Included here are tropical parts of Laos, Vietnam, Cambodia and a small part of Thailand.

North Indochinese Calcareous Evergreen, Semi-Evergreen and Mixed Montane Forest

The ancient montane karst lands of North Indochina support rich forests up an altitude of about 1700 m. Several zones can be distinguished. At the lowest elevation (300-900 m) evergreen forests predominate and these give way to semi-deciduous and conifer forests at higher elevation (1400-1700 m). The evergreen stands are closed, wet forests with a canopy heights ranging from 25-30 m, but emergent trees can reach heights of up to 50 m. Dominant upper tier trees may include Burretiodendron hsienmu, Hopea mollissima, Ormosia balansae, Phoebe angustifolia and Symingtonia populnea. The sub-canopy and undergrowth strata comprise numerous trees and shrubs from a wide variety of families. Typical genera include Canthium (Rubiaceae), Callophyllum (Clusiaceae), Dimerocarpus, Ficus, Streblus, Teonongia (Moraceae), Diospyros (Ebenaceae), Eriobotrya (Roaceae), Heritiera, Pterospermum (Sterculiaceae), Jasminum (Oleaceae), Mitrephora (Annonaceae), Murraya (Rutaceae), Sinosideroxylon (Sapindaceae), Trigonostemon (Euphorbiaceae) and Xerospermum (Sapindaceae).

The semi-deciduous and conifer forests tend to be more open. Typical conifers include Pinus kwangtungensis, Pseudotsuga brevifolia and Tsuga chinensis, but various other gymnoperm trees may be encountered such as Amenthotaxus argotaenia, Cupressus torulosa, Dacrycarpus imbricatus, Dacrydium elatum, Forkienia hodginsii, Keteleeria davidiana, Nageia fleurii, Podocarpus neriifolius, Taxus chinensis and the endemic or near endemic Cephalotaxus manni (Cephalotaxaceae) and Xanthocyparis vietnamensis (Cupressaceae). Cycads are also well represented with species such as Cycas balansae, C. diannanensis, C. miquelii, C. multifrondis and C. taiwaniana. The upper deciduous and semi-deciduous elements include Platycarpa strobilacea and species of Acer, Alangium, Carpinus, Lithocarpus, Quercus and Ulmus. At sub-canopy level, species such as Illicium difengpi, Pistacia weinmannifolia, Schefflera pes-avis, Tirpitzia sinense predominate together with species of Euonymus, Madhuca, Photinia and Sorbus. Shrubs and small trees include numerous species of Rhododendron and Vaccinium together with species of Celastrum, Lespedeza, Pittosporum, Sophora and Wikstroemia. The undergrowth may also include various dwarf palms including species of Guihaia, Livistona, Licuala and Rhapis. The herbaceous layer is extremely rich particularly in the higher more open forests where ground level light levels are much higher. Typical herbaceous genera include Alpinia, Airnsliaea, Arisaema, Aspidistra, Begonia, Disporum, Elatostema, Hedychium, Laportea, Lysimachia, Ophiopogon, Peliosanthes, Pellea, Pellionia, Polygonatum, Selaginella and Tupistra. There are also a number of interesting succulent forms of Impatiens and many species of Carex and Scleria (sedges), but orchids again reach extraordinary levels of abundance and diversity. Many of the ground layer or terrestrial species growing in the undergrowth or on rocks and bluffs are large and shrubby and can reach heights of over one metre. These include Acampe rigida, Aerides rosea, Cleisostoma paniculatum, Hygrochilus parishii, Flickingera fimbriata, Renanthera coccinea, Thrixspermum calceolus, Vanda fuscoviridis, Vandopsis gigantea and the endemic or near endemic Renanthera vietnamensis (Orchidaceae). There also a number of species that appears to obligate lithophytes such as Cheirostylis bipunctata, Hemipilia calophylla, Liparis cordifolia, Oberonia ensiformis, Paphiopedilum helenae, Thunia alba and the endemic or near endemic Cheirostylus cochinchinensis and Paphiopedilum vietamense (Orchidaceae). As is often the case the epiphytic flora is also extremely rich in orchids many of which are regarded are obligate epiphytes although some are also occasionally found on limestone in these semi-deciduous forests. Typical species include Bulbophyllum hirtum, Chiloschista trudelii, Cleisostoma birmanicum, Cryptochilus lutea, Dendrobium cariniferum, Epigeneium chapaense, Gastrochilus minutiflorus, Halcoglossum wangii, Liparis delicatula, Luisia morsei, Phalaenopsis lobbii, Porpax lanii, Schoenorchis gemmata, Thelasis pygmaea and Trichotosia velutina.

