1. Tropical Wet Evergreen Forests
These forests are mainly found in north-east India, western parts of the Western Ghats and Andaman-Nicobar islands where the amount of annual rainfall is more than 250 cm, average annual temperature between 25°C and 27°C and average annual humidity exceeding 77 per cent.
These forests are very dense and composed of tall (45 m) trees, epiphytes, parasites, lianas and rattans so as to look like a green carpet when viewed from above. Trees have multi-storied structure with good canopy.
They do not shed their leaves annually and hence are evergreen. The floor, due to deep shade, lacks grasses and good under-growth but a tangled mass of canes, palms, bamboos, ferns and climbers makes the passage difficult.
These forests contain various plant species of high economic value, because of the timber being hard, durable and fine-grained. Mesua, white cedar, callophyllum, toon, dhup, palaquium, hopea and canes are main plant varieties in the Sahyadris while gurjan, chaplas, mesua, agor, muli and bamboos grow well in the north-east. Due to obstructing under-growths, mixed species and lack of transport facilities these forests have not been properly exploited.
2. Tropical Semi-Evergreen Forests
Where the amount of annual rainfall ranges between 200 and 250 cm, the mean annual temperature lies between 24°C and 27°C and humidity percentage is 80, the evergreen forests degenerate into semi-evergreen forests. Such forests are found along the Western Coast, in upper Assam, lower slopes of the eastern Himalaya, Orissa coast and neighbouring hills.
These forests are characterised by evergreen trees mixed with deciduous (height 24-36 m), having typical features like less dense canopy, grew- gariousness, frequent buttressed trunks, thicker and rougher barks, and heavy climbers. Although bamboos are less abundant but epiphytes are present in large number. Important plant varieties include aini, semul, gutel, mundani, hopea, benteak, kadam, irul, laurel, rosewood, haldu, kanju, bijasal, kusum, bomsum, Indian chestnut, litsea, holloch, champa and mesua etc. These forests are less dense and can be easily exploited.
3. Tropical Moist Deciduous Forests
These are the typical monsoon forests in areas where the amount of annual rainfall ranges between 100 cm and 150 cm with mean annual temperature of 24°C to 27°C, and humidity percentage of 60 to 80.
They mostly occur along the eastern slopes of the Western Ghats, north-eastern part of the Peninsula and along the foothills of the Himalaya in the Siwaliks, the Bhabar and the Tarai. These forests, on the whole, have gregarious species, trees attaining average height between 30 and 40 m and shedding their leaves during spring and early summer (March- April).
Sal (Shorea robusta) and teak (Tectona gradis) are commercially the most significant species; the former occupying the relatively wetter north-eastern parts of the Peninsula. Teak is more suited to the drier Madhya Pradesh. Other hardwood species such as shisham (Dalbergia sissoo) along the eastern sub- Himalayan zone, Karnataka and Maharashtra; sandal wood (Sandalum album), rose wood of the Karnataka forests are in great demand for construction, furniture, carved boxes etc. Sandal wood oil is in great demand in India and abroad.
The Harra (Terminalia chebula) is more important for its fruits and myrobalans providing tanning material on commercial scale. Mahua (Bassia palifolia), Khair (Acacia catechu), toon (Cedrelatoona), tomentosa, kusum and lend etc are other significant widely distributed species.
Tropical moist deciduous forests are commercially most exploited. Recently great attention is being paid to regenerate these forests through scientific methods of conservation and management.
4. Tidal Forests
These forests form a fairly continuous fringe along the deltas of the Ganga, the Mahanadi, Godavari, Krishna and Kaveri. They occur in and around the tidal creeks and the tide-washed coasts where m silt and saline water have accumulated. Mangro which attain 30 m of height is the most import tree in these forests which is utilised for fuel purpose. The famous Sundarban delta (Ganga) is covered by the Sundari (Heritiera minor) tree which supplies hard durable timber for construction, building purposes and boat making. Here higher ground supports screw pines (Pennanus spp.). Napa frit cans (a palm) occupy the creeks and have direct emergence from the marshes. Epiphytes are predominant all over the region.