Sumatran Vegetation

Plant Formations in the Sumatran BioProvince

Peter Martin Rhind

Sumatran Lowland Dipterocarp Forest These luxuriant forests are some of the most diverse on Earth with comparable levels of species diversity to the richest forests in Borneo and New Guinea and comprise over 100 species of dipterocarps, six of which are endemic. Some of the mature parts can have up to four distinct tree stories as well as shrub and herbaceous layers. The emergent trees, which can reach heights of 60 m, are mainly dominated by dipterocarps such as Anisoptera costata, Dipterocarpus crinitus, Hopea dryobalanoides, Parashorea lucida and Shorea macrocarpa. Other important upper canopy trees are Dyera costulata, Fragraea gigantea, Koompassia malaccensis, Mangifera rigida, Myristica gigantea, Polyathia hypoleuca and the endemic Heritiera sumatrana (Sterculiaceae), Horsfieldia triandra (Myristicaceae) and Polyalthia sumatrana (Annonaceae). Among the many trees of the sub-canopy are Aporusa elmeri, Dacryodes rugosa, Diospyros buxifolia, Diplospora singularis, Drypetes longifolia, Gironniera hirta, Nephelium cuspidatum, Timonius hydrangefolius and Xanthophyllum elmeri, while smaller trees of up to 15 m include an abundance of Aglaia tomentosa, Aporosa frutiscens, Baccaurea javonica, Croton oblongus, Fordia johorensis and Koilodepas glanduligerum. The endemic small tree Baccaurea sumatrana (Euphorbiaceae) like many other trees of these forests produces flowers and fruit at the base of its trunk - a phenomenon known as cauliflory. Other endemic small trees are Casearia cuspidata (Flacourtiaceae), Daphniphyllum sumatraense (Daphniphyllaceae), Diplycosia apiculifera (Ericaceae) and Gomphandra fusiformis (Icacinaceae).

In the undergrowth shrubs such as Agrostistachys longifolia, Gonocaryum gracile, Psychotria robusta and Rinorea anguifera are common as is the small tree fern Cyathea moluccana and palms like Licuala ferruginea and Pinanga malaiana. Endemic shrubs include Arthrophyllum papyraceum (Araliaceae), Clethra sumatrana (Clethraceae), Saraca tubiflora (Fabaceae) and Thottea reniloba (Aristolochiaceae). Lianas and climbers are common especially climbing palms mostly represented by rattans like Calamus flabellatus, Daemonorops depressiuscula and Korthalsia rigida, while other climbing species include Agelaea macrophylla, Fissistigma kentii, Hugonia costata, Salacia macrophylla, Sarcostigma paniculata, Smilax leucophylla, Uncaria calophylla, Willughbeia firma and endemic Aristolochia singalangensis (Aristolochiaceae) and Erycibe ramiflora (Convolvulaceae). On the ground some of the most common species are Hanguana malayana, Labisia pumila, several orchids such as Cystorchis saceosepala and ferns like Lindsaea doryphora. These forests are also famously know as habitat for the plant with the world’s largest flower (Rafflesia arnoldii), which is a parasite of the vine Tetrastigma, and the plant with the world’s tallest flowers, the endemic Amorphophallus titanium (Araceae). This magnificent arum has flowers up to 2 m tall and produces a fetid odor that attracts small bees that act as pollinators.

Sumatran Riparian Forest These forests, confined to riverbanks, undergo temporary flooding during heavy rain. They show considerable floristic diversity and vary according to location and flooding regime. On the west coast the enormous Canarium pseudodecumanum is often the dominant emergent species reaching heights of up to 50 m, while the main canopy trees, at heights of 25 m, include Antiaris toxicaria, Blumeodendron kursii, Dracontomelon dae, Pometia pinnata, Pterospermum javanicum, Santiria apiculata and the endemic Neoscortechinia sumatrensis (Euphorbiaceae). In southern areas other species may dominate including Copyright © 2010 Peter Martin Rhind Alstonia spathulata, Canthium dicoccum, Dillenia excelsa, Ficus retusa, Gluta renghas, Kayea ferruginea, Koompassia excelsa, Myristica elliptica, Neesia malayana and several endemic species like Mangifera gedeba (Anacardiaceae), Shorea sumatrana and Vatica venulosa (Dipterocardiaceae).

