CSEC Geography- Vegetation and Soils. This document defines an ecosystem and describes the major components of an ecosystem. It also looks on the two major biomes, tropical rainforest and tropical marine.

1. CSEC Geography
Physical Geography
Vegetation and Soils
O.Johnson
What is an ecosystem?
An ecosystem is a community of plants and wildlife, together with the environment in which
they live. All parts of the ecosystem are interconnected. They affect each other in several
different ways. There are flows of energy and nutrient, and a change in one part of the ecosystem
will have effects on the other parts.
Being a system, an ecosystem is in balance, unless something happens to upset that balance.
People, as part of an ecosystem, are most likely to upset that system. A sudden physical change ,
such as natural disaster – for example a volcanic eruption or a hurricane- will upset the balance
for a while, but the system will recover in a surprisingly short time. The scale of ecosystems
varies hugely. An ecosystem can be something as small as a pond, an individual tree, a garden, a
beach or a field ; or it can be something much larger; a rainforest, a region of grassland , a whole
island. An ecosystem is a whole community, including plants, animals, insects, bacteria, climate,
soils, rock type and relief. Within the community plants and wildfire rely on each other. For
example, insects pollinate flowering plants and in return feed on the nectar- both are satisfied.
This relationship is called symbiosis. The species in an ecosystem change and develop over time.
They react to their circumstances and environment and adapt to them.
The earth’s surface can be divided into larger- scale ecosystems, each covering a huge area on
the land surface. These larger systems are called biomes. Each biome takes its name from its
dominant type of vegetation. Examples include rainforest, savanna, temperate deciduous
woodland, tundra and desert.
How does an ecosystem function?

2. Components and functions of an Ecosystem
An ecosystem is made up of living and non-living components
Living (biotic) components: This includes all organisms in an ecosystem including plants and
animals from the very large to the microscopic. The living components of an ecosystem can be
further subdivided into the following groups:
 Producers: Producers are the green plants and they are the basis for the other living parts of
the ecosystem. Ecosystems receive their energy from the sun. Solar radiation (the sun’s
energy) enters the atmosphere and is absorbed by chlorophyll in leaves. The process of
photosynthesis then takes place. In simpler terms, they use carbon dioxide, water and
sunlight to make food. The energy created from these processes then flows through the rest
of the system. This is the called the food chain. It is the series of events where one species
eats another. Each level of plants or animals becomes the food for the species above it in the
system. There are many types of producers, from the largest trees in the rainforest to
microscopic algae. All other organisms in an ecosystem are dependent on producers either
directly or indirectly.

3.  Primary consumers: These are organisms (birds, insects) which obtain their nutrients
directly from plants. They are also known as herbivores. Examples of primary consumers
include grasshoppers, goats, parrots, monkeys, tapirs and zebras.
 Secondary consumers: Carnivores are meat eaters and so they feed on the herbivores or on
other, smaller carnivores. Usually those that eat other carnivores are the larger species and
are known as the higher carnivores; these include the big cats like jaguars, lions and
cheetahs. Lizards, spiders and eagles are examples of lower carnivores.
 Decomposers: Another part of the food chain which cannot be ignored is the decomposers.
Decomposers are bacteria and fungi which rot down dead plant and animal material. They
make the nutrients in these materials available to the next generation of plants. Small soil
fauna (animals and insects) work as an important part of the system too. Once dead plants
and animals are rotted down (decomposed) by the decomposers their remains are mixed into
the soil by earthworms and ants. The material is called humus and it is packed with
nutrients that will feed the next generation of plants. In this way the whole cycle or system
is completed.

4. Non-living (abiotic) components: These components include sunlight, temperature, water and
soil. These components play an important role in determining the types of ecosystems which
develop in particular areas. Inputs add nutrients, water or energy to the system. The main ones
are rainwater, sunshine and minerals. The sun’s energy, which gives the whole system its
energy. Rainfall, which is important in two ways:
- It adds a few nutrients to the system, minerals which are dissolved in the rain water
- The water itself is essential for plant growth and for animal life
All systems have inputs, processes and outputs. The outputs are losses of water and nutrients
from the system. Some rain falling on the ground trickles through the litter and is lost (runoff).
As it passes through the litter it dissolves some nutrients, so they are also lost from the system.
Water that reaches the soil may also be lost, deeper underground, again taking nutrients with it.
Climate, Soil and Ecosystems
Ecosystems are influenced by thefollowingfactors:
Climate:
Climate plays a major role in determining the type of ecosystem which develops in an area. Plant
growth is encouraged where there is a warm climate, withhigh rainfall all year round, as in a rainforest.
When plants grow rapidly, thereis plentyof food for primaryconsumers; these in turn become food forthe
secondaryconsumers. The amount of rainfall experienced annually in an area will affect the types
of plants and animals which can survive there. For instance, in an area which experiences very

5. little rainfall, you will only find plants and animals which are able to survive in the dry
conditions. Temperature is also an important factor in determining the type of ecosystem which
develops in an area. In areas which are very cold you will find plants and animals which are
adapted to survive in low temperatures. Similarly, in areas which are very hot you will find
organisms which are adapted to survive in high temperatures. Therefore, when studying an
ecosystem, it is important to acknowledge the influence of the climate.
Soil
Soil often plays a major role in the development of an ecosystem. Soil is composed of weathered
material, organic matter, water and air. There are many types of soil. The type of soil which is
found in an area is influenced greatly by the climate and also the type of rock which is weathered
to produce the soil. The type of soil found in an area