Bengal Vegetation

Plant Formations in the Bengalian BioProvince

Peter Martin Rhind

Bengalian Tropical Evergreen Forest In places such as the Patloi Range and Naga Hills in the Assam Valley these forests are characterized by the giant dipteropcarps Dipterocarpus macrocarpus and Shorea assamica, which can attain heights of up to 50 m. They often occurs as emergents standing over a canopy at about 30 m. Common canopy trees are species of Mesua (such as M. ferrea) and Vatica (such as V. lanceaefolia), but many others occur such as Altingia excelsa, Amoora wallichii, Artocarpus chaplasha, Canarium species, Dysoxylum procers, Stereospermum personatum and the endemic or near endemic Mallotus roxburghianus (Euphorbiaceae). There is also a rich understory of bamboos, palms and shrubs such as Bambusa pallida, Livistona jenkinsiana, Pseudostachyum polymorphum and the endemic bamboo Dendrocalamus hamiltonii (Poaceae). Climbers and epiphytes are also well represented but the shaded ground layer can be almost devoid of plants. On the other hand, colourful species such as Thunbergia grandiflora may be present. In the upper Assam Valley these forests eventually give way to tropical evergreen forests of a lower stature. These include forests dominated by Kayea assamica (Kayea Forests), found on the northern bank of the Brahmaputra Valley, and forests dominated by species of Mesua (Mesua Forest), which occur, for example, in the foothills of the Balipara Frontier.

Bengalian Tropical Semi-Evergreen Forest Forests made up of predominantly evergreen trees but with varying amounts of deciduous species extend from Puri in Orissa to Assam. The deciduous components include some of the more typical species and usually lose their leaves for a short period during the dry season. These forests have a dense canopy reaching heights of up to 36 m and a well- developed middle storey. In West Bengal the characteristic canopy trees include Ailanthus grandis, Canarium sikkimense, Castanopsis indica, Eugenia formosa, Mangifera indica, Michelia champaca, Phoebe hainesiana, Talauma hodgsoniii, Terminalia myriocarpa and Tetrameles nudiflora. Among the common sub-canopy trees are Amoora wallichii, Gynocardia obovata, Meliosma simplicifolia, Turpinia pomifera and the endemic or near endemic Actinodaphne obovata (Lauraceae). In the undergrowth bamboos are largely absent but there are many evergreen shrubs, particularly of the Rubiaceae, and perennials. Species may include Curcuma aromatica and Leea crispa. Climbers and epiphytes are common.

Bengalian Tropical Moist Deciduous Forest (Sal Forest) It is often possible to divide these forests into either Sal (Shorea robusta) or mixed deciduous types, but the predominance of Sal in certain areas is probably due to years of human intervention. It is generally more aggressive than its associates and can regenerate well under both grazing and burning management. Consequently, it now constitutes up to 90% of the canopy in places. In West Bengal associated canopy species include Aphanamixis polystachya, Canarium sikkimense, Castanopsis tribuloides, Cedrella microcarpa, Chukrasia tabularis, Dillenia pentagyna, Duabanga grandiflora, Ficus indica, Gmelina arborea, Lagerstroemia parviflora, Litsea macropetala, Schima wallichii, Sterculia villosa, Syzygium cumini, Terminalia bellerica and T. tomentosa. The canopy is normally fairly dense and can reach heights of up to 40 m. The second story typically includes Aporosa roxburghii, Baccaurea sapida, Bahinia purpurea, Bridelia retusa, Careya arborea, Caryota urens, Castanopsis indica, Dendrocalamus hamiltonii, Emblica officinalis, Firmiana colorata, Garuga pinnata, Grewia vestita, Helicia erratica, Heynea trijuga, Machilus glaucescens, Mallotus philippensis, Oroxylum indicum, Premna corymbosa and Copyright © 2010 Peter Martin Rhind Sarcosperma arboreum. There is usually shrubby undergrowth of mainly evergreen shrubs but bamboos are largely absent. Shrub species typically include Ardisia solonacea, Dendrocnida sinuata, Maesa macrophylla, Mussaenda glabrata and the endemic or near endemic Coffea bengalensis (Rubiaceae). Climbers can be conspicuous and often festoon the crowns of trees particularly in the more open stands, but the number of species is relatively small. Examples include Bauhinia vahlii, Cissus repanda, Ichnocarpus frutescens, Mucuna macrocarpa and Dioscorea species. Epiphytes are also prominent especially in shaded areas and are mainly represented by epiphytic orchids and ferns.

