Included here are tropical parts of Laos, Vietnam, Cambodia and a small part of Thailand. The seasonal forests can be broadly divided into deciduous and semi-deciduous types.

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 andspecies 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 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.

Indochinese Semi-Deciduous Forest

These forests are widely distributed and constitute the main vegetation type of this area. 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.


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