Sumatran Swamp Forest These forests occur in areas that are periodically flooded for relatively long periods of up to four months or more, and their floristic composition varies according to factors such as frequency and duration of flooding. As a result they are much more varied than forests of well-drained ground. In east Sumatra the main canopy trees are Artocarpus kemando, Baccaurea bracteata, Blumeodendron tokbrai, Campnospermum auriculatum, Mangifera paludosa and Parartocarpus venenosus. These can reach heights of up the 25 m or so, but often towering above these are various emergents like Alstonia pneumatophora and several dipterocarps such as Dipterocarpus apterus and Shorea balangeran that can reach 50 m or more. Among the associated endemic trees are Casearia gigantifolia (Flacourtiaceae) and Vatica teysmanniana (Dipterocarpaceae). In the undergrowth palms like Eleiodoxa conferta, Licuala spinosa, Oncosperma tigillarum are common as are various rattans such as Calamus caesius, Daemonorops geniculata and Korthalsia flagellaris. Shrubs may be present including the endemic Erycibe sumatrensis (Convolvulaceae). Ferns are also characteristic and besides Stenochlaena palustris, a climbing species with edible shoots, there are species such as Mesophlebion chlamydophorum, Microsorum musifolium, Paragramma longifolia, Pyrrosia lanceolata, Vittaria elongata, and in more open areas tree ferns like Cyathea contaminan. At ground level, not surprisingly, members of the Cyperaceae are common and may include Thoracostachyum bancanum and the endemic Scleria sumatrensis.

Sumatran Peat Swamp Forest Mainly confined to the east coast at the central and southern parts of the island, these forests are particularly abundant from the Musi delta to the Siak River. The peat deposits are usually about 50 cm deep but can be up to 20 m in places, and as a result of the low nutrient status and high acidity of these soils their floras are not as species-rich or as rich in endemics as other forests. Their floristic composition varies from place to place, but in southern Sumatra the most representative canopy trees are Campnospermum coriaceum, Durio carinatus, Mezzettia leptopoda, Santiria laevigata, Tetramerista glabra and Xylopia fusca. These reach heights of 35 m, but exceeding these by a further 15 m or so are various emergents like Dyera lowii and Shorea teijsmanniana. Among the many smaller, sub-canopy trees are Blumeodendron tokbrai, Combretocarpus rotundatus, Parastemon urophyllus, Tetractomia obovata, the endemic Neoscortechinia sumatrensis (Euphorbiaceae) and numerous species of Diospyros. The few palms include the emergent Livistonia hasseltii and the bright-red sealing wax palm Cyrtostachys lakka. Shrubs in the undergrowth are mostly Antidesmus montanum, Dacryodes rostrata, Eugenia setosa, Goniothalamus malayanus, Ixora malayana and Memecylon oligoneura. However, the flora that is specific to peat swamps is very limited, but includes, for example, the endemic dipterocarp Vatica teijmanniana (Dipterocarpaceae). Some of these peat swamp forests are described as pole forests because of the dominance of long straight trees.

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,

Copyright © 2010 Peter Martin Rhind 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

Copyright © 2010 Peter Martin Rhind 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).

Sumatran Rhododendron-Vaccinium Alpine Scrub Above an altitude of about 3000 m most trees give way to a dense ericaceous scrub characterized by Rhododendron retusum and the endemic Vaccinium miquelii (Ericaceae). There are also many other endemic ericoids including Diplycosia atjehensis, D. glauciflora, D. sumatrensis, Gaultheria acroleia, G. atjehensis, G. kemiriense, Rhododendron adinophyllum, R. aequabile and R. sumatranum, while other endemic shrubs or small trees include Lithocarpus atjehensis (Fagaceae) and Symplocos sumatrana (Symplocaceae). One of the last trees to peter out is Myrica javanica but at these altidudes it grows no more than about 8 m high. The ground layer consists of tussocky species like Carex hypsophyla and Gahnia javanica and occasional herbs such as Anaphalis javanica and the two endemic species Pyrola sumatranum (Pyrolaceae) and Senecio sumatrana (Asteraceae). Ferns, such as Dicranopteris pubigera, Gleichenia volubilis and Hypolepis punctata, are also present.

Further information required.

References

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