V A S C U L A R P L A N T S A N D V E G E T A T I O N OF M O T U O P A O I S L A N D , N O R T H L A N D , N E W Z E A L A N D

by Lisa J. Forester Department of Conservation, PO Box 842, Whangarei

S U M M A R Y

Motuopao Island, off Cape Maria van Diemen in the Far North has a colourful history of settlement. Fifty-two years ago it was abandoned as a lighthouse station and the vegetation left to regenerate. This study of the vegetation of the island was done during a programme of kiore (Rattus exulans) eradication during 1988-90. The island was visited on four occasions and also flown over by helicopter.

Vascular plant species are recorded and eight vegetation types are described and mapped. Regeneration is discussed as are interesting records, the island's vegetation values and weed threats.

I N T R O D U C T I O N A N D H I S T O R Y

Motuopao Island (Lat. 34° 28'S, Long. 172° 38' E) lies 500m off Cape Maria van Diemen at the north-western tip of the North Island. Covering 30ha, the island comprises two hills with moderately rolling inland slopes and steep basaltic seaward cliffs separated by a wide sand saddle with major valleys running to the west and east. The longest eastern valley faces the mainland and terminates in an open sand beach pounded by heavy surf.

Conditions on the island are harsh and dry with a mean annual temperature of 15.5°C and a mean annual rainfall of 992mm (NZ Meteorological Service 1919-1980, Cape Reinga). Soil evaporation is probably very high as the island is windswept especially by frequent strong westerlies. Rough and unpredictable seas make access to Motuopao difficult.

A colourful history of settlement is reflected in the amount of disturbance and relics of human activity on the island. During pre-European times, it was a Maori fishing camp (Shirley 1985) and middens, hangi and stone heaps have been recorded (NZ Archaeological Association Site Record Form NZMS 1 Site Numbers N l and N2/1062-1068).

In 1879 a wooden lighthouse, servicing the Far North, was built on the northern high point and three families took up residence in houses downhill from the lighthouse. During a second phase of settlement, two of the houses were moved to less sandy ground on the southern hill and other buildings and modifications were added. A tiny Post Office was even opened on the island (Shirley 1985).

33 Tane, VoL 34, 1993

Remains of the houses, outbuildings and old lighthouse are still present today. There are parts of a system of tramways and the solid concrete foundations of a large crane which off-loaded supplies brought in by boat. Old winches from a "flying fox" conveyor which carried fresh supplies and occasionally people across the channel between Cape Maria van Diemen and the island are buried in the dense flax.

The extreme isolation, water shortages and frequent westerly gales which piled massive drifts of sand up around some of the buildings made life on Motuopao difficult. There were even family feuds and a double drowning tragedy. By 1940, after 62 years of continuous settlement, the light was dismantled for shipment to Cape Reinga and the island was abandoned.

Although little has been recorded about the vegetation on the island during the time it was settled, Shirley (1985) states that flax (Phormium tenax) was abundant whilst most of the island was covered by sand with only patches of toetoe (Cortaderia splendens) and low scrub and bush. A sheep (Ovis aries) skeleton found in the old dump during this study suggests that the island was grazed.

Motuopao Island is now a Nature Reserve under the Reserves Act (1977) administered by the Department of Conservation.

In recent years, two separate ecological surveys have been conducted:

1. In 1981 the island was visited as part of a Wildlife Service survey and a plant species list and vegetation map was produced by Mark Bellingham in an unpublished internal report by Anderson (1982); and

2. On 3 December 1983, a brief visit was made to the island by members of the Offshore Islands Research Group returning from an expedition to the Three Kings Islands. Less than one hour was spent on the island exploring the western side, and E K Cameron and A E Wright made preliminary records of the flora and collected plant specimens.

The present account deals with four separate visits to the island by the author (27 to 28 September 1988, 6 to 11 October 1989, 18 to 20 October 1989, 1 to 3 February 1990) during a programme of kiore survey and eradication by Department of Conservation staff. Approximately 30 minutes was spent by the author on the rock stack off the northern tip of the island. The island was also flown over by helicopter and oblique aerial photographs were taken to help map the vegetation types.

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VASCULAR FLORA OF MOTUOPAO ISLAND

Species List

One hundred and thirty-three vascular plant taxa are listed for Motuopao Island.

