Flora of New Zealand Series

THE NEW ZEALAND BOTANICAL REGION

This consists of the islands lying within 29º-55º South latitude and 158º East-176º West longitude (except Lord Howe Island and Norfolk Island). Cockayne's Vegetation of New Zealand, 1928, gives a detailed account which includes sketches of the physiographic and climatic features and of the distribution and composition of the flora.

Kermadec Islands (see Oliver 1910), 33 sq. Km. Raoul or Sunday Island, of 28 sq. Km., is a crater with small lakes. Some 120 species, with about 15 endemics, including Cyathea kermadecensis and C. milnei.

Three Kings Islands (see Oliver 1948, Baylis 1958), 8 sq. Km. Some 175 species with about a dozen endemics, including Alectryon grandis, Paratrophis smithii and Tecomanthe speciosa. Plectomirtha and Elingamita appear to be endemic genera.

North Island and adjacent islands, 113, 400 sq. Km. Chief offshore islands: Poor Knights (see Oliver 1925, Cranwell 1937), Great Barrier, Little Barrier (see Hamilton 1937), Kapiti (see Cockayne 1907).

South Island and adjacent islands, 148,700 sq. Km. Chief offshore island: D'Urville Island (see Oliver 1944).

Stewart Island and adjacent islands (see Cockayne 1909), 1720 sq. Km. Chief adjacent island: Solander (see Cockayne 1909). Some 12 endemics, including Raoulia goyenii.

Chatham Islands (see Cockayne 1902), 950 sq. Km. Chief islands: Chatham, Pitt. Some 40 endemics, including the genera Coxella, Myosotidium.

Subantarctic Islands (see The Subantarctic Islands of New Zealand, ed. C. Chilton, 1909):

Snares, 2·6 sq. Km. Some 25 species, including the endemic Kirkophytum robustum.

Antipodes, 60 sq. Km. Some 60 species, including the endemic Senecio antipodus.

Aucklands, 600 sq. Km. Some 160 species, including the endemics Ranunculus aucklandicus, Geum albiflorum, Gentiana concinna, Plantago aucklandica.

Campbell (see Sorensen 1951), 113 sq. Km. Some 115 species, including the endemics Gentiana antarctica, Myosotis antarctica, Dracophyllum scoparium.

Macquarie (see Taylor 1955), 118 sq. Km. Some 35 species, including the endemic grasses Puccinellia macquariensis, Deschampsia penicillata, Poa hamiltonii.

TOPOGRAPHY

The coastline of the main islands provides many habitats: sandy, gravelly and rocky shores, extensive dune-complexes, salt marshes, brackish-water lagoons, storm-lashed promontories and sheltered inlets. The physiography in general is dominated by the mountain ranges, bout three-quarters of the area lying over the 200 m. contour-line. The ranges of North Island barely attain 1800 m., but the semi-active volcano peaks rise higher; Tongariro 1968 m., Ngauruhoe 2291 m., Ruapehu 2797 m.; the extinct Egmont reaches 2517 m. In South Island the Main Divide, running the length of the island, gives off numerous subsidiary chains; over 50 peaks surpass 2750 m. Rivers and streams abound; in North Island 25 and in South Island 45 are more than 50 Km. long. Thermal springs occur in both islands and are important in the Volcanic Plateau area. There are numerous cold lakes and innumerable tarns. Twelve lakes are 65 sq. Km. or more in area, the largest being: Taupo, 600 sq. Km.; Te Anau, 347 sq. Km.; Wakatipu, 290 sq. Km.; Wanaka, 200 sq. Km.; the tidal Ellesmere, 180 sq. Km. Important plains are the Heretaunga of North and the Canterbury and Southland of South Island.

Glaciers are practically confined to South Island, but there extend from Arthur Pass to the southern fiords, themselves of glacial origin. The Tasman Glacier near Mount Cook is some 29 Km. long. The Franz Josef and the Fox, west of the divide, descend to lowland forest.

CLIMATE

The chief controlling factors are: latitude, relation to surrounding oceans, high relief. Latitude: the main islands are narrow, no point being more than 145 Km. from the sea, and lie between 34º 4' S and 47º 2' S in a curve with the concave side facing the west, and between the high-pressure belt of the sub-tropics and the low-pressure trough in the Southern Ocean. Oceanic surround: the islands are isolated from any land-mass on all sides by large expanses of ocean water, providing abundant supplies of moisture; the Australian coast is some 1610 Km. away at the nearest point. High relief: the main ranges follow the curve of the islands and lie more or less athwart the prevailing westerly winds. The islands are subject to the rapid fluctuations of weather produced by a procession of anticyclones and troughs, with occasional depressions. The relief also causes important local modifications. The strong winds have a marked effect on plant growth and form. The "north-westers" passing over the divide cause heavy rain on the western side and pronounced Fohn effects on the eastern. Wind-caused soil erosion and redeposition are often marked.

