The valley lies between the Himalayas to the north and the Lushai hills to the south and when the river floods during the June to September monsoon it brings up to 300 cm of water onto the plain carrying rich soils to create a fertile environment which has been extensively farmed for thousands of years.
Typical canopy trees include the evergreen Syzygium, Cinnamomum and Magnoliaceae along with deciduous Terminalia myriocarpa, Terminalia citrina, Terminalia tomentosa, Cinnamomum cassia, Durio zibethinus, Artocarpus heterophyllus, Ficus benghalensis, Gnetum gnemon, Mangifera indica, Toona ciliata, Toona sinensis, Cocos nucifera, Ginkgo biloba, Prunus serrulata, Camphora officinarum, Cathaya argyrophylla, Taiwania cryptomerioides, Cyathea spinulosa, Sassafras tzumu, Davidia involucrata, Metasequoia glyptostroboides, Glyptostrobus pensilis, Castanea mollissima, Quercus myrsinifolia, Quercus acuta, Quercus glauca, Machilus thunbergii, Tetracentron, Tsuga dumosa, Ulmus lanceifolia, Tectona grandis, Larix gmelinii, Larix sibirica, Larix × czekanowskii, Betula dahurica, Betula pendula, Pinus koraiensis, Pinus sibirica, Pinus sylvestris, Picea obovata, Abies sibirica, Quercus acutissima, Quercus mongolica, Prunus padus, Tilia amurensis, Salix babylonica, Acer palmatum, Acer campbellii, Populus tremula, Ulmus davidiana, Ulmus pumila, Pinus pumila, Haloxylon ammodendron, Elaeagnus angustifolia, Tamarix ramosissima, Pinus roxburghii, Pinus hwangshanensis, Juniperus tibetica, Olea europaea subsp.
Understory trees and shrubs include the laurels Phoebe, Machilus, and Actinodaphne, Polyalthias, Aphanamixis, and cultivated Mesua ferrea and species of mahogany, cashews, nutmegs and magnolias, with bamboos such as Bambusa arundinaria and Melocanna bambusoides.
Despite the centuries of human clearance and exploitation, the forests and grasslands along the river remain a habitat for a variety of wildlife including tiger (Panthera tigris), clouded leopard (Pardofelis nebulosa), capped langur (Semnopithecus pileatus), gaur (Bos gaurus), barasingha deer (Cervus duvaucelii), sloth bear (Melursus ursinus), wild water buffalo (Bubalus arnee), India's largest population of Asian elephants (Elephas maximus) and the world's largest population of Indian rhinoceros, while Asian black bears live in the higher slopes of the valley sides.
The valley is home to rich bird life with 370 species of which two are endemic, the Manipur bush quail (Perdicula manipurensis) and the marsh babbler (Pellorneum palustre) and one, the Bengal florican is very rare.