Tuatara: Volume 8, Issue 3, April 1961
The Montane Vegetation of New Guinea
The Montane Vegetation of New Guinea
On the high mountains of central New Guinea there are tropical montane forests, alpine tussock grasslands and herbfields which bear a remarkable physiognomic resemblance to similar communities in New Zealand and in which moreover, occur many species indicative of a yet closer affinity.
Many of these relationships stem from past tropical migrations southwards from Malaysia as for example the climbing Freycinetia and the terrestrial Elatostema. Of greater interest, however, are those plants which are apparently representative of a once more general distribution of a great southern flora which extended over Australia and reached out as far as South America.
These remnant plant distribution patterns evoke a stirring history of ancient plant migrations, of invasion and decimation under the influence of vast climatic fluctuations, of long-vanished land bridges and shifting continents. Was there once a warm and verdant Antarctica? Have islands and continents once close to each other, now drifted apart leaving deep intervening oceans? Were whole floras affected by the great ice ages? These are some of the problems of plant geography the solving of which depends upon data still being actively collected.
In this respect New Guinea with its large imperfectly known flora is emerging as an important refugium for much of the ancient southern flora which once covered the postulated southern continent of Gondwanaland. New and recent plant discoveries, particularly in the botanical exploration of the central mountains, are shifting the known generic centre of distribution in many instances. Even the typically subantarctic genus of Nothofagus is now represented by some sixteen species in New Guinea and a further five in New Caledonia. This contrasts with the two species remaining in Australia and the four to five in New Zealand. The New Guinea species produce pollen of the brassii type which is found only as Miocene fossils in New Zealand. Another example is the genus Carpodetus long quoted as monotypic to New Zealand, when in fact it has about six species in New Guinea. Recent collections in New Guinea's botanically unexplored mountains are adding new links with southern genera. This is particularly so in groups like the mosses. As late as 1942 E. B. Bartram wrote: ‘An interesting feature that does not seem to have been previously remarked is the close relationship of the alpine and page 122 subalpine mosses of New Guinea with genera and species typical of Australia, Tasmania and New Zealand.’ Since then the list of such species has grown impressively. Undoubtedly the next few years will bring about a reassessment of the phytogeography of the whole south Pacific and changing our ideas which, in the past, have been based so much on mere priority of exploration and taxonomic descriptions.
This does not necessarily signify that the centre of origin is in any way shifting to New Guinea but only that the high mountains of New Guinea may well represent a more important area for relicts of the ancient southern flora than New Zealand itself!
Large areas of New Guinea remain virtually unexplored in the botanical sense and with new species continually being added to the estimated total flora of some fifteen to twenty thousand species it is difficult to keep up to date with any taxonomic assessment. An ecological assessment of the vegetation is only in its initial phases.
One of the most comprehensive accounts of the mountain vegetation is to be found in Brass, 1941. This account deals with the results of the Third Archbold Expedition in 1938-39 to the Snow Mountains forming part of the Central Range in the Netherlands New Guinea. Of the eastern end of this Central Range, lying in Australian New Guinea, very little is known.
Until 1933 it was shown on maps as a rugged and uninhabited region. The Leahy brothers made the first penetration of the central highlands and their amazing discovery of a thriving stone-age population in these high mountain valleys still makes fascinating reading. It is well told in Colin Simpson's Adam in Plumes.
In 1956 Messrs. Hoogland and Pullen from C.S.I.R.O. carried out botanical collecting in the highlands area. This was in preparation for a full-scale land resources survey which was made during the following year. Some 4,000 square miles comprising the western and eastern highland district were surveyed in regard to soils, vegetation and geomorphology during a season lasting four months. The writer was plant ecologist with this team. Later (1958) Dr. R. D. Hoogland, taxonomist, published an account of the alpine flora of Mt. Wilhelm based on the collections made during the surveys and an account of the vegetation will be found in Robbins (in press). Mt. Wilhelm is the highest peak in eastern New Guinea and it is of interest to mention that Mr. L. J. Brass, botanist with the Archbold Expeditions, has recently returned from this area.
The Populated Highland Valleys
The Wahgi River valley, some seventy-five miles long and up to ten niles wide, constitutes the main highlands valley. The floor is some 5,000 eet above sea level and enclosed by two great mountain ranges running east-west. To the north is the Wahgi-Sepik Divide, part of the Bismarck Range system. Several high peaks are included along its length but lominating all is the massive granodiorite peak of Mt. Wilhelm rising to 5,000 feet and the highest point in Australian New Guinea.page 123
The southern flanks are formed by the Kubor Ranges where many individual peaks attain heights of over 10,000 feet. Blocking the western end of the Wahgi valley is the volcanic Mt. Hagen.