The average precipitation over the greater part of the country lies between 750 and 1500 mm., control by topography being very close. On the summit ridges of most of the main ranges rainfall reaches 5000 mm., and for a considerable area in the Southern Alps it is believed to average over 7000 mm. Hawke's Bay, Wairarapa, and Manawatu, with rainfalls mainly 750-1000 mm. a year, are the driest parts of the North Island. East of the main divide in the South Island rainfall rapidly diminishes to 1000 mm.; the Wairau Valley of Marlborough and the greater part of Canterbury and Otago receve less than 750 mm. The driest area in New Zealand is the inland basin of Central Otago, most of which has 330 to 500 mm. Approximate rainfall records are given in the accompanying table, together with some mean temperature figures.

Permanent snow is absent from North Island except on Mounts Ruapehu and Egmont. In South Island the snow-line lies at about 2200 m. The forest line falls from about 1500 m. in North Island to 900 m. in Stewart Island. Frosts may occur in any month, but in most parts there are few between December and March. Cockayne (1921, Cawthron Lecture) instances Celmisia haastii, C. viscosa and Danthonia australis as indicators of the "line marking the average limits of the winter snow". He also emphasizes "that many-perhaps most-species of New Zealand vascular plants, even those of the high-mountains, will only tolerate a comparatively small amount of frost, while not a few, even where they grow wild, are very near their frost-tolerating limit."

The Kermadecs have a typical sub-tropical island climate. The mean annual temperature is 19º C, with a range of 6º C between February, the warmest month, and August, the coolest month. The mean daily range of temperature is 5º C. Extremes recorded range between 28º C and 8º C. Rainfall is well distributed throughout the year but with a winter maximum; the annual average is 1510 mm. The mean relative humidity in the mid-afternoon is 73 per cent. The prevailing wind is easterly.

The Chatham Islands have a cloudy, humid climate. The mean annual temperature is 11º C. The annual range (difference between the means of the warmest and coldest months) is 7º C, and the mean daily range is 5º C. Extremes of recorded temperature are 23º C and - 3º C. The annual rainfall averages 850 mm. Sunshine is about 4·2 hours per day, which is rather lower than in the North or South Island. The average mid-afternoon relative humidity is rather high at 84 per cent, with little variation throughout the year. The prevailing wind is south-westerly.

The Subantarctic Islands lie to the south of New Zealand where mean wind speeds and cloudiness both increase rapidly. Taylor (1955) says of the Macquarie Island climate: "The lack of any period of warm temperatures, the prevalence of high winds and little sunshine combine to provide a habitat most unfavourable for plant growth and soil development." This statement applies equally well to Campbell Island and to a large extent also to the Auckland Islands, except that this group is a little less windy than the islands further south.

Some temperature figures for these subantarctic islands, in the order Mean Temperature, Annual Range and Mean Daily Range are (in ºC): Auckland Id, 8, 5, 6; Campbell Id, 7, 5, 4; Macquarie Id, 4, 3, 3.

The average annual rainfall of Campbell Island and of the Auckland Islands is 1450 mm., but Macquarie Island receives only 1020 mm. An important feature of all of these islands is the high frequency of precipitation-some rain or snow falls on more than 300 days in the year. On both Campbell and Macquarie Islands sunshine averages only 1·8 hours per day. Prevailing winds are from a westerly quarter, and gusts exceeding 200 Km. per hour have been recorded at the two southernmost islands on several occasions.

The above summary is based on data supplied for the purpose by the Director of N.Z. Meteorological Service. More detailed information about the main islands is to be found in "New Zealand Weather and Climate" (N.Z. Geographical Soc. Publ. 1950, ed. B. J. Garnier) especially the chapters on "The Elements of New Zealand's Climate" by E. Kidson and "The Climates of New Zealand according to Thornthwaite's Classification" by B. J. Garnier.

SOILS

The following notes are contributed by the Director of the Soil Bureau. More details and a soil map appear in "A Descriptive Atlas of New Zealand" (Govt. Printer 1959); "The Soil Pattern of New Zealand" by N. H. Taylor and J. E. Cox (D.S.I.R. Soil Bureau Publ. 113, 1956) gives a concise account with frequent reference to the vegetative cover and present-day usage.

