The region has one of the heaviest rainfalls in the world . Although the average annual rainfall of the region is about 250 cm it varies from place to place. The windward sides (of SW Monsoon ) of the foothills generally receive 300 cm to 400 cm rainfall while the plains receive 200 cm to 300 cm annually. The leeward sides of the hills , as the Lanka-Lumding -Namber region receives only 100 cm annually. The high Himalayas, on the other hand, experience frost and snowfall.

            As the physiography varies from lowlying swamps and marshes to high mountain  ridges lying above 6000 m, the soils vary from sand, silt and loam to laterite.

 Classification :

            Three variations have give rise to various types of flora in North East India. Of all the physical factors, it is climate which seems to have the most telling effect on the vegetation type. The heavy rainfall which comes from May to September, keeps the relative humidity of the area very high throughout the year . Temperature variation is low, remaining normally between 12 ⁰ C and 35 ⁰ C except in the high hills. These favourable  climatic conditions , augmented by fertility of the soils have provided luxuriant  growth of numerous species of plants . Based on the physiognomy, foliation and flowering characters and gregariousness or otherwise, the natural vegetation of North East India can be divided into the following groups :

            1. Tropical Evergreen Forest : Those parts of the region where average annual rainfall is more then 200 cm and  temperature is 25⁰ C there grow tall trees with evergreen foliage. The Himalayan foothills region from Panch Nai eastward upto Luhit district of Arunachal  the  foothills of Changlang and Tirap district of Arunachal, Nagaland and their adjoining plains district of the Brahmaputra Valley, North Cachar Hills, the northern and eastern foothills adjoining the Barak plain and higher altitude of the Meghalaya Plateau (860 m - 1600 m ) bear tropical evergreen forests. The tropical evergreen forests of this Plateau  include pine vegetation and the temperate broad -leaved trees of the higher altitudes. Similarly, over the hills of Arunachal Pradesh, Patkai  Range and Manipur hills at altitude between 800 m to 1200 m, one can see the tropical evergreen forests.

            A common feature of the evergreen forests is the presence of a thick undergrowth at ground level and many creepers and lianas at  upper  level. In the pine forests, however, these are absent.

            The common plants of the tropical evergreen forests of this region are Nageswar or Nahar (Messua ferrea), Halong (Dipterocarpus macrocarpus) Hallock, Makari  Sal or Makai(Shorea assamica), Shishu (dulbargia sisso),Titachampa (Atrocarpus chaplasa) Champa, Garjan (Dipterocarpus turbinatus ), Bonsom (Phoebe goalparensis ) , Amari  (Amoora wallichii ), Agaru (Aquilaria agallocha) Khakan, Beyleaf   Banaria Am (Mangifera sylvatica), etc. At higher altitudes these forests  also contain Chestnut , Maple, Magnolia, Laurel, Alder and  Birch besides rhododendron, willow, juniper and various sub- species of pine . The pine forests are common in the higher altitudes of Meghalaya. Manipur and Nagaland. In the Himalayas pine forests are located between 1200 m and 2000 m height.

            The tropical evergreen forests of North East India contain numerous varieties of orchids, some of which are rare and valuable. These forests also support various sorts of climbers including cane.

            These forests generally support soft wood for plywood industry and packing boxes for tea industry.

            2. Tropical Deciduous Forest : Deciduous forests are found in those areas of North East India where the average annual rainfall is 80 cm to  200 cm. The districts of Dhubri, Kokrajhar, Bongaigaon , Goalpara  Barpeta Nalbari, Kamrup , Darrang, Marigaon Nagaon,, Sonitpur,, Karbi Anglong, North Cachar Hills and the and  drier parts of the Barak Valley in Assam support tropical forests. In Meghalaya these forests are found in Garo and  Jaintia hills. The drier parts of Tripura, Mizoram, Manipur and Nagaland also have deciduous forest. In Arunachal pradesh the deciduous forests are limited  to a very narrow zone of foothills. 

            The common species of tropical deciduous plants are Sal (Shorea robusta), teak (Tectona grandis ), gamari (Gmelina arborea ), Simul (Bombax malabaricum), khoir (Acacia catechu), Au tenga (Belenia indica), Jack fruit (Atrocarpus integrifolia ), Kadam, Siris, Arjun, Silikha, Bhomora, etc.

