Forest Types of Assam : Assam Geography
Forests of Assam have rich biodiversity of flora and fauna. It has a wide range of forests viz. Evergreen and Semi Evergreen forests, Mixed Deciduous forests, Sal forests, Riverine forests, Moist Savannah, Dry Savanna and Dry Miscellaneous type of forests. Managing these vast natural and life sustaining ecosystems is a herculean task in itself. The State Government accords top most priority for the conservation of these diverse ecosystems while keeping the needs and aspirations of the people into consideration and remembering that we owe this for the future generations.
The climatic conditions cause prevalence of highly humid weather coupled with heterogenic physiography Assam a distinct identity phyto-geographically, many a species are endemic to this region and it is also the center of origin for commercially important plants including Banana, Citrus, Mango, Zizyphus, and Tea.
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.
Evergreen forests – The reserved forests of the State are distributed mainly in a few definite areas .These are along the foothills of the Himalayas; in deep alluvial land commonly known as the Bhabar and Terai tracts; along the southern edge of the Brahaputra Valley, touching the foothills of the central hilly region and lastly in the hills surrounding valley of the Barak and its tributaries.
The evergreen forests of most of the districts are composed of broad leafed species where rainfall is usually heavy. Both evergreen and semi-evergreen forests flourish in alluvial soil having capacity to retain water. Heavy rainfall exceeding 254 cms a year is required for their growth. Distribution of plants depends on rainfall and geographical configuration of the country. In heavy rainfall areas, the incidence of plants of different varieties is also heavy.
The main species found in these forests are Sal, Bonsum, Titasopa, Hollock, Khokan, Gameri and other species. Usually these forests contain from Sal (Shorea robusta) to miscellaneous evergreen forest trees.
It appears that both evergreen and semi-evergreen forests are represented by varieties of important trees. It may also mention that Sal is one of the important naturally durable timber species of India, which predominates in the southern part of Kamrup district.
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.
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 cordifolia 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.
This type of forests occur in patches in most of the reserved forests of the State particularly in North Kamrup, Darrang, Sonitpur, Kokrajhar, Dhubri, Bangaigaon, Goalpara and Nowgong.
In Central Assam, Dry Savannah type forest occurs in open areas in dry miscellaneous forests and are characterised by species like Ulu, Khagari and other grasses. Besides, grasses like Ikara and Nal are also in this type of forests. Sporadiccaly in certain areas under this type species like Bejaowe, Simul Sida, Udal, Jamuk ,Kuhir, Khoir, Bohera, Kum,etc.,are also found.
The grass forests of Savannah type gets burnt every year making the soil very dry and unfit for the invasion and establishment of other species towards the climax forests. But whenever for some reasons fire cannot penetrate, there is a tendency towardsmixed deciduous forests. Though at present such forests have not got much commercial
importance except for catering to the needs of the villagers for the grazing of cattle and requirement of agricultural and constructional materials, great improvement can be made to such forests by improving the stock by artificial regeneration and complete protection from fire.
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.
In the riverine forests, Simalu (Bombax malabaricum) and Sisso (Dulbergia Sissso) are found. In the district of Kamrup, evergreen trees contain Bhelu (Trameles grandis), Satiana, Amari, Gandhsorai, Poma, Bogipoma, Titasopa, Bota (Morus Lacvigata) Bhomora, Silikha, Paruli (Stariospermum Chelenoides), Dhuna, Gogra, Maz, Seling, Borhamthuri, Jaipoma, Gohara, Owtenga, Sal, Jamuk, Koliori, Uriam, Letaku, Ritha, Rudrakhya, Thekera, etc.
Most of these trees as useful as timber, medicinal matter and food. The riverine forests of the State are mainly found along the banks of big streams or Chaparis of big rivers. The forest areas found in Kanamakra, Manas, Beki, Pagladiya and Puthimari, Barnadi, Nanoi etc., are instances of riverine forests. Usual combination or Khoir and Sissioais found in this group of forests.
In Kamrup, Nalbari and Barpeta districts, this type of forest with Sissoo first coming in and then khoir has the tendency to change over to the mixed decidious forests if left to nature alone, by subsequent invasion of species like Simul, Koroi, Udal, Kuhir, Khokan, Gomari, Sida,etc.,and hence is an early stage of succession towards the climax forests. In the Brahmaputra alluvium of the State, the principal species of this group of forests is Simul or Simalu. The Jamuna and the Kapili valley alluvoums in central Assam contain the mixed type of forests and is composed of trees like Koroi, Ajhar, Uriam, Simalu, Outenga,etc., and also in the well drained soils the better species like Sopa, Poma, Gandhsorai,Amari,etc, are to be seen.