The valley landscape is now one of open grassland throughout which are groves of Casuarina trees, clumps of feathery bamboos, native garden patches, tall cane grasses and remnant oak forest outliers. For perhaps hundreds of years the native inhabitants of the valley have progressively cleared back the forest in their quest for new garden land. Moving over the foothills to the very flanks of the ranges and along the small side valleys up to an altitude in some places of 7,000 to 8,000 feet, they have left behind them areas of short mixed grassland. Representing an entrenched disclimax, these grasslands are perpetuated and extended by the practice of burning off the grasses periodically in search of small game. Grass species here are common to the extensive lowland grasslands of the adjacent Markham and Ramu valleys and with other plants associated with the domesticated parts of the highlands no doubt followed man in his migrations from the lowlands.
On dry sites Australian kangaroo grass (Themeda australis) dominates, otherwise a complex of Imperata (kunai grass), Arundinella, Sorghum nitidum, Ophiuros, and Capillipedium is found. Ischaemum barbatum covers moister depressions. Throughout these grasslands are a variety of associated herb species, mostly tropical weeds.
Regrowth, apart from the garden weeds springing up in abandoned plots, cannot be said to be a feature of the highlands. In the lower and drier eastern highlands around Goroka township the country is of rolling treeless grassland giving a pastoral aspect to the landscape. Further west in the Wahgi valley the Mt. Hagen volcanic ash is covered with a growth of tall canegrass, Miscanthus floridulus, and associated tree-fern and woody shrub regrowth. Here Dodonaea viscosa may be a common shrub together with Grevillea papuana, Pittosporum ramiflorum, the coprosma-like Wendlandia paniculata, Buddleia asiatica, Schuurmansia, Schefflera and page 124 species of Saurauia and many Urticaceae. Macaranga and Homalanthus are representative of the many Euphorbiaceae while Coriaria papuana and Muehlenbeckia monticola may appear along stream banks. Present as small trees up to 30 feet high are Carpodetus arboreus and C. major. Remnants of a mixed oak forest which probably once covered the whole valley bottom are now to be found only in river gullies. An exception was probably the extensive swampy floodplains of the middle Wahgi valley which are covered with the tall swamp canegrass, Phragmites karka. Locally small sedge bogs occur where Cladium, Scirpus, Cyperus, Fimbristylis, Eleocharis, Schoenus, Fuirena and Carex are found. Common bog herbs belong to the following genera, Astilbe, Hydrocotyle, Epilobium, Haloragis, Eriocaulon and Centella.
In making gardens, the natives start by felling the forest trees and burning the wood. Narrow lines of trenches are then dug in a squared pattern across the plot. The loose earth is heaped up on to these small squares and cuttings of the sweet potato vine, or ‘kau kau’, are planted. The highland natives are vegetarian apart from the odd pig-feasting days and sweet potatoes together with sugar-cane, bananas and, more recently, peanuts, corn, Irish potatoes and other European vegetables form the staple diet.
In garden areas many Casuarina tree seedlings are carefully planted and tended to later provide housing material, fuel and the split timber staves for the stout picket fences which enclose the gardens against the ubiquitous pigs raised for ceremonial feasting.
The natives have a flair for landscape gardening and line the roadways with useful and ornamental trees and shrubs. Features of the highlands are the park-like sing-sing or dancing grounds. These are bright with the variegated foliage of Acalypha, Cassia, Croton, Cordyline terminalis, Coleus, Salvia, Balsam and copper-leaved sugar cane. Forest tree seedlings such as Podocarpus and Papuacedrus are brought down from the mountains to plant in these sing-sing grounds. In the eastern districts the indigenous Eucalyptus deglupta and Araucaria cunninghamii are found as specimen trees in the villages.
The Lower Montane Forests
Podocarp species which are common in the lower montane forest are Podocarpus ledermannii, P. rumphii, P. imbricatus, P. amarus and P. neriifolius. The last three of these are the most frequent and seedling page 126 regeneration is active. P. amarus and P. neriifolius are both types with broad flat leaves and may be found occasionally in the lowland forests. Two species of Dacrydium also occur in the highlands. Dacrydium falciforme is a small tree resembling the New Zealand miro, while D. elatum is close to rimu in appearance. Both, however, are local to rare in the montane forests. Phyllocladus hypophyllus, and Papuacedrus (until recently Libocedrus sp.) belong more to the high montane forests.
