A) Moist Tropical Forests:

Moist tropical forests are found in regions with high rainfall, temperatures, and humidity. These forests are dense, evergreen, and support a rich variety of plant and animal species. There are different types of tropical forests based on their rainfall, temperature, and distribution. The following are the sub-categories of tropical forests:

1. Tropical Wet Evergreen Forests (Rainforests)

Climatic Conditions:

• Annual Rainfall: Exceeds 250 cm.
• Temperature: The annual temperature ranges between 25°C to 27°C.
• Humidity: Average annual humidity exceeds 77%.
• Dry Season: The dry season is distinctly short.

Characteristics:

• Evergreen: The trees do not shed all their leaves together, which is typical of regions with high heat and humidity.
• Lofty Trees: Trees often reach heights of 45 to 60 meters, towering above the forest.
• Thick Canopy: The forest has a thick canopy, and from the air, it appears as a dense cover of foliage. Sunlight has difficulty reaching the ground.
• Epiphytes: The lack of sunlight on the forest floor results in fewer undergrowth plants, but epiphytes like orchids and ferns thrive in the canopy.
• Understory: Since the sun cannot penetrate the dense canopy, the understory is mainly composed of bamboos, ferns, and climbers.

Distribution:

• Western Ghats (500 to 1370 meters above sea level).
• Some regions in the Purvanchal Hills.
• Andaman and Nicobar Islands.

Timber:

• Hardwood: These forests are known for fine-grained, hard, and durable timber.
• Commercial Value: The timber has high commercial value but is difficult to exploit due to dense undergrowth, the absence of pure stands, and the lack of transport facilities.

Important Species: Mahogany, Mesua, White cedar, Jamun, Canes, Bamboo, etc.

2. Tropical Semi-Evergreen Forests

These forests act as transitional forests between tropical wet evergreen forests and tropical deciduous forests. They are relatively drier compared to tropical wet evergreen forests.

Climatic Conditions:

• Annual Rainfall: 200-250 cm.
• Mean Temperature: Between 24°C and 27°C.
• Relative Humidity: About 75%.
• Dry Season: The dry season is not as short as in tropical evergreen forests.

Characteristics:

• Less Dense: These forests are less dense and contain more pure stands than tropical wet evergreen forests.
• Buttressed Trunks: Trees often have buttressed trunks, providing support in the nutrient-poor soils.
• Epiphytes: Abundant epiphytes on tree trunks.
• Species: These forests support a wide variety of species, including both evergreen and deciduous trees.

Distribution:

• Western Coast.
• Assam.
• Lower slopes of the Eastern Himalayas.
• Odisha.
• Andamans.

Important Species: Laurel, Rosewood, Mesua, Thorny Bamboo, White Cedar, Indian Chestnut, Champa, Mango, etc.

Timber: Hardwood: Timber from these forests is of high quality but more accessible than that from tropical evergreen forests. The trees are often in more pure stands, making timber exploitation easier.

3. Tropical Moist Deciduous Forests

These forests occur in regions that experience a distinct dry season. They shed their leaves during the dry period.

Climatic Conditions:

• Annual Rainfall: 100 to 200 cm.
• Mean Temperature: Around 27°C.
• Relative Humidity: 60 to 75%.
• Dry Period: The spring and summer are dry.

Characteristics:

• Leaf Shedding: Trees shed their leaves during the spring and early summer when moisture availability is low.
• Bare Appearance: The forest appears bare during extreme summers (April-May).
• Undergrowth: These forests have a more complete undergrowth compared to tropical evergreen forests.
• Top Story: The top story of the forest ranges from 25 to 60 meters in height.

Distribution:

• Along the Western Ghats, surrounding tropical evergreen forests.
• Shiwalik range, Terai, and Bhabar regions.
• Manipur, Mizoram, Chhattisgarh, and Odisha.

Timber:

• Valuable Timber: These forests provide valuable timber such as Teak.
• Species: Teak, Sal, Laurel, Rosewood, Amla, Jamun, Bamboo, etc.
• Exploitation: Timber extraction is easier than in tropical evergreen forests due to the high degree of gregariousness and more pure stands of trees.

