Key Words:Nothofagus; New Caledonia; Ecology; Ultrabasic soils.

Abstract

Nothofagus aequilateralisis a tree of low to medium altitudes in New Caledonia. It does not form extensive forests but is in isolated patches over a wide geographic range, suggesting fragmentation by man-induced fires.

Its soil tolerance is wide, as it grows on moister midslope and colluvial footslope young soils derived from ultrabasic rocks, and also in schist-derived soils on drier ridge tops.

N. aequilateralis regenerates well after disturbance other than fire, and in such regeneration is often accompanied by species of Agathis.

Introduction

Subtropical Nothofagus forests in New Caledonia are of limited extent and scattered. Dawson (1966) found that on soils formed from ‘normal’, as opposed to ultrabasic rocks, the Nothofagus forests grow at moderate altitudes (500m-1000m) only on ridge crests where moistures and nutrient stress inhibits competition by rain forest. He suggests that at higher altitudes Nothofagus would be found more extensively. This has since been found not to be the case, on Mt Panic (1628m in alt.) there has been as yet no Nothofagus found (M. Brinon pers. comm.). The occurrence of Nothofagus at mid-altitudes in New Caledonia thus parallels other members of its N. “brassii pollen group in New Guinea (Wardle 1973). This distribution contrasts strongly with that of the New Zealand N. “menziesii and N. “fusca pollen group, whose representatives form alpine treelines. Likewise in Argentina and Chile members of the N. “dombeyi (N. “fusca) pollen group also form alpine treelines (McQueen 1977).

The known distribution of three of the five species of Nothofagus in New Caledonian (van Steenis 1971, Jaffré 1974) is fragmented. It is not a distribution of localised endemics in each area but of fragmentation of what may have been, once, a far more continuous distribution.

If the Nothofagus forests of New Caledonia can only migrate frontally, as do their New Zealand counterparts, their present fragmented New Caledonian distribution may represent a more continuous forest of Pleistocene conditions, further fragmented by fires, as Melanesian man has been in New Caledonia since 1600 B.C. (Frimigacci and Maitre 1981).

The three widely distributed species (van Steenis 1971) are:

N. aequilateralis (B. - B.) Steen.

N. codonandra (Baill.) Steen.

N. balsanae (Baill.) Steen.

All three species grow on soils formed from the large areas of ultrabasic peridotite rocks in New Caledonia. The ecology and pedology of vegetation on such soils, including N. codonandraand and N. balsanae is described by Jaffré (1974, 1980). As well the three species are found on normal soils formed from sedimentary and metamorphic rocks (van Steenis 1971).

N. aequilateralis is one of these species of wide, but scattered distribution, and the present paper gives the results of a field reconnaissance of its site relations over a range of soil parent materials, both from ultrabasic and normal rocks, in August 1976.

Climate (from Jaffré 1980)

At altitudes where N. aequilateralis grows, the annual precipitation is ca. 2000mm per year. There are two dry seasons; April-May and September-November, and monsoon heavy rains from December to March. At Noumea mean temperature in January is 26.2° and in August is 19.9°C. Frosts are unknown at sea level, but can occur occasionally above 1000m.

Soil Formation on Ultrabasic Rocks in Subtropical Conditions

In tropical soil formation lateritisation on non-ultrabasic rocks Si and Al are leached down, leaving a carapace dominated by iron, on plateaux and gentle slopes (Duchaufour 1970).

Jaffré (1974) describes a catena, from ridge crest to valley bottom. On the ridge crests and plateaux there is a carapace of 70% Fe₂O₃, up to 2.5% Ni, and up to 10% Cr. Soils formed there have acid pH (3.5-6.5), little clay and a very low cation exchange capacity (10m.-eq.%) mostly occupied by Mg. Mid-slope soils have a pH close to 7, high clay content and a higher cation exchange capacity (50m.-eq.%). Footslope colluvium and alluvium are younger than those above, with little profile development, alkaline pH and higher cation exchange capacity than soils higher up the catena. All three soils in this catena are abnormally low in Ca, K, and P, and except under forest, have very low N levels.

Nothofagus Aequilateralis on an Ultrabasic Catena

In the area of the Plaine des Lacs, N. aequilateralis does not grow on the carapace of surrounding plateaux and slopes nor on the carapace of the basin of the Plaine des Lacs. It does however, flourish in sites of relatively recent soil renewal, in the concavities formed by erosion of the carapace on slopes. It also grows, and regenerates well on a colluvial/alluvial fan spreading on to the floor of the basin.

Table 1 summarises the field features of this catena.

