Included here is the island of Sumatra and surrounding islands such as Nias, Siberut, Bangka and Belitungare

Sumatran Hill Forest

In certain places, such as the Barisan Hills, the forest between altitudes of about 150-500 m has a different species composition from lowland forests. They are still classed as dipterocarp forests and have canopies reaching 40 m or so. The emergent species reach heights of 55 m and typically include Shorea bracteolate, S. gibbosa and S. hopefolia, while the canopy may include Albizia spendens, Alstonia scholaris, Artocarpus anisophyllus, Magnolia elegans, Whitfordiodendron atropurpurea and the endemic Parashorea aptera (Dipterocarpaceae). The middle and lower tiers show the appearance or greater abundance of Aidia cochinchinensis, Chisocheton patens, Crypteronia griffithii, Ctenolophon parvifolius, Diospyros lanceifolia, Gymnacranthera farquhariana, Horsfieldia polyspherula, Kitabalia maingayi, Pellacalyx lobbii and the endemic Knema lampongensis (Myristicaceae). Other endemic trees include Knema sumatrana (Myristicaceae), Shorea conica and Vatica obovata (Dipterocarpaceae). At ground level, the steep slopes are one of the favourite habitats of Rafflesiaceae. Species include Rafflesia arnoldi, the endemic R. gadutensis and the more modest but just as fascinating Rhizanthes zippelii. 

Sumatran Submontane Forest

These forests range in altitude from about 800 to 1400 m and can be just as majestic as the lowland forests with emergent trees reaching heights of 50 m or so, and many of the trees have large buttresses. This is despite the fact that dipterocarps are far less common and is largely superseded in terms of dominance by the Clusiaceae, Euphorbiaceae, Fagaceae and Myrtaceae. Lauraceae, on the other hand, which you would expect to be one of the dominant families of these forests, is not as prominent on Sumatra. The characteristic upper canopy and emergent species include Altingia excelsa, Drypetes minahassae, Lithocarpus hystrix, Neesia altissima, Parkia singularis, Podocarpus imbricatus, Quercus oidocarpa, Santiria laevigata, Sarcosperma paniculatum, Shorea platyclados and Toona sinensis.  There are also numerous strangling figs such as Ficus distica and F. elastica. In the sub-canopy between heights of 25 to 30 m the Fagaceae and Myrtaceae become even more pronounced with species such as Castanopsis tungurrut, Lithocarpus elegans, Quercus longiflora and at least 20 species of Eugenia - species from other families include Casearia tuberculata, Chionanthus exycarpus, Cryptocarya ferrea, Dacrydium elatum, Engelhardtia serrata, Radermachera pinnata, Talauma candolei, Terminalia myriocarpa and endemics like Michelia salicifolia (Magnoliaceae) and Trevesia arborea (Araliaceae). Smaller trees and shrubs include Ardisia blumii, Bennettiodendron leprosipes, Canthium horridum, Diospyros subrhomboides, Ellipanthus tomentosus, Garcinia urophylla, Symplocos fasciculate and a number of endemics such as Dehaasia sumatrana, Gomphandra fusiformis (Lauraceae) and Vaccinium gracilipes (Ericaceae). Tree ferns are locally abundant but mainly represented by Cyathea hymenoides and the endemic Cyathea alderwereltii (Cyatheaceae). Most of the lanoid species are similar to those of lowland forests, but Chilocarpus costatus, Tetrastigma lanceolata, Uncaria elliptica and Ziziphus horsfieldii appear to be characteristic of the sub-montane zones. Characteristic ground layer species are Crytandra pilosa, Gomphostemma microcalyx, Pleomele angustifolia, Phrynium capitatum and Sarcandra glabra.  Grasses are rare but may include Oplismenus compositus. Among the endemic herbaceous flora is Gomphostemma dolichobotrys (Lamiaceae).

Sumatran Montane Forest

These forests occur between altitudes of about 1400 and 1900 m and can be seen, for example, on Mount Kerinei (Sumatra’s highest mountain), and an active volcano. They usually consist of two tree layers - the canopy that reaches heights of 30 m and a sub-canopy between 10 and 20 m. Below this is a shrub layer ranging in height from 5 to 10 m. Fagaceae (including Lithocarpus pallidus and Quercus gemelliflora), Lauraceae (including Litsea tuberculata), Myrtaceae (including several species of Eugenia), some Theaceae (including Haemocharis buxifolia and Schima wallichii) and a number of Sapotaceae constitute the main upper canopy species. In places the endemic Trevesia sumatrana (Araliaceae) grows gregariously by virtue of its root and stem-suckers. Other endemic trees include Horsfieldia atjehensis (Myristicaceae) and Mastrix octandra (Cornaceae).  Common sub-canopy trees are Actinodaphne glomerulata, Chionanthus oxycarpus, Cinnamomum subavenium, Cryptocarya densiflora, Distylium stellare, Drypetes subsymetrica, Elaeocarpus mastersii, Eugenia longiflora, Ficus lanatus, Garcinia gaudichaudii, Lindera subumbelliflora, Memecylon oleifolium, Notaphoebe umbelliflora and Urophyllum arborescens. There are also many endemic small trees such as Brassaiopsis sumatrana (Araliaceae), Gomphandra dolichocarpa (Icacinaceae), Illicium sumatranum (Illiciaceae), Xanthophyllum ancolanum (Polygalaceae), and several endemic tree ferns like Cyathea senax and C. verrucosa (Cyatheaceae). Climbers are still relatively common and include, for example, the endemic Passiflora sumatrana (Passifloraceae). There are also many epiphytic species such as the endemic fern Pyrrosia asterosora (Polypodiaceae). The undergrowth is typically very rich in Myrsinaceae (such as Ardisia korthalsiana) and Rubiaceae (such as Hypobathrium microcarpum) but here also can be found several endemics like Lithocarpus orbicularis (Fagaceae), Polygala sumatrana (Polygalaceae), Rhododendron frey-wysslingii (Ericaceae) and Rubus banghamii (Rosaceae). The endemic titan arum, Amorphophallus titanium (Araceae) also occurs at these altitudes, and these forests form the main habitat of the magnifcent, endemic parasites Rafflesia micropylora and R. gadutensis (Rafflesiaceae) where they parasitize vines of the genus Tetrastigma.  The herb layer mainly includes members of the Gesneriaceae (such as Cyrtandra anisophylla), Liliaceae (such as Dianella ensifolia) and Rubiaceae (such as Ophiorrhyza sansuinea). Other herbaceous ground layer species include several grasses like Lophatherum gracile and Joinvillea borneensis, ferns such as Diplazium cordifolium, and the endemic Trigonotis hirsuta (Boraginaceae), which seems to be mainly confined to elephant trails.