Bengalian Tropical Dry Deciduous Forest Remnants of these forests can be found throughout this BioProvince particularly in parts of West Bengal and Orrisa, but possible the best examples occur of the Chhota-Nagpur Plateau, which extends through the states of Bihar, Madhya Pradesh and West Bengal. In their climax state these forests usually have a thin but fairly complete canopy, but can be open in some of the dryer areas. On the Chhota-Nagpur Plateau the main trees include Anogeissus latifolia, Aegle marmelos, Croton oblongifolius, Lagerstroemia parviflora, Pterocarpus marsupium, Shorea robusta, Symplocos racemosa, Syzygium operculatum and Terminalia alata. The canopy can reach heights of up to 25 m and there is usually a sub-canopy at between 10-15 m. The shrub layer ranges from about 3-5 m. These forests support a number of endemic plants such as Aglaia haselettiana (Meliaceae), Carum villosum (Apiaceae) and Pycnocycla glauca (Apiaceae), but also a number of critically endangered species such as Butea monosperma, Diospyros melanoxylon, Madhuca longifolia and Shleichera oleosa. Away from the plateau species composition of these forests varies somewhat. In the districts of Bankura, Birbhum and Puruliya in West Bengal the main canopy trees include Bridelia squamosa, Buchanania lanzan, Butea monosperma, Cochlospermum religiosum, Diospyros exculpta, Haldina cordifolia, Madhuca indica, Schleichera oleosa, Shorea robusta, Sterculia urens, Tectonia grandis, Terminalia arguna and T. chebula. The shrubs include Antidesma acidum, Flacourtia indica, Meyna spinosa, Woodfordia fruticosa and Zizyphus rugosa, while common climbers are Aristolochia indica, Asparagus racemosus, Combretum roxburghii, Derris scandens and Tinospora cordifolia.

Bengalian Sundarbans Tidal Forest The tidal forests of Sundarbans occupy some 7800 km2 and represent the most extensive stretch of mangroves forest in the world. They are subject to massive amounts of freshwater flushing from upland snowmelt and the heavy monsoonal rainfall and so salinity remains relatively low. In fact, one of the principal trees Heritiera fomes has little adaptive tolerance to high salinity and is unknown from any other mangrove swamp. Nevertheless, virtually all plants of this ecosystem are distributed according to variations in salinity caused by tidal inundation. In the Sundarbans of Bangladesh the main arboreal species include Dalbergia spinosa, Heritiera fomes, Phoenix paludisa and Sonnerata apelata, while the nipa palm Nypa fruticans is abundant in the most frequently inundated, low salinity areas adjacent to riverbanks. In the driest areas typical mangrove species become less conspicuous while species like Casuarina equisetifolia, Ipomoea pescapre, Pongamia pinnata, Tamarix dioica and Vitex trifolia often dominate. The mangroves Rhizophora apiculata and R. mucronata occur in southern areas but are mostly shrub-like and in fact, species of Rhizophora are generally of minor importance compared with most of the other world’s mangrove swamps. On the other hand, the Sundarbans support a huge diversity of plants but very few are of economic importance. Some other the typical herbacous species include Cyperus tegetiformis, Fimbristylis ferruginea, Mariscus albescens, Bulbophyllum xylocarpi, Dendrobium rhizophoretii, Pandanus fascicularis, Andropogon squarrosus, Oryza coarctata, Zoysia pungens, Typha elephantina, Finlaysonia maritima, Hoya

Further information required.

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