Species and Varieties of New Zealand Beech

Five species of Nothojagus were formerly recognised in New Zealand, but more recently two of these have been combined as varieties of one species.⁹⁰

Nothofagus menziesii: silver beech (the bark is white and silvery particularly in young trees).

Nothofagus fusca: red beech (the timber is reddish in colour).

Nothofagus truncata: hard beech (the wood has a high silica content making it hard).

Nothofagus solandri var. solandri: black beech (the bark is very dark partly due to the growth of a sooty mould).

Nothofagus solandri var. cliffortioides: mountain beech (grows mainly at higher altitudes than the other beeches).

Silver beech has thick, almost circular leaves, 0.5-1.5 cm long and wide, bearing a few domatia on the underside and small, rounded marginal teeth often in pairs (Fig. 69). The leaves of red and hard beech are similar to each other, 2-4 cm long by 1.5-2.5 cm wide and with saw-like marginal teeth. Hard beech has rather thicker leaves with 8-12 page 122teeth per side compared with 6-8 for red beech; red beech alone has domatia. Black and mountain beech have small smooth-margined leaves, hairy below, 1-1.5 cm long by 0.5-1 cm wide. It is difficult to distinguish the leaves of the last two forms. Mountain beech at higher altitudes often has leaves that taper from the base, while the leaves of black beech at low altitudes are oblong, but there are intergrading forms in many places.

Silver, hard and red beech may become large trees 30 m or more in height with trunks 2 m or more in diameter. The trunk bases of the

Figure 69 Silver beech foliage and young fruits with glandular hairs. Photo: M. D. King.

page 123first two have low, rounded buttresses while those of the latter are high and narrow. The larger trees of mountain and black beech are generally below 25 m in height with unbuttressed trunks of about 1m in diameter.

The bark of all the beeches, except when young, is rough and fissured. The tree crowns, especially in more open situations, are wide and deep and particularly in mountain and black beech, the foliage is often arranged in distinctive horizontal layers. The male and female flowers at the tips of twigs are wind-pollinated and inconspicuous, although in good flowering years coloured anthers in the male flowers may impart a reddish glow to the crowns of black and mountain beech particularly. More brilliant splashes of colour, contrasting with the dark green of the foliage, may be provided by certain mistletoes which commonly parasitise the beeches. Peraxilla colensoi, usually found on silver beech, and 2 tetrapetala have bright red flowers. Alepis flavida with orange-yellow to yellow flowers used to be common, but has now been depleted by opossums. Heavy flowering of all the beech species in New Zealand takes place every few years with little or no flowering in the other years. It is suggested that 'flowering years' follow hot summers which encourage the initiation of flower buds.⁹¹ buds.⁹¹

The beech seed are 5-8 mm long with narrow wings. It is considered that they are not capable of being dispersed for more than a few kilometres and then only with strong winds.⁹²

Silver beech stands apart from the other species in several respects. Some of the more striking differences are:

For the last reason our species have been assigned to two informal groups within the genus, both of which are also represented in Australia and South America — the 'menziesii group' and the 'fusca group'. A third 'brassii group', with a third pollen type, is restricted at present to New Caledonia (Fig. 70) and New Guinea.⁹³

Figure 70 New Zealand and New Caledonian Nothofagus leaves.
New Caledonia: Nothofagus codanandra; A, juvenile leaf; B, adult leaf; C, twig with a cupule with 3 flat seeds; D, Nothofagus sp.; E, Nothofagus equilateralis.
New Zealand: F, Nothofagus fusca (red beech); G, N. truncata (hard beech); H, N solandri var. clijfortioides (mountain beech); I, N. menziesii (silver beech); J, N. s. var. solandri (black beech).
Photo: M. D. King.

Figure 71 Nothofagus forest in the Travers Valley, northern South Island. Note the even treeline. Photo: J. W. Dawson.