On the carapace (1) the zonal vegetation is an open woodland, dominated by Agathis ovata, with flattened crowns, with, slightly lower, the candelabra forms of Casuarina deplancheana and Dacrydium araucarioides. (Fig. 1)

The basins occupied by Nothofagus aequilateralis are steeply sloping to streams or dry gullies, and have the appearance of being fire survival sites. But the change from Agathis woodland to Nothofagus forest coincides with the boundary from carapace to slope soil, with an interspersed eroded peridotite zone on steeper slopes. This steeper eroded zone is covered with a low (lm-2m) scrub. There seems little to support agriculture on the ultrabasic areas, so probably fire intensity was lower there than elsewhere (Jaffré 1980) and the pattern is edaphic.

The steeper slopes above the Nothofagus gully forests are generally severely eroded blockfields of unweathered peridotite, with residual pockets of soil, similar to the lower part of the soil beneath Nothofagus.

Within the basin forest, (2) the ultrabasic influence is shown in the understorey by several species of open ultrabasic country: Exocarpus phyllanthoides, Schizaea dichotoma, as well as by frequent saplings of Agathis ovata. Nothofagus seedlings were not found, despite the presence of abundant cupules on a felled tree on the road bisecting the forest. (Fig. 2)

It is clear that, if the site were analagous to those described by Jaffré (1974), the soil was still influenced strongly by ultrabasic parent material, in a high Mg content, low Ca and K, and low P.

The presence of coralloid rootlets and hyphae in the soil suggest high mycorhizal activity, suggesting low available PO₄, as described by Birrell and Wright (1945) and Jaffré (1974).

The stand on colluvial/alluvial soil (3) was a pole stand; resulting from logging, possibly in the 1939-45 war. Reject logs, of spiral grain, suggested that Agathis was the tree extracted. The pole stand was in an extensive valley bottom fan, of finer material derived apparently from eroded blockfields above. The young trees were dense, at about 2m average spacing, and at 15m height and maximum diameter of 20cm were vigorous, with some self-thinning in process. A 10% cover of Agathis lanceolata up to 5m high, beneath N. aequilateralis suggested eventual succession to an Agathis-Nothofagus mixture, similar to that on metamorphic rocks (below).

The stand merged with an intact stand of N. aequilateralis, similar in position to the midslope mature stand described above.

Nothofagus Aequilateralis on Soils Derived from Metamorphic Rock

Two stands were visited on the east of the main axis, in a higher rainfall than at the Plaine des Lacs. The first, on a logging road at 550m, 17km SE of the Col des Roussettes, just E of the main divide, was in fact among those described by Dawson (1966) who then was given the name N. balsanae for the dominant species. In fact the species found was N. aequilateralis (T. Jaffr'e pers. comm.).

The stands were on ridge tops, and small plateaux, possibly old peneplain remnants. Nothofagus forest extended only a short way down, before an abrupt transition to a mixed broadleaf forest of some complexity. Sporadic clearings along the road, colonised by tall grass, and by Melaleuca quinquenervia indicated a series of fires.

Despite the flatness of the ridge top plateaux, there was no sign of a true laterite carapace. During the postulated Miocene peneplanation and lateritisation of the ultrabasic derived rocks (Jaffr'e 1980) the soils on metamorphic rocks had apparently weathered, possibly to red tropical soils in some areas and yellow-brown earths in others. The latitude (ca. 22°S) and altitude apparently determined this line of pedogenesis. Hence the grass clearings were not, as in equatorial areas, the result of locally xeric conditions produced by a laterite crust.

Fig. 1. Vegetation on ultrabasic carapace, foreground, dominated by Agathis orata and Casuarina deplancheanea. Road Plaine de Lacs—Yate, New Caledonia. (D. R. McQueen)

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Fig 2. N. aequilateralis in basin below locality of Fig. 1. Agathis ovata on right on a fresh road cut. The peridotite blocks are up to 2m across. (D. R. McQueen)

The Nothofagus forests themselves were dense, with a relatively even canopy, at 20m height but with occasional emergent trees of Agathis moorei. Both trees were regenerating on the forest floor, with Agathis predominating.

In the understorey, the major cover was by Cyathea sp. with Meryta sp. and Marattia sp. common.

Furthur down slope, into the mixed forest, the understorey was much denser, and the ridge top Nothofagus site seemed to be the most xeric in this forest complex.

The subsoil of yellowish red to red clay continued down, in road cuts, for 10m to weathered schist. The A_2.1 horizon had clean sand grains, and leaching appeared to be the case.

Further N at Po Vila, on the hills above Poindimie a ridge stand of Nothofagus aequilateralis was located on greywacke, at 350m—450m. Here again the Nothofagus-Agathis combination appeared. The stand was a narrow band along a steeply dissected ridge crest, of 20°-30° flank slope, with an abrupt boundary to mixed broadleaf forest below. N. aequilateralis was 10m-15m high and 75% cover with Agathis moorei at 20m accounting for 25% of the canopy cover. A. moorei was regenerating well beneath N. aequilateralis. but no seedlings of the latter were seen. (Fig. 3)

The understorey was relatively open, of Cyathea sp., Freycinetia sp., Smilax sp., Elaeocarpus sp. and Meryta sp.

