Tropical Vegetation: Rainforest and Savanna

This section explores the distinctive vegetation characteristics of rainforest and savanna ecosystems found in tropical environments. We will examine the adaptations of plants to these climates and the key factors influencing their distribution.

Rainforest Ecosystems

Characteristics

Rainforests are characterized by high rainfall, high temperatures, and incredible biodiversity. They are typically found near the equator.

Vegetation Layers

Rainforest vegetation is highly stratified, forming distinct layers:

• Emergent Layer: The tallest trees (up to 60m) that rise above the canopy. They receive direct sunlight.
• Canopy Layer: A dense, continuous layer formed by the crowns of most rainforest trees. This layer intercepts most of the sunlight.
• Understory Layer: A darker, more humid layer below the canopy, with smaller trees and shrubs adapted to low light conditions.
• Forest Floor: The ground layer, receiving very little sunlight. It is often damp and rich in decaying organic matter.

Adaptations to Rainforest Conditions

Rainforest plants have evolved numerous adaptations to thrive in this environment:

• Large, broad leaves: To maximize light capture in the shaded understory.
• Drip tips: Leaf tips are shaped to allow rainwater to run off quickly, preventing fungal growth.
• Buttress roots: Large, above-ground roots provide stability in shallow, nutrient-poor soils.
• Epiphytes: Plants that grow on other plants (e.g., orchids, ferns) to reach sunlight.
• Lianas: Woody vines that climb trees to reach sunlight.
• Rapid nutrient cycling: Decomposition occurs quickly due to warm, humid conditions.

Soil Characteristics

Rainforest soils are generally nutrient-poor. The rapid decomposition of organic matter means nutrients are quickly taken up by plants and are not retained in the soil.

Table: Comparison of Rainforest and Savanna Vegetation

Feature	Rainforest	Savanna
Rainfall	High (2000-10000 mm)	Moderate (500-1500 mm)
Temperature	High and consistent	Warm with distinct wet and dry seasons
Vegetation Type	Dense, multi-layered	Grassland with scattered trees
Soil Fertility	Generally poor	More fertile than rainforest soil

Savanna Ecosystems

Characteristics

Savannas are grasslands with scattered trees, typically found in tropical regions with distinct wet and dry seasons.

Vegetation Types

Savanna vegetation is dominated by grasses, but also includes a variety of trees and shrubs adapted to drought conditions:

• Grasses: Various species of tall, coarse grasses are the primary vegetation.
• Scattered Trees: Trees are often drought-resistant, with adaptations like deep roots and thick bark. Examples include acacia trees.
• Shrubs: Drought-tolerant shrubs are also common.

Adaptations to Savanna Conditions

Savanna plants have evolved adaptations to survive the seasonal droughts:

• Deep roots: To access water deep underground.
• Thick bark: To reduce water loss through transpiration.
• Deciduous leaves: To shed leaves during the dry season, reducing water loss.
• Tolerance to fire: Some grasses and trees are adapted to survive or regenerate after fires, which are common in savannas.

Soil Characteristics

Savanna soils are generally more fertile than rainforest soils, due to the seasonal wet and dry cycles. The dry season allows for the accumulation of organic matter.

Figure