Nomenclature of indigenous species follows Druce (1991) whilst nomenclature of naturalised flora follows Webb et at. (1988).

Some of the species listed by Mark Bellingham in 1981 (Anderson 1982) were not substantiated and some are considered dubious. Two species which are common on the island (Isolepis nodosa and Parsonsia capsularis) are not recorded by Bellingham and are possible candidates for mis-identifications. These unsubstantiated records are listed below.

Key to Symbols

Frequency of species -

* = adventive R = garden relic a = abundant c = common 0 = occasional r = rare 1 = local ? = unknown

Records -

C W = E K Cameron and A E Wright (3 December 1983) + = new record

SPECIES

Ferns and Fem A l l y Vouchers

Adiantum cunninghamii A. hispidulum Asplenium oblongifolium A. northlandicum Doodia media subsp. australis

o A K 198061 o + r A K 185551, A K 186057, A K 205000, A K 205001 r A K 195838, A K 164774 c A K 205005

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Pteridium esculentum o Pyrrosia eleagnifolia r +

Dicotyledons

Apium prostratum subsp. prostratum c 1 Anagallis arvensis subsp. arvensis* o A. arvensis var. coerula* o Blackstonia perfoliata* o + Brassica juncea* o 1 + B. napus* o 1 + B. oleracea*R r 1 + Cakile edulenta* r + Calystegia marginata r 1 + C. soldanella c Centella uniflora o + Centaurium erythraea* o + Cerastium glomeratum* o Cheiranthes cheiri*R r 1 + Chenopodium album* r Cirsium vulgare* r + Conyza albida* o Coprosma acerosa c C. repens c C. acerosa x C. repens

(- C. kirkii) r 1 + C. propinqua x C. robusta r 1 + Dichondra repens o + Disphyma australe c 1 Einadia allanii ? r + £. trigonos r + Galium aparine* Geniostoma ruprestre

subsp. ligustrifolium c Geranium homeanum ? r + G. molle* r G. solanderi "coarse hairs" r + Gnaphalium coarctatum* o + G. gymnocephalum o + G. simplicicaule* o + Hypochoeris radicata* o Lavatera arborea*R r Leontodon taraxicoides* o Lepidium oleraceum r 1 A K 195840, Leucopogon fasciculatus o + Lilaeopsis novae-zelandiae 1 C W Linum bienne* o + Lobelia anceps c

A K 195839, A K 204992, A K 164778 A K 186053 A K 185552

A K U 15596, A K 164773 A K 195762, A K 195766

A K 185965 A K 198058 A K 195841 A K 195823 A K 185964

A K 195833

A K 185962 A K 198059

A K 195769 A K 196232, A K 198066

A K 198053, A K 198067, A K 206414 A K 195764

A K 186063 A K 198051 A K 195771

A K 185960

A K 195777 A K 185554 A K 198064

A K U 15599, A K 164768

A K 196229, A K U 22184, A K U 22185

A K 204995 A K 195836

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Lupinus arboreus* (single plant removed) Macropiper excelsum var. excelsum Matthiola incana*R Medicago lupulina* M. nigra* Melilotus indicus* Modiola caroliniana* Muehlenbeckia complexa Myoporum laetum (single plant) Oenothera stricta Orobanche minor* Oxalis rubens Parietaria debilis Parsonsia capsularis Picris echioides* Pimelea prostrata agg. Plantago australis* P. lanceolata* P. major* Polycarpon tetraphyllum* Pseudognaphalium luteo-album Rorippa nasturtium-aquaticum* Sagina apetala* Samolus repens Sarcocornia quinqueflora

subsp. quinqueflora Senecio lautus S. vulgaris* Sicyos australis Silene gallica* Solanum americanum* S. tuberosum*R Sonchus asper* S. oleraceus* Spergularia media Stellaria media* Tetragonia tetragonioides T. trigyna Trifolium spp.* Vicia saliva*

Monocotyledons

Ammophila arenaria* Arthropodium cirratum Asparagus asparagoides* Baumea juncea Bromus diandrus*

