Tropical deciduous forest

Also called: Monsoon forest · Topic: Natural Vegetation and Forests of India · NCERT: Class 11, Ch 5 "Natural Vegetation"

Meaning

A tropical deciduous forest (also called a monsoon forest) is a forest whose trees shed their leaves once a year in the dry season. It grows where rainfall is 70-200 cm a year.

It is the most widespread forest type in India. It also supplies the country's most valuable timber trees, teak and sal.

Explanation

Why the trees shed their leaves

• The dry season brings little rain.
• The soil holds very little water.

• Leaves keep losing water into the air through transpiration (water leaving a plant through tiny pores in its leaves).

• The tree drops its leaves.

• With fewer leaves, it loses less water.

• It survives until the next monsoon and then grows new leaves.

• It is called the monsoon forest because its yearly cycle of growth follows the monsoon rains.

Two sub-types, split by rainfall

Feature	Moist deciduous	Dry deciduous
Rainfall	100-200 cm	70-100 cm
Look	Tall forest that loses its leaves in the dry season	Parkland: trees standing in open, grassy spaces
Key species	Teak, sal, shisham, hurra, mahua, amla, semul, kusum, sandalwood	Tendu, palas, amaltas, bel, khair, axlewood
Main threat	Clearing	Fire and clearing

• Moist deciduous is the wetter type. Two trees lead it in two different regions:
• Teak leads in the Peninsula.

• Sal leads in the east and in the Himalayan foothills.

• Dry deciduous is the drier type.

• In the dry season the trees lose all their leaves.

• The forest then looks like a grassland with bare trees.

• Sandalwood is a sweet-smelling tree, valued for its oil and for carving. NCERT classes it as a deciduous species.

Transition zones

• A transition zone is a belt where one forest type slowly changes into another.
• Dry deciduous forest has transition zones on both sides:
• On its wetter edges it changes into moist deciduous forest.

• On its drier edges it changes into thorn forest (rain under 50 cm).

• Across India, rainfall 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.

Why dry deciduous forest burns easily

• There is a lot of fuel.
• The dry season is long.

• Fallen leaves and dry grass pile up on the forest floor.

• The fire spreads fast.

• One spark can start a ground fire.

• The open, grassy parkland lets the fire run quickly.

• 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].

Where it occurs

• Moist deciduous (100-200 cm):
• Northeastern states, along the foothills of the Himalayas.
• Eastern slopes of the Western Ghats. These slopes are the rain-shadow side (the side facing away from the south-west monsoon wind, so it gets less rain). The wet western (windward) slopes carry evergreen forest instead.

• Odisha.

• Teak belt (Peninsula): Madhya Pradesh, Maharashtra, Karnataka, Kerala.

• Sal belt:
• Chota Nagpur plateau (mainly Jharkhand), Odisha and Chhattisgarh.

• 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: Karnataka and Tamil Nadu.

• Dry deciduous (70-100 cm):
• The rainier parts of the Peninsula.

• The plains of Uttar Pradesh and Bihar.

• Western and southern Rajasthan has very little vegetation because rain is low and animals have overgrazed the land (eaten plants faster than they can grow back).

• World: monsoon forests grow in the monsoon lands of South and Southeast Asia, where a wet season and a long dry season follow each other every year.

Don't confuse with

• Tropical evergreen forest: it keeps its leaves all year and grows on the wet western slopes of the Western Ghats. Moist deciduous forest grows on the drier eastern slopes.
• Tropical thorn forest: rain is under 50 cm. It looks like scrub (short, scattered bushes) with plants leafless for most of the year. Dry deciduous forest gets 70-100 cm and looks like parkland.
• Moist vs dry deciduous: teak and sal belong to the moist list. Tendu, palas, amaltas, bel, khair and axlewood belong to the dry list.
• Sandalwood vs evergreen: sandalwood grows in South India, but it is a deciduous species. It does not belong to the evergreen forest.

Prelims Hooks

• Most widespread forest type in India: tropical deciduous (monsoon) forest, with 70-200 cm of rain.
• Rainfall order: 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.
• Moist deciduous forest grows on the eastern (rain-shadow) slopes of the Western Ghats, not the western slopes.
• Khair and palas appear in both the dry deciduous and the thorn forest lists. This is a common "which of the following" trap.
• Dry deciduous forests are the most fire-prone. Fire-prone forest was 35.47% of India's forest cover (ISFR 2021) [2].

Mains Points

• Rainfall decides the pattern (GS-I):
• As rain falls towards the west and north-west, moist deciduous forest gives way to dry deciduous and then to thorn forest, through slow transition zones.

• Shedding leaves in the dry season is how these trees adapt to a long dry spell.

• Forest fires and degradation (GS-III):

• A long dry season, thick dry leaf litter and open grassy cover make dry deciduous forest the most fire-prone type [2].
• Fire hotspots fell from 2,23,333 in 2021-22 to 2,03,544 in 2023-24 (ISFR 2023). A fire hotspot is a spot that a satellite picks up as unusually hot, which means a likely active fire [3].

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

• Pressure at the dry edge (GS-III):

• Clearing and overgrazing push dry deciduous forest towards scrub. Western and southern Rajasthan shows the result: very little vegetation.
• Protecting this belt needs grazing control and community protection.

Related concepts

• Moist deciduous forest
• Dry deciduous forest
• Sandalwood
• Tropical thorn forest

Read more

• Tropical deciduous and thorn forests