Unit 5: Phytogeography
Table of Contents
1. Principles of Phytogeography
Phytogeography (or plant geography) is the branch of biogeography that studies the geographical distribution of plant species and their influence on the earth's surface.
Core Principles:
- Descriptive Phytogeography: Focuses on the description of floral regions.
- Interpretative (Historical) Phytogeography: Explains the reasons for the distribution patterns based on past events and evolutionary history.
2. Continental Drift and Theory of Tolerance
The current distribution of plants is heavily influenced by geological history and the environmental limits of the plants themselves.
Continental Drift
This theory explains how landmasses moved over time, causing the isolation of plant populations or creating "land bridges" that allowed migration. This movement explains why closely related plant species are sometimes found on different continents.
Theory of Tolerance
This theory states that a plant's distribution is limited by its range of tolerance for various environmental factors (like temperature, moisture, and light). A species will only exist in areas where the environmental conditions fall within its physiological limits.
3. Concept of Endemism
Endemism refers to the condition of a plant species being unique to a specific geographic location, such as a specific mountain range, island, or country, and not found naturally anywhere else.
- Causes: Physical barriers (mountains, oceans), climate changes, or recent evolution in a specific spot.
- Significance: Endemic species are often highly vulnerable to extinction due to their restricted range.
4. Major Terrestrial Biomes
Biomes are large geographical areas characterized by their climate, soil, and specific types of vegetation.
| Biome Type | Climate Characteristics | Vegetation Type |
|---|---|---|
| Tropical Biome | High temperature and rainfall year-round. | Tropical Rainforests, high species diversity. |
| Temperate Biome | Moderate temperatures with distinct seasons. | Deciduous forests or grasslands. |
| Tundra Biome | Extremely cold, short growing season. | Mosses, lichens, and dwarf shrubs; lack of trees. |
5. Phytogeographical Divisions of India
India is divided into several phytogeographical regions based on varied climatic and topographic features. These divisions typically include the Western Himalayas, Eastern Himalayas, Indus Plain, Gangetic Plain, Central India, Malabar (Western Ghats), Deccan, and the Andaman/Nicobar Islands.
6. Vegetation of NE India and Assam
North-East India is a significant biodiversity hotspot with a wide array of vegetation types.
Vegetation Types in NE India:
- Tropical Evergreen and Semi-evergreen Forests: Found in areas with very high rainfall.
- Deciduous Forests: Common in the plains and foothills of Assam.
- Grasslands: Found in riverine areas and high-altitude plateaus.
- Alpine Vegetation: Restricted to the high-altitude regions of the Eastern Himalayas.
Special Reference to Assam: The vegetation is dominated by tropical evergreen, semi-evergreen, and moist deciduous forests, with significant riverine grasslands in areas like Kaziranga.
7. Exam Focus: Tips and FAQs
Common Pitfalls
- Mistake: Confusing a "Biome" with an "Ecosystem." Correction: A biome is a large regional unit based on climate/vegetation; an ecosystem is a smaller functional unit of interaction.
- Mistake: Thinking endemic species are just "rare." Correction: Endemic species are rare because they are restricted to a specific area; not all rare species are endemic.
Frequently Asked Questions
Q: What is the significance of Continental Drift in phytogeography?
A: It explains the "disjunct distribution" of plant families, where identical or related plants are found in widely separated parts of the world.
Q: Why is NE India called a biodiversity hotspot?
A: Due to its unique position at the junction of three biogeographical realms, leading to exceptionally high species richness and endemism in its vegetation.