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B. fonkii* B. hordeaceus* B. willdenowii* Carex c. f. dissita C. Lambertiana C. ochrosaccus C. pumila C. solandri C. spinirostris C. testacea Cordyline australis Cortaderia splendens Cyperus ustulatus Dactylus glomerata* Desmoschoenus spiralis Deyeuxia billardierei Dichelachne crinita Gladiolus cardinalis*R Isolepis cernua I. nodosa I. sepulcralis Lachnagrostis filiformis var. littoralis

Lagurus ovatus* Lepidosperma australe Leptocarpus similis Lolium perenne* Microtis unifolia Narcissus tazetta*R Paspalum dilatatum* P. vaginatum Phormium tenax Poa pusilla P. pratensis* Polypogon monspeliensis* Rytidosperma unarede Spinifex sericeus Sporobolus africanus* Stenotaphrum secundatum* Thelymitra longifolia Triglochin striata Zoysia planifolia

1 + 1 C W 0 +

? r + 1 C W

1 C W ? C W o + c + r 1 c r 1 o r 1 +

o 1 a ? o 1 +

r + 0 1 + r r + 1 C W o ? o l

.' o + c o + a o + C W ? o +

A K 195773

A K 195829

A K U 15603, A K 164775 A K 205004

A K 198057 A K 198054, A K 198055

A K 195763, A K 195765, A K 196780 A K 204996, A K 204997

A K 204994

A K 164765, A K 195842, A K U 15604 A K 195834

A K 164770, A K 198062 A K 195830, A K 196236 A K 195831, A K 186062 A K 196233, A K 198052

A K 195835

A K 195828 A K 204993 A K 195776

A K U 15601, A K 186052 A K 164 766, A K 196231, A K U 15590

A K 195824 A K 186055

A K 185550, A K 186061, A K 204999

A K 164779, A K 196237, A K U 15594

Unvouchered records by Mark Bellingham (1981) unsubstantiated by this survey:-

Blechnum penna-marina - possibly mis-identified Doodia media Coprosma crassifolia Conyza canadensis - probably mis-identified C. albida

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Cyathodes juniperina - possibly Leucopogon fasciculatus Dianthus caryophyllus Gladiolus natalensis - possibly mis-identified G. cardinalis Juncus maritimus - possibly mis-identified Isolepis nodosa Kunzea ericoides Ileostylis micrantha - probably mis-identified Parsonsia capsularis Malva sylvestris - probably mis-identified Lavatera arborea Taraxacum officinale - probably mis-identified Leontodon taraxicoides

VEGETATION TYPES

Eight basic vegetation types have been mapped for the island (Fig. 1). Although similar to those recorded by Bellingham in 1981 (Anderson 1982) more detail and accuracy has been possible. Photographic methods in conjunction with

Locality Map

E l taupata - iceplant

PTJ buffalo grass

^ other grasses

I I flax assoc iat ion

8 2 brackish seepage

marram

G-D spinifex with shore b indweed

and knobby club-rush

Coprosma acerosa -

Muehlenbeckia complexa,

Motuopao Island

- ridges

beach

J sand

I—1 building ruins

o derelict l ighthouse

5 0 0 metres rock

Fig. 1 Map of Motuopao vegetation types.

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field survey were used initially and the draft map was refined during subsequent visits. Photographs were taken from the ground and oblique aerial photographs were taken by helicopter. A 1:10000 scale aerial black and white print was also used.

Appearance types in vegetation were distinguishable from both the overhead black and white airphotos and the oblique airphotos taken from the helicopter. In addition, the island was small enough to allow foot coverage and transects along the same 50 m grid lines used during the kiore eradication programme were walked. The basic mapping technique is descriptive and qualitative using estimates of percentage cover of the plant crowns of the leading species. To try to quantify this, in general dominant species occupy more than 80% of the cover whilst abundant species cover more than 50%, frequent species cover more than 20% and occasional species more than 5%. "Scattered" describes individual plants dispersed over a wide area whilst "local" describes patchiness or clumping often associated with distinct microhabitats.

Structural classification used in the descriptions follows Atkinson (1985).