Again, as at the Col des Roussettes, there is evidence of leaching. A pole stand, of fire origin, was examined in the same area. Dominated by N. aequilateralis 6m high, it was dense, with maximum diameter 15cm. There were occasional but vigorous Agathis moorei seedlings up to 2m high and a sparse understorey of Blechnum sp. and Freycinetia sp. The soil profile was similar to that of the mature stand.

Conclusion

N. aequilateralis on ultrabasically derived soils prefers moister sites, and certainly is not found in the lateritic carapace of mature soils, but grows in comparatively young slope soils, in basins. In this respect its behaviour is similar to N. codanandra and N. balsanae (Jaffré 1974). His mention of phosphate deficiency seen in all ultrabasic soils is borne out by the high degree of development of mycorrhizae on roots of N. aequilateralis on the ultrabasic sites examined in the present survey. page 68

Fig. 3. A ridge top, partly disturbed stand of N. aequilateralis, with Agathis moorei to right. On greywacke derived soil at 400m, above Po-Vila. (D. R. McQueen)

On clay rich soils from metamorphic rocks, N. aequilateralis is found only on the ridge crests and small plateaux, by inference the driest sites. On the moist flanks, competition from the mixed broadleaf forest excludes it. Such soils are possibly higher in phosphate as mycorrhizal development was far less in all stands examined.

The appearance in soil profiles, on schist and greywacke, of a thin leached horizon suggests N. aequilateralis is of a relatively low fertility requirement; a character consistent with its tolerance of nutrient disequilibrium on ultrabasic soils.

It displays, as possibly do N. balsanae and N. codanandra (Jaffré 1974), a behaviour paralleled by N. solandri var. cliffortioides in New Zealand. This species, widespread in many sites, of all N.Z. Nothofagus tolerates the poorest nutrient and drainage conditions on non-ultrabasic soils (Adams 1976). It will grow, stunted, on young soils formed from dunite boulders, provided the moisture supply is adequate, in the Upper Motueka Valley in the Red Hills massif of Marlborough, and on the ultrabasic rock of N.W. Otago (Molloy 1977).

The relation between Nothofagus and Agathis is important in New Caledonia. Agathis is far more widely distributed in New Caledonia than Nothofagus.

In areas from which Nothagus is absent, Agathis occupies similar ridge crest sites, in a more open mixed forest. The dominant Agathis ovata of ultrabasic laterite carapace will invade N. aequilateralis mature stands on younger soils. The appearance of A. lanceolata saplings in regeneration of Nothofagus on a site that may formerly have been Agathis forest, suggests that on an ultrabasic, young colluvium, Nothofagus may be seral, towards an Agathis forest, or a Nothofagus-Agathis mixture. In the stands on metamorphic rocks, Agathis moorei seems to co-exist with Nothofagus aequilateralis, a balance reflected in the regeneration of the two species together after fire.

Acknowledgements

I should like to express my gratitude to M. and Mme. T. Jaffré, and M. and Mme. M. Brinon for hospitality and guidance in New Caledonia, to my wife, Pamela, for field assistance, and to Dr J. W. Dawson for critically reading the manuscript. The Internal Research Grant Committee of Victoria University of Wellington contributed to the cost of field work.

References

Adams, J. A. 1976. Nutrient requirements of four Nothofagus species in North Westland, as shown by foliar analysis. N. Z. Journal of Botany 14:211-23.

Birrell, K. S., Wright, A. C. S. 1945. A serpentine soil in New Caledonia. N.Z. Journal of Science and Technology 27:72-76.

Dawson, J. W. 1966. Observations on Nothofagus in New Calendonia. Tuatara 14, 1: 1-6.

Duchaufour, Ph. 1970. Précis de pédologie. Masson et Cie Paris 481 pp.

Frimigacci, D., Maitre, J. C. 1981. in Sautter, G. L'atlas de la Nouvelle Caledonie et dependances. Edition de I'ORSTOM Paris: 53 pp.

Jaffre, T. 1974. La végetation et la flore d'un massif de roches ultrabasiques de Nouvelle-Caledonie: le Koniambo. Candollea 29: 427-456, 1974.

Jaffre, T. 1980. Etude ecologique du peuplement végetal des sols derivés des roches ultrabasiques en Nouvelle Caledonie. Travaux et Documentes de I'ORSTOM, Paris: 273 pp.

McQueen, D. R. 1976. The ecology of Nothofagus and associated vegetation in South America. Tuatara 22, 3: 233-244.

Molloy, L. F. 1977. Red Mountain—National Park or asbestos mine? Supplement to Forest and Bird, August 1977.

Van Steenis, C. G. G. J. 1971. Revision of Nothofagus in New Caledonia. Adansonia, ser. 2, 11(4): 615-624.

Wardle, P. 1973. New Guinea, our Tropical Counterpart. Tuatara 20, 3: 113-124.