4. Littoral and Swamp Forests

Littoral and swamp forests are found in coastal areas and around deltas, estuaries, and tidal regions. These forests thrive in both fresh and brackish water.

Climatic Conditions:

• Water Type: They can survive in both fresh and brackish water, which is a mixture of seawater and freshwater found in estuaries. The salinity ranges from 0.5 to 35 ppt.

Characteristics:

• Deltas and Estuaries: These forests are found in areas influenced by tides, such as deltas, estuaries, and creeks.
• Mangroves: Dense mangroves grow in sheltered estuaries, tidal creeks, backwaters, salt marshes, and mudflats, providing crucial ecological benefits.

Distribution:

• Found in coastal areas, especially along the Ganga, Mahanadi, Godavari, Krishna, and Cauvery deltas.
• Prominent in the Sunderban region in the Ganga Delta.

Timber:

• Hard and Durable Timber: Littoral and swamp forests provide hard and durable timber used in construction, boat-making, and other building purposes.
• Important Species: Sundri (Heritiera), Agar, Rhizophora, Screw pines, Canes, and Palms.

B) Dry Tropical Forests:

1. Tropical Dry Evergreen Forests:

Distribution: These forests are primarily found along the coasts of Tamil Nadu, India.

Climatic Conditions:

• Annual Rainfall: About 100 cm, mainly from the northeast monsoon winds between October and December.
• Mean Annual Temperature: Around 28°C.
• Humidity: Approximately 75%.

These forests are unusual because evergreen forests typically require higher rainfall, making their existence in areas with such low rainfall quite peculiar.

Characteristics:

• The trees are short-statured, typically reaching up to 12 meters in height.
• These forests have a complete canopy with limited presence of bamboos and grasses.

Key Species:

• Jamun, tamarind, and neem are common in this forest type.
• Much of the land in these areas has been cleared for agriculture or casuarina plantations.

Benefits:

• The line planting of casuarina helps control wind damage in coastal areas.
• It is a useful resource for firewood, and the wood is excellent for paper pulp and manufacturing paper.
• Medicinal value of casuarina is recognized in some traditional uses.

Wasteland Development:

• Casuarina is known for its adaptability to a wide range of habitats, including salt tolerance and drought resistance, making it ideal for reclaiming wastelands and stabilizing sand dunes.
• Intercropping with groundnut, cucumber, watermelons, sesame, and pulses is possible alongside casuarina plantations, improving soil health and land productivity.

2. Tropical Dry Deciduous Forests:

• Climatic Conditions:
  • Annual Rainfall: Ranges from 100-150 cm.

• Characteristics:
  • These forests are similar to moist deciduous forests but are adapted to areas with lower rainfall.
  • The trees shed their leaves during the dry season to conserve moisture.
  • The forest canopy is closed but uneven, with some areas being denser than others.
  • The forests are a transitional type, representing a mix of moist deciduous and thorn forests.
  • Key Species: Teak, axlewood, rosewood, common bamboo, red sanders, laurel, and satinwood.
  • Undergrowth: Sufficient sunlight reaches the ground to support grasses and climbing plants.

• Distribution:
  • These forests are found in a broad irregular strip from the foot of the Himalayas to Kanniyakumari, excluding Rajasthan, Western Ghats, and West Bengal.
  • Large portions of these forests have been cleared for agriculture, and many areas suffer from overgrazing and fires.

3. Tropical Thorn Forests:

• Climatic Conditions:
  • Annual Rainfall: Less than 75 cm.
  • Humidity: Below 50%.
  • Mean Temperature: Between 25°C to 30°C.

• Characteristics:
  • The trees are low, typically ranging from 6 to 10 meters in height, and are widely scattered.
  • Species like acacias and euphorbias dominate these forests.
  • The Indian wild date and some grasses grow, particularly during the rainy season.

• Distribution:
  • These forests are common in Rajasthan, south-western Punjab, western Haryana, Kachchh, and parts of Saurashtra.
  • They transition into desert-like conditions in the Thar Desert.
  • These forests also exist on the leeward side of the Western Ghats, covering areas in Maharashtra, Karnataka, Telangana, Andhra Pradesh, and Tamil Nadu.

• Key Species: Neem, babul, and cacti are prevalent in tropical thorn forests.