North Indochinese Acidic Evergreen Forest

These forests of acidic, silicate soils range from the lowlands to an altitude of about 1000 m. They are mostly are very wet and very closed, and the largest trees can reach heights of 50 m and have diameters of more than 2 m. Among the dominant canopy families are Fabaceae, Fagaceae, Lauraceae, Magnoliaceae and Myrtaceae, while common genera from other families include Acer (Aceraceae), Swintonia (Anacardiaceae), Anisophyllea (Anisophylleaceae), Alstonia (Apocynaceae), Canarium (Burseraceae), Calophyllum (Clusiaceae), Dipterocarpus (Dipterocarpaceae), Elaeocarpus (Elaeocarpaceae), Macaranga (Euphorbiaceae), Ixonanthes (Ixonanthaceae), Aglaia (Meliaceae), Artocarpus (Moraceae), Celtis (Ulmaceae), Sapindus (Sapindaceae), Scaphium (Sterculiaceae) and Schima (Theaceae). In the wetter conditions at altitudes above 600 m gymnosperms become a major component of the canopy with species such as Dacrycarpus imbricatus, Dacrydium elatum and Podocarpus neriifolius. Several other tree strata can often be distinguised ranging from 5-15 m. Common genera among these are Ilex (Aquifoliaceae), Garcinia (Clusiaceae), Elaeocarpus (Elaeocarpaceae), Baccaurea (Euphorbaceae), Lithocarpus (Fagaceae), Apodytes (Icacinaceae), Engelhardtia (Juglandaceae), Lindera (Lauraceae), Manglietia (Magnoliaceae), Chisocheton (Meliaceae), Horsfieldia (Myristicaceae), Cinnamonmum (Myrtaceae), Pygeum (Rosaceae), Meliosma (Sabiaceae), Mischocarpus (Sapindaceae), Symplocos (Symplocaceae), Pyrenaria (Theaceae) and Xanthophyllum (Xanthophyllaceae). Lianas like Ancistrocladus cochinchinensis and Pseudostachyum polymorphum are important together with strange orchid lianas like Arachnis annamensis, Callostylus rigida, Epigeneium ampilum, Renanthera annamensis, Staurochilus fasciatus, Thrixspermum centipeda and the remarkable leafless, achlorophyllous, mycotrophic Galeola nudifolia which can reach 10 m or so in length. Mention should also be made of the rattans. Species such as Calamus bousinggonii, C. pseudoscuttellaris and C. tetradactylus can be important particularly in the uplands.

The herb layer of these shady, humid forests is also surprisingly rich with orchids again being one of the most conspicuous groups. Some of the common orchids include Acanthephippium odoratum, Anoectochilus roxburghii, Calanthe lyroglossa, Cephalantheropsis longipes, Corymborkis veratrifolia, Cymbidium sinense, Geodorum densiflorum, Habenaria seshagiriana, Hetaeria pauciflora, Liparis nigra, Ludisia discolor, Malaxis octodentata, Paphiopedilum callosum, Phaius flavus, Tainia angustifolia and Tropidia curculigoides. Also at ground level are a number of the unusual achlorophyllous, mycotrophic orchids like Aphyllorchis annamensis, Didimoplexiopsis khiriwongensis, Epipogium roseum, Lecanorchis javanica and Stereosandra javanica. Not surprisingly the epiphytic flora of these humid forest is very rich with orchids again being one of the most important groups. In fact, more than half of all the orchids of these forests are epiphytes. Commonly occurring species include Acampe ochracea, Acriopsis indicam Aerides falcata, Agrostophyllum brevipes, Appendicula hexandra, Bulbophyllum affine, Ceratostylis radiata, Cleisostoma duplicilobum, Dendrobium amabile, Eparmatostigma dives, Eria acervata, Flickingeria forcipata, Gastrochilus intermedius, Liparis elliptica, Luisia pysche, Microptera poilanei, Ornithochilus difformis, Pholidota leveleana, Polystachya concreta, Pomatocalpa spicata, Pteroceras leopardinum, Robiquetia succisa, Sarcoglyphis mirabilis, Thecopus maingayi, Thecostele alata, Thrixspermum pauciflorum, Trias nasuta and Trichotosia dalatensis.

References

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Campbell, D. G. & Hammond, H. D. 1989. Floristic Inventory of Tropical Countries. The New York Botanical Garden.

Vidal, J. E. 1979. Outlines of the ecology and vegetation of the Indochinese Peninsula. In: Tropical Botany. Eds. K. Larsen and L. B. Holm-Nielsen. Academic Press.

Vidal, J. E. 1997. Paysages vegetaux et Plantes de la Peninsule indochinoise. Karthala and Agency of Francophony, Paris.

Walker, E. H. & Pendleton, R. L. 1953. A survey of the vegetation of southeastern Asia. The Indo-Chinese Province of the Pacific Basin. Proceedings of the 8th Pacific Science Congress, 4: 99-144.

Werger, M. J. A., Nghia, N. H. & Zuidema, P. A. 1967. Demography of threatened tree species in Vietnam. Plant Ecology and Plant Science Group, Utrecht University, Tropenbos International and the Forest Science institute of Vietnam.

Williams, L. 1965. Vegetation of Southeast Asia. Studies of Forest Types. 1963-1965. Agricultural Research Services. U.S. Department of Agriculture.