The correct option is (a).
Explanation
In mountainous regions, the decrease in temperature with increasing altitude leads to a corresponding change in natural vegetation. This creates a distinct succession of vegetation belts from the tropical foothills to the alpine peaks, similar to the transition observed from the equator towards the poles.
Altitudinal Zonation of Vegetation in the Himalayas:
- Foothills (Region 1): The foothills of the Himalayas are dominated by Tropical Deciduous Forests. Valuable timber species like Sal are prominent in these regions.
- Height of 1000–2000 m (Region 2): In this altitude range, particularly in the wetter Eastern Himalayas, Wet Temperate Forests are found. These forests are characterized by evergreen broad-leaf trees such as oaks and chestnuts.
- Height of 1500–3000 m (Region 3): Between these altitudes, Temperate Forests containing coniferous trees cover the southern slopes of the Himalayas. Common species include pine, deodar, silver fir, spruce, and cedar.
- Height > 3600 m (Region 4): At high altitudes, temperate forests and grasslands give way to Alpine Vegetation. Silver firs, junipers, pines, and birches become stunted as they approach the snowline. Beyond this, mosses and lichens (Tundra vegetation) are found.
Therefore, the correct sequence from lower to higher altitude is: Deciduous → Wet Temperate → Temperate Coniferous → Alpine.
Key Takeaway:
Vegetation in the Himalayas follows a vertical stratification based on altitude: Tropical Deciduous (Foothills) → Wet Temperate (1000–2000 m) → Temperate Coniferous (1500–3000 m) → Alpine (>3600 m).