Included here is New Guinea, the Aru Islands, Misool Island, Salawati, Weigeo, the Schouten Islands, the Trobriand Isands, Murua Island, the D’Entrecasteaux Islands and the Louisaide Archipeligo.

Papuan Castanopsis Montane Forest

Forests dominated by almost pure stands of Castanopsis acuminatissima occur on ridge crests and slopes at altitudes ranging from about 500 to 2300 m. Their dense canopies limit the development of lower layers, which are usually limited to an open shrub and a sparse ground layer of herbs. The few associated trees include a number of endemic species such as Chisocheton pohlianus (Melicaceae), Elaeocarpus tariensis (Elaeocarpaceae), Helicia olivacea (Proteaceae), Hopea similis (Dipterocarpaceae), Kibara sleumeri (Monimiaceae), Myristica laevifolia (Myristicaeae), Podocarpus pseudobracteatus (Podocarpaceae), while the many endemic shrub layer species include Dimorphanthera elegantissima (Ericaceae).

Papuan Nothofagus Montane Forest

Altogether there are some 19 species of Nothofagus (southern beech) in Papua New Guinea and several of these, including N. brassii, N. carrii, N. crenata, N. flavirama, N. grandis, N. nuda, N. perryi, N. pseudoresinosa, N. pullei, N. resinosa, N. rubra and N. womersleyi are endemic to this zone. Nothofagus is the only genus of the Fagaceae found in the southern hemisphere and its presence in Papua New Guinea is still a mystery. Members of the genus start to appear at an altitude of about 600 m but only assume dominance between 1500 and 3000 m. However, the species have a very patchy distribution tending to be most frequent on ridge crests and upper slopes, and may be very frequent in one locality but absent from an adjacent one with apparently similar conditions. Associated trees include many endemics such as Clethra papuana (Clethraceae), Dryadodaphne crassa (Monimiaceae), Dryadodaphne novoguineensis (Monimiaceae), Dubouzetia novoguineensis and Elaeocarpus trachophyllus (Elaeocarpaceae), Fagraea amabilis (Loganiaceae), Helicia calocoma (Proteaceae), Kibara streimannii (Monimiaceae), Myristica fusiformis (Myristicaceae), Sarcopteryx caudata (Sapindaceae), Symplocos composiracemosa (Symplocaceae) and Vaccinium crassistylum (Ericaceae). These forests are also well endowed with endemic tree ferns such as Cyathea hooglandii, C. nigropaleata and C. womersley (Cyatheaceae). A shrub layer can usually be distinguished supporting endemic species such as Dimorphanthera alpina (Ericaceae), Elaeocarpus sayeri (Elaeocarpaceae), Kibara versteeghii (Monimiaceae), Rhododendron asperum (Ericaceae), Steganthera cyclopensis (Monimiaceae), Trochocarpa arfakensis (Epacridaceae) and Vaccinium angiense (Ericaceae). Many of the endemic shrubs, especially ericoids such as Diplycosia muscicola and Rhododendron warianum (Ericaceae), are epiphytic, but ferns, such as the endemic Elaphoglossum thamnopteris, probably constitute the main epiphytic species. Among the liana species is the endemic Vaccinium fissiflorum (Ericaceae), and an interesting endemic parasite of these forests is Langsdorffia papuana (Balanophoraceae).

Papuan Araucaria Montane Forest

In Papua New Guinea these forests are characterized by the presence of two endemic taxa – Araucaria cunninghamii var. papuana and A. hunsteini (Araucariaceae). The latter is a massive tree reaching heights of 89 m and girths of well over 3 m, and often towers up to 30 m above the associated mixed broad-leaved forest. Araucaria cunninghamii is not quiet as large but has a wider altitudinal and geographical distribution, although both species often occur together on a variety of landforms and soils. They can be found at altitudes ranging from about 750-2200 m. These are ancient conifers and some authors believe that they are relicts slowly being ousted by the more recently evolved components of the mixed broad-leaved forest. On the other hand, both still regenerate well and continue to be viable components of these forests.  Among the associated trees are many endemic species such as Hopea papuana (Dipterocarpaceae) and Myristica crassipes (Myristicaceae).

Papuan Coniferous Forest

Forests in which conifer genera such as Araucaria, Dacrycarpus, Papuacedrus, Phyllocladus and Podocarpus dominate occur in many upland areas above altitudes of about 2400 m. The pyramidal crowns of emergent trees of the endemic Papuacedrus papuana (Cupressaceae) can be seen from a great distance. However, near the upper limit of tree growth at about 3900 m many of the trees become stunted and shrub like, although certain conifers such as the endemic Dacrycarpus compactus, Podocarpus brassii (Podocarpaceae) retain their true tree structure even within the alpine shrub forests. Other endemic conifers found in these mountain forests include Falcatifolium papuanum and Podocarpus archboldii (Podocarpaceae), while the few endemic broad-leaved trees are Harmsiopanax ingens (Araliaceae) and Pittosporum berberidioides. In the lower stories there are tree ferns such as the endemic Cyathea muelleri (Cyatheaceae) and a multitude of endemic shrubs especially of the Ericaceae family such as Dimorphanthera callinsii, Rhododendron correoides and Vaccinium densifolium, while other endemic shrubs include Trochocarpa dispersa (Epacridaceae). Many of the Rhododendron shrubs are epiphytic such as the endemic R. microphyllum and there are also a number of endemic aerial semi-parasitic shrubs such as Amyema dilatipes (Loranthaceae).

