Northeast India is rich in various types of natural vegetation. The climate, physiography, and soils of the region have provided favorable conditions for the growth of natural vegetation.
The northeast region of India supports almost all types of
vegetation from cultivated plains to grasslands, meadows, marshes, swamps, scrub forests, tropical forests, temperate forests, and alpine vegetation.
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 altitude variations from 200-5000 m and the presence of deep
valleys, and hills provide a range of ecological variations thereby producing
different types of climatic conditions from warm subtropical in the foothills,
moderate in the middle, and cool temperate in high hills, which determine the
vegetation pattern of this region
The Forest of Northeast India may be broadly classified into 1. Tropical
forest, 2. Subtropical forest, 3. Temperate forests, 4. Sub-Alpine forests and
5. Alpine forests.
Forest Types in Northeast India
1. Tropical Forest
Tropical forests confine up to an elevation of 1000 m
altitude with heavy rainfall and humidity and are highly rich in floral
diversity. Depending upon the location and degree of precipitation they are broadly
discussed bellow
1.1 Tropical Evergreen and Semi-Evergreen Forests
In those parts of the region where the average annual rainfall is
more than 200 cm and the temperature 250 C, there grow tall trees with
evergreen foliage.
Such forests with an average rainfall coupled with high relative humidity are confined to the foothills of Sikkim, Arunachal Pradesh
comprising of Kameng, Subansiri, Lohit, Tirap district, Assam valley, parts of
South Kamrup district and Narduar reserved forest in Sibsagar district, Kakoi, and Dulong reserved forest in North Lakhimpur district, parts of Cachar
district, the western and northwestern parts of Nagaland and Manipur forest areas
adjacent to Burma, Southern and northern slopes of Meghalaya and Dharamnagar, Kaiiashahr,
Beionia and Sadar Sub-division of Tripura. It also covers the forests of
Bamihat and Umtru.
The common plants of the tropical evergreen forest of this
region are Nahar, Halong, Hallock, Makari Sal, Titachampa, etc.
1.2 Tropical Dry and Moist Deciduous Forest
This forest is found in areas where the average annual
rainfall is 80 cm to 200 cm. The
tropical moist and dry deciduous forests remain dry period from December to March.
These types of forests are confined in parts of Goal para,
Nowgoan, Darrang, and Kocharigaon in Assam, the northern slopes of Meghalaya,
northern and northwestern parts of Garo hills, Amarpur, Sonamura, Dharamnagar,
Belona, Udaipur and Sadar subdivision in Tripura, northern sides of the forests
areas of Kawnpuri, Hortaki, Bhairabi, Kolarib, Vairentee and western part of
Mizoram bordering Tripura, etc.
The common species of tropical deciduous plants are Sal,
Teak, Gamari, Simul, khoir, Elephant Apple. Economically the most important
products of the deciduous forest are Sal and Teak.
1.3 Tropical Grassland
Grassland is not uncommon in Northeast India. However, most
of the grasses of the region, except the alpine grass of high altitude in the Himalayas,
are not climogenic. There are several factors associated with the production of
this grassland.
Some of this grassland grow because the original forests were
earlier destroyed for shifting cultivation. There are tall grasses in the Tarai
region of Brahmaputra valley, due to the ground always remaining saturated with
water and hence tall trees do not grow.
The sandy Charlands (River Bank) normally can’t support
tall trees but can grow seasonal grasses.
The swamps and marshes support swamp vegetation which includes mostly
grasses.
2. Subtropical Forests
The subtropical forest has a cooler and more humid climate and is found at an altitude of 1000 to 2000 meters.
2.1 Sub-Tropical Mixed Forests
These forests with an annual rainfall of 150 - 400 cm are the evergreen and semi-evergreen type with enormous diversity being confined to the
hilly regions of Assam slopes of Meghalaya, Koupru hills, Nongmaijing areas
bordering Myanmar (Burma), Manipur and Mizoram and Patkoi ranges in Nagaland, etc.
Some of the important timber species in this type are –
Koroi (Abelmoschus), Pomas (Chukrasia), Sopas (Magnolia), Gamari (Gmelina),
Hollock (Terminalia), Sam (Betula nigra), Am (Mangifera), Badam (Prunus),
Betula and Alseodaphne petiolaris (Ban-hanwalu), Antidesma bunius, Betula
alnoides, Cleidon speciflorum etc. Higher up pure stands of Pinus
kesiya(Khasi-pine)
2.2 Sub-Tropical Pine Forests
The subtropical pine (Pinus kesiya) forests cover an extensive
area between 800 and 2000 m altitude in all the hilly states of northeast India.
They have come to stay as a fairly stable community and have not succeeded
for a long period of time by the subtropical broad-leaved primary forests,
which represent the climax formation of the area.
These forests with moderate rainfall occupy the areas in the
Khasi and Jaintia Hills of Meghalaya (Jowai, Pynursla, Cherrapunjee, and
Nongstoin areas) as well as Rupa valley in the kameng district of Arunachal
Pradesh, Ukhrul, eastern and southeastern parts of Tuensang and Phek districts
in Nagaland, Mao and Sugnu areas in Manipur, hilly tracts around Champhai
Northial and Phawngpui in Mizoram
Pinus kesiya is the most dominant species in the Khasi and
Jaintia Hills whereas Pinus wallichiana is found in the Rupa valley area along
with Berberis, Rhododendron arboreum, Quercus griffitthii and members of
Rosaceae and the presence of large areas of Chir pine in Arunachal Pradesh
2.3 Sub-Tropical to Temperate Grassland
The grasslands wherever present are a biotic climax due to the removal of the original forest cover. The rolling grasslands around Nongstoin,
Mawsynram, Mawphlong, Mawsmai, Cherrapunjee, Jowai, Haflong, and major parts of
Garo hills in Meghalaya, Ukhrul in Manipur, etc.
3. Temperate Forests
The type of vegetation is found in altitudes ranging
from 2000 to 3500 m and is confined to small pockets along the southern slopes of
the Khasi and Jaintia hills, especially the sacred groves viz. Shillong peak,
Law Lyngdoh at Mawphiang and Lawkyntang at Mawsmai, etc.
The sacred groves largely fall under this category and are
the relic type that evolved through millions of years. The common trees are
Lithocarpus fenestratus, Castanopsis kurzii, Quercus griffithii, Q.
semiserrata, Schima khasiana, Myrica esculenta, Symplocos glomerata, Photinia
arguta, Ficus nemoralis, Manglietia caveana, Acer spp., Exbucklandia populnea,
Engelhardtia spicata, Betula alnoides, Rhododendron arboretum, etc.
Shrubs include Mahonia pycnophylla, Daphne papyraceae,
Polygala arillata, Camellia caduca, Rubus spp., etc.
These forests are exceptionally rich in epiphytic flora
comprising Ferns, Lichens, Mosses, Orchids, Zingibers, etc.
4. Sub-Alpine Forests
This type of vegetation is confined to higher ranges of the Himalayas. Ranges surrounding Thangu, Yumthang, Sandakphu, Changu, and Kapup areas in the Sikkim Himalayas and higher ranges of Lohit in Arunachal present; Saramati and Japvo hills in Nagaland; Chingsaw, Japvo, Kowpur, Shiroy and Somra hill ranges of Manipur.
Alpine shrublands, characterized by rhododendrons,
predominate at lower elevations, close to the treeline. The rhododendron flora
of the ecoregion is quite varied, with species composition changing as one move
from west to east along with the range.
This subalpine type of vegetation is associated with shrubby and bushy species of Abies densa, A.spectabilis Berberis, Betida utilis, Cotoneaster, Cypressus torulosa, Juniperus, Lonicera, Picea spimdosa Rhododendron, Salix, and a few others. In the spring and summer, the alpine meadows are covered with brightly colored flowers.
5. Alpine Forests
Although Northeast India falls within the relatively low
latitudes, It has high Himalayas where the temperature is low.
Vegetation from the sub-alpine region gradually merges with the complete disappearance of tree growth into the alpine type as the altitude
increases from 4500 m up to 5000 m, which is more or less the limit of plant
life.
The vegetation is known as alpine grass. Apart from various species of grass, it also contains some varieties of juniper, rhododendron, shrubs, and mosses.