Included here are lower courses of the Ganges and Brahmaputra, the lowlands of Orissa north of the Mahanadi River and the tropical parts of Assam, Manipur, Nagaland and Tripura. Thre type of seasonal forest are recognised: semi-evergreen, moist deciduous and dry deciduous

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 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.

References

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Champion, H. G. & Seth, S. K. 1968. A revised survey of the forest types of India. The Manager of Publication, Government of India, Nasik.

Giri, G. S. & Nayar, M. P. 1983, Some Threatened Plants of Bengal Plains. In: An assessment of the threatened plants of India. Eds. S. K. Jain and R. R. Rao.Botanical Survey of India. Botanic Garden Howrah.

Kundu, S. R. 2004. Studies on the endemic plants of West Bengal. Geobios, 31: 61-64.

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Puri, G. S., Gupta, R. K., Meher-Homji, V. M. & Puri, S. 1989. Forest Ecology. Plant form, diversity, communities and succession. 2nd Edition. Volume 2. Oxford & IBH Publishing Co. PVT. Ltd.

Rao, A. S. 1974. The vegetation and phytogeography of Assam-Burma. In: Ecology and Biogeography in India. Ed. M. S. Mani, 178-196. Dr W. Junk B. V. Publishers The Hague.

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