1. Tropical Dry Deciduous Forests
This type is a degraded version of the moist deciduous. It occupies a vast area of the country between moist deciduous (in the east) and tropical thorn (in the west) forests. Here the amount of annual rainfall lies between 70 cm and 100 cm with average annual temperature between 15.5°C and 22.2°C and relative humidity from 63 to 77 per cent.
These forests cover a very large area, especially in an irregular wide strip running north-south from the foothills of the Himalayas to Cape Camorin (except in Rajasthan, Western Ghats and West Bengal). They occupy a sizeable area in Uttar Pradesh, Maharashtra, Tamil Nadu and Karnataka.
The important trees of these forests are teak, tendu, sal, bijsal, rose-wood, palas, amaltas, bel, lendi, axlewood, anjair, harra, laurel, khair, satin- wood and ghant. Large tracts of these forests have been cleared for agricultural activities.
2. Tropical Thorn Forests
These forests are confined to areas where the rainfall is very low (50 cm to 75 cm), the mean annual temperature 25°C to 27°C and the low humidity (below 47 per cent). The main areas include south-western Punjab, western Haryana, and western Uttar Pradesh, central and eastern Rajasthan, western Madhya Pradesh, Kachchh and neighbouring parts of Saurashtra, leeward areas of the Sahyadris. Here due to paucity of rainfall the trees are stunted (height 6-9 m) with large patches of coarse grasses.
The typical vegetation consists of widely spaced acacias, euphorbias including the typical spiny and thorny varieties and clumps of wild palms (Phoenix Sylvester’s) here and there. Other important trees include jhand, tamarix, khair, kokko, dhaman, reunjha, thor, cactii, khejra, kanju and palas etc.
3. Tropical Dry Evergreen Forests
These forests usually occur along the Coromandel Coast which receives about 100 m of rainfall by the retreating monsoon from October to December. The annual mean of temperature is 28°C and that of humidity 74 per cent. Trees in these forests have low height (9-12 m) exhibiting canopies. Bamboos are rare or absent and grasses not very conspicuous. Important species are khirni, jamun, kokko, ritha, tamarind, neem (Azadirachta indica), toddy palm, gamari and cane etc.
C. MONTANE SUB-TROPICAL FORESTS
4. Sub-tropical Moist (Pine) Forests
Such forests are found in north-western Himalaya (except in Kashmir), Khasi hills, Nagaland and Manipur between altitude of 1000 m and 1800 m. Here the amount of annual rainfall ranges between 100 cm and 200 cm, with average annual temperature of 15°C – 22°C and humidity of 63-77 per cent (Ranikhet). Chir is the main tree but quercus and broad leafed trees are also found in the areas of higher humidity. Besides chir, jamun, oak, rhododendron are other important trees with thick grass cover during rainy season.
5. Sub-tropical Dry Evergreen Forests
These forests occupy piedmont area of Himalaya in Punjab, Haryana and Kashmir (Salt Range and Black Tiger Hills) from 450 to 1500 m of height. Here average annual temperature is 20°C (January 10°C, June 32°C) with rainfall between 50 cm and 100 cm and number of rainy days from 26 to 38.
Vegetation of this region resembles the dry evergreen Mediterranean type dominated by thorny shrubs (height 1.8-3.0 m) with short leaves. It includes various species of acacia with main trees like olive, acacia modesta, and pistacia etc. Grasses and shrubs appear during rainy season.
6. Sub-tropical Wet Hill Forests
Such forests are found in Nilgiri, Palni hills (height 900 m to 1650 m), Mahabalesh war, Pachmarhi (900 m), lower slopes of the eastern Himalaya (90 m-180 m) and Assam hills. These areas experience annual rainfall of more than 150 cm (rainy days 78 to 146), average annual temperature between 18°C and 24°C and humidity from 51 to 81 per cent.
These forests exhibit a mixture of tropical and temperate wet evergreen trees with main species like jamun, machilus, elaeocarpus, celitis, etc. Trees have an average height between 15 m and 30 m with less dense canopy and scrubs. Oak and chestnut are the main trees in the eastern Himalayas.