The Forests of Manas National Park are classified into 6 types in accordance with the classification system of Champion and Seth. These are as follows:-
a) 2 B/C/s – Sub Himalayan High alluvial Semi Evergreen Forests:-
This formation occurs in the northern belt of the Park. There is an emergent layer of Bhelu (Tetrameles nudiflora) trees which is characteristic of this type. Below this emergent layer of deciduous species, the top storey is formed by Badam (Mansonia dipikae), Bogijam (Eugenia jambos), Bonsum, Amari (Amoora wallichii), Parali, Bogipoma (Chukrassia tabularis), Khokan (Duabanga grandiflora) etc. The middle storey is made up of Jia (Lannea grandis), Udal (Sterculia vilosa), Gohera (Zanthoxylum rhetsa), Brajanali, Lauraceous plants etc. The ground cover is made up of evergreen shrubs. Climbers are abundant and some of the species met with such formation are Vitis, Thunbergia, Piper and Mikania spp etc.
b) 3C/cb – Eastern Bhabhar Sal Type Forests:-
The Pure patches of Koroi (Albizia procera) occur in the moister parts along the bank of streams and rivers. Koroi occasionally pre-dominates such patches and associates are Simul (Bombax ceiba), Jam (Eugenia jambolana), Gamari (Gmelina arborea) and Udal (Sterculia vilosa). The middle storey is made up of young Bhelkhor, Macaranga species and occasionally Palash (Butea monosperma). The ground cover consists of fern, Colocassia spp, Solanum spp, etc. with occasional Zizyphus spp and Eupatorium odoratum in open locations. Infestation of the climber Mikania scandens is rather heavy and it forms a thick cover on the ground.
c) 3c/c3 – East Himalayan Moist Mixed Deciduous Forests:-
The formation covered by this type occupies some of the hill slopes near the northern boundary and the plain in Bhabhar areas. This type also occurs as strips and belts along the watercourses in the midst of savannah formations. The forests appear to be transitional in nature and are likely to pass on to the next stage (Semi evergreen) in presence of favourable circumstances like protection from fires in course of succession. Some of the other top storey spp met within the above formation are Premna spp Kathia, Koroi (Albizia procera), Kanchan (Bauhinia purpurea), Hatipolia (Pterospermum acerifloium), Dudhi, Siris (Albizia lebbek), Brajanali (Zanthophylum rhetusa) etc. The middle storey is occupied by sapling of Sida, Bohera (Terminalia belerica), Hilikha (Terminalia chebula), Simul (Bombax ceiba), Parali, Jia, Poma, Kuhir and Hatipolia etc.
d) 3/s – Low Alluvial Savannah Woodlands:-
This type of forest occupies extensive area, which are subject to annual fires. Very scattered and stunted growth of Sida, Udal, Oxi, Kum and occasional Gamari is common site in such areas. Due to the absolute open conditions no differentiations into top-storey, mid storey is practicable. However, smaller saplings of tree species mentioned above along with Amlakhi (Emblica officinalis), Khair (Acacia catechu), Gundali etc. are also observed in such formation. Rare and solitude Sal (Shorea robusta) trees as well as in small groves are found in a few locations in the Park. Grasses occurring in this type are Imperata cylindrica, Saccharum arundinaceum, Narenga porphyroconia, Arundinella bengalensis etc. Brynea bengalensis, Grewia sapida, Premna, herbacea etc. and terrestrial orchids are characteristic associates in this grassland.
e) 2B/c/ (a, b) – Assam Valley Semi-Evergreen Forests:-
This type occupies in patches in the moister soil of terrain belt of the Park. The top storey species in this formation are Paruli, Hatipolia, Owtenga (Dillenia indica), Poma, Uriam (Bischofia javanica) etc. The middle storey is made up of Kuhi, Kathia Koroi etc. The ground cover is represented by Leea spp Desmodium spp and Alipinia spp and various monocots. Epiphytic orchids like Cymbidium aloifolium, Acampe multiflora, Dendrobium aphylum, Dendrobium jenkinsii, Aerides multiflora, Rhynchostylis retusa, etc. are wide spread.
f) 4D/2S2 – Eastern Wet Alluvial Grassland:-
On badly drained and low-lying locations, there is a change in composition of the crop and in such locations occasional Koroi, Urium (Bischofia javanica), Owtenga (Dillenia indica), Bhelkor and Simul (Bombax ceiba) are common. Some of the grasses found in such areas are Saccharum procerum, Saccharum spontaneum, Apluda aristata, Erianthus spp etc. In the extreme form of this type of forest containing perennial water bodies (swamps) and occasionally found trees are Salix spp, and Polygonum spp.
