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The Vegetation of New Zealand

Chapter I. — General Observations on the Coastal Vegetation

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Chapter I.
General Observations on the Coastal Vegetation.

Brief account of the coast-line.

The coast-line offers most diversified stations for plant-life. Not only does it face the actual ocean for more than 4800 km. but it extends far inland in many places either as shallow estuaries, tidal rivers, drowned valleys or fiords of profound depth. The actual coast may be quite low, more or less hilly, or high mountains may rise precipitously from the water's edge. There are vast stretches of dunes; long lines of cliffs; sandy, muddy, gravelly or shingly shores; low-lying flats exposed to inundation by brackish water; tidal waters where portions of the muddy floor lie bare at low-tide and rocks extending far out into the sea. Lying off certain parts of the coast at various distances are islands differing greatly in size. These offer less complex ecological conditions than does the mainland and, in certain cases, their plant-covering is yet quite virgin. Finally, there are ancient coast-lines where certain maritime species still exist.

Floristic statistics.

The coastal species fall into the two categories of those confined, or virtually so, to the shore-line, or its immediate neighbourhood, and those which belong equally to inland formations, some of this latter class being sufficiently abundant to affect in parts the coastal landscape.

The true maritime vascular plants number 185 species, or well-marked varieties, together with 16 groups of hybrids, which belong to 55 families and 107 genera. One hundred and thirty nine of the species are confined to the actual coast, or thereabouts, while 46 occur inland to a limited extent but, with few except ons, these latter are negligible so far as the general page 61inland vegetation is concerned. Resolved into their phytogeographical elements 134 (72%) are endemic, 24 (of which one or two extend to New Caledonia &c.) Australian, 8 subantarctic South American (2 Australian also), 2 Norfolk Island, and 17 cosmopolitan or sub-cosmopolitan. The larger families and genera and the number of species in each are as follows: (families) Compositae 23, Gramineae 22, Scrophulariaceae 13, Cyperaceae 10, Umbelliferae 9, Chenopodiaceae 8 and Filices, Cruciferae and Rubiaceae 6 each; (genera) Hebe 9, Senecio and Poa 7 each, Coprosma 6 Carex, Lepidium, Pittosporutn and Olearia 5 each.

The following 9 families and 35 genera containing 41 species are purely coastal or almost so in New Zealand, the remaining 144 (nearly 78%) being related to inland species: — (families) Nyctagifiaceae, Aizoaceae, Corynocarpaceae, Tiliaceae, Primulaceae, Sapotaceae, Myoporaceae, Cucurbitaceae and Goodeniaceae*; (genera) Ruppia*, Zannichellia*, Zostera (Potamoget.), Spinifex, Atropis, Bromus* (Gramin), Desmoschoenus (Cyper.— end.), Hydatella (Centrolep.), Leptocarpus* (Restionac), Macropiper* (Piperac), Salicornia, Rhagodia*, Suaeda1), (Chenopod.), Pisonia (Nyctaginac), Mesem-bryanthemum, Tetragonia (Aizoac), Spergularia (Caryophyll.), Clianthus* (Legum.), Euphorbia (Euphorbiac), Corynocarpus* (Corynocarp.), Dodonaea* (Sapindac), Entelea (Tiliac), Hibiscus (Malvac), Stilbocarpa, Meryta (Araliac.). Samolus (Primulac), Sideroxylon (Sapotac), Eryngium, Apium* (Umbell.), Ipomaea (Convol.), Avicennia (Verbenac.), Mimulus (Scroph.), Myoporum* (Myopor.), Sicyos (Cucurbit.), Selliera* (Goodeniac.) and Sonchus2) (Compos.),

The 16 groups3) of hybrids (there are certainly more) belong to the following genera: Asplenium, Paratrophis, Pittosporum, Acaena, Plagianthus, Hymenanthera, Pimelea, Pseudopanax, Apium, Hebe, Coprosma, Olearia and Cassinia.