The canopy of the lower montane forest is made up of a number of broadleaf species often reaching 100 feet or more in height. Genera such as Opocunonia, Schizomeria and Aistopetalum belonging to the Cunoniaceae are frequent. Elaeocarpaceae contribute many species of Elaeocarpus and Sloanea, while several Cryptocarya spp., a genus close to Beilschmiedia, represents the Lauraceae. Also here are Syzygium spp. (cf. Eugenia), and the lesser associates, Albizia, Astronia, Alphitonia, Elmerillia, Fagraea, Ficus, Guioa, Garcinia, Himantandra, Ilex, Planchonella, Pygeum, Perrottetia, Sterculia and Zanthoxylum.
In the second tree stratum with limits between 40-60 feet are to be found Elaeocarpus, Ackama, Weinmannia, Pullea and Gillbeea, all of the Cunoniaceae, Ficus and Syzygium spp., and a host of small trees such as Sphenostemon papuanum, Sloanea, Sericolea, Myristica, Daphniphyllum, Dillenia montana, D. schlechteri, Diospyros, Quintinia, Casearia pachyphylla, Litsea, Couthovia, Zanthoxylum, Discocalyx, Rapanea, Ardisia, Pittosporum pullifolium, Helicia microcarpa, Timonius, Evodia, Eurya, Gordonia papuana, Ternstroemia and the giant stinging tree, Laportea.
A dense shrubby layer includes the following: Olearia, Casearia angiense, Bubbia, Aglaia, Dichroa febrifuga, Rhododendron, Geniostoma, Mearnsia cordata, Decaspermum, and Xanthomyrtus.
Members of the Rubiaceae such as Amaracarpus, Psycotria, Mussaenda and Gardenia are very frequent while Melastomataceae is represented by Medinilla, Everettia and Poikilogyne. Small Pygeum spp., Eurya meizophylla and the ubiquitous Symplocos, also Pittosporum berberidoides, P. inopinatum, a new species discovered during the survey, Acronychia, Rhamnus, Evodia, Perottetia moluccana. Chloranthus and Ascarina are among the sub-shrubs.
Small palms, Pandanus spp., tree ferns such as Cyathea contaminans, Dicksonia and a tall Marattia as well as masses of climbing bamboo all contribute to the forest structure.
Nothofagus beech forest covering rugged topography in the Kubor Ranges at the head of the Minj River valley. Tufted Cordyline and the plumed heads of swordgrass marked the edge of a garden at 8,000 feet. Casuarina trees may be seen at the left in the inhabited valley below.
Among the small climbers and scramblers present are Parsonsia, two species of Freycinetia, Rubus, Clematis, Smilax, Celastrus, Alyxia, Hoya and Secamone as well as members of the Gesneriaceae, Monimiaceae, and Bignoniaceae.
Epiphytes include Pittosporum ramiflorum, Schefflera, climbing ferns and orchids (including Dendrobium and Bulbophyllum) and parasitic Loranthaceae.
An excellent account of the discovery of extensive Nothofagus forests in New Guinea will be found in Van Steenis (1953). Some sixteen species are now recognised although the question of hybrids remains. With further recent collections, including those made by the C.S.I.R.O., a revision is already due.
Most of the New Guinea beeches are relatively large-leaved and with entire margins. However, on fruiting morphology van Steenis traces affinities with the New Zealand N. fusca group.
Beech forest has been recorded from about 3,000 feet to 10,000 feet in New Guinea but in the highlands its range was found to be between 7,500 feet to 9,000 feet. It descends, however, as a mixed element down to 4,500 feet in the eastern highlands. Nothofagus was not found to play any part in the formations above 9,000 feet and its true status appears to be as a member of the lower montane rain forest formations.
The New Guinea beech forest is a two-layered forest with a closed canopy of spreading and interlocking crowns which may consist of 75 per cent. Nothofagus species 90-100 feet high. It often forms a mosaic with the mixed broadleaf-podocarp forest occupying only one flank of the range or dominating on the ridges. In July the reddish flush of young leaves distinguished this pattern from some distance away while the distinctive crowns show up well on aerial photos flown at 25,000 feet. In the highlands the largest continuous areas of beech are to be found along the southern Kubor Range and it is virtually absent from the ranges flanking the northern periphery of the valley. The beech trees are seldom found as scattered individuals but even in mixed forest form small isolated gregarious stands. No doubt some interesting correlation with migration paths and environment as is evident in New Zealand will emerge when the full pattern of the New Guinea Nothofagus forest is mapped.