Vegetation types are:-

Taupata - iceplant Shrubland with abundant taupata (Coprosma repens) and occasional ice plant (Disphyma australe) is found on the steep coastal cliffs and banks both on the main island and rock stack to the north. Patches of soil on the upper cliffs support frequent harestail (Lagurus ovatus), knobby club-rush (Isolepis nodosa) and Mercury Bay weed (Dichondra repens) with occasional Pimelea prostrata and taupata. Around the splash zone are the more salt-tolerant herbs including shore groundsel (Senecio lautus), sea celery (Apium prostratum), Samolus repens and patches of glasswort (Sarcocornia quinqueflora). The fern Asplenium northlandicum was also seen growing lower down above the splash zone. At the mouth of a wide valley on the south side of the island taupata forms a dense 3m canopy which is open underneath and burrowed by seabirds.

Buffalo grass On the northern faces of both hills grassland dominated by buffalo grass (Stenotaphrum secundatum) forms a dense sward with scattered flax (Phormium tenax) and knobby club-rush. On the ridge-tops are some patches of bracken and toetoe On the southern hill knobby club-rush and Muehlenbeckia complexa are also found.

Other grasses

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A grassfield comprising mainly Bromus spp. has developed in a small, discrete area at the northern tip of the island. The same association appears to occupy the top of the rock stack near the northern tip though this was too steep to check in the time available.

Flax association Rax tussockland occurs on the ridge-tops and on the southern sides of both hills. Although scattered individuals of flax are common across the whole island these tussocklands have dense flax with frequent toetoe, hangehange (Geniostoma rupestre), Parsonsia capsularis, and mingimingi (Leucopogon fasciculatus) and locally frequent bracken. On the ridge-tops the vegetation is less dense and lower in stature (to 2m) with open areas of bracken or grasses and herbs where there has been additional disturbance. In the sheltered gullies flax becomes dominant and dense to 3m tall. Kawakawa (Macropiper excelsum) was recorded in a flax gully on the northern side.

Brackish seepage A herbfield in a brackish seepage at the western mouth of the central valley supports a patch of watercress (Rorippa nasturtium-aquaticum) and salt-tolerant herbs - oioi (Leptocarpus similis), sea celery, glasswort, Samolus repens and Isolepis cernua.

Marram A bank of marram (Ammophila arenaria) grassland runs across the central valley on the eastern side of the dividing saddle. This is broken by patches of bare sand. It may be the remnants of an earlier attempt to stabilise the sand in this area.

Spinifex with shore bindweed and local knobby club-rush The majority of the central valley is sandfield with spinifex (Spinifex sericeus), shore bindweed (Calestegia soldanella) and knobby club-rush, especially towards the lower end of the valley. Also present are scattered flax, New Zealand spinach (Tetragonia spp.), Coprosma acerosa and Muehlenbeckia complexa.

Coprosma acerosa - Muehlenbeckia complexa Dense patches of a low shrubland association comprising Coprosma acerosa and Muehlenbeckia complexa have occasional flax, toetoe and knobby club-rush. There are also many bare sand patches. This association extends up a shallow branch of the valley towards the high point on the southern hill and has been intensively burrowed by seabirds.

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DISCUSSION

In the last 52 years since the lighthouse was abandoned, the regeneration on Motuopao Island has been limited with no tall forest species recorded so far.

The lack of a nearby seed source is probably the main factor restricting the introduction of canopy species, the nearest seed source being Cape Maria van Diemen headland, which itself is an "island" separated from the rest of Te Paki by a bare sand tombolo. Cape Maria van Diemen is vegetated by dry secondary shrubland with pockets of tall canopy species restricted mainly to the gullies.

Another factor slowing regeneration are the harsh conditions on the island. Skeletal soils, and the dry, exposed environment of almost all sites probably makes seedling establishment difficult. Although the rainfall is moderate (992 mm) the extremely windy conditions on the island probably cause excessive evaporation meaning that available soil moisture is low. In addition salt spray is probably also a factor limiting colonisation. Much of the central valley is bare sand which is unstable and has probably only ever supported dune species. Dense swards of flax or buffalo grass over much of the rest of the island prevent establishment of other species, but also serve to stabilise erosion and curb sand movement. However, flax appears to be slowly expanding into buffalo grass areas.

The presence of kiore may also have had an effect on the seed source on the island as since their removal several plant species have been noted with moderate to heavy fruit. During January 1990 Coprosma acerosa and Muehlenbeckia complexa were fruiting heavily whilst in January 1992 R. Pierce records eight species in fruit including abundant fruit on hangehange, shore bindweed and taupata (Northland Department of Conservation file, DOC 258).

