Tropical deciduous and thorn forests

Detail

At a glance: the three forest types

Feature	Moist deciduous	Dry deciduous	Tropical thorn
Annual rainfall	100-200 cm	70-100 cm	Under 50 cm
Main areas	NE states along Himalayan foothills; eastern slopes of Western Ghats; Odisha	Rainier parts of the Peninsula; plains of Uttar Pradesh and Bihar	Semi-arid SW Punjab, Haryana, Rajasthan, Gujarat, Madhya Pradesh, Uttar Pradesh
Look	Tall forest that loses its leaves in the dry season	Parkland: trees standing among grass	Scrub: plants leafless for most of the year
Key species	Teak, sal, shisham, hurra, mahua, amla, semul, kusum, sandalwood	Tendu, palas, amaltas, bel, khair, axlewood	Babool, ber, wild date palm, khair, neem, khejri, palas
Main threat	Clearing	Fire and clearing	Low rain and overgrazing

Tropical deciduous forest (monsoon forest)

• Tropical deciduous forest: a forest of trees that shed their leaves once a year, in the dry season. It is also called the monsoon forest because its growth follows the monsoon rains.
• It is the most widespread forest type in India.
• Rainfall range: 70-200 cm a year.
• Why the leaves fall:
• The dry season brings little rain, so the soil holds little water.
• Leaves lose water into the air (transpiration: water leaving a plant through tiny pores in its leaves).

• The tree drops its leaves, so it loses less water and survives until the next monsoon.

• Rainfall splits it into two sub-types: moist deciduous and dry deciduous.

Moist deciduous forest (100-200 cm)

• Moist deciduous forest: the wetter type of deciduous forest. It grows where rain is 100-200 cm a year.
• Where it grows:
• Northeastern states, along the foothills of the Himalayas.
• Eastern slopes of the Western Ghats. These slopes face away from the south-west monsoon wind, so they get less rain than the western (windward) slopes. The wet western slopes carry evergreen forest. The drier eastern slopes carry deciduous forest.

• Odisha.

• Species: teak, sal, shisham, hurra, mahua, amla, semul, kusum, sandalwood.

• Two leading trees, two regions:
• Teak leads in the Peninsula: Madhya Pradesh, Maharashtra, Karnataka, Kerala.
• Sal leads on the Chota Nagpur plateau (mainly Jharkhand), in Odisha and Chhattisgarh, and in the terai-bhabar belt of the Himalayan foothills.
• Bhabar: a narrow belt of pebbles and boulders at the foot of the Siwaliks, where streams sink underground.
• Terai: a wet, marshy belt south of the bhabar, where those streams come back to the surface.

Sandalwood

• Sandalwood: a sweet-smelling tree, valued for its oil and for carving.
• Main states: Karnataka and Tamil Nadu.
• NCERT classes sandalwood as a deciduous species. This is the answer to the Class 11 exercise question on it.
• Exam trap: sandalwood grows in South India, but it does not belong to the tropical evergreen forest.

Dry deciduous forest (70-100 cm)

• Dry deciduous forest: the drier type of deciduous forest. It grows where rain is 70-100 cm a year.
• Where it grows:
• The rainier parts of the Peninsula.

• The plains of Uttar Pradesh and Bihar.

• Look of the landscape:

• It is like a parkland: teak and other trees stand in open spaces covered with grass.

• In the dry season the trees lose all their leaves. The forest then looks like a grassland with bare trees.

• Species: tendu, palas, amaltas, bel, khair, axlewood.

• Transition zones (where one forest type slowly changes into another):
• On wetter edges it changes into moist deciduous forest.

• On drier edges it changes into thorn forest.

• Western and southern Rajasthan has very little vegetation, for two reasons:

• Rain is low.
• Animals have overgrazed the land (eaten the plants faster than they can grow back).

Dry deciduous forest and fire

• The dry deciduous forest is the type most exposed to fire and clearing. Forest fires are covered in natural-hazards-disasters.
• Why fire spreads here:
• The dry season is long, and fallen leaves and dry grass pile up on the forest floor.
• These act as fuel. One spark can start a ground fire.

• The open, grassy parkland lets the fire spread fast.

• Official data agrees:

• Severe fires occur in many forest types, particularly dry deciduous forests. Evergreen, semi-evergreen and montane temperate forests catch fire less often [2].
• Fire-prone forest was 35.47% of India's forest cover (ISFR 2021) [2].
• Fire hotspots fell from 2,23,333 in 2021-22 to 2,03,544 in 2023-24 (ISFR 2023) [3].

