Natural Vegetation in Assam
Assam, located in the northeastern part of India, lies in a biodiversity hotspot with diverse natural vegetation influenced by its :
- Subtropical climate,
- High rainfall (1500-3750 mm annually),
- Varied topography (Brahmaputra and Barak valleys, hills), and
- River systems.
As per the latest Indian State of Forest Report (ISFR) 2023, Assam’s forest cover stands at 36.10% of geographical area, down from ISFR 2021 data of 36.11%.
| Parameter | ISFR 2021 | ISFR 2023 |
|---|---|---|
|
Forest Cover (sq km) |
28,326 |
28,313 |
|
Percentage of Geographical Area |
36.11% |
36.10% |
India’s ISFR defines forest cover :
Key Criteria to define forest cover ;
Minimum area: >1 hectare land area
Canopy density: ≥10% tree canopy cover
Tree height potential: ≥2 meters at maturity
Forest Density :
| Class | Canopy Density |
|---|---|
| Very Dense Forest | ≥70% |
| Moderately Dense | 40-70% |
| Open Forest | 10-40% |
| Scrub Forest | <10% |
Natural Vegetation in Assam ranges from tropical wet evergreen and semi-evergreen forests in high-rainfall areas to moist deciduous forests, grasslands, and subtropical pine forests in hills.
Accordingly , Assam has five major vegetation types:
- Tropical Wet Evergreen,
- Tropical Semi-Evergreen,
- Tropical Moist Deciduous,
- Tropical Dry Deciduous, and
- Subtropical Pine Forests.
Rich in flora, Assam has extensive bamboo groves (38 native species), orchids (best in evergreen/semi-evergreen forests), and medicinal plants. Vegetation supports iconic wildlife like one-horned rhino, tiger, and elephants.
Factors Influencing Natural Vegetation
- Climate: Heavy monsoon rainfall, high humidity, moderate temperatures promote luxuriant growth.
- Topography: Valleys favour alluvial grasslands and deciduous forests; hills support evergreen and pine forests.
- Soil: Alluvial in plains (fertile for grasslands); lateritic/acidic in hills.
- Altitude: From tropical in plains to subtropical in hills.
- Human Impact: Deforestation, jhum cultivation, tea plantations have reduced original cover.
Major Types of Natural Vegetation
1. Tropical Wet Evergreen Forests
Distribution
- Upper Assam, foothills of Eastern Himalayas, parts of southern hills (e.g., Borail Range, Dima Hasao).
- Associated with highest rainfall areas.
Characteristics
- Multi-layered canopy, tall trees (up to 50m), dense undergrowth, epiphytes, climbers abundant.
- No distinct dry season; trees evergreen.
Dominant Species
- Hollong (Dipterocarpus macrocarpus – State Tree), Mekai, Nahar (Mesua ferrea), Gurjan, Agar.
Significance
- High biodiversity; timber value.
Diagram
2. Tropical Semi-Evergreen Forests
Distribution
- Northern and southern reserve forests (e.g., Kaziranga fringes, Upper Assam, Barak Valley areas like Inner Line, Sonai RF).
Characteristics
- Mix of evergreen and deciduous species; transitional between evergreen and moist deciduous.
- Dense, with bamboos common.
Dominant Species
- Hollong, Nahar, Champa, Garjan (Dipterocarpus turbinatus in south), teak plantations in some areas.
Significance
- Rich in orchids and wildlife habitats.
3. Tropical Moist Deciduous Forests
Distribution
- Central and lower Brahmaputra Valley (e.g., Nagaon, Kamrup, Goalpara districts); foothills.
Sub-types
- Sal Forests: Prominent in central Assam.
- Mixed Deciduous: With sprinkling of evergreen species.
Characteristics
- Trees shed leaves in dry season; sal dominant in pure stands.
Dominant Species
- Sal (Shorea robusta), Teak, Sissoo, Khair, Bhelkar.
Significance
- Commercially important timber; supports mixed wildlife.
4. Grasslands and Savannahs
Distribution
- Floodplains of Brahmaputra (Kaziranga, Manas, Pobitora, Orang, Dibru-Saikhowa NPs/WS).
Characteristics
- Tall elephant grasses, short meadows; wet savannah due to floods.
- Vital for herbivores.
Dominant Species
- Elephant grass (Saccharum spp.), thatch grass.
Significance
- Home to one-horned rhino, tiger, deer; key conservation areas.
picture
5. Hill and Subtropical Forests
Distribution
- Karbi Anglong, Dima Hasao (North Cachar Hills).
Sub-types
- Subtropical Broadleaved Hill Forests.
- Subtropical Pine Forests (higher elevations, e.g., Hamren subdivision).
Characteristics
- Broadleaved at lower hills; pure pine stands higher up.
Dominant Species
- Pinus kesiya (Khasi Pine), oak, rhododendron associates.
Significance
- Watershed protection; orchids and ferns abundant.
6. Other Vegetation Types
- Riverine Forests: Along rivers; riparian species.
- Bamboo Brakes: Widespread; 38 species, e.g., Bambusa tulda.
- Wetlands and Swamps: Beels, haors in valleys; aquatic vegetation.
Regional Variations
- Brahmaputra Valley: Semi-evergreen patches, moist deciduous, extensive grasslands.
- Barak Valley: More evergreen/semi-evergreen influence; higher rainfall uniformity.
- Hill Districts: Subtropical broadleaf and pine; shifting cultivation impacts.