South Indochinese Vegetation

Plant Formations in the South Indochinese BioProvince

Peter Martin Rhind

South Indochinese Evergreen Forest Closed evergreen forest can be found, for example, in southern Vietnam where the high rainfall compensates for the short dry season. These are structurally complex with at least three vertical stories and have well-developed undergrowth of shrubs. The upper canopy can reach heights of up the 50 m and is typically dominated by dipterocarps such as Anisoptera cochinchinensis, Dipterocarpus alatus, D. costatus, D. dyeri, D. turbinatus, Shorea vulgaris and species Hopea. Other common trees include the endemic or near endemic Dalbergia cochinchinensis (Fabaceae) and Sindora cochinchinensis (Fabaceae). Apart from Dipterocarpaceae other common plant families are Ebenaceae, Fabaceae, Hypericaceae and Meliaceae.

South Indochinese Dry Evergreen Forest In the Kampong Thom area of Cambodia these forests are structurally complex with up to four vertical layers and range in height from 20-40 m. The main indicator species include the middle layer trees Carallia brachiata, Diospyros bejaudii, Syszygium grande and the endemic Sindora siamensis (Fabaceae), and the small tree Mitrella mesnyi, but at least two different stand types are recognized. The taller forests of up to 40 m have an upper canopy typically dominated by Anisoptera costata and Dipterocarpus costatus, while the main lower canopy species is Vatica odorata. In the shorter forests of up to 25 m the canopy is typically dominated by species of Syzygium and Vatica odorata, but these are often overtoped by the deciduous Dipterocarpus intricatus and the conifer Pinus merksii.

South Indochinese Deciduous Forest In Cambodia these can be divided into dipterocarp dominated forests and mixed forests. In the former there may be almost pure stands of Dipterocarpus obtusifolius in places, but in the mountainous areas north of Mondolkiri these forests become more diverse with the endemic Shorea siamensis (Dipterocarpaceae) being one of the main dominant species. In the Kratie area the dominants are Dipterocarpus tuberculatus, Shorea obtusa and Shorea siamensis. Other species encountered include the middle tier trees Anneslea fragrans, Gluta laccifolia, Mitragyna rotundifolia and the small tree Quercus kerii. Mixed deciduous forest can be found in the Mondolkiri area. Here the main components are species of Dalbergia and Lagerstroemia (such as Lagerstroemia calyculata) and Xylia xylocarpa. There is also a conspicuous presence of bamboos. In more northern parts of Vietnam similar forests are almost semi-deciduous with some trees (e.g. Tetrameles nudiflora and species Bombax) losing their leaves for an extended period during the dry season while others such as Dipterocarpus dyeri, D. turbinatus, Shorea talura and Sindora cochinchinensis only losing their leaves for a short period, in some cases for just a few days. Other common trees in these forests include Dipterocarpus tonkinensis, Pometia tomentosa and the endemic Endospermum chinense (Euphorbiaceae). In Vietnam there are also semi-closed deciduous forests largely dominated by species of Lagerstroemia particularly L. angustifolia, but also including L. duperreana, L. floribunda, L. macrocarpa and L. thorelii, together with Sindora cochinchinensis, Vitex pubescens and Xylia xylocarpa. The undergrowth is often dominated by bamboo particularly species of Oxytenanthera. These forests seem to be transitional between closed evergreen forests and fully open forests. In other places they are open with scattered trees and shrubs and a grassy ground layer. In general lianas and epiphytes diversity is comparatively low with most of the common epiphytes being large ferns of the genera Drynaria, Platycerium and Polypodium, but small succulent epiphytic vines like Dischidia and Hoya may also be Copyright © 2010 Peter Martin Rhind common. At ground level grasses often dominate and can reach heights of up to 1.5 m. Typical species include Heteropogon contortus, Imperata cylindrica and Themeda triandra. Nevertheless, there is still a relatively high diversity of herbaceous ground species including many geophytes.