The soils of New Zealand are classified in three major divisions: the zonal groups which embrace the soils formed on normal sites from ordinary siliceous rocks and whose main differentiating characteristics are due to processes controlled by the climate and vegetation of the zone, the intrazonal groups with distinguishing characteristics reflecting the strong impress of some local factor such as a particular kind of rock or closeness of the water table to the surface, and the azonal groups whose characteristics are strongly modified by such causes as instability or shortness of time during which the soil has been developed. The zonal groups occupy about 28 per cent of the main islands and include the brown-grey earths of semi-arid and near semi-arid areas (non-calcic brown soils), yellow-grey earths of subhumid areas (plano-solic grey-brown podzolic soils and planosols) and related stony soils, high country yellow-brown earths of the cold humid uplands of South Island, subalpine gley soils and gley podzols of the cold superhumid mountains, southern and central yellow-brown earths of the cool to mild humid areas (brown earths and grey-brown podzolic soils) and their podzolised counterparts, gley podzols of cool to mild superhumid areas, and the northern yellow-brown earths of warm humid areas (yellow podzolic soils) and their podzolised counterparts. The intrazonal groups occupy about 17 per cent of the main islands and contain the rendzina and other lime-rich soils, yellow-brown sands from dune sands, yellow-brown pumice soils, yellow-brown loams from fine volcanic ash, red-brown loams from basalt (latosolic soils and latosols), brown granular clays from andesites, organic soils, and the gley soils with high ground-water. The azonal groups occupy about 55 per cent of the main islands and include the recent soils from alluvium and volcanic ash (regosols), and the steepland brown-grey earths, steepland yellow-grey earths, etc. (which are lithosolic in part).

SUBDIVISION OF THE REGION

Cockayne (1917) made a tentative subdivision of the region into provinces and districts, based partly on floristic, partly on ecological criteria. Modifications have been suggested by Cockayne and Allan (1926), Martin (1935), Zotov (1938), Simpson and Thomson (1938). The subdivisions are not taken up in this Flora as much work is still required before satisfactory delimitations can be made. Details, now in need of revision, will be found in Cockayne's Veg. N.Z. 1928, 378-400.

J. T. Holloway (T.R.S.N.Z. 82, 1954, 329-410), under the title "Forests and Climates in the South Island of New Zealand", has made a valuable contribution to our knowledge of the forests of South Island. His summary includes: "an analysis is made of the many striking pecularities of forest species and forest type distribution and behaviour evident in the forests of Western Southland. These peculiarities are shown to be explicable in terms of an hypothesis stating, briefly, that the forests, as a whole, are in an unstable condition consequent on comparatively recent changes in regional climates; and that, as a result, an active re-distribution of species is in progress with resultant development of a wide range of new, though by no means stable, forest types". His studies of other forests of South Island are considered to support this thesis. Holloway concludes by emphasizing that "all that has been attempted in this report has been the tentative exposition of ideas gained during the course of a primary and incomplete survey of the forests. For proof or disproof we must look to workers in other fields of enquiry".

ELEMENTS OF THE FLORA

Cockayne (loc. cit. 1928, 403-417) distinguishes:

An Endemic Element. Some 80 per cent of the flora, including more than 40 endemic genera: e.g., Alseuosmia, Corallospartium, Dactylanthus, Hoheria, Ixerba, Loxoma, Pachycladon, Rhabdothamnus, Stilbocarpa. Cockayne further suggests that "it seems right to consider that tertiary New Zealand possessed a flora part of which had originated on her own soil, and that there exists to-day an ancient New Zealand element." Among examples of this possibly paleozelandic element he lists: Aciphylla, Anisotome, Astelia, Carmichaelia, Celmisia, Coprosma, Dacrydium, Hebe, Melicytus, Phyllocladus, Phormium, Pleurophyllum, Pseudopanax, Raoulia.

An Australian Element. About 40 genera, including: Clianthus, Craspedia, Logania, Microlaena, Persoonia, Phebalium, Swainsona, Townsonia. Over 200 species are thought to be common to both regions.

A Subantarctic Element. Common to N.Z., Eastern Australia, Tasmania, southern South America. Among the genera he lists are: Abrotanella, Aristotelia, Danthonia, Dicksonia, Griselinia, Leptocarpus, Libertia, Libocedrus, Nothofagus, Phyllachne, Phrygilanthus, Podocarpus, Tetrachondra, Vincentia.

A Paleotropic Element. Cockayne lists 28 families, including Cucurbitaceae, Gesneriaceae, Lauraceae, Meliaceae, Monimiaceae, Moraceae, Myrsinaceae, Palmae, Pandanaceae, Passifloraceae, Rubiaceae, Santalaceae, Verbenaceae.

A Cosmopolitan Element. Cockayne here includes all those species "that have a considerable range in either temperate or warm climates". Cockayne lists a number of species, but emphasizes that more intensive comparative studies should be made, e.g., Asplenium trichomanes, Calystegia soldanella, Cystopteris fragilis, Luzula campestris, Montia fontana, Potamogeton polygonifolius. For some of the wide-ranging species it remains uncertain whether they are truly indigenous or were introduced at an early date.