Chapter 5: Spatial Distribution of Tropical Rainforests and Mangroves

What’s considered high? What’s considered low?

Temperature conditions

• Mean Annual Temperature: High: >25℃, Low: <20℃

• Annual Temperature Range: Large: >10℃, Small: <5℃

A small range means that the temperature is consistent throughout the year, while a large range will show distinct summer / winter seasons. 

Total Annual Rainfall: 

• High: >1500mm, Low: <1000mm 

Not all climates with high annual rainfall show consistently high rainfall throughout the year. Some months may have extremely high rainfall whole other months may be dry seasons.

Describing Climograph

*Uniform rainfall is >60mm for every month; highest month not more than double of lowest month

Otherwise, just state that it is relatively uniform.

distinct wet and dry season

• Rainfall is unevenly distributed throughout the year. 

• There is a distinct wet and dry season. The wet season begins from June to October, and the dry season from December to April.

CHARACTERISTICS & CONDITIONS OF GROWTH OF TRF

• Characteristics include:

  • Structure

  • Density of vegetation

  • Type of flora and fauna (plant and animal)

Layers of TRF

Emergent, canopy, undergrowth

Emergent layer >30 m

Description:

Tallest

Characteristics:

Tall, straight trunks, Small, pointed leaves 

Why this matters:

Being very tall allows trees to receive maximum sunlight, reducing competition with other plants.

Canopy layer 20-30m

Description:

A continuous layer formed by the crowns of tall trees

Characteristics:

• Dense cover, Broad, waxy leaves, Many branches

• Prevents 97-98% of the sunlight from reaching the forest floor

• Highest biodiversity 

Why this matters:

The dense canopy captures most of the sunlight, allowing trees to photosynthesise efficiently and support many animals.

Undergrowth layer <20m

Description:

• Smaller trees and shrubs growing beneath the canopy

Characteristics:

• Very little sunlight able to reach this layer

  • Vegetation is relatively sparse 

  • Except smaller plants ones that can grow in the shade and the seedlings of taller trees (shorter plants, shade-tolerant plants)

  • When gaps form in the canopy, more sunlight reaches the undergrowth layer, allowing certain species of plants to grow rapidly upwards and fill these gaps. 

• Plants that have large, broad leaves

• Thick layer of leaf litter

Why this matters:

• Large leaves help plants capture limited sunlight that filters through the canopy.

• Limited sunlight restricts plant growth, but rapid decomposition returns nutrients quickly to the soil for reuse.

types of ADAPTATIONS OF THE PLANTS IN THE TRF

drip tips,broad leaves, waxy leaves, buttress roots

Drip tips

What do you observe about the shape of the leaf? 

Small, narrow tips that point downwards

Why do you think it has this shape? 

This allows rainwater that falls onto them to flow off easily.

Together with waxy leaf surfaces, both adaptations allow leaves to dry easily and prevents harmful bacteria or fungi from growing on them, as high rainfall and temperatures of tropical climate promote the growth of bacteria.

Broad leaves

What do you observe about the shape & size of the leaf? 

Leaf is large with a wide surface area

Why do you think it has this shape & size? 

Enables plants to absorb as much sunlight as possible in order to photosynthesize

Waxy leaves

What do you observe about the texture & shape of the leaf? 

Glossy (smooth and shiny) appearance on the surface

Why do you think it has this texture & shape? 

This reduces the amount of water vapour that it loses to the atmosphere through transpiration because of the high temperatures in the tropical rainforest.

Buttress roots + Shallow + extended roots: 

What do you observe about the shape & size of the root? 

Buttress roots: Tall (up to 5m ABOVE the ground surface), large and wide

Shallow + extended roots: Spread out above the ground near the base of the tree

Why do you think it has this shape & size? 

Buttress roots: 

Support the great weight of trees, that had grown as tall as possible to get maximum sunlight

Keep them upright and prevent them from toppling over. 

Shallow + extended roots: 

Given the rapid rate of decomposition, humus/nutrients are formed rapidly in the topsoil, which is the uppermost layer of the soil. The trees tend to have shallow underground roots that spread wide to absorb as much nutrients as quickly as possible.

3 lattitudes

tropic of cancer, tropic of capricorn, equator

Areas with TRF

• Amazon Rainforest, Brazil, South America

• Congo Basin, Congo, Africa