Geography – Soils in rainforests and savannas | e-Consult

Pedogenesis, the process of soil formation, occurs at different rates and with different characteristics in tropical and temperate climates. These differences are primarily driven by variations in weathering rates, vegetation cover, and climate.

Tropical Climates:

• High Weathering Rates: High temperatures and abundant rainfall lead to intense chemical weathering, particularly hydrolysis and solution. This results in the rapid breakdown of rocks and the formation of clay minerals.
• Vegetation Cover: Vegetation cover is often sparse, particularly in later stages of soil development. This exposes the soil to direct rainfall and reduces the input of organic matter.
• Soil Profile: Tropical soils often exhibit a distinct soil profile with a well-developed Oxisols or Ultisols. These soils are typically acidic, leached of nutrients, and have a low cation exchange capacity. The eluvium (leached zone) is often brightly coloured due to the accumulation of iron and aluminium oxides.
• Rapid Soil Development: Due to the intense weathering and rapid leaching, soil development is relatively rapid in tropical climates.

Temperate Climates:

• Lower Weathering Rates: Temperatures are generally cooler than in tropical climates, leading to slower weathering rates. Chemical weathering is still important, but physical weathering plays a more significant role.
• Vegetation Cover: Vegetation cover is typically dense, particularly in forest ecosystems. This provides a significant input of organic matter and protects the soil from direct rainfall.
• Soil Profile: Temperate soils often exhibit a more developed soil profile with horizons such as A, B, C, and R. The A horizon is rich in organic matter, the B horizon may show signs of leaching, and the C horizon is composed of weathered parent material.
• Slower Soil Development: Soil development is generally slower in temperate climates compared to tropical climates due to the slower weathering rates and the accumulation of organic matter.

Comparison: Both tropical and temperate climates experience weathering and soil formation. However, the rate and type of weathering, the amount of organic matter input, and the resulting soil profile differ significantly. Tropical soils are characterized by rapid weathering and leaching, while temperate soils exhibit slower weathering and a greater accumulation of organic matter. The vegetation cover is a key factor influencing these differences.