The Flora and Vegetation of Old Man Rock, Mercury Islands Group

Transactions of the Royal Society of New Zealand : Botany, Volume 1, Issue 23, 3 August 1962, Page 285

The Flora and Vegetation of Old Man Rock, Mercury Islands Group

I. A. E. Atkinson

By

[Received by the Editor, November 28, 1961.]

Abstract

A description is given of the vegetation and soil covering Old Man Rock, a small islet off the coast of the Coromandel Peninsula. A list of the plants found is included.

Old Man Rock is a precipitous-sided stack, less than an acre in area, which rises straight out of the water to a height of 225 ft. It lies approximately 12 miles north-east of Whitianga in Mercury Bay, is miles east of the Coromandel coastline at its nearest point, and 1£ miles north-west of Ohena Island. A rock specimen collected was identified by Dr W. A. Watters (N.Z. Geological Survey) as basalt.

The writer had a chance to visit the islet on July 11 and 12, 1961, when the battery-operated navigation light was being serviced from H.M.N.Z.F.A. Hauraki.

Landing is difficult except during calm weather.

The scrub which covers Old Man Rock looks undisturbed, and it is possible that this vegetation was never burnt during Maori times. It is therefore worthwhile to put on record details of the composition of the islet’s plant covering together with a list of the species found.

The vegetation of the upper two-thirds of the islet is a Paratrophis-ka.ro-houpara scrub in which the dark green foliage of karo ( Pittosporum crassifolium) contrasts with the paler greens of Paratrophis banksii, houpara ( Pseudopanax lessonii) and other shrubs. The scrub canopy is for the most part 5-10 feet high with a few trees emerging to a height of 14 feet. An understory is practically absent apart from the fern Asplenium lucidum. The soil is a shallow powdery loam with many shattered rocks exposed at the surface. Bluffs are numerous.

The scrub covering the small flat-topped summit of the islet contains a high proportion of wharangi ( Melicope ternata) and a soil profile here showed:iin—dark brown loam; loose; fine granular structure.

12in —dark brown loam with stones; very friable; moderately developed

very fine crumb structure.

Roots throughout; well drained.

To obtain a more exact picture of composition, 25 canopy shrubs were counted along a transect up the southern face of the islet and a contour transect was made at the summit where 20 shrubs were counted.

On the lower western slopes of the islet, the scrub canopy is discontinuous with patches of Disphyma australe, Deyeuxia billardieri, and Poa anceps in openings. Salicornia australis appears to be the main plant of the halophyte zone above high water mark, but it was not possible to examine this zone properly. The lower part of the eastern face is a vertical cliff 50ft high.

Several petrel burrows were noticed near or on the summit of the islet. Birds either seen or heard were silvereye, chaffinch, blackbird and a parakeet. Geckos (Hoplodactylus sp.) and skinks (Leiolopisma sp.) were found under rocks. Chewed foliage of Disphyma suggested that rats may possibly be present.

A total of 40 species of plants were seen during three hours of searching. In the list below, numbers in brackets refer to specimens lodged in the BotanyDivision herbarium, Lincoln. Names of ferns and dicotyledons follow Allan (1961) and names of monocotyledons follow Cheeseman (1925). Where departures have been made from Cheeseman, his name is placed in brackets. The abundance ratings used are as follows: a—abundant, plants generally distributed over the islet. m—many, plants seen only in parts of the islet. f—few, plants seen only at one or two points. * —introduced species.

Species Family Abundance Asplenium flaccidum var. Aspleniaceae a A. lucidum Aspleniaceae m Astelia banksii Liliaceae f Collospermum hastatum (Astelia solandri) Liliaceae f Coprosma repens Rubiaceae m Plants up to 12ft in height Deyeuxia billardieri Gramineae a Dichondra repens Convolvulaceae m Disphyma australe Aizoaceae m Hymenanthera novae-zelandiae Violaceae a Hypochoeris radicata* Gompositae a, summit Jsolepis cernua (Scirpus cernuus) Cyperaceae m Lepidium oleraceum (121207) Cruciferae f Linum monogynum (121203) Linaceae f Lycium ferocissimum* (121201) Solanaceae f Two plants seen on northern part of summit Mariscus ustulatus Cyperaceae f Melicope ternata Rutaceae f Metrosideros excelsa Myrtaceae f Plants up to 12ft in height Microlaena polynoda (121204) Gramineae f, summit Muehlenbeckia complexa Polygonaceae a Oplismenus undulatifolius Gramineae m Paratrophis banksii (121202) Moraceae a Parietaria debilis Urticaceae f Peperomia urvilleana Piperaceae £ Phormium tenax Liliaceae m Pittosporum crassifolium (121206) Pittosporaceae a Plants up to 14ft in height Planchonella novo-zelandica Sapotaceae m Poa anceps Gramineae m Pseudopanax lessonii Araliaceae a

Species Family Abundance Pyrrosia serpens Polypodiaceae a Rhagodia triandra Ghenopodiaceae m Salicornia australis Ghenopodiaceae m Scirpus nodosus Cyperaceae f Senecio lautus lautus Gompositae f Sicyos angulata Cucurbitaceae m Solarium nigrum* Solanaceae f Sonchus littoralis Compositae f Stellaria media* Caryophyllaceae f Tetragonia trigyna Aizoaceae a Thelymitra longifolia Orchidaceae f Wahlenbergia gracilis (121205) Campanulaceae a, summit

References

Allan, H. H., 1961. Flora of New Zealand. Volume 1. Govt. Printer, Wellington. Cheeseman, T. F., 1925. Manual of the New Zealand Flora. 2nd Edition. Govt. Printer, Wellington.

Mr I. A. E. Atkinson, Botany Division, D.5.1.R., Taita Experimental Station, Eastern Hutt Road, Lower Hutt.

S aspect slope (30°) Summit Number Composition Number Composition Species Counted % Counted % Faratrophis banksii 8 32% 4 20% Pittosporum crassifolium 6 24% 2 10% Pseudopanax lessonii 6 24% 1 5% Hymenanthera novae-zelandiae 2 8% 3 15% Coprosma repens 1 4% 2 10% Metrosideros excelsa 1 4% 1 5% Planchonella novo-zelandica 1 4% 1 5% Melicope ternata 0 — 6 30% ' 25 100% 20 100%

Table 1 .—COMPOSITION OF COASTAL SCRUB CANOPY ON OLD MAN ROCK.