• A fire hotspot is a spot that a satellite picks up as unusually hot, which means a likely active fire.

• Policy response: the National Action Plan on Forest Fire, 2018 sets out steps to prevent forest fires and to train communities to control them [3]. The Forest Survey of India (FSI) runs an upgraded Forest Fire Alert System [3].

• Wider context: India's forest cover was 7,15,343 sq km (21.76% of its area) in ISFR 2023. Forest and tree cover together was 8,27,357 sq km (25.17%) [3].

Tropical thorn forest (under 50 cm)

• Tropical thorn forest: a low, open, scrubby forest of thorny plants. It grows where rain is under 50 cm a year.
• Where it grows: the semi-arid areas (dry, but not true desert) of:
• south-west Punjab
• Haryana
• Rajasthan
• Gujarat
• Madhya Pradesh

• Uttar Pradesh

• Look: the plants have no leaves for most of the year, so the area looks like scrub (short, scattered bushes).

• Tussocky grass: grass that grows in thick clumps. Here it grows up to 2 m tall.
• Species: babool, ber, wild date palm, khair, neem, khejri, palas.
• Adaptations (special features that help plants survive the dry climate):

Feature	How it helps
Long roots	Reach water deep underground
Thick, fleshy stems	Store water
Small leaves	Lose less water through transpiration
Thorns (leaves turned into spines)	Lose even less water and keep grazing animals away

Khejri and the Bishnois (beyond NCERT)

• Khejri: a thorn-forest tree of Rajasthan's dry lands. The Bishnoi community treats it as sacred and protects it.
• Khejarli, 1730:
• The king of Jodhpur ordered khejri trees cut at Khejarli, Rajasthan.

• More than 360 Bishnois, led by Amrita Devi, refused to let the trees be cut. They were killed on the king's orders [4].

• Today: the Government of India marks 11 September as National Forest Martyrs Day because of this event [4].

• Class 10 (Forest and Wildlife Resources) describes Bishnoi villages in its box on sacred groves. It is a good example of community conservation (local people protecting nature through their own beliefs and rules).

Prelims Hooks

• Most widespread forest type in India: tropical deciduous (monsoon) forest. Its rainfall range is 70-200 cm.
• Rainfall bands: moist deciduous 100-200 cm > dry deciduous 70-100 cm > thorn under 50 cm.
• Teak leads in the Peninsula (MP, Maharashtra, Karnataka, Kerala). Sal leads on the Chota Nagpur plateau, in Odisha and Chhattisgarh, and in the terai-bhabar.
• Sandalwood (Karnataka, Tamil Nadu) is a deciduous species, not an evergreen one.
• Moist deciduous forest grows on the eastern (rain-shadow) slopes of the Western Ghats, not the western slopes.
• Tendu, palas, amaltas, bel, khair, axlewood → dry deciduous. Babool, ber, wild date palm, khejri → thorn forest.
• Khair and palas appear in both the dry deciduous and thorn lists. This makes a common "which of the following" trap.
• Dry deciduous forest looks like parkland. Thorn forest looks like scrub, with tussocky grass up to 2 m.
• Dry deciduous forests are the most fire-prone. Fire-prone forest was 35.47% of forest cover (ISFR 2021) [2].
• Khejarli (Rajasthan), 1730: Bishnois led by Amrita Devi gave their lives for khejri trees. 11 September is National Forest Martyrs Day [4].

Mains Points

• Pattern of distribution (GS-I): in India, rainfall decides forest type.
• Rain falls from about 200 cm to under 50 cm as you move west and north-west into Rajasthan.
• The forest changes in the same order: moist deciduous → dry deciduous → thorn.
• Each type changes slowly into the next across transition zones.

• Plants adapt to dryness by shedding leaves, growing small leaves and thorns, and storing water.

• Fire and degradation (GS-III): dry deciduous forests have a long dry season, a thick layer of dry leaves and open grassy cover. This makes them the most fire-prone forest type [2].

• Hotspots fell to 2,03,544 in 2023-24 (ISFR 2023) [3].

• The National Action Plan on Forest Fire, 2018 and FSI's Fire Alert System form the policy response [3].

• Thorn forests and desertification (GS-III): low rain and overgrazing leave western and southern Rajasthan with very little cover.

• Thorn and scrub forests guard the land against the spread of the Thar Desert.

• They need grazing control and community protection.

• Community conservation (GS-I/III): the Bishnoi protection of khejri trees (Khejarli, 1730) [4] shows that local beliefs can protect fragile dry-land trees. It supports the people-centred approach of the National Forest Policy, 1988.