The tropical vegetation covers areas upto an elevation of about 1,000m. The majority of the forest fall in this zone.
It embraces evergreen, semi-evergreen and deciduous forests, bamboo thickets and grasslands including riparian forests and swamps. These forests mainly consists of Shorea robusta and in certain area Tectona grandis has also been introduced. The tallest trees are Schima wallichii, Terminalia belirilia belirica, Engelhardtia spicata, Aesculus assamica, Aporusa wallichii, Bridelia retusa, Cryptocarya andersonii, Talauma hodgsonii, Lagerstroemia parviflora, Gmelina arborea etc.
Miliusa velutina, Hibiscus macrocarpus, Zizyphus rugosa, Helicia robusta, Engelhardtia spicata var. Colebrooliana and Ficus prostrata etc. form the lower canopy. The main components of Shrubby species are – Capparis zeylanica, Garcinia lancifolia, Bauhinia acuminata, Mimosa himalayayana, Acacia Concinna, Mussaenda Roxburghii, Eupatorium Modiflorum, Solanum Kurzii and Phlogacanthus tubiflorus etc. In a few areas, numerous lianas intertwining the trees e.g. Dysolobium grande, Mucuna bracteata, Fissistigma wallichii, Paederia scanders, Solena heterophylla and Aristolocjia saccata are prominent. Rarely, Aristolochia cathcartii may be seen in certain forests. Several species of bamboo stretch for long distances forming thickets of secondary vegetation without any competition.
A few palms like Areca, Caryota, Pinanga and Didymosperma are also conspicuous. The ground flora in deciduous forests is very poor and seasonal, while in evergreen forests, species of Alpinia, Amomum, Colocasia, Costus, Hedychium etc are not uncommon. The epiphytic climbers viz. Rhaphidophora spp., members of Gesneriaceae, Hoya app. With beautiful bunches of star like flowers and stem parasites of Loranthaceae and total root parasite Cuscuta reflexa are also seen. A few species of epiphytic orchids are seen in the evergreen forests but they show less species diversity. The herbaceous vegetation is less profuse and includes the members of Oxalidaceae, Balsaminanceae, Acanthaceae, Leeaceae, Fabaceae, Asteraceae and Poaceae. Ferns and fern-allies, liverworts and mosses etc. are also seen on old tree trunks and stones etc. near water sources, in shady places. Due to excessive ‘Jhum’ practice most of the forest areas are cleared and secondary monoculture forests of Shorea robusta established. In more or less open moist localities and near water sources, herbs like Dictyospermum, Aneilema Scaberrimum, Burmania Sp., Coiictyospermum, Aneilema Scaberrimum, Burmania Sp., Coix sp. Cyprus spp., Oxalis Corniculate, Anemone spp. and Ericcaulon can be seen.
The large number of mammalian fauna includes the followings: Hoolock gibbon, Stump-tailed macaque, Rhesus macaque, Assamese macaque, Slow loris, Golden langur, Capped langur, Common monkey, Tiger, Leopard, Clouded leopard, Golden cat, Leopard cat, Marbled cat, Jungle cat, Large Indian civet, Masked Palm civet, Binturong, Yellow Throated marten, Yellow-Bellied weasel, Madras Tree shrew, Indian flyingsquirrel, Malayan Giant squirrel, Bandicoot rat, Lesser Bamboo rat, Black Napped hare, Rufous-tailed hare, Sambar, Gaur, Indian Crested porcupine, Cheetal, Muntjac or Barking deer, Indian elephant, Wild dog, Indian Wild boar, Different Species of Bats.
Different varieties of beautiful birds are in abundance in the forest areas of the region. They are Indian black baza, Barred jungle owlet, Red jungle-fowl, Thick-billed green pigeon, Blue throated barbet, Long-tailed broadbill, Grey-headed myna, Jungle myna, Green magpie, Indian house crow, Red winged crested cuckoo, Large green-billed malkoha, Crow pheasant, Red headed trogon, Redwattled lapwing, piedhornbill, Broad-billed roller.
Some other varieties of birds like the White-crested Laughing Thrush, Scarlet Minivet, Black-headed Oriole, Cockoo-shrike, Green Barbet, Chloropsis, Green Himalayan Barbet, White–capped Redstart, Magpie Robin, Yellow Bulbul, Brown Fish Owl, Bee-Eaters, Serpent Eagle, Hill Myna, Pied Myna, Grey-headed Sibia, Slaty-headed Scimitar Babbler as well as various species of Hornbills, Nightjars, Egrets, Parrots, Swallow-Shrikes have also been reported.
Reptile fauna include different varieties of lizards, snakes, turtle/tortoises. Different species of lizards, geckos and skinks include Calotes Emma, C. Maria, C. Versicolor, Cnemaspis Jerdoni, Cytodac Tylus Khasiensis, Cosymbotus Platyrus, Hemidactylus Brooki, H. Frenatus, Gekko Gecko, Japalura Planidorsata etc.
Different species of snakes include Blind snakes, Indian Gamma, Checkered Keelback, Red necked Keelback and others. Important poisonous species include Indian Cobra and Vipers.