Structure and Composition of New Zealand Beech Forests

Seen from either the inside or the outside, pure beech forest in New Zealand has a very different appearance from conifer broadleaf forest. Externally (Fig. 71), for example when viewed on the steep side of a mountain valley, beech forest has a uniform, generally dark green colour and a smooth to moderately uneven surface. There are no emergent j trees. There is none of the tangled profusion of the conifer broadleaf page break

Figure 72 (opposite) Interior of red beech (Nothofagus fusca) and silver beech (N. menziesii) forest near the Maruia Saddle, South Island. Photo: J. H. Johns.

page 127forest within the beech forest (Fig. 72), particularly when rainfall is moderate or low. There are clearly fewer species present and because of the sparse undergrowth and absence of vines, one can walk freely among the rough-barked trunks. Vascular epiphytes too are generally absent, although there are often epiphytic mosses and lichens on the trunks and branches. The forest floor has a deep carpet of leaf litter, soft cushions of the pale green milk moss (Leucobryum candidum) and masses of the translucent fans of the kidney fern (Trichomanes reniforme). Among the scattered shrubs which may be present, the small leaved Styphelia (Cyathodes) fasciculata, S. juniperina (soft and prickly mingi-mingi respectively), Coprosma rhamnoides and C. microcarpa are most frequently encountered. Light filtering through the attractive layers of the beech foliage contributes to the typically tranquil, orderly atmosphere of this type of forest. Beech forest becomes more complex with higher rainfall, as on the west of mountains at higher altitudes. Its growth appears more luxuriant, largely as a result of the profusion of lichens, mosses, liverworts and moss-like filmy ferns clothing the forest floor and trunks and branches of the trees. Where the canopy is partly open there are also more species of small trees and shrubs involved although none is restricted to beech forests. Broadleaf (Griselinia littoralis)Pseudopanax simplex, Coprosma foetidissima and others may contribute to a subcanopy and there is often a shrub layer of small-leaved coprosmas, the smallleaved Myrsine divaricata, the mountain horopito (Pseudowintera colorata) and others.

Larger ferns on the forest floor include the well-known crepe fern or Prince of Wales Feathers (Leptopteris superba) and Blechnum discolor. Two small flowering plants growing in moss cushions are characteristic of this type of forest — Luzuriaga parnflora with spreading wiry stems, two-ranked leaves and large spongy white berries, and Libertia pulchella with half erect fans of grasslike leaves.

These wet beech forests in New Zealand are sometimes swathed in mist; forests of a similar character elsewhere in the world are often referred to as cloud or mossy forest, or more romantically 'goblin forest' or 'elfin woodland'.

At the other extreme, some of the beech forests in relatively dry sites on the east of the South Island mountain axis are among the simplest of forests anywhere, consisting of virtually a single species — mountain beech.

As a generalisation, where there is a trend away from mild, moist conditions and fertile soils towards cooler or drier conditions and less fertile soils, or combinations of these, there is often a transition from conifer broadleaf to beech forest.

Lowland Beech Forest

Black beech and hard beech are often referred to as the lowland beeches because they are generally found in the same altitudinal zone as the conifer broadleaf forest. They reach their southern limits in the northern South Island, with a disjunct occurrence of hard beech in south Westland.

The lowland beeches generally do not become components of the conifer broadleaf forest, however, but form instead mainly narrow strips of forest on the thin, stony, infertile soils of ridge crests (Fig. 73) or cliff edges. Often the change from dense conifer broadleaf forest to open beech forest is very abrupt. In the steepest, stoniest and driest sites only black beech may be present⁹⁴ but elsewhere the two species may intermingle or, on somewhat better soils, hard beech may predominate.

Montane Beech Forest

In many places in New Zealand, conifer broadleaf forest gives way at higher elevations to a beech forest dominated by one or more of the montane beeches — red, silver or mountain. This occurs because of the decrease of temperature as altitude increases. Naturally the altitudes at which the transition takes place varies with latitude: at 38 to 39°S from East Cape to the central North Island it ranges from about 850 to 1000 m; at 41°S in the southern North Island it is at about 750 m; at 45°S in the south-west South Island it is at about 450 m; and at the southern end of the South Island at 46°S, montane beech forest approaches sea level in places.

