A Proposed New Botanical District for the New Zealand Region.
[Read before the Philosophical Institute of Canterbury, 12th November, 1924; received by Editor, 31st December, 1924; issued separately, 6th March, 1926.]
In 1921 (The Vegetation of New Zealand, p. 303) L. Cockayne extended the boundaries of his Marlborough-Sounds Subdistrict southwards and westwards, and changed the name to “Sounds-Wairau.” As defined by that author, the area was bounded on the south by the River Wairau, and on the west by the average limit of the westerly rainfall. Although this area in that portion of its coastal-lowland-montane belt exposed to a forest-climate may rightly be united to the North Island part of the Ruahine-Cook Botanical District, yet its mountainous portion above the forest-line is markedly different, containing as it does so many species absent on the Ruahine-Tararua Range. It seems to us better, then, to raise it to the rank of a botanical district, under the name “Sounds-Nelson.” Even when this is done there are three distinct sections–(1) the former Marlborough Sounds Subdistrict; (2) the area lying westwards and southwards of Nelson City between the mountains (Ben Nevis, Gordon's Nob, &c.) and Tasman Bay, extending to the western boundary; and (3) the high mountains as a whole.
This separation of the South Island portion of the Ruahine-Cook Botanical District raises the North Island part to the rank of a district, to which we apply the name “Ruahine-Cook.” Thus the North and South Islands are kept distinct floristically and ecologically.
The flora of the Sounds-Nelson Botanical District is marked by a fairly high degree of local endemism, as shown by the following list:—
Gramineae.—Poa acicularifolia–a variety probably confined to the Mineral Belt; Festuca–a species possibly confined to the Mineral Belt.
Ranunculaceae.—Clematis parviflora var. depauperata—given on the authority of Man. N.Z. Flora, but we know. nothing about it.
Cruciferae.—Notothlaspi australe var. stellatum.
Leguminosae.—Probably an undescribed species of Carmichaelia—grows in the Rai and Pelorus Valleys, the stems extremely slender. the flowers small.
Scrophulariaceae.—× Hebe Simmonsii Ckn. et Allan comb. nov. = × Veronica Simmonsii Ckn. in Trans. N.Z. Inst., vol. 48, 1916, p. 202; H. rigidula Ckn. et Allan comb.' nov. = Veronica rigidula Cheesem. in Man. N.Z. Flora, 1906, p. 514; H. divaricata Ckn. et Allan sp. nov. = Veronica Menziesii Benth. var. divaricata Cheesem. in Man. N.Z. Flora, 1906, p. 512; H. Gibbsii Ckn. et Allan comb. nov. = Veronica Gibbsii T. Kirk in Trans. N.Z. Inst., vol. 28, 1896, p. 524.
Compositae.—Olearia serpentina Ckn. et Allan sp. nov. ined.—Common on the Mineral Belt at all altitudes; Celmisia Rutlandii C. cordatifolia, C. Macmahoni; Raoulia Gibbsii; Cassinia Vauvilliersii (Homb. et Jacq.) Hook. f. var. serpentina Ckn. et Allan.
With regard to the vegetation, that of the northern and eastern portions of the district in the coastal-lowland-montane belt has a plant-covering similar to that of the southern part of the Ruahine-Cook Botanical District. Thus the lowland forest is taxad or Beilschmiedia tawa rain-forest on the better ground, and Nothofagus truncata-N. Solandri forest in exposed positions or where the soil is poorest, while near the sea there is on the most fertile soil Dysoxylum spectabile coastal-forest.
On coastal rocks Arthropodium cirratum (absent in Ruahine-Cook), Phormium Colensoi, Astelia Solandri, and Griselinia lucida are characteristic. Digitalis purpurea, Rubus fruticosus (agg.), and the indigenous Cassinia leptophylla are common weeds which form pure associations. Dairy-farming is carried on in the fertile valleys on artificial meadows which replace rain-forest proper.
In the lowland-montane area southwards and westwards from Nelson City, which is the driest part of the district, there are wide stretches of Leptospermum scoparium, mostly induced. In places this has been replaced by orchards. The hills are occupied by Leptospermum scoparium, Pteridium esculentum, or Danthonia pilosa grassland. As the western boundary of the district is approached Nothofagus forest again puts in an appearance with the addition of N. fusca and N. Menziesii. Where forest extends, or did originally extend, continuously from the North-western District to the Sounds-Nelson, it is not easy to decide to which of the two it belongs, but certain forest species are peculiarly North-western—e.g., Podocarpus acutifolius, Dracophyllum latifolum, and Senecio Hectori.
The Mineral Belt is a striking feature of the district. It extends south-west from D'Urville Island for a distance of about sixty miles, and is clearly marked out from the forest by its stunted vegetation, due probably to excess of magnesia in the soil. It is usually quite narrow, being in one part barely 100 yards wide, but its widest part, on the flanks of the Dun Mountain, is more than three miles across. It occurs from sea-level to the subalpine belt, its plant-covering changing considerably with increase of altitude.
The subalpine flora of the district is rich in species, since near its western boundary it has, in addition to its flora proper, a good many species in common with the adjacent North-western District. Much of the high-mountain area is insufficiently explored botanically, so we can give no details of real value.