South Indochinese Semi-Deciduous Forest These forests are widely distributed and constitute the main vegetation type of this BioProvince. On the so-called ‘terres rouges’ soil formed from basaltic material these diverse semi-deciduous forests can reach heights of up to 50 m. They also occur on deep alluvial soils developed from schistic and granitic material. The dominant canopy trees here include Adina cordifolia, Afzelia xylocarpa, Amoora gigantea, Anisoptera costata, Anogeissus acuminata, Cassia siamea, Celtis sinensis, Cratoxylum formosum, Dipterocarpus alatus, Heritiera javanica, Holoptelea integrifolia, Hopea odorata, Irvingia malayana, Lagerstroemia angustifolia, Palaquium obobatum, Peltophorum dasyrachis, Pometia pinnata, Pterocarpus macrocarpus, Pterospermum megalocarpus, Schleichera oleosa, Shorea guiso, Sindora siamensis, Sindoricum indicum, Sterculia hypochra, Swintonia griffithii, Syzygium zelandicum, Terminalia bellirica, Tetrameles nudiflora, Toona ferifuga, Vitex pubescens and the endemic or near endemic Dracontomelum duperreanum (Anacardiaceae). The subcanopy also includes a rich diversity of trees. Typical species include Baccaurea oxycarpa, Diospyros nitida, Gelonium multiflorum, Gironniera subaequalis, Harpullia arborea, Knema linifolia, Lagerstroemia flos-reginae, Macaranga henricorum, Macropanax concinnum, Miliusa velutina, Polyalthia evecta, Symplocos longifolia, Xerospermum laoticum and the near endemic Polyalthia jucunda (Annonaceae). In the undergrowth there are often dense stands of bamboo particularly Bambusa arundinacea and B. beecheyi together with Pandanus species. The latter can form dense tickets along riversides. At ground level large grasses and herbs of the families Araceae, Marantaceae and Zingiberaceae are common. The trees typically support many lianas and epiphytes particularly in the more humid riverine areas.

South Indochinese Swamp Forest These forests occur throughout the BioProvince in swampy areas and are also found on wet sandy soil in the Kampong Thom area of Cambodia. In Cambodia Melaleuca cajuputi seems to be the exclusive dominant of many of these forests, while other species include Parinari annamensis. Vast areas of swamp forest also occur in Mekong floodplains. Typical species here include Adina cordifolia, Calophyllum inophyllum, and Sandoricum indicum together with species of Eugenia, Elaeocarpus and Sterculia. Palm species are conspicuous and in some areas almost pure stands of the endemic Livistona cochinchinensis (Arecaceae) occur. Melaleuca cajuputi is also common here particularly in exploited valley bottoms or on humus-rich soils where it forms stands with bushes of Alstonia spathulata, Polybotrya appendiculata and Stenochlaena palustris. On more sandy soils Melaleuca cajuputi forms assemblages with other species such as Ilex godajama. In the immediate hinterland of mangroves forest in areas less affected by brackish water another species of Melaleuca (M. leucadendron) can be found.

South Indochinese Mountain Forest In Vietnam forests at increasing altitudes are characterized by a gradual reduction in dominating trees and an increasing abundance of epiphytes. Dipterocarps slowly peter out with Hopea odorata up to about 800 m, Shorea obtusa up to about 900 m and Dipterocarpus obtusifolius up to about 1300 m. These are gradually replaced by Lauraceae taxa like Phoebe cunata and species of Cinnamomum and Lindera, together with Fagaceae taxa such as species of Castanopsis, Lithocarpus and Quercus, and species of Juglandaceae, Magnoliaceae and various conifers. In fact, conifers can be a

Copyright © 2010 Peter Martin Rhind major compoent of these upland forests and may include Pinus dalatensis, Taxus buccata, together with species of Glyptostrobus, Libocedrus and Podocarpus. In the mountainous areas in more northern parts of Vietnam mountain forests are the dominant vegetation types. Here conifers such as Fokienia hodginsii, Keteleeria davidiana, Pinus armanda and P. kremptii dominate together with species of Ericaceae and Fagaceae.

Further information required.

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