron, Jessica Beever (mosses), John Braggins (liverworts), and Patrick Brownsey (ferns) for botanical assistance and to Graeme, Ewen, Anthony Wright and Alan Jones for commenting on the manuscript.

REFERENCES

Beadel, S.M. 1992: Threatened and local plants of the Bay of Plenty Conservancy. Department of Conservation, Rotorua. Technical Report Series No. 13.

Molloy, J. & Davis, A. 1994: "Setting priorities for the conservation of New Zealand's threatened plants and animals (2nd edition collated by C. Tisdall)". Department of Conservation, Wellington.

Schmidt, K.P. 1953: A visit to Karewa Island, home of the tuatara. Fieldiana Zoology 34: 153-164. Sladden, B. 1924: Karewa: an island sanctuary. New Zealand Journal of Science and Technology

7: 182-187.

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