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General Account
Dacrydium biforme is conspicuous where the soils are cold and poorly drained. Such conditions occur on gentle slopes where the soil texture is too fine to permit free vertical drainage. On old moraine in the top Toaroha basin, Dacrydium biforme is important on puggy soils, which have developed an alpine gley profile. The following soil description is typical of alpine gley:
Surface flat. Altitude, 2,500ft. The soil forms a matrix between morainic boulders.
¼in: Litter.
4–6in: Greyish brown, fine sand with loose, weak crumb structure. Many roots. Transition to:
3–4in: Bluish-grey, fine sand, puggy and compact, with blocky structure. Weathering pebbles present, and there are also conspicuous reddish-brown blotches which appear to represent the last traces of pebbles destroyed by weathering. Sharp and irregular transition to:
¼in: Reddish-brown, soft iron pan. This gradually lightens in colour to:
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2–4in: Light reddish-brown, moderately compact fine sand with weathering pebbles. Gradual transition to:
≥ 4in: Light brown, with a bluish tinge, compact sand. Samples taken from a soil of this type gave the following pH values:
| Depth | pH |
|---|---|
| 0–2in | 4.6 |
| 4in | 4.4 |
| 12in | 4.8 |
Most of the Dacrydium trees here are growing over morainic boulders which project up to 2 feet above the level of the surrounding ground. They accumulate from several inches to a foot of black raw humus between their roots. A sample of this humus gave a pH value of 4.3.
Where the soil is shallow over solid rock, as in the typical community, the soil water is kept near the surface and conditions again induce Dacrydium biforme scrub. Dacrydium biforme is also common on poorly drained soils in the forest zone, right down to lowland terraces where it is joined by the other Dacrydium spp. characteristic of the “pakihi” habitat.
(C.f. cupressoid-podocarp scrub, Cockayne, 1928, p. 279.)
Cliff Communities.
Under the excessively wet climate of Westland, cliffs cut in moraine and alluvium support dense vegetation. In the scrub zone, the characteristic species are Olearia arborescens, Dracophyllum longifolium, Carmichaelia grandiflora, Coprosma depressa, Phormium colensoi, Danthonia cunninghamii, and Blechnum minus.