            Economically the most important products of the deciduous forest are sal and teak. These two species of plants supply hard wood for construction of buildings bridges and railway sleepers. The sal and teak forests are confined to two distinct belts in Assam. Firstly there is a long strip of land in the south bank of the Brahmaputra  from Mankachar to Marigaon along the Meghalaya foothhills, and  seccondly, there is another strip in the northern part of Kokrajhar and Bongaigaon districts.

            3. Tropical Grassland : Grassland  is not uncommon in North East India. However, most of the grasses of the region, except  the alpine grasses of high altitude in the Himalayas, are not climogenic, i.e. they are not produced due to climatic reasons, such as inadequate rainfall and temperature. Firstly, some of the grasses, found on the hill slopes of North East India are there because the original forests were  earlier destroyed for shifting  cultivation. This also led to depletion of the soil cover,. Such areas subsequently have given rise to grasses only.. Secondly there are tall grasses in the Tarai region of the Brahmaputra Valley because here the ground always remain saturated with water and hence tall trees do not grow. Thirdly, the river banks and charlands are normally sandy. Such land cannot support tall tree but gives forth luxuriant  seasonal grasses. Lastly, the swamps and marshes support swamp vegetation which include mostly grasses.

            (A) The grasses found on the hill slopes come up as a secondary growth after people  clear the land for shifting cultivation and settlement. The human interference since time immemorial has given rise to many grasslands over the hills on depleted soils of North East India. These grasses include various types of thatch and other members of the gramminaceae family.

            (B) The foothill tarai region, especially on the north bank of the Brahmaputra Valley, also support tall grasses, such as various type of reed and thatch. As mentioned above, damp ground of this region favours the growth of tall grass only. The grassland of Manas Sanctuary is an example of this type.

            (C) The river banks and riverine islands are mostly made of sandy soil. This type of soil cannot retain water for a long time. Hence tall trees, except a few varieties like simul, khoir etc. cannot grow on these areas. The plants that grow on the river banks and  islands are known as riperian vegetation. The riperian vegetation in North East India is mostly tall grass. The grasslands of Dhemaji, Majuli, Kaziranga, Bhurbandha Pabitara, Orang, etc. on the banks of the Brahmaputra belong to this  category. Along with grasss these areas also contain simul, khoir karoi kadam and local plum (zyzyphus) trees.

            (D) In the  plains of North East India, especially in the Brahmaputra and Barak Valleys and Manipur Basin, there are many marshes and swamps. These support various types of swamp grasses and other plants like lily, lotus, waterwort, water hyacinth, taro, etc.

            4. Alpine Grassland : Although North East India falls within the relatively low latitudes, it has high Himalayan mountains where temperature is low. The higher mountain slopes of the Himalayas at an altitude of 4000 m to 5200 m in Arunachal Pradesh, one can see lush green grass coming up in late spring. This vegetation is known as alpine grass. Apart from various species of grass, it also contains some varieties of juniper, rhododendron, shrubs and mosses. This zone of grass lies above the coniferous forest belt which is mentioned in the evergreen group.

 The Specialty of the Forests of N.E. India :

            Heavy rainfall, high humidity throughout the year and high temperature of North East India have made the region very rich in floral resources. Some of the important features of the forests of the region are noted below :

            1. In the evergreen forests of Assam one  can find  Makari Sal (Shorea assamica) which are one of the tallest trees in India. It grows to a height of 60 m -70 m. In fact, there are several other species of plant in this region which are ranked as some of the tallest trees of the country.

            2. The forests of the region contain about 400 varieties of rare orchids which are regarded as one of the richest occurrence of these plants in the world. It also contains rare pteridophytes like tree fern.

            3. Side by side with broad leaved forests there are coniferous forests also in the region.

            4. There are some varieties of carnivorous plants in this region. In Garo and Khasi  hills of Meghalaya, alone there are there varieties of carnivorous plants, viz. pitcher plant, bludderwart and Surujneor.

            5. There are many varieties of saprophytic and parasitic plants apart from epiphytes in this region. Monotropa, Belonifora, etc. are some of  the  examples of these varieties.

            6. The region is also very in medicinal plants. Besides, the region is also native to beverage plants like tea.

 Forest Resources of North-East India:

Forests are a precious resource given by nature. It is often termed as multipurpose resource. Forests supply us raw material for construction of building , bridge, ship railway wagon, rail track, boat, etc. These  also  supply raw materials to industries for production of paper, pulp plywood, etc. Besides, the forests supply medicinal plants ornamental plants and above all fuel wood for domestic consumption. Forests also supply food to some extent to men and to all animals. From the view point of environment, forests are important because they influence  rainfall and protect soils from being eroded besides keeping the carbon dioxide and oxygen levels steady.

