savanna grassland Flashcards
facts
cover 20% of earths surface (15% more than rainforests)
dominated by shrubs and trees
two sub-biomes: temperate grassland and tropical grasslands
tropical savanna grassland
transitional biome
(a theoretical ecocline: a transition between two biomes where there is no distinct boundry)
cover over half of land in africa
outer reaches of the tropical zone
900 mm of rainfall
dry and wet seasons due to being close to the tropical zone
high temperatures at 30+ degrees
growing season is only in the wet season (around 4 months)
free draining acidic and thin layer of organic humus
not very fertile but has a top fertile layer than can not support deep wooded root plants like trees
typical plant species: baobab, acacia, and grasses
typical animal species: elephants, giraffes and elephants
climate - most important factor
hot and warm
distinct wet and dry periods
fires occur in the dry season to maintain the grassland
climatic savanna
natural succession
annual fires maintain
trees cannot survive long dry seasons
edaptic savanna
soil conditions keep them small
hills and ridges form where soil is shallow
valleys of clay create waterlogged soils
savanna productivity
vegitation biomass is 9% of tropical rainforests
npp decreases with dry season and latitude from equator
npp is higher where there are grazing animals as nutrients is recycled through decomposition and defecation
animal productivity is higher than in a tropical rainforest
nutrient cycling
stores are more even - less affected by leaching due to less precipitation
seasonal variations
dry season along with natural wildfires creates a short growing season - biomass store is overall 1/3 less than a rainforest
higher transfer of nutrients from biomass to litter at the start of the dry season because trees loose their leaves and grasses die back
litter store is small due to fires - decomposition is slow
transfer to soil is small
soil store is larger - vegetation demand is smaller and uptake is restricted to the wet season
savanna soil profile
climate is the dominant factor
up to 2m in depth
porous = rapid water drainage
thin humus layer - only support low lying plants with non-wooded root systems or small roots
acidic with a laterite layer which hardens in the dry season and stops roots from penetrating
soil moisture budget
fluctuates
wet season = surplus
dry season = deficit
July, August, September - only months where there is a surplus (Sept) and recharging of ground water (Jul/Aug)
potential evaporation is greater than precipitation inputs for 2/3 of the year
general savanna plant characteristics
xerophytic
deciduous trees that loose leaves in summer to conserve water in the dry season
grasses are pyrophytic - fire resistant
grass fires restore nutrients to the soil in the dry season
baobab tree
prehistoric plant species
absorbs and stores water in the trunk during the wet season, allowing it to produce nutrient-dense fruits in the dry season – “tree of life”
thick bark to resist fires
long tap roots to reach the water table
few leaves reduces transpiration loss
acacia tree
“umbrella tree”
20 meters tall
crown provides animals with shade
and reduces evaporation from the soil
symbiotic relationship with stinging ants - they feed on nectar produced by the tree and make sharp hollowed out thorns to protect from predators
central to life in the savanna – seed pods dropped are eaten by rhinos and monkeys and the bark is made into string by the people of Tanganyika
general animal adaptations
each species grazer has a preference of grass which maintains biodiversity
adapted:
migration
hibernation
grazing animals like zebra and gazelle have stripes to create an optical illusion and protect against predators
nocturnal and burrowing – safe from fires in the dry season and avoid predators
savanna ecosystem services
water
food
fuel
benefit nomad tribes (Maasai of kenya)
human impacts
land use change
landscape fragmentation
climate change