Included here is Borneo (Kalimantan) and adjacent islands such the Bunguran (Natuna) Islands, Calamian Islands, Jolo Island, Laut Island, Palawan Island, Pangutaran Islands and the Tawitawi Islands.

Bornean Dipterocarp Lowland Rainforest

In these forests Dipterocarpaceae with some 267 species, 155 of which are endemic, dominate.  In fact, Borneo is the world’s epicenter for dipterocarp diversity producing some of the tallest forests on earth. One species, Koompassia excelsa (Fabaceae) regularly exceeds 60 m and some individuals have nearly reached 90 m. In fact, this tree is regarded as the tallest broadleaf tree in the world. These luxuriant forests have a complex vertical structure with at least two tree layers and a shrub layer. The canopy normally reaches heights of about 36 m, but often towering above this are various emergents that can exceed 60 m. Most of these emergents are dipterocarps of the genera Dipterocarpus, Dryobalanops and Shorea, but may also include several other genera such as Koompassia (Laurelaceae). Among the larger endemic species are Dryobalanops beccarii and Shorea ferruginea (Dipterocarpaceae). The canopy also includes many dipterocarps of the genera Hopea and Vatica, but in addition, species of the Berseraceae and Sapotaceae are also well represented. Many of these canopy trees are endemic and include, for example, Carallia borneensis (Rhizophoraceae), Chisochaeton setosus, Dysoxylum pachyrache, Sandoricum borneense (Meliaceae), Crypteronia borneensis (Crypteroniaceae), Dipterocarpus stellatus, Shorea quadrivervis, Upuna borneensis (Dipterocarpaceae), Gonystylus borneensis (Thymeleaceae), Gymnacranthera contracta, Myristica borneensis (Myristiacaeae), Hydnocarpus borneensis, Ryparosa kostermansii (Flacourtiaceae), Lithocarpus ferrugineus (Fagaceae), Meliosma sarawakensis (Sabiaceae), Sarcotheca macrophylla (Oxalidaceae), Semecarpus rufo-velutinus (Anacardiaceae), Scaphium borneensis (Sterculiaceae) and Scorodocarpus borneensis (Olacaceae). Below is a sub-canopy layer of smaller, shade tolerant trees, which includes a number of families, but species of the Euphorbiaceae are particularly well represented. This layer is also characterized by the presence of many species, such as Durio testudinarum, that bear their flowers and fruit on their trunks – a phenomenon known as caulifory. Among the many endemic smaller trees are Gonocaryum minus (Thymelaeaceae), Horsfieldia tenuifolia, Knema minima (Myristicaeae) and Sandoricum caudatum (Meliaceae).

The shrubs layer is again rich in endemic species such as Magnolia persuaveolens (Magnoliaceae), Rinorea iliaspaiei (Violaceae), Thottea curvisemen (Aristolochiaceae) and Vaccinium bigibbum (Ericaceae). Draping over many of the trees are various lianas and climbers such as the endemic Phytocrene racemosa (Icacinaceae) and Bauhinia sylvani (Anacardiaceae) and various semi-parasitic aerial shrubs of the family Loranthaceae including endemics like Macrosolen brevitubis and Trithecanthera flava. Epiphytes, including many bryophytes, ferns and orchids cling to virtually all-damp substrates at all levels of the forest. In addition, there are many epiphylls i.e. species that can colonize the surface of leaves such as various algae, bryophytes and lichens. On the forest floor, herbs such as the endemic Tacca bibracteata (Taccaceae), seedlings and shade-tolerant palms exploit the few places that receive light. A striking feature of many of the rainforest herbs is the red and silver colouring and variegation of their leaves, which is apparently an adaptation to exploit the meager, light levels in these dark forests.  The forest floor is also the place to find the spectacular Rafflesia plants including Rafflesia arnoldii, which produces the largest flowers in the world. Its huge red-brown flowers can measure up to a 60 cm across. Another giant is Dawsonia superba, the largest moss in the world, which can grow up to a metre in length. Other species include the endemic Rafflesia keithii and R. pricei (Rafflesiaceae).  Rafflesias are all parasitic plants with no leaves and derive their sustenance from the ground vine Tetrastigma leucostaphylum. Their flowers smell like rotting meat, which attracts the attention of various insect pollinators.

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