            Although North East India was once rich in forest resources, it is no longer so now. Reckless cutting  of tree and clearing of forest and  a lack of concerted effort in afforestation have made it poor now  in this  precious  resource. Following figures give the statewise forest coverage  of North East India in 1990 based on satellite imagery (basic statistics 1995, NER)

These  forests  provide hard wood for construction. soft wood for  plywood and manufacture,  bamboo and grass for paper and pulp, fuelwood, lac khoir, gum, bamboo, thatch, cane, various medicinal and ornamental plants, vegetable, fruits, honey and many varieties of wild animals and birds and products from them. Many of these have demand in international market.

            Some of the economically very important trees found in North East India are Agaru, sal, neem, champa, tea and bamboo. Agaru or Agar has become a rare plant now. In the olden days people used to prepare thin long sheets out of its wood  for writing. It is locally known as Sanchi tree. One can still find hundreds of valuable and rare manuscripts written on Sanchi sheet during the six hundred years prior to the advent of the British into North East India. Besides providing writing sheets, Agaru or Agar contain a very valuable  oily essence from which a precious perfume and some drugs are prepared . It is still found, although infrequently, in the forests of Golaghat, Jorhat , Sibsagar , Nagaland and Manipur. Sal (shorea robusta ) is another valuable species of plant found in North East India. It provides extremely hard wood for construction of buildings, bridges and railway sleepers . It also  provides gum and essence. Pine tree not only provides soft wood but it  also supplies  turpentine and resin. Neem, plant abundantly found in the region is one of the most important medicinal plants. Champa also provides an essence used as perfume. Tea plants  are used for extracting tennin and other colouring juice apart from extracting their leaves as a source of beverage.

            The  forests of the North East India are also rich in fauna. The mammals include various types of primates carnivores and herbivores, Hoolock gibbon, one of the 4 types of apes found on the earth today, occurs in this region. The region also has one horned rhinoceros in the forests like  Kaziranga, Laokhowa, Orang, Paabitara and Manas. Some of these forests Kaziranga, Laokhowa Pabha, aand Manas also have wild buffalo. There are as many as 11 varieties of monkey including the rare golden langur and capped langur in this region . Elephants abound the foothill regions of all the states of North East  India. The four horned antelope, deer, barking deer, musk deer, Pigmy hog , bison and wild boar are some of the important herbivores of the region. The most  important carnivores found here are Royal Bengal Tiger, Leopard, various other  large wild cats, civet cats, snow leopard, Himalayan bear. etc.

            Some important products of the wild mammals of North East India  found mention in the ancient Indian classics and travel accounts. Of these ivory i.e. elephant tusk, horn of the one-horned rhinoceros and Kasturi or perfume glands of the naval region of musk deer are the main. The elephant tusk which provides the precious ivory was a much prized possession of the kings and emperors in India since time  immemorial. The kings  and chiefs of North East India used to trade with these commodity and pay tributes  to other kings and emperors with whom they  came in contact. One of the reasons why the rulers of Delhi in the mediaeval period used  to invade North East India time and again is to lay hands on its rich forest products including tuskers and ivory. The so called horn of rhinoceros is widely used in China and  south west Asia as a very rare drug. That is why it is considered to be very  valuable and poaching of the animal still goes on . The musk deer, especially its male ones, bear some special glands in its intestine which secretes a precious juice. This juice is considered to be a very important drug in China.

            There is also a rich reptile population in North East India. It has marsh crocodile, fresh water gharial turtle, tortoise , varieties of monitors, chamelions , lizards and snakes. Of the  important  snakes, the python is ubiquitous in the hills ,while krait , viper and cobra are found in the tropical forests and  grasslands of the plains.

            As in the other families of fauna, north East India is rich in avifauna also . It has scores of species of birds-large and small, charming mocking and terrifying . Stork, peacock, pelican , various types of ducks, pheasant , vulture , kite , eagle , varieties of doves and parrots, wren, linnet , tit, etc. are the common birds of this region.

            As  North  East India abounds in water  bodies, swamps and marshes there are numerous varieties of fish fauna in the region. Some of the  fish live in the numerous streams and rivers and some in equally numerous beels, jheels and swamps. In fact fish used to be so abundant  in the region that to an inhabitant of it, fish as an item of food, is important next only to rice. It is the main source of protein supply to them.  But of  late many beels and swamps have become silted up. Further, the ever increasing population of the region  have taken to indiscriminate catching of fish. These have led to an scarcity of fish in the region.