The three montane beech species differ ecologically. Red beech gives way to silver beech, which gives way to mountain beech as temperatures become colder and soils become thinner and less fertile. Thus if the three occur together on the same mountain, red beech often dominates immediately above the conifer broadleaf forest giving way upwards to silver beech, which in turn gives way to mountain beech towards the treeline.

Figure 73 Aerial view of inland Taranaki forests with strips of dark-coloured lowland beech forest on the ridges and conifer broadleaf forest on the slopes and in the valleys.
Photo: White's Aviation.

Mountain beech is also more tolerant of drier conditions than the other two species so on the drier eastern sides of the mountain ranges, particularly in the South Island, it is often the only beech species present pr even virtually the only tree species present as already mentioned. Conversely, on wetter sites, for example to the west of the mountain ranges, mountain beech becomes much less common or absent and its place at treeline may be taken by silver beech.

Treeline

Where beech forest is present and when temperatures become too cold for tree growth as the altitude increases, there is often an abrupt change from the uppermost trees to a vegetation of alpine herbs and/or shrubs.

The highest treelines are those where mountain beech is present. In the central North Island at 39°S the mountain beech treelines range from about 1350 to 1500 m; in the north-eastern South Island at 42°S, 1300 to about 1550 m; and in the southern South Island at 45°S from 950 to 1250 m.

Compared with treelines at comparable latitudes on a continent, those in New Zealand are unusually low.^95,96 For example, at 39°N in the Rocky Mountains of North America, the treeline can be as high as 3630 m, This apparent anomaly seems to relate to the difference in summer temperatures between continents and islands at comparable latitudes. Land heats up much more in summer than the sea, so a continent will attain higher temperatures at given latitudes and altitudes than a narrow island surrounded by the relatively cooler sea. Consequently vegetation zone boundaries, including the treeline, are higher on continents than on islands. It is estimated that a mean warmest month temperature of 10°C determines the upper limit of tree growth and this seems to hold as true for the relatively low beech treelines in New Zealand as for the higher continental treelines.

On this basis it might be expected that mountains furthest from the sea in New Zealand with more 'continental' climates would have higher treelines. This proves to be the case. The highest treelines in New Zealand are on Mt Ruapehu in the central North Island (ca. 1500 m) and on the mountains at the centre of the northern South Island (ca. 1550 m). Inverted treelines occur where there are flat valley floors not far below the normal treeline. In frosty weather the coldest air sinks to the valley floor, which as a result experiences much lower temperatures than the valley sides, despite their higher altitude. In these circumstances the valley floor is occupied by an open vegetation of an alpine/subalpine character, while the slopes support forest.

Beech Gaps

There are regions in New Zealand where beech species are completely absent, even though at appropriate altitudes conditions seem entirely suitable for them. Such regions are: Mt Taranaki (Egmont), an isolated volcanic cone in the west of the North Island; the southern Ruahines and adjacent northern Tararuas in the south of the North Island; in the South Island, a strip to the west of the high central third of the mountain axis (Westland) with a narrower gap on the east; and Stewart Island. For page 131the central South Island at least it is suggested that beech was eliminated there during the last glaciation and because of its slow rate of dispersal has not yet fully reinvaded from southern and northern refugia.⁹⁵ As a consequence more readily dispersing conifer broadleaf forest species have established in sites perhaps better suited to beech species particularly at higher elevations. (See Chapter 12 for further discussion of the discontinuous distributions (disjunctions) of the beeches and other native species.)

Intermediate Forest Types

Forests comprising mixtures of conifer broadleaf forest species (particularly the conifers) and beech can be found throughout New Zealand. In the north of the North Island there are even a few localities where hard beech intermingles with kauri (Agathis).

Such intermediate forests may be found in the transition from conifer broadleaf forest to pure beech forest on mountain slope, but to the north and south of the Westland beech gap, there are more extensive mixed forests at lower and middle elevations. Some workers have suggested that this results from the slow replacement by advancing beech forest of the Westland conifer broadleaf forest.^69,97,98

Beech Forest Regeneration