Climate:
- Average annual rainfall is about 2000 mm. Every month receives rainfall of at least 200mm.
- Most of the rainfall is through convectional mechanism leading to heavy downpour through cumulonimbus clouds.
- Mean annual temperature is around 20 degrees Celsius but the highest temperature of the year touches 30 degree Celsius.
- Annual range of temperature is around 1 degree Celsius but daily range is around 5 degrees Celsius.
Regions:
- It extends between 10-degree N and 10-degree S.
- Maximum development of this biome is has taken place in Amazon basin, Congo basin and Indo-Malaysian basin.
- In some areas, spatial coverage of this biome extends beyond the Equator also.
This biome is called ‘Optimum Biome’ because of uninterrupted supply of abundant moisture, water and heat throughout the year which ensure continuous growth of plants. The upper canopy of tallest trees receives maximum sunlight, and the lower levels experience maximum darkness. This sets in keen competition among plants and trees to reach to the highest levels and hence the grate heights of trees in this Biome.
There is maximum interception of falling rains by the uppermost canopy of the forest and thus the intercepted water reaches the surface through leaves, branches and stems of trees in the form of ‘aerial streamlets’ which allows maximum infiltration of rainwater in the ground surface. Primary productivity of tropical rainforest biomes is the highest of all biome types of the world.
Species Composition:
- It accounts for the largest number of plant species.
- There is almost uniformity and similarity in the life forms across all the parts of the world.
- Tree is the most significant member. It has a huge diversity.
- Creepers and climbers are the second important floral members. In constant struggle for light, they have developed mechanism for reaching the high insolation areas. Rainforests account for 90% of all the climber species.
Climbers and creepers both are weak-stemmed plants and, as a result, fail to grow erect in the absence of any support. The main difference between them is that creepers grow along with the soil horizontally, while climbers can grow vertically. Epiphyte is a type of climber which do not have their own roots, also called air plant, any plant that grows upon another plant or object merely for physical support. Epiphytes have no attachment to the ground or other obvious nutrient source and are not parasitic on the supporting plants. Epiphytes obtain water from rain and water vapour in the air; most absorb water with their roots, though many have specialized leaves that also take in moisture.
Vertical stratification of vegetation communities: Vertical stratification refers to the division of an ecosystem into different layers based on the height of the vegetation. In an evergreen forest, there are typically several distinct layers. The five-fold vertical division of evergreen vegetation typically includes the following layers:
- Canopy: The uppermost layer of the forest, made up of the tallest trees and their branches and leaves. This layer receives the most sunlight and is the most productive in terms of photosynthesis and biomass. This is the dominant layer and its height ranges between 30m and 60m.
- Sub-canopy: This layer is located immediately below the canopy and is made up of smaller trees. It receives less sunlight than the canopy layer and is less productive. It is the codominant layer and height ranges from 25m to 30m.
- Third layer: The understory is made up of smaller trees that receive very little direct sunlight. Leaves of these trees have broader leaves to capture more sunlight.
- Fourth layer: This is the shrub layer. It is fragmented and includes some dwarf or stunted plants and trees.
- Fifth layer: This is dominated by herbaceous plants.
Animal Life:
- Number, density and diversity of animals increase from the ground layer towards increasing strata.
- Most of the animals are arboreal (tree living) and therefore they are provided with additional features to climb trees like claws, adhesive pads, fingers etc.
- Some animals develop the ability to glide like tree frogs, squirrels etc.
- Since the food is available in abundance, animals do not have to migrate for larges distance and hence the animals in rainforests are least mobile.