In these New Guinea mountains, beech forests exist side by side, as in New Zealand, with a mixed broadleaf-podocarp forest with usually a sharp boundary between the two. However, here one is in a montane forest of the tropics and the aspect is of a more luxurious and humid forest than in a subantarctic beech forest in New Zealand. There is less contrast with the adjoining mixed forest and indeed many of the subordinate species overlap. The fagaceous trees dominate and have a similar layered appearance and even-formed canopy as in New Zealand but mixed under-layers including Pandanus and climbing forest bamboo are present. The leaf litter is not heavy and topsoil, while tending to be acidic, is closely page 129 approximate to conditions in the mixed forest. Ferns, herbaceous plants and bryophytes may form a rich ground cover. The masses of climbing bamboo and the palm-like, stilt-rooted Pandanus, present also in the mixed forest, impart a distinctive physiognomy to the beech forests of the New Guinea highlands.
Species to be found in the upper stratum include several Nothofagus species, Ackama, and other Cunoniaceae, Quintinia, and Podocarpus with oaks, Cryptocarya, Zanthoxylum and Alphitonia.
The second stratum at about 30 to 50 feet may be sparse although rich in species. The smaller trees here include Nothofagus, Weinmannia and Pullea. Also several Ficus species, the Rubiaceous Timonius and Psychotria, two species of Drimys, Rapanea and other Myrsinaceae, Syzygium spp., Evodia (cf. Melicope) and Couthovia, a Schefflera, and Sloanea (Elaeocarpaceae).
Common members of the shrub layer are Symplocos, Sphenostemon papuanum, Polyosma, Medinilla, Piper, Pittosporum pullifolium, Helicia microcarpa.
Epiphytes are quite frequent, consisting mainly of pteridophytes, a small Freycinetia, orchids and scrambling Gesneriaceae.
The ground layers include ferns such as Blechnum and Hymenophyllum, with Pilea and Elatostema, terrestrial orchids, lycopods and bryophytes.
Montane Cloud Forest
At 9,000 feet above sea level there is a change, often quite abrupt, in the forest formation. Above this level in the highlands are the regions of prolonged daily cloud cover and the so-called ‘mossy’ forest commences.
A single tree-layered community, montane cloud forest is dominated by species of Myrtaceae and Podocarpaceae. The canopy is compact and low, being 35-40 feet high, and made up of close slender trees often crooked in growth. The branches and indeed the whole forest floor are typically festooned and carpeted with masses of bryophytes, both mosses and liverworts.
The bamboo and screwpines of the lower montane zone forest are now absent altogether and filmy ferns and tree ferns find true expression. All tropical features have gone and the atmosphere is damp and dripping. The leaves are smaller, coriaceous and dark green, giving a drab appearance to the forest.
Myrtaceae are well represented by species of Decaspermum, Xanthomyrtus, Eugenia and Syzygium. Also Schefflera, Daphniphyllum, Quintinia, Elaeocarpus azaleifolius, Rapanea, Carpodetus, Drimys, Schuurmansia, Eurya, Pygeum, and Rutaceae.
The mountain podocarps include Podocarpus compactus, P. brassii and P. pilgeri. Papuacedrus and Phyllocladus are also frequent.
A sparse shrub layer may include Polyosma, Rhododendron spp., Vaccinium spp., Amaracarpus, Symplocos, Pittosporum spp., Piper and, appearing here for the first time, a low Coprosma.page 130
Orchids, ferns and bryophytes make up the ground layer which, in more open glades may include Acaena anserinifolia, Libertia pulchella, Uncinia sp., Elatostema and Pterostylis.
At altitudes of 11,000 feet the upper limits of the cloud forest are fringed with a dense, low, woody vegetation or alpine shrubbery, patches of which may extend out into the alpine grassland.
The closed shrub layer, 15-20 feet high, consists of many Rhododendron and Vaccinium species together with Acronychia, Olearia, Saurauia, Schefflera, Sericolea, Symplocos, Pygeum, Decaspermum, Rapanea, Quintinea, Coprosma, Pyschotria, and Amaracarpus, Pittosporum, Polyosma, Eurya and Drimys.
These levels are above the prolonged mists of the cloud forest and emergent Podocarpus and Libocedrus may occur but there is little development of the high mountain forest formation described by Brass around Lake Habbema in Dutch New Guinea and also reported for the Owen Stanley Range.
Mosses and liverworts are abundant in the alpine shrubbery. Epiphytes include Loranthaceae, Orchidaceae and Pteridophyta while as a ground cover are Polystichum, Belvisia, Blechnum and the herbs Trigonotis, Libertia pulchella, Cardamine altigena, Acaena anserinifolia, Triplostegia glandulifera, Oxalis magellanica, Rubus moluccanus, Lycopodium, Galium, Epilobium and Geranium.
