The Equatorial Climate and Rainforests

Point on the Specification

Characteristics of an equatorial climate (tropical rainforests)

• Average temperature around 26 degrees (due to heavy cloud and rainfall)
• A small annual and daily diurnal temperature 
• Average annual rainfall over 1500 millimeters
• High relative humidity (over 75%)

Relationship of the ecosystem

Food Web

Relationship of the ecosystem

Emergents – tallest trees emerge through the main canopy layer

(Main) canopy layer – most animals live here

Lower/Under canopy layer – small trees and saplings grow in shady, humid conditions

Shrub layer – smaller trees and ferns grow in deep shade

Ground layer – leaf and animal remains cover the ground

Roots of plants take up water from the ground and rain is intercepted as it falls (canopy level)

As the rainforest heats up, the water evaporated into the atmosphere and forms clouds to make the net day’s rain. This is convectional rainfall

Rainforest Nutrient Cycle

• rainforest nutrient cycling is rapid 
• the hot, damp conditions on the forest floor allow for the rapid decomposition of dead plant material
• this provides plentiful nutrients that are easily absorbed by plant roots
• however, as these nutrients are in high demand from many plants in the rainforest they do not remain in the soil for long and stay close to the surface of the soil. 
• This is why when vegetation is removed, the soils quickly become infertile and vulnerable to erosion. 

Rainforest soils – red due to high iron and aluminium content, thick layer of leaf litter and decomposing matter on the surface

Adaptations in Plants 

• Drip-tip leaves – pointed tips and glossy leaves to remove water quickly

• Buttress roots (found on large, shallow rooted trees) – supports tree and gathers more nutrients

• Epiphytes – these plants live on the surface of other plants, mostly tree trunks and branches. This allows them to make the most of the sunlight in the canopy layer

• Stilt roots – In a similar way to buttress roots, these provide tall rainforest trees with support as they are anchored in the shallow rainforest soils

Deforestation in Malaysia

Causes 

• cattle ranching

• palm oil plantations
• mining
• infrastructure leading to an increase in tourism and industrial output
• Logging (timber and hardwoods)

Specifics/Details

• Malaysia has 2199 endemic species , 18% of these are listed as endangered
• One of the most threatened animals is the pygmy elephant
• The Penan tribe of Borneo are facing a fight for survival (due to logging and dam construction)

Local Consequences

• loss of biodiversity (risks extinction of animals like orangutans)
• loss of local resources (such as medicinal plants for making medicines)
• pollution of waterways which leads to water shortages (affecting people all over Malaysia)
• Soil erosion
• Soil becomes infertile
• Climate gets drier as there are no longer trees that give off moisture through transpiration

Global Consequences

• Exacerbates the greenhouse gas effect and climate change
• Contributes to the rise in global temperatures

• Where Hadley and Ferrel cells meet, air descends creating high pressure. 
• Low pressure is created where the two Hadley cells meet and air rises, when this air cools it becomes denser and falls towards the ground leading to high pressure, This cool air warms as it reaches the Earth’s surface, causing any clouds to evaporate. Heavy rain at the equator means that most of the moisture had gone by the time the air reaches the subtropics

• High-pressure systems – clear skies and dry, hot weather. 
• Low pressure causes warm air to rise, after which it cools and condenses to form clouds.
• Moisture falls from the atmosphere as rain, sleet, snow or hail (collectively known as precipitation). 
• Differences in temperature between day and night are unlikely to be large as the cloud cover reflects solar radiation during the day and traps it at night.

Atmospheric air pressure – the force exerted on the Earth’s surface by the weight of the air, measured in millibars

Low pressure – occurs when the air is rising, so less air is pressing down on the ground; air rises as it warms, leading to low pressure at the surface. 

High pressure – occurs when there is more air pressing down on the ground caused by air sinking; air descends as it cools, leading to high pressure at the surface.

Why does is it rain so much on the equator?

The equator has high insolation all year round which causes the water from the sea to evaporate a lot. The heated warm ocean and ground, heats the air causing air to cool and rise. The water vapour in the air then condenses and becomes rain. This is why there is a large amount of rainfall on the equator.

Key Terms

• Ecosystem – a community of living organisms (eg. plants, animals) living in conjunction with the nonliving components of their environment (eg. water, air) interacting as a system
• Latitude – measurement of distance north or south of the equator (measured with lines that form circles around the Earth, parallel to the equator)
• Weather – day-to-day conditions of the atmosphere (eg. precipitation, temperature)
• Climate – average weather conditions of an area over a long period of time
• Producer – plants (makes food by photosynthesis from the energy of the sun) (1st in a food chain)
• Consumer – organisms that feed on plants (2nd in food chain)
• Food Chain – is a linear sequence of organisms through which nutrients and energy pass as one organism eats another 
• Food Web – consists of many interconnected food chains (is a more realistic representation of consumption relationships in ecosystems)
• Biodiversity – refers to the different kinds of life found in an area (the variety of animals, plants, fungi, microorganisms etc. that make up our natural world)
• Deforestation – clearing of forested land
• Soil erosion – the displacement of the upper layer of soil (form of soil degradation). It is caused by dynamic activity of erosive agents (eg. water, ice, animals, humans)