Broadleaved forests

Closed broadleaved forests on dry lands

Tropical rain forests

Tropical rain forests are found in ever-wet and semi-wet climates up to approximately 1 300 m elevation. They are mixed, evergreen, multi-storeyed forests with many canopies 30 to 50 m high, with emergents. The most important timber species are those of the Dipterocarpaceae family with, as main genera, Shorea, Hopea, Dipterocarpus, Dryobalanops, Anisoptera, Parashorea and Vatica. These trees form the main frame of the forest (canopy and emergents) throughout the type in Sumatra and Kalimantan but become scarcer in Sulawesi, the Maluku and Irian Jaya, although in the latter area they are still represented locally as major timber species. Usually there are several co-dominants in a locality and dominance of one species is rare (e.g. Dryobalanops). Crowns of dipterocarps often reach 60 m high. Other major representatives in the canopy are Agathis, Altingia, Diospyros, Duabanga, Dyera, Eusideroxylon, Intsia, Koompassia, Palaquium and Pometia spp. There are well-pronounced varieties of the type, e.g., riverine forests with Dipterocarpus oblongifolius, Eugenia, Ficus, Gluta renghas, Octomeles sumatrana, Pometia, Saraca spp. and slope forests (often with Tristania spp. in Kalimantan). Pioneer plants that invade the land after repeated clearance of rainforest types are often introduced from outside the region. These may form dense vegetative cover that prevents early regeneration (Eupatorium spp., Hyptis suaveolens, Lantana camara and Mimosa invisa). Regular burning gives rise to fields of Imperata grass (alang-alang), a most unsuitable habitat for germination and seedling growth of rainforest plants. Ferns of Blechnum, Nephrolepis and Gleichenia spp. may invade clearings on poor soils, forming impenetrable thickets. In the regeneration stages of rainforests, the following genera are well represented: Adinandra, Engelhardtia, Homelanthus, Macaranga, Mallotus, Melochia, Oreocnide, Parasponia, Peronema, Ploiarum, Psidium, Schima, Trema, Vitex and Weinmannia.

Montane rain forests These forests are found between approximately 1 300 and 2 300 m elevation. They are mixed forests like the tropical rain forests of the lowlands but with far fewer representatives of the typical families of the latter, including the Dipterocarpaceae, which fade away entirely around 2 000 m. They are replaced by representatives of families found in the humid sub-tropics, e.g., Lauraceae, Fagaceae, (especially Quercus and Castanea spp. in Sumatra and Kalimantan and Nothofagus spp. in Irian Jaya), Cunoniaceae, Monimiaceae, Acer, Ulmus (northern Sumatra), Magnoliaceae, Hamamelidaceae, Raponea, Leptospermum, Ericaceae (tree ferns) and increasing numbers of conifers. In secondary stages, thickets of the fern Gleichenia spp. often develop with Ericaceous species. Below the summits of active volcanoes, under the influence of mudstreams and on lapilli cones, dwarf forests are found as well as stands of Pinus merkusii (Sumatra), and Dodonaea viscosa, Trema and Parasponia spp. (eastern Java and Nusatenggara islands). In fire-swept areas, the following species occur extensively: Albizia lophanta (on Java), Engelhardtia spp., Eucalyptus spp. (in Timor), Pinus merkusii (northern Sumatra) and Casuarina junghuhniana (eastern Java and Nusatenggara). null

Sub-alpine rain forests

These sub-alpine forests occur up to about 3 500 m and consist of stunted trees of Araucaria (Irian Jaya), Dacrydium, Podocarpus, Libocedrus, (Irian Jaya), Ericaceae, Leptospermum, Olearia, Quercus, Rapanea, Schefflera and Xanthomyrtus spp. The type is replaced after destruction by alpine grasslands, which can be found extensively in Irian Jaya, on which forest regenerates very slowly due low temperatures.

Monsoon forests

Monsoon forests occur up to about 1 000 m in areas with a dry- to wet-period ratio higher than 1:3. They are mixed stands of simpler structure than rain forests, with a canopy 25 to 30 m high and fewer emergents (e.g. Gossampinus and Tetrameles). Most trees shed their leaves during the dry period. There are always some evergreen species (e.g. Azadirachta spp.) found from north-western Java through the Nusatenggara islands to southern Irian Jaya, as well as in southern and south-eastern Sulawesi; in the western tip of central Sulawesi and the southern parts of its northern arm; and in the Buru and Seram islands of the Maluku. Typical species that do not occur in rainforests are: Acacia leucophlea, Acacia tomentosa, Actinophora fragrans, Aegle marmelos, Albizia chinensis, Albizia lebbeckioides, Azadirachta indica, Borassus flabellifer, Butea monosperma, Caesalpina digyna, Cassia fistula, Casuarina junghuhniana, Corypha utan, Dalbergia latifolia, Dichrostachys emerea, Eucalyptus alba, Feronia elephantum, Garuga primata, Homalium tomentosum, Lagerstroemia cinera, Lannea grandis, Melaleuca spp., Melia azadarach, Santalum album, Schleichera oleosa, Stereospermum suaveolens, Streblus asper, Tamarindus indica, Tectona grandis, Tetrameles nudiflora, and Zizyphus mauritiana. In the dry belt of southern Irian Jaya, several Australian floristic elements are included, such as various species of Eucalyptus and the families Myrtaceae and Protaceae (Banksia and Grevillea spp.). Burning over the centuries has resulted in typical pyrogenic types with a single dominant species, e.g., Tectona grandis on Java, Melaleuca leucadendron in the Maluku and Irian Jaya, Eucalyptus alba in Nusatenggara and Irian Jaya, other species of Eucalyptus in southern Irian Jaya, Banksia dentata (Irian Jaya and Aru islands), Timonius sericeus, Borassus flabellifer and Corypha utan in Nusatenggara.

