Forest Vines to Snow Tussocks: The Story of New Zealand Plants
Subalpine Shrubs or Small Trees
Subalpine Shrubs or Small Trees
In the lower or subalpine parts of the shrub zone the species composition depends on soils and aspect. In the Westland beech gap Wardle134 recognises a number of subalpine low forest or shrub communities which are in part typical for New Zealand as a whole. They include:
Hoheria glabrata low forest
Hoheria glabrata or mountain ribbonwood colonises young, deep, moist, well-drained and often stony soils such as those provided by slips, talus slopes and alluvial fans. This small tree, being one of the few in New Zealand that is strongly deciduous, has attractive yellow to red leaves in the autumn. Its clusters of white flowers, each up to 4 cm across, are also a striking feature. Olearia ilicifolia (the holly-leaved daisy tree) also contributes to the canopy and the ground beneath has a dense cover of the fern Polystichum vestitum.
Dracophyllum-Olearia Low Forest and Scrub
This occupies similar but older sites than Hoheria glabrata low forest. Dominance is shared by the mountain ribbonwood (low forest only), Dracophyllum longifolium (scrub only), D. traversii and Olearia lacunosa, the last two being up to 7 m tall. The genus Dracophyllum, although belonging to the dicotyledon class of the flowering plants has long, narrow, parallel-veined leaves similar, in the larger examples, to those of such monocotyledons as the cabbage tree (Cordyline australis) or even the pineapple. Indeed, mountain groves of Dracophyllum traversii are sometimes known locally as 'pineapple forests'. This species with its candelabra-like form, and its sword-like leaves forming a deep litter on the forest floor, is certainly the most distinctive member of the community.
Olearia lacunosa also has narrow, although net-veined leaves, which are somewhat like those of juvenile lancewood (Pseudopanax crassifolius). Some of the other shrub species with relatively large thick leaves are Griselinia littoralis (broadleaf), Pseudopanax colensoi (mountain five-finger) and Olearia colensoi (leatherwood). Pseudopanax simplex has somewhat page 167smaller, thinner leaves and Myrsine divaricata and Coprosma pseudocuneata have very small leaves. Prominent ground plants are Blechnum 'procerum' and the tussock-like Astelia nervosa.
Dominance of the shrub species varies from place to place in this community type, but it is at its most impenetrable where Olearia colensoi with its stiff almost cardboard-like leaves predominates, as in the North Island ranges, the westernmost coastal ranges in the South Island and in Stewart Island.
This occurs on old, leached infertile soils and is a low shrubbery from 0.5 to 1.5 m tall in which the small conifers Halocarpus biformis and Phyllocladus aspleniifolius var. alpinus (mountain celery pine) share dominance with Olearia colensoi and Dracophyllum longifolium.
Both the conifers also occur in the lowlands of Westland where they become small trees. In the greyish-green mountain celery pine, what appear to be fan-like or rhomboidal leaves are in fact flattened branchlets termed phylloclades.
These are some of the community types of subalpine shrubs and small trees, but there are a number of others related to special habitats or resulting from disturbances, whether caused by nature or by humans. Many of the species of these communities may grow in the montane forests especially towards their upper limits.