India is one of the 17 Megabiodiverse countries in the world and accounts for 7-8 % of the recorded species. The State of Assam is a constituent unit of the Eastern Himalayan Biodiversity Region; one of the two biodiversity “Hot Spots” in the country .The climatic condition and wide variety in physical features witnessed in Assam have resulted in a diversity of ecological habitats such as forests, grasslands ,wetlands, which harbour and sustain wide ranging floral and faunal species placing
The word “Assam” has its origin in the Sanskrit Word “Asom” meaning unparalleled or peerless. Indeed Assam is unparalleled as nature has been uniquely generous in endowing the State with such bounties that Assam is part of one of the 25 mega diverse region on planet earth.
However, today, Assam is not only more fancied, but also known for its ecological diversity, for the range of floral and faunal species and for the conservation successes achieved. Kaziranga, Manas, Pobitora, Orang, Dibru-Saikhowa are names recognized world over and bring laurels to the people of this magnificent State.
The forest in Assam can be described into following types/ sub types.
– Tropical Wet Evergreen Forests.
– Tropical Semi Evergreen Forests.
– Tropical Moist Deciduous Forests.
– Sub-tropical Broadleaf Hill Forests.
– Sub-tropical Pine Forests.
– Littoral and Swamp Forests.
– Grassland and Savannahs.
Tropical Wet Evergreen Forests are found in the districts of Golaghat, Jorhat, Sibsagar, Tinsukia, Dibrugarh and in a narrow stretch in Lakhimpur and Dhemaji districts along foot hills. These forests also occur in the southern part of the State at lower elevations in Borail Range, and in Loharbund, Sonai, Longai and Dholia Reserve Forests in Cachar and Karimganj Districts.
Hollong (Dipterocarpus macrocarpus), the tallest tree of Assam and also the “State Tree” is the most predominant constituent of these forests. The associated species are Borpat, Jutuli ,Sam, Dewa sam, Nahar , Teeta chap, Bhelu, Mekai etc.
Forests in Southern Assam have, however, Dipterocarpus terbinatus(Garjan) in association with Mesua ferrea ( Nahar), Mesua floribunda ( Bolong)), Michelia glabra (Champ), Palaquium polyanthum (Kathalua) etc
One witness luxuriant growth of epiphytes and trees with fissured bark support magnificent ornamental orchids of Assam. Lianas, vines and climbers are plentiful twining round trees in middle canopy. Almost all the tree ferns of Assam growing majestically in these forests present a treat to the eyes. The undergrowth is dense with both low shrubs and herbs occupying the space. Canes, palms and bamboos grow along edges of forests.
Tropical Semi Evergreen Forests occur mostly in Hallangapar, Abhoypur, Dilli, Dhansiri, Kholahat, Mayong, Garbhanga, Rani, Mahamaya, Guma, Haltugaon, Kachugaon, Gali, Pobha, Ranga, Kakoi, Nauduar, Batasipur, Dohalia, Singla, Longai, Bhuban Pahar, Sonai, Barak and Inner Line Reserve Forests along Northern and Southern parts of the State.
These forests have mostly medium size trees with few large trees. Shrubs, lianas, climbers, orchids and ferns grow copiously. At the fringe bamboos and canes occupy the space.
Species association and frequency of their occurrence vary from forest to forest, but the ones commonly found are Actinodaphne obovata (Petarichawa), Aesculus species (Ramanbih), Artocarpus chama(Sam), Albizia species(Siris, Sau, Koroi), Anthocephalus chinensis (Kadam), Duabanga grandiflora (Khakan), Castonopsis species (Hingori, Dhobahingori, Kanchan),Dillenia indica (Ou-tenga), Bauhinia purpurea ( Kanchan), Lagerstroemia species( Jarul, Ajar,Sidha), Magnolia species(Phulsopa, Gahorisopa, Pansopa, Kharikasopa, Kathalsopa, Duleesopa),Mallotus species( Sinduri, Joral, Dudhloti, Buritokan), Michelia champaca(Teeta campa), Syzygium species( Paharijam, Mokrajam, Berjamu, Kolajamu, Bogijamu, golapjamu). Schima wallichii (Bolem,Ghugra), Terminalia species, ( Hilikha, Bohera, Bhomora), Trewia nudiflora( Bhelkor), Hatipolia, Holok etc.