Mountain monsoon forests

Monsoon forests are found above 1 000 m elevation, occurring originally as a mosaic in mixture with rainforests. Increased susceptibility to destruction by fire has resulted in typical secondary types such as open grasslands, Casuarina junghuhniana stands in eastern Java, Eucalyptus-Casuarina forests in Nusatenggara, stands of Cyathea spp. on the eastern plateaus of Irian Jaya and Pinus merkusii stands in highlands of northern Sumatra.

Closed broadleaved forests on (at least periodically) water-logged lands

Mangroves

Under tidal influence, mangroves are mainly found along the eastern shore of Sumatra, the western and eastern shores of Kalimantan, the western and southern shores of Bird¿s Head as well as the southern shore of Irian Jaya, and the shores of the Aru islands, with limited other areas in south-eastern Sulawesi and along the northern shore of Java (Martosubroto and Naamin, 1977). Their structure is simple and they constitute belts of (mainly) Rhizophora, Avicennia, Sonneratia, Ceriops, Xylocarpus and Lumnitzera species, determined by soil, current and inundation patterns. Tree heights are usually between 7 and 25 m. Large areas of mangrove, especially near the estuaries of major rivers, have been disturbed by extraction for fuelwood, charcoal and tannin production. Continuing cutting has given rise to thickets of the fern Acrostichum aureum and Acanthus spp., by which natural regeneration is greatly impaired.

Fresh water Swamp forests

These forests occur on alluvium with or without a thin layer of muck or peat, mostly along the lower course of rivers, behind the mangrove belt in areas more or less permanently freshwater-logged. Vast tracts are found on the eastern coast of Sumatra, the western coast of Kalimantan and in the basin of Irian Jaya north of the Central Range as well as in the whole southern part. Trees are of great height (emergents reach 50 to 60 m) and mostly of the same genera as those of the dryland rainforest, but of different species. These forests are floristically very variable with a local dominance more pronounced than in the dryland rainforests. The main families, genera and species are: Sapotaceae, Adina, Alstonia, Campnosperma, Coccoceras, Couthovia (Irian Jaya), Dillenia, Dyera, Erythrina, Eugenia, Lophopetalum, Memecylon, Metroxylon, Pandanus, Parkia (Irian Jaya), Serianthes (Irian Jaya), Shorea, Timonius (Irian Jaya) Pentaspadon motleyi and Vatica rassak. Sago palms are found extensively in this type in Irian Jaya. Periodic fires have a distinctively selective effect, leading to the predominant occurrence of fire-resistant species (e.g., extensive areas of Melaleuca leucadendron, that cover extensive areas in southern Sumatra, south-western Kalimantan and Irian Jaya).

Peat swamp forests

Peat swamp forests occur on alluvial lands with a peat layer from 0.5 m up to 20 m thickness, entirely rain-fed with highly acid, oligotrophic water conditions ("blackwater rivers"), almost sterile. The vegetation at the centre of the peat-dome is poor, scattered trees and Pandanus. Peat swamp forests are found only in ever-wet climates in Sumatra, Kalimantan and Irian Jaya. The main characteristic tree families, genera and species are: Sapotaceae, Alstonia, Amoora, Anisoptera, Calophillum, Campnosperma, Cratoxylon, Eugenia, Gonystylus, Jackia, Koompassia, Litsea, Lophopetalum, Melanorrhea, Parastemon, Shorea, Tristania, Zylopia, Combretocarpus rotundatus, Durio corinatus, and Tetramerista glabra.

Heath forests

Heath forests are found on podsolized siliceous soils under ever-wet conditions, with a hard pan of dark coloured humus substance at a depth of 1 to 2 m, temporarily inundated after heavy rain. Tree vegetation is similar to dryland rainforests but with thinner stems. Heath forests occur in the climatic zones of ever-wet conditions, mainly in Kalimantan, but also on Sumatra, Bangka, Belitung, Karimata, Anambas and Natuna Besar (Bunguran) islands and locally in Sulawesi and Irian Jaya. Dominant species in Kalimantan are Myrtaceae, Dipterocarpaceae (Shorea spp.) Gonystylus, Agathis, Dacrydium elatum, Styphelia and Bachea spp. Regrowth after destruction of the climax type is very slow, giving rise to "padang" vegetation of easily flammable brushwood between open sandy spaces. Vegetation on limestone hills, frequently found in southern Sulawesi, northern Irian Jaya and eastern Kalimantan, have a similar composition.

last updated: Monday, January 12, 2004