One of the most important factors which determines the presence or otherwise of forests is wind. Where constant high winds are the rule, even though every other condition is eminently favourable, very few trees can gain a footing on the ground, while if such have in addition to contend against other plants better equipped for the contest, especially such as are provided with strong subterranean members, they must succumb. This accounts, I believe, for the absence of forest over much dry ground quite suitable for its reception and maintenance. For the plant-formation of such ground I propose the term “heath” rather than “meadow,” since the latter name suggests the presence of grasses as the dominant plants, whereas here these latter are in the minority, and bracken fern is the most important constituent. The whole of this formation, no matter where it occurs on the island, is a modified one, so no exact presentation of its original aspect is possible. It seems to follow directly after the bog formartions, and it may, I think, replace them without any intermediate stage of Olearia-Dracophyllum bog or Dracophyllum scrub having occurred.*
[Footnote] * For meaning of these terms, see “Bog Formations,” further on.
The presence of the heath plant-formation seems to depend upon the amount of water in the soil, and, as mentioned above, upon the exposure of the station to wind, while, according to the relative dryness of the substratum, certain plants may be present or absent. Thus, the following occur only on the driest ridges: Leucopogon richei, Cyathodes robusta, Pimelea arenaria, Isolepis nodosa, Libertia ixioides, var. In such a position L. ixioides at times almost constitutes a subformation, forming, thanks to its power of spreading by underground stems, very large patches. Its xerophytic, coriaceous, vertical, iris-like leaves also help to maintain the plant in its dry station. Growing in these Libertia patches, but in very limited quantities, are Agrostis œnmula, Gnaphalium involucratum, Acœna novœ-zelandiœ, and a few stunted plants of Dracophyllum paludosum and Pteris esculenta. In many places the heath consists of nothing but Pteris esculenta, which often grows with great luxuriance, and attains a height of 1.5 m. or more. Where the fern is not so tall a number of other plants are found in association with it. In such positions the following were noted: Epilobium sp. (perhaps related to E. novœ-zelandiœ), Lagenophora forsteri, Gnaphalium filicaule, Oreomyrrhis colensoi, Gentiana pleurogynoides var. umbellata, Pratia arenaria, Isolepis nodosa, Acœna novœ-zelandiœ, Hydrocotyle moschata, Danthonia semi-annularis, Dichelachne crinita, Thelymitra longifolia, Microtis porrifolia, Luzula sp. Also plants of Dracophyllum paludosum and Olearia semidentata are occasionally present, a remnant of the original bog formation.
The soil of this formation is usually peaty loam, varying much in the amount of water it contains, but except on the ridges mentioned before it is never really dry. Formerly there was probably, as pointed out further on, only a limited extent of heath, with bracken as the dominant plant, and undoubtedly Phormium tenax would play a very important part in the vegetation. A proof of this is afforded by Phormium occurring in very large quantities in the hollow before mentioned, where the peat had been burned, and the steep sides of which prevent the entrance of grazing animals.
Except on the southern tableland the heath formation is found in all parts of the island; indeed, so far as I can judge, it occupies a larger area than any other formation. On the large extent of flat land raised a little above sea-level, marked “Kekerione” on the map (49), and intersected here and there by puny watercourses, wherever the surface sinks a little below the general level is boggy ground; but all the remainder, by far the greater part, is covered with bracken, varying from a vegetation of almost pure Pteris
esculenta to one in which that fern and Gleichenia, circinata occur in almost equal quantities.