Papuan Mossy Forest

Moving into the region of prolonged cloud cover at about 9000 ft there is often an abrupt change in forest formation. Above this height is the realm of the so-called ‘mossy’ forest or ‘cloud’ forest, which are extremely damp and characterized by constantly dripping water. They normally have a singletree layer commonly dominated by the angiosperm family Myrtaceae (with genera such as Decaspermum, Eugenia, Syzygium and Xanthomyrtus), and the coniferous family Podocarpaceae. The canopy never reaches more than about 40 ft in height, and is typically made up of close, slender often gnarled and crocked trees, with leaves that are usually small, coriaceous and dark green giving the forest a gloomy appearance. But the most distinctive feature of these forests is the predominance of mosses and liverworts, which festoon all of the trees and carpet the forest floor. Filmy ferns and tree ferns also reach their pinnicle of diversity here. The many endemic trees include Casearia archboldiana (Flacourtiaceae), Dacrydium spathoides (Podocarpaceae), Dysoxylum enantiophyllum (Meliaceae), Elaeocarpus latescens (Elaeocarpaceae), Fagraea salticola (Loganiaceae), Geniostoma randianum (Loganiaceae), Guioa pseudoamabilis (Sapindaceae), Harmsiopanax ingens (Araliaceae), Hartleya inopinata (Icacinaceae), Helicia archboldiana (Proteaceae), Horsfieldia schechteri (Myristicaceae), Kibara karengana (Monimiaceae), Levieria nitens (Monimiaceae), Libocedrus papuana (Cupressaceae), Parasponia rigida (Ulmaceae), Pittosporum sinuatum (Pittosporaceae), Podocarpus brassii, P. crassigemmis (Podocarpaceae), Prunus brassii (Rosaceae), Rhododendron agathodaemonis (Ericaceae), Rhyticaryum lucidum (Icacinaceae), Sarcopteryx rubiginosa (Sapindaceae) and Steganthera myrtifolia (Monimiaceae). Endemic shrubs include Agapetes stenantha (Ericaceae), Casearia ledermannii (Flacourtiaceae), Dimorphanthera denticulifera (Ericaceae), Fagraea dodenii (Loganiaceae), Gaultheria pullei (Ericaceae), Helicia microphylla (Proteaceae), Mackinlaya radiata (Araliaceae), Polyscias philipsonii (Araliaceae), Rhododendron culminicolum (Ericaceae), Rubus megacarpus (Rosaceae) and Sarcopteryx coriacea (Sapindaceae). There are also a number of endemic epiphytic shrubs such as Agapetes viridiflora (Ericaceae), Coryphopteris ledermannii (Thelypteridaceae), Dimorphanthera nigropunctata (Ericaceae), Diplycosia edulis (Ebenaceae), Rhododendron papuanum (Ericaceae) and Rhus caudata (Anacardiaceae), and these are joined by occasional lianas such as the endemic Palmeria clemensae (Monimiaceae). The rich endemic tree fern assemblage includes Cyathea arfakensis, C. foersteri, C. ledermannii, C. percrassa and C. rigens, with some reaching heights of up to 10 m. In addition to bryophytes, ferns such as the endemic Dicksonia hieronymi (Dicksoniaceae), Elaphoglossum idenburgensis (Elaphoglossaceae) and Gleichenia pulchra (Gleicheniaceae), and orchids make up the ground layer. 

References

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Merlin, M. D. & Juvik, J. O. 1995. Montane cloud forest in the tropical Pacific: some aspects of their floristics, biogeography, ecology, and conservation. In: Tropical Montane Cloud Forests. Eds.  L. S. Hamilton, J. O. Juvik and F. N. Scatena. Ecological Studies 10. Springer-Varlag.

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Robbins, R. G. 1971. The montane vegetation of New Guinea. In: World Vegetation Types.  Ed. S. R. Eyre. Macmillan.

Steenis, C. G. G. J. van. 1957. Outline of the vegetation types in Indonesia and some adjacent regions. Proceedings of the Pacific Scientific Congress, 8: 61-97.

Womersley. J. S. (ed). 1978. Handbook of the flora of Papua New Guinea. Vol. I. Melbourne University Press.