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With regard, to the coastal-inland species it is hardly possible to supply detailed statistics. According a forest, tussock-grassland, or shrubland approaches high-water mark so will a considerable percentage of its species be present. All depends upon the climatic and edaphic conditions of the locality and, in many instances, except close to the water's edge, the special coastal ecological factors may be absent. But, on the other hand, many inland plants tolerate fairly intense maritime conditions, so that more than 100 species thrive on one part or other of the true coast-line. The following, for example are in places sufficiently abundant to be of prime physiognomic importance: Freycinetia Banksii, Arundo conspicua, Mariscus ustulatus, Cladium Sinclairii, C. junceum, Phormium tenax, P. Colensoi, Urtica ferox, Muehlenbeckia australis, M. complexa var. microphylla, Leptospermum scoparium, L. ericoides, Metrosideros lucida, M. perforata, Griselinia lucida, Dracophyllum longifolium, Hebe salicifolia, Pachystegia insignis, Cassinia fulvida, C. Vauvilliersii and Gnaphalium trinerve, but this list could be greatly extended.

General conditions regulating the coastal vegetation.

The special conditions to which coastal plants are subject consist of a greater amount of salt in the soil than ordinary land-plants can tolerate, exposure to salt-laden winds which are frequently both violent and of long duration and, in some stations, strong insolation. The coastal climate is generally uniform; frost is absent or trifling in North Island while in South Island too it is of little moment, except on the coast of the Canterbury Plain where it may reach — 9° C. Excess of salt in the soil and salt-laden winds are by far the most important of the above factors, and on such depend the characteristic coastal formations and the "adaptations" or capabilities of the species. At the same time, a salt soil is frequently absent, as on dune-areas where the power to tolerate salt winds or indeed violent wind in general is a matter of prime moment. From the above it follows that ground subject to flooding with brackish water or to frequent wetting by sea-spray is the chief home of halophytes, and that other formations will be governed first of all by position with regard to the prevailing wind and its frequency. The composition of coastal shrub associations is distinctly in harmony with the wind-factor. At the base of Bluff Hill, Southland at the spot where the frequent south-west wind strikes with full force, the mixed shrub association of a calmer atmosphere is either absent or replaced by a pure scrub of the xerophytic Olearia angustifolia. So too at the water's edge of the inlets of Stewart Island Senecio rotundifolius replaces, fern-forest, but is itself replaced on the more exposed headlands by Lepto-spermum scoparium (Fig. 2).

The rainfall strongly influences the general vegetation of the shore-line since the number of rainy days determines the presence or absence of forest. Where the maximum of wet days occurs as on the west coast of South Island, page 63rain-forest comes almost to the water's edge. Dune and salt-meadow, special edaphic formations, are but little affected by rainfall and bear their characteristic plants equally in the wettest or driest districts. The semi-subantarctic climate of the South Otago, Fiord and Stewart districts favours plants with subalpine "adaptations" so that there. are not only such amongst the true coastal species, but actual subalpine species, rare or absent inland except in the high mountains, may occur close to the sea.

The winter cold of the Canterbury Plain offers an impassable barrier to certain northern plants (e. g. Mariscus ustulatus, Macropiper excelsum, Dodonaea viscosa, Corynocarpus laevigata) which, in consequence, have their eastern southern limit on Banks Peninsula, while, on the west, the rainforest climate offers an obstacle of another description, but it permits (e. g. Freycinetia Banksii, Ascarina lucida, Hedycarya arborea) certain forest plants to extend further southwards.

The plants themselves play no small part in their own distribution so far as they supply shelter and make soil; trees, shrubs and tussock plants supplying the former and certain coastal ferns and herbs the latter in the form of raw humus or peat. Other factors of local importance receive mention when dealing with the communities.

1 1) It is well to explain that the figures given here and elsewhere in this book, are based on personal judgement. No two observers would be likely to agree as to whether certain species should be considered coastal or not. Also species of wide distribution are not included in the Australian or South American estimates, notwithstanding their occurrence in those regions, and, again, "wide distribution", "cosmopolitan" &c. are quite loose terms.

2 An asterisk denotes that the species though nearly always coastal does occasionally extend inland. Should a species occur at 100 m. or more altitude on a small island, or a hill adjacent to the coast, it is here considered coastal.

3 3) Generally the groups are polymorphic, in which case they are called "swarms". Any name, or formula, applies to a whole group or swarm, the individuals, each of which is a hybrid, do not bear the name of the swarm but are each one of the swarm. For instance, Paratrophis miopaca (P. microphylla × opaca) is the collective name of the polymorphic group of individual hybrids composing the swarm, each of which is a hybrid belonging to the group × P. miopaca. Generally, in taxonomic writings, an individual hybrid bears the name-of the group which (the group) also is called a hybrid, but such which of course it cannot be. In many cases, the hybrid individuals are present in great numbers and this applies for the whole region.