Sumatran Upper Montane (Mossy) Forest

These forests range roughly between altitudes of 1900 to 2500 m in a zone where the cloud layer is relatively constant allowing moss and liverworts to flourish. On mountains such as Sinabung and the Talamau this generally coincides with a belt of the endemic Pandanus sumatranus (Pandanaceae), but the principal tree families are Fagaceae, Mystaceae and Theaceae. Other abundant canopy trees are Acronodia punctata, Lithocarpus suffruticosus, Symingtonia populnea and Vernonia arborea, which can reach heights of 25 m. Other noteworthy trees of the canopy are the three endemic species Glochidion lutescens (Phyllanthaceae), Rhododendron atjehense (Ericaceae) and Quercus steenisii (Fagaceae). Characteristic trees of the underlying layers are Michelia salicifolia, Saurauia micrantha, Weinmannia blumei and the endemic Symplocos robinsonii (Symplocaceae). Most trees are covered in a thick layer of epiphytic mosses and branches are usually festooned with Usnea lichens. Another characteristic feature of these forests is the abundance of aerial, epiphytic shrubs of the family Ericaceae such as the endemic Diplycosia cinnabarina, Rhododendron pibigermen and Vaccinium bartlettii, while other epiphytes include various endemic ferns of the genus Selliguea (Polypodiaceae) such as S. bakeri, S. brooksii and S. pseudoacrostichum. The shrub layer is often dominated by Ardisia javanica, while other less common species include Casearia tuberculata, Ilex triflora, Macropanax dispermus, Meliosma lanceolata, Myrica javonica, Neolitsea javonica, Saurauia micrantha, Schima wallichii, Viburnum lutescens, various endemic ericoids like Diplycosia tetramera and Rhododendron ridleyi (Ericaceae), and the endemic tree ferns Cyathea punctulata and C. trachypoda (Cyatheaceae), although neither of these is more than about 50 cm tall. On the ground common species are Calanthe flava, sedges like Carex cruciata and C. myosorus and ferns such as Asplenium caudatum, Athyrium gedeanum, Belvisia mucronata and Dryopteris poleacea.

Sumatran Subalpine Forest

Above the upper montane forest on Mt Kerinii from about 2400 to 2700 m is a peculiar zone dominated by ferns of the family Gleicheniaceae such as Dicranopteris pubigera and Gleichenia volubilis.  It has never been fully explained in ecological terms since above this zone is another forest zone. These sub alpine forests, however, are very twisted and stunted and rarely achieve more than about 15 m in height. The dominant canopy trees are Ilex pleiobrachiata and Symplocos cochinchinensis var. sessilifolia, while a sub-canopy at about 10 m largely consists of Ardisia laevigata, Meliosma lanceolata and the endemic tree fern Cyathea trachypoda (Cyatheaceae). Below this are various shrubs including the endemic Gaultheria abbreviata and Rhododendron aequabile (Ericaceae). The forest floor is typically covered with the fern Plagogyria pycnophylla and the brambles Rubus elongatus and R. alpestris. Among the endemic herbaceous species at this altitude is Heracleaum sumatranum (Apiaceae).

References

Bihari, M. & Lal, C. B. 1989. Species composition, density and basal cover of tropical rainforest of central Sumatra. Tropical Ecology, 30: 118-137.

Laumonier, Y. 1997. The Vegetation and Physiography of Sumatra. Kluwer Academic Press.

Leith, H. & Werger, M. J. A. 1989. Ecosystems of the World 14B - Tropical Rain Forests. Elsevier Scientific Publishing Company.

Ohsawa, M., Nainggolan, P. H. J., Tanaka, N. & Anwar, C. 1985. Altitudinal zonation of forest vegetation on Mount Kerinci, Sumatra: with comparisons to zonation in temperate regions of East Asia. Journal of Tropical Ecology, 1: 193-216.

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.

Whitten, T., Damanik, S. J., Anwar, J. & Hisyam, N. 2000. The Ecology of Sumatra. Periplus.