Savanna ecosystems Flashcards
(11 cards)
Savanna ecosystems
- Areas of tropical grassland
- Occur with or without trees and shrubs
- Widespread in low latitudes
- Covers approximately ¼ of the world’s land surface – 18 million km2
Origin of savannas -
Climate: Seasonal rainfall and dry periods favour grasses over trees
Soils: Infertile or well-drained soils support grassland, not forest
Geomorphology: Drainage patterns and landscape position affect moisture availability
Burning: Regular fires prevent forest growth and maintain open grassland
Grazing: Overgrazing removes grasses and increases runoff
Savannas are often shaped by long-term human land use
Type of savanna
- Savanna woodland
- Grassland savanna
- Savanna parkland
- Termite savanna
Climate
Savannas have a tropical wet and dry climate with distinct wet and dry seasons.
Wet season (summer):
- Caused by convectional/monsoonal rainfall
- Rainfall varies: 500–2000 mm/year
Dry season:
- Lasts 1 to 8 months
- Causes grass dominance over trees
Temperatures:
- High all year: 23–28 °C
- Evapotranspiration is high → strong seasonal contrast between water surplus and water deficiency
Vegetation
Xerophytic (adapted to drought)
Pyrophytic (adapted to fire)
Drought adaptations:
- deep tap roots,
- reduced or no leaves,
Fire adaptations:
- thick bark,
- underground growth tissues,
- fast regeneration
Grasses dominate due to fire and grazing; growth tissue at base protects from damage
Examples: trees like acacia, baobab, and palms reach up to 12 m with flattened crowns and strong roots
Elephant grass can grow over 5 m tall
Net primary productivity (NPP):
900 g/m²/year average
Animals in savanna ecosystem
Termites: aerate soil, decompose up to 30 kg of cellulose/ha/year, up to 600 mounds/ha
Locusts: can devastate large grass areas quickly
Grazers: over 40 species (e.g. giraffe, zebra, gazelle, elephant)
Selective feeding allows niche diversity
Carnivores: lions, cheetahs, hyenas
Tropical rainforest soils
Soils are mostly ferralitic/oxisols/latosols
Highly leached, acidic, low in nutrients
Rainforest soils: deep, red or red–brown, high in iron and aluminium
Savanna soils: more weathered ferruginous types
Most nutrients are stored in the biomass, not the soil
Rapid litter decomposition, fungi transfer nutrients directly to trees
Soil regolith may be up to 150 m deep in stable shield areas
Ferralitic soils
(Oxisols, latosols)
Deeply weathered tropical soils
Nutrient poor
High levels of iron (Fe)
Common in tropical rainforest regions
Form under hot, humid conditions over long periods
Often red in colour and infertile
Ferruginous soils
Weathered ferralitic soils found mainly in savanna regions.
Less leached than rainforest soils
Contain more base nutrients and may support grassland vegetation
How does deforestation affect rainforest soils?
Topsoil is lost, removing most of the organic matter and nutrients
Soil compaction from machinery reduces infiltration (from 200 to 39 cm/hr)
Moisture content drops due to loss of mulch and organic matter
Burning temporarily improves fertility by reducing acidity and adding ash nutrients
However, both burning and bulldozing reduce long-term fertility and increase erosion
How can the impact of rainforest clearance on soils be reduced?
Improve land productivity using appropriate crops and techniques
Use less damaging clearance methods and time them carefully
Focus on restoring degraded land instead of clearing new forest
Recognise that cleared rainforest becomes vulnerable to nutrient loss, erosion, and long-term degradation if not managed properly
