North East India comprising Assam, Arunachal Pradesh, Manipur, Meghalaya, Mizoram, Nagaland, Tripura and Sikkim is rich in various types of natural vegetation. Climate, physiography and soils of the region have provided favorable conditions for luxuriant growth of natural vegetation.
The region has one of the heaviest rainfalls of the world. The windward sides of the foothills receive 300 cm to 400 cm of rainfall while the plains receive 200 to 300 cm annually. The leeward sides of the hills, as the Lanka –Lumding –Nambar region receives only 100 cm of rainfall annually. The high Himalayas, on the other hand, experience frost and snowfall.
1. Tropical Evergreen forest- Tropical evergreen forest are found in those parts of the region where average annual rainfall is more than 200 cm and temperature is 25°C.The Himalayan foothill region from Panchnoi eastward upto Lohit district of Arunachal, the foothills of Changlang and Tirap districts of Arunachal, Nagaland and their adjoining plains of the districts of the Brahmaputra Valley, North Cachar Hills ,the northern and eastern foothills adjoining the Barak plain and higher altitudes of the Meghalaya Plateau (860-1600 meter) bear tropical evergreen forests. The tropical evergreen forest of this plateau includes 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 meter -1200 meter, one can see tropical evergreen forest.
The common plants of the tropical evergreen forest of this region are Nageswar or Nahar (Messua ferrea), Halong (Dipterocarpus macrocarpus, Hallock, Shisu (Dalbargia sisso), Titachampa (Atrocarpus chaplasa), Makari Sal (Shorea assamica), Bay leaf, Amari (Amoora wallichi) etc. At higher altitude these forest also contain chestnut, maple, magnolia, alder and birch. The pine forests are common in the higher altitudes of Meghalaya, Manipur and Nagaland. In the Himalayas pine forest are located between 1200 -2000 meter heights. The tropical evergreen forests of North –East India contain numerous varieties of orchids, some of which are rare and valuable.
2. Tropical Deciduous Forests- These forests are found in those areas where the average annual rainfall is 80 cm to 200 cm. The districts of Dhubri, Kokrajhar, Chirang, Udalguri, Goalpara, Baksa, Barpeta, Nalbari, Kamrup, Darrang, Morigaon, Nagaon , Sonitpur, Karbi Anglong, Dima Hasao, and the drier parts of the Barak valley in Assam support tropical deciduous forest. In Meghalaya these forest 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 forest are limited to a very narrow zone of foothills.
The common species of tropical deciduous forest are Sal (Shorea Robusta, Teak (Tectona grandis), Gamari (Gmeline arborea), Simul (bombax malabaricum, Elephant Apple, Jack fruit etc.
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 of the Himalayas are not climogenic i.e. they are not produced due to climatic reasons but rather they are found because –
a. The original forest were earlier destroyed for shifting cultivation which led to depletion of soil cover and subsequently given rise to grasses only.
b. There are tall grasses in the Tarai region of the Brahmaputra valley, because here the ground water remains saturated with water and hence tall grasses do not grow.
c. The river banks and char lands are normally sandy and such and cannot support tall tress but gives forth luxuriant seasonal grasses.
d. The swamps and marshes support swamp vegetation which include mostly grasses.
The grasses found on the hill slopes came up as secondary growth after people clear the land for shifting cultivation that has given rise to many types of grassland like thatch and other members of the gramminaceae family. The foothill tarai region, especially on the north bank of the Brahmaputra valley also supports tall grass (The grasslands of Manas Sanctuary). The river banks and riverine islands are mostly made of sandy soil. The plants that grow on the river banks and islands are known as riparian vegetation. The grasslands of Dhemaji,Majuli, Kaziranga,Pabitara ,Orang etc belong to this category. In the planes of North-East India, there are various types of Swamp grasses and other plants like lily, lotus, taro, water hyacinth etc.
4. Alpine Grassland- The higher mountain slopes of the Himalayas at an altitude of 4000-5200 meter in Arunachal Pradesh, one can see lush green grasses coming up in the late spring. This vegetation is known as Alpine Grass. Apart from various types of grass, it also contains some varieties of juniper, rhodendron, shrubs and mosses.
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