Moist Deciduous Forests can further be described as Sal Forests and Mixed Deciduous Forests. Sal Forests occupy considerable forest area in the Central and Lower parts of the State in the Districts of Nagaon, Morigaon, Kamrup, parts of Nalbari and Barpeta, Darrang, Dhubri, Kokrajhar and Goalpara.
In these forests, Sal grows in association with Lagerstroemia species( Jarul, Ajar), Schima Wallichii( Ghugra), Stereospermum personatum (Paruli), Adina cordifolia (Haldu), Artocarpus species ( Sam), Ficus species( Bor, Dimoru, Dhupbor, Bot, Athabor, tengabor, Lotadioru, Khongaldimoru), Bischofia javanica (Uriam), Gmelina arborea (Gomari), Michelia champaca(Teeta champa), Terminalia species (Hilikha, Bhomora, Bohera). Toona ciliate (Poma) etc.
Moist Deciduous Mixed Forests occur at the foot of hills in Lakhimpur, Dhemaji, Karbi-Angong and N. C. Hills districts. Trees are mostly deciduous with Sprinkling of few evergreen and semi-evergreen species. Important plant species growing in these forests include Adina cordifolia9 Haldu), Albizia species(Siris, Kolasiris, Koroi, Sau) Alstonia scholaris(Satiana), Artocarpus chama (Sam), Careya arborea( Kumbhi), Dalbergia species(Sissoo, Medelua), Ficus species (Bot, Bor, Dimoru), Lagerstroemia species (Jarul, Ajar), Mallotu species (Senduri, Joral, Dudhloti) etc.
These forest harbour rich diversity of shrubby and herbaceous ground vegetation. Some of the Reserve Forests also have teak plantations.
Bordering Moist Deciduous Forests in rain shadow areas are found forests which has been referred to as “Dry Forests” by Kanjilal. This type of forests are encountered in the Lumding, Langting, Mailongdisa Reserve Forests. A typical example is the Umananda Island in the middle of Brahmaputra North of Guwahati. Important species include, Aegle marmelos(Bel), Albizia species(Siris), Cassia fistula(Sonaru), Bombax (Simul), Alstonia scholaris(Satiana), Ficus species(Bor), Litsea species( Loban, Bagnola, Mezankori, Honwalu,Digloti) Melia azedarach( Neem), Moringa oleifera(Sajana), Orosylum indicum(Bhatgila), Mallotus species(Senduri), Terminalia species(Hilikha,Bhomora) etc.
Sub-tropical Broad Leaf Hills forests and Sub-tropical Pine forests occur in the districts of Karbi-Anglong and N. C. Hills. Species commonly occurring are Alseodaphne petiolaris(Ban-hanwalu), Antidesma bunius, Betula alnoides, Cleidon speciflorum etc. Higher up pure stands of Pinus kesiya(Khasi-pine) are found particularly in the Hamren sub-division in Karbi-Anglong district.
Grass land and Savannahs are grass dominated biomes and form the major part of vegetation in Kaziranga National Park, Pobitora, Orang, Sonai-Rupai, Laokhowa, Barnadi, Burachapori, Dibru-Saikhowa Wildlife Sanctuaries and some part in Manas National Park. Grasslands support important wildlife population in Assam. Important grasses are Apluda mutica, Phragmatis karka, Sclerostachya fusca, Saccharum species etc. These species grow gregariously at the onset of monsoon and grow even upto 6 meters tall.
Littoral and Swamp forests have almost lost their identity because of biotic pressure on land. Presently sedges and grasses form the largest component of vegetation. Important species include Ageratum conyzoides, Alocasia species, Alpinia species., Amaranthus species., Bacopa species., Blumea species., Bombax species., Crotolaria species. etc.
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