Above the tree-line at 11,000 to 12,000 feet the vegetation becomes tussock grassland. Extensive alpine grasslands occur on the summit areas of Mt. Giluwe, Mt. Hagen and Mt. Wilhelm and make an appearance on some of the higher isolated peaks of the two ranges. Here a New Zealand botanist is quite at home. Large tussocks of Hierochloe longifolia and Deschampsia Klossii dominate, forming clumps 2-3 feet high. In between grow the smaller tuft grasses represented by Danthonia archboldii, D. vestita, D. schneideri, and D. semiannularis.
Other grasses recorded are Deyeuxia, Agrostis, Anthoxanthum, Festuca papuana and the minute Poa crassicaulis and P. callosa.
Alpine herbs, many of which form cushion plants, grow among the tussocks in a mat of mosses and lichens. Here may be found Centrolepis phillippinensis, Hydrocotyle sibthorpioides, Oreomyrrhis papuana (syn. andicola), two species of Potentilla and several minute blue-flowered Gentiana. Of interest is the terrestrial Astelia papuana which is possibly identical to the New Zealand A. linearis of similar habitat. Several Epilobiums, a Pratia and Euphrasia rectiflora are present while mountain daisies are represented by the genera, Anaphalis, Gnaphalium, Tetramolopium and Keysseria.
Fringe of the alpine shrubbery on Mt. Wilhelm at approximately 13,000 feet a.s.l., showing silvery foliage of Olearia sp. and undergrowth of Coprosma sp.
Interior of tall Nothofagus beech forest in the eastern highlands. Pandanus and climbing bamboo form an undertier.
On higher slopes the soil is drier and more shallow with rocky outcrops. The tussocks thin out and small woody shrubs include Styphelia, Gaultheria mundula, Drimys brassii, Detzneria tubata, Kelleria (syn. Drapetes) papuana, Coprosma, Eurya brassii var. erecta, Hypericum macgregorii, Hebe albiflora and H. celiata. The last-mentioned are not whipcord hebes but similar to the New Zealand H. catarractae.
At the highest point on Mt. Wilhelm, 14,950 feet above sea level, plants still form a sparse rock crevice community between the moss-covered granodiorite rocks. Here the mountain mosses Andreaea rupestris and Rhacomitrium lanuginosum var. pruinosum, which occur together with Rhacomitrium crispulum, were collected for the first time in New Guinea. All are common New Zealand alpine mosses. The plants recorded here are the grasses Danthonia vestita, Poa callosa, Festuca papuana, Deyeuxia, Agrostis; the ferns Papuapteris linearis, Gleichenia bolanica and the small herbs, Cerastium keysseri, Lactuca, Ischnea elachoglossa and Trigonotis papuana. While again there are sufficient New Zealand genera and even species to strongly ‘flavour’ the vegetation an anlysis of the Compositae and the Ericaceae, for example, shows a marked difference, and reduces the apparent affinity.
The vegetation of montane New Guinea is only just becoming known. Already some confusion in the available literature reflects the great variation in local sites throughout this great island - hence the present account must be taken as referring essentially to the central highlands in Australian New Guinea.
The fascination of these montane forests lies in their affording a key to past southern floras. Thus the mixed lower montane forests of the highlands may be regarded as tropical outliers, now relict, of New Zealand's podocarp-broadleaf forests of tawa-hinau-kamahi and scattered rimu-totara-matai and miro.
In addition it contains many genera and species lost in New Zealand during the general post-Miocene regression as, for example, the warmthloving Nothofagus brassii group.
In the central highlands the major plant formations encountered are:
|Lower montane rain forest||3,000 to 9,000 feet|
|Montane cloudy forest||9,000 to 11,000 feet|
|Alpine shrubbery||11,000 to 12,000 feet|
|Alpine grasslands||11,000 to 14,000 feet|
BRASS, L. J., 1941 - The 1938-39 Expedition to the Snow Mountains, Netherlands New Guinea. Journ. of the Arnold Arboretum, Vol. 22, 271-342.
VAN STEENIS, C. G. G. J., 1953 - Papuan Nothofagus. Journ. of the Arnold Arboretum, Vol. 34, No. 4, 301-374.
HOOGLAND, R. D., 1958 - The Alpine Flora of Mount Wilhelm (New Guinea). Blumea. Suppl. IV, Dr. H. J. Lam Jubilee Volume, 220-238.
ROBBINS, R. G. (in press) - Montane formations in New Guinea. U.N.E.S.C.O. Symp. on Veg. of humid Tropics. Bogor, Indonesia, 1958 (in press).