Of the 133 recorded vascular plant tax a, 60 (45 %) are naturalised and are mostly dicotyledonous herbs and grasses. Most of these are unlikely to upset the island's ecology. A single shrub of tree lupin (Lupinus arboreus) was vouchered and removed whilst smilax (Asparagus asparagoides), recorded by Cameron and Wright in 1983, was not seen on this survey. A patch of marram in the central sand gully should be monitored and if necessary eradicated. Although not recorded so far, pampas grass (Cortaderia selloana), now becoming established in Te Paki, should be watched for and removed.

Of interest are plants persisting from gardens around the old house sites. These relics include the red-throated gladiolus (Gladiolus cardinalis), jonquils (Narcissus tazetta- recorded by Cameron and Wright in 1983), three colour variants of wallflower (Cheiranthes cheiri) and pink-flowered stocks (Matthiola incana). On other parts of the island three species of Brassica are found, Indian mustard (B. juncea), rape (B. napus) and wild cabbage (B. oleraceus). A potato plant (Solarium tuberosum) was found in the sand valley whilst occasional tree

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mallow (Lavatera arborea) are widespread across the island. Bellingham recorded carnations (Dianthus caryophyllus) in 1981.

Several native species are worth comment. Calystegia marginata was seen in one small area in a gully on the inside of the northern hill. In the same area was a large patch of native cucumber (Sicyos australis). This plant is now largely restricted to offshore islands in northern New Zealand (Cameron 1992). The fern Asplenium northlandicum was uncommon above the coastal rock platforms whilst Cook's scurvy grass (Lepidium oleraceum) was seen on fertile sites on the rock stack and in one place on the southern seaward faces. One plant of pingao (Desmoschoenus spiralis) was recorded behind the beach.

The two species of New Zealand spinach, Tetragonia trigyna and T. tetragonioides were found. T. tetragonioides is now a plant of limited distribution in New Zealand (A E Wright pers. comm.) and may warrant threatened status (P J de Lange pers. comm.).

A single giant shrub of ngaio covering several metres and a small group of cabbage trees are found near one of the house-sites on the southern hill .

An old record of Senecio rufiglandulosus (WELT 31720) is of interest as it represents the northernmost collection of this plant and was probably collected by J Buchanan in 1877 (Taylor and Cameron 1990). Senecio specimens collected on this survey are all Senecio lautus (E K Cameron pers. comm.) which has similar looking seedlings, but a thorough search for Senecio rufiglandulosus on the island should be made.

A C K N O W L E D G E M E N T S

A number of colleagues assisted with plant records, collections and vegetation mapping whilst working on the kiore eradication programme, notably Peter Anderson, Mike Aviss, Don McKenzie, Richard Parrish, Ray Pierce and Tim Shaw. To all the others who offered good company, even during trying weather conditions, many thanks. For safe transport thanks go to (Captain) Sid Roberts and our patient helicopter pilot "Prickles" de Ridder. Pam and Dick Gillet provided logistic support from Cape Reinga. Thanks also go to Ewen Cameron, Peter de Lange and Anthony Wright for assisting with the manuscript, Barbara Lyford for typing and Terry Conaghan for draughting the map.

R E F E R E N C E S

Anderson, R .A . 1982: Motuopao Island. Unpublished Internal N Z Wildlife Service Report. Atkinson, I .A.E. 1985: Derivation of Vegetation Mapping Units for an Ecological Survey of

Tongariro National Park North Island, New Zealand. New Zealand Journal of Botany 23(3):36l-378.

Cameron, E .K . 1992: Decline of mawhai (Sicyos australis). New Zealand Botanical Society Newsletter No. 28 June 1992: 11-12.

Druce, A.P. 1991: Indigenous Higher Plants of New Zealand. 7th (partial) revision. Unpublished. Shirley, P. 1985: Ghost Lighthouse of the Far North. Historic Places September 1985.

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Taylor, G .A . and Cameron, E . K . 1990: Kauwahaia Island - Te Henga, west Auckland. Auckland Botany Society Journal 45(2): 71-77.

Webb, C.J., Sykes W.R. & Garnock-Jones P.J. 1988: Flora of New Zealand Volume IV. Botany Division, DSIR, Christchurch.

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