Savannas & Tropical Seasonal Forests
Savannas and Tropical Seasonal Forests (TSFs) are rolling grasslands with scattered shrubs and isolated trees. Savannas tend to receive less annual rainfall (40-100 cm), and TSFs receiving more (150-200 cm). Both are found in tropical to warm temperate areas. Plants are able to withstand long periods of drought. The savannas of Africa tend to support large herds of large herbivores (e.g. antelope, wildebeest, etc.)
Climate
Warm year round
Long dry winter and wet summer
Rainfall
40 – 200 cm/yr
Savanna less rain
Seasonal Forests more rain
Temperature
Annual average between 20 – 30°C
Regional Expressions
Mostly Africa, northern Australia, India
Soil
Moderately fertile soil
Flora
Plants highly specialized to grow during long periods of drought
Adaptations
Long tap roots
Thick bark
Deciduous leaves
Water storage
Above: A Whittaker Graph showing where savannas occupy this abiotic space, based on precipitation and temperature
Evolution of the biome
The origin of savannas is linked to the evolution of grasses, although seasonal tropical forests probably existed before savannas
The oldest evidence of grasses from 100–97 Ma from phytoliths but early grasses may have been marsh-edge plants, and not forming grassland biomes at this point
It is assumed that grasslands / savannas become prominent around 30 million years ago (Oligocene Epoch)
Additional Resources
Afforestation carbon sequestration projects found to be less effective than grasses in tropical savannas (Phys.org 29Aug2023)
Soil carbon in tropical savannas mostly derived from grasses (Zhao et al. 2023)