Vegetation Cover Types in Barnadi Wildlife Sanctuary:-
As per Champion and Seth, 1968, The forest types of Barnadi can be categorised as follows:-
- Pioneer Euphorbiaceous Scrub (1/2/2/B/C1/2S1)
- Eastern Himalayan Moist Deciduous Forest (3C/C3b)
- Eastern Hollock Forests-Terminalia -Duabanga (1S2(b)
- Eastern Wet Alluvial Grasslands (1/4/4D/2S30)
- Khair-Sissoo Forests (11/5/1S2)
- Pioneer Euphorbiaceous Scrub: In moist evergreen and semi-evergreen forests, if a heavy or clear felling is made and the area is left to its natural regrowth, it very commonly occurs that a cover of quick growing but short lived small trees is quickly established. The Euphorbiaceous general Macaranga, Mallotus and Trema usually predominate as a first in the secondary sere providing shade and shelter under which the slower and the less adaptable of the latter stages become established and ultimately push through and supplant the pioneers. The principal species are Alpinia mollucensis, Casearia verca, Laportea crenulata, Malastoma malaburicum, Phrynium spp.
- Eastern Himalayan Moist Mixed Deciduous Forest (3C/C3b): This type consists of deciduous forests occupying well –drained soils on the bhabar terraces and comparatively higher uplands. The forest is tall and more or less closed. The individual trees often run to large size. The species ar well mixed by small groups. There is abundant under wood and shrubby undergrowth without grass unless burnt. With burning, grass may become heavy through coarse tufted species are absent.
- The principal species are Langerstroemia parviflora,Terminalia bellerica, Sterculia villosa, Salmalia malabarica, Schima wallichii, Careya arborea, Bauhinia purpurea, Amoora spp. etc. However this is not a seral type, the succession being slow on the intensively drained soils occupied.
- Eastern Hollock Forests-Terminalia -Duabanga (1S2(b)): This develops on the young alluvium of large rivers. It is an irregular forest in which the Terminalia myriocarpa and Duabanga usually predominate being more or less evergreen and contributes the dominant canopy and form a fairly complete second story. The other species found are Pterospermum, Ailanthus grandis and Vatica Lanceaefolia.
- Eastern Wet Alluvial Grasslands (4D/2S2) : The grasslands occur in the cut-off meanders of the river Brahmaputra and similar low alluvial sites. These are deeply flooded (2-3m) during the monsoon but the stiff soil dries out completely in hot weather. This alternation appears to be too severe for tree growth and presumably the grassland formation will remain until slow siltation has raised the level considerably. Controlled annual burning, an important management intervention in habited management arrests the vegetation progression. Thus this type may be regarded as an early arrested stage of the primary sere. The grasses are up to 5m high and very dense. The characteristic grass is Saccharum procerum, associated with it are Phragmites kerka, Saccharum spontaneum etc. Scattered trees of Bombax malabaricum, Albizzia procera and Bischofia javanica occur.
- Khair-Sissoo Forests (5/1S2): It is a deciduous forest in which Dalbergia sissoo predominates. The canopy is light but fairly complete and 18 to 25m high. Acacia catechu is usually but not always present, it does not grow as tall as the Dalbergia and in the mixture is often relatively inconspicuous, but sometimes it occurs pure. the older woods have more or less definite under storey, which is mainly composed of young trees, which will in time replace the Khair- Sissoo as the natural succession takes place. There is often dense deciduous shrubby undergrowth in the older woods still living much of the sandy soil exposed, the opener parts carry a few herbs of which Cannabis sativa is locally dominant and the grass of one or two species among which the xerophytic Saccharum spontaneum is very characteristic. These woods have one marked feature in which they resemble the moist more than the dry deciduous in that they come early leaf (March) and are in full leaf throughout the hot weather, this is however, actually a specific character of the dominant Dalbergia not shared by most of its associates.