C) Montane Sub-Tropical Forests:

1. Sub-tropical Broad-leaved Hill Forests:
   • Climatic conditions:
     • Annual rainfall: 75-125 cm.
     • Average annual temperature: 18°C – 21°C.
     • Humidity: 80%. 
       • Distribution:
         • Found in the Eastern Himalayas east of 88°E longitude at altitudes of 1000 to 2000 meters. Also occurs in the Nilgiri and Palni hills at 1070-1525 meters.
       • Characteristics:
         • Evergreen species dominate, including oaks, chestnuts, ash, beech, and pines.
         • Climbers and epiphytes are common.
         • Found as “stunted rainforests,” less luxuriant than true tropical evergreen forests.
         • Other areas include the higher parts of the Western Ghats and the summits of Satpura, Maikal Range, Bastar highlands, and Mt. Abu in the Aravali Range. 
2. Sub-tropical Moist Pine Forests:
   • Distribution:
     • Found in the Western Himalayas between 73°E and 88°E longitudes at altitudes of 1000 to 2000 meters. Also occurs in Arunachal Pradesh, Manipur, Naga Hills, and Khasi Hills.
   • Timber:
     • Chir or Chil is the dominant tree, forming pure stands.
     • Provides valuable timber for furniture, boxes, and buildings.
     • Used for producing resin and turpentine.
3. Sub-tropical Dry Evergreen Forests:
   • Distribution:
     • Found in the Bhabar, Shiwaliks, and the western Himalayas up to around 1000 meters above sea level.
   • Climatic Conditions:
     • Annual rainfall: 50-100 cm, with 15-25 cm from December to March.
     • Hot summers and very cold winters.
   • Characteristics:
     • Low scrub forests with small evergreen stunted trees and shrubs.
     • Common species include olive, acacia modesta, and pistacia.

D) Montane Temperate Forests:

1. Montane Wet Temperate Forests:
   • Climatic Conditions:
     • Found at altitudes of 1800-3000 meters.
     • Annual rainfall: 150-300 cm.
     • Annual temperature: 11°C – 14°C.
     • Humidity: Over 80%.
   • Distribution:
     • Found in higher hills of Tamil Nadu, Kerala, and the Eastern Himalayan region.
   • Characteristics:
     • Evergreen forests with large girth trunks.
     • Mosses, ferns, and other epiphytes cover branches.
     • Trees rarely exceed 6 meters in height.
     • Important species include deodar, chilauni, chestnut, birch, plum, machilus, cinnamomum, litsea, magnolia, blue pine, oak, and hemlock.
2. Himalayan Moist Temperate Forests:
   • Climatic Conditions:
     • Annual rainfall: 150-250 cm.
   • Distribution:
     • Found between 1500-3300 meters in the temperate zones of the Himalayas in Kashmir, Himachal Pradesh, Uttarakhand, Darjeeling, and Sikkim.
   • Characteristics:
     • Composed mainly of coniferous species like pines, cedars, silver firs, and spruce.
     • Trees reach heights of 30-50 meters.
     • Form high but open forests with shrubby undergrowth, including oaks, rhododendrons, and bamboos.
   • Timber:
     • Provides high-quality wood for construction, timber, and railway sleepers.
3. Himalayan Dry Temperate Forests:
   • Climatic Conditions:
     • Precipitation: Below 100 cm, mostly in the form of snow.
   • Characteristics:
     • Coniferous forests with xerophytic shrubs.
     • Important trees include deodar, oak, ash, and olive.
   • Distribution:
     • Found in the inner dry ranges of the Himalayas, where the southwest monsoon is weak (e.g., Ladakh, Lahul, Chamba, Kinnaur, Garhwal, and Sikkim).

E) Alpine Forests:

• Altitude: 2,900 to 3,500 meters above sea level.
• Alpine forests can be divided into:
  1. Sub-alpine forests:
     • Located at lower altitudes, transitioning into alpine scrub and grasslands.
  2. Moist Alpine Scrub:
     • Found at higher altitudes, with dense evergreen growth of rhododendrons and birch.
  3. Dry Alpine Scrub:
     • Occurs at altitudes above 3000 meters, extending to the snowline, characterized by xerophytic, dwarf shrubs such as juniper and honeysuckle.