Environment of Earth

March 11, 2008

PHYTOGRAPHICAL REGIONS OF INDIA

Filed under: terrestrial vegetation — gargpk @ 1:47 pm
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A phytogeographical region is defined as an area of uniform climatic conditions and having a distinctly recognisable type of vegetation. According to D. Chattarjee (1962), India can be divided into nine phytogeographical regions.

  1. Western Himalayas

This region comprises north and south Kashmir, part of Punjab and Kumaon region of Uttaranchal. Average annual rainfall in the region is 100-200 cm. The region is wet in outer southern ranges and slightly dry in the inner areas. At high altitudes, snowfall occurs during winters. The region is subdivided into three zones.

  1. Submontane (lower, tropical and subtropical) zone: This zone includes outer Himalayas i.e. regions of Siwalik Hills and adjoining areas from 300 to 1500 m altitude. Average annual rainfall of the zone is around 100 cm. The vegetation consists of subtropical dry evergreen, subtropical pine and tropical moist deciduous forests.

  2. Temperate (montane) zone: This zone extends in the western Himalayas between the altitudes 1500 and 3500 m. The climate is wet between the altitudes 1500 and 1800 m and is drier at higher altitude. The vegetation consists of wet forests, Himalayan moist and Himalayan dry temperate forests.

  3. Alpine zone: This zone extends between 3500 m and 5000 m altitudes. The rainfall is very scanty and climate is very cool and dry. The vegetation consists of alpine forests.

  1. Eastern Himalayas

This region extends in the Himalyas from east of Nepal up to Arunachal. The climate is warmer and wetter than in western Himalayas. Tree line and snow line are higher by about 300 m than in the western Himalayas. The tropical temperature and rainfall conditions result in vegetation of the region having greater general species diversity, greater variety of oaks but lesser variety of conifers than in the western Himalayas. This region is also divided into three zones.

  1. Submontane (lower, tropical and subtropical) zone: This zone extends from the foothills up to the 1850 m altitude. The climate is nearly tropical and subtropical. The vegetation consists of subtropical broad-leaved forests, pine forests and wet temperate forests.

  2. Temperate (montane) zone: The zone extends from 1850 m to 4000 m altitude, about 500 m higher than in the western Himalayas. The vegetation consists of typical temperate forests with oaks and Rhododendron at lower and conifers at higher altitudes.

  3. Alpine zone: This zone extends from 4000-5000 m altitude. The climate is very cool and dry. The vegetation consists of alpine forests.

  1. Indus plain

This region comprises a part of Punjab, Delhi, Rajasthan, a part of Gujrat and Cutch. The climate has very dry and hot summers alternating with dry and cold winters. The annual rainfall is generally less than 70 cm and may be 10-15 cm in some areas. Most of the region is desert today though it had dense forests about 2000 years ago that were destroyed due to biotic factors particularly extensive cattle grazing. The vegetation today consists of tropical thorn forests and grasslands in some areas.

  1. Gangetic plain

This region covers part of Delhi, Uttar Pradesh, Bihar, West Bengal and part of Orissa. Average annual rainfall ranges from 50 cm to 150 cm from east to west. The vegetation consists of tropical moist deciduous forests, dry deciduous forests, thorn forests and mangrove forests.

  1. Assam

The region covers most of the Assam. The climate is characterized by very high temperature and rainfall. The vegetation consists of tropical evergreen and wet temperate forests in the lower plains while hilly tracts up to 1700 m altitude have subtropical pine forests.

  1. Central India

This region comprises part of Orissa, Madhya Pradesh, Vindhyan region and Gujrat. The areas are mostly hilly with some places at 500-700 m altitude. The average annual rainfall is 100-170 cm. Biotic disturbances are very common in this region resulting in degradation of forests into thorny forests in the open area. The vegetation consists of tropical moist deciduous forests, chiefly Sal forests in areas of annual rainfall above 150 cm and mixed deciduous forest in areas of 125-150 cm annual rainfall. Tropical thorn forests are found in the areas of annual rainfall below 125 cm.

  1. Western coast of Malabar

This is a small region extending from Gujrat to Kanyakumari along Western Ghats. The climate is warm humid having annual rainfall over 400 cm. The climate is tropical on the coasts and temperate in the hills. The vegetation consists of tropical wet evergreen, moist evergreen and moist deciduous forests. Wet temperate forests (Sholas) are present in Nilgiri while mangrove forests are found in the saline swamps on the coasts.

  1. Deccan

The region comprises southern Peninsular India from southern Madhya Pradesh up to Kanyakumari excluding the Western Ghats. The average annual rainfall in the region is about 100 cm. The vegetation consists of tropical dry evergreen, dry deciduous and swamp forests.

  1. Andman and Nicobar

This region includes Andman and Nicobar Islands. The climate of the region is warm and humid with very high temperature and annual rainfall. The vegetation consists of littoral mangrove, evergreen, semi-evergreen and deciduous forests.

March 9, 2008

Climatic indices and biogeographical zones


Radiation balance (source of heat energy)

Radiation index of dryness (moisture conditions)

Less than 0 (Highly excessive moisture)

Between 0 and 1.0

Excessive moisture

Optimal moisture

Moderate dryness

Dryness

Excessive dryness

0 – 0.2

0.2 – 0.4

0.4 – 0.6

0.6 – 0.8

0.8 – 1.0

1.0 – 2.0

2.0 – 3.0

> 3.0

< 0 (High altitude)

I

Eternal snow

0 – 50 kcal/cm2/yr (South Arctic, sub-arctic and moderate latitudes)

IIa

Arctic desert

IIb

Tundra (with islands of sparse forests in south), bow forests in swampy areas

IIc

Northern and middle taiga

IId

Southern taiga and mixed forests

IIe

Deciduous forests and forest-steppe

III

Steppes

IV

Semi-deserts in temperate belts

V

Deserts in temperate belts

50 – 75 kcal/cm2/yr

(Subtropics)

VIa

Regions of subtropical semi-gilei with large swamp areas

VIb

Subtropical rain-forests

VII

Hard-leaved subtropical forests & brush, deciduous forests

VIII

Subtropical semi-deserts

IX

Sub-tropical deserts

> 75 kcal/cm2/yr

(Tropics)

Xa

Regions of equatorial forest swamps

Xb

High humidity equatorial forests with major swamps

Xc

Moderate humidity equatorial forests with moderate swamps

Xd

Equatorial forests, passing to light lropical & deciduous savannahs

XI

Arid savannahs, deciduous forests

XII

Semi-desert savannahs (tropical semi-deserts)

XIII

Tropical deserts