Tropical Equatorial Rainforest
SEASONAL VARIATIONS IN CLIMATE IN MANAUS, BRAZIL
Manaus sits 3 degrees south of the equator. Its proximity to the equator means that its seasonal climate is influenced by the movement of the Inter-tropical convergence zone. (ITCZ)
The Inter-tropical convergence zone is found on (or near) the equator. The air from the tropics meets and rises by convection due to insolation from the sun. This results in the formation of cumulonimbus clouds and therefore high rainfall.
The Earth's tilt means that the area of highest insolation shifts seasonally, moving the ITCZ and resulting in seasonal variations in precipitation and an annual temperature variation of 2 degrees.
DIURNAL (DAILY) VARIATIONS IN CLIMATE IN MANAUS, BRAZIL
Daytime temperatures rise rapidly to 30 degrees due to intense insolation from the sun - which is directly overhead.
In mid-to-late afternoon, thunderstorms begin as a result of rapid evapotranspiration in the humid forest. Low pressure conditions means that the clouds are rapidly uplifted.
ANNUAL CHANGES IN SOIL MOISTURE BUDGET
Surplus (Jan - May): Precipitation is double evapotranspiration from January to April, and 75mm higher than PET in May. (ITCZ directly overhead)
Utilization (Jun - July): PET 25mm higher than precipitation. 1 degree increase in temperature
Deficiency (Aug - Oct): Precipitation 3 x lower than PET. (ITCZ moving into Northern Hemisphere)
Recharge (Nov - Dec): Rapid rise in precipitation. Precipitation 10mm higher than PET in November and 75mm higher in December.
ADAPTATION OF SPECIES
- Trees grow 50m tall for maximum photosynthesis
- Thin, flexible trunks to withstand high winds at height of canopy
Cacao Tree: Fruit on trunk allows pollination by midges (Forcipomyia) below canopy
- Few leaves on lower branches
- Thick, leathery, waxy cuticles withstand intense insolation
- 'Drip tip' channel water to prevent rotting or snapping
Calathea 'Medallion': Red undersides to reflect light energy for secondary photosynthesis
Mahogany: Widespread shallow root systems: Latosols have most nutrients in shallow horizons due to litter decomposition
Rosewood: Butress roots up to 3m above ground anchor tree
Epiphytes e.g Lianas: Use trunks of trees to reach canopy - aerial root systems catch dripping water
Goeldi's Monkeys: Curved claws for gripping branches. Long tail allows 4m leaps. 3D vision allows judgement of distance
Red Billed Toucan: Two toes forward & two toes backwards: grip branches. Long beaks for seeds
Poison Dart Frogs: Suckers on feet allow them to climb to Bromeliad (Epiphyte) leaves to rear young in pools of water. Red - poisonous.
RAINFOREST SOILS: LATOSOLS
Despite continual nutrient input from leaf litter decomposition, the nutrient content of rainforest latosols is in fact poor. This is for two reasons:
- Plant uptake is roughly equal to input via decomposition
- The year-long growing season means that the uptake of nutrients is constant
There is constant input of nutrients from leaf litter. However, soluble silica minerals are washed into the sub soil by eluviation (leaching). This leaves a concentration of the less soluble iron and aluminium oxides in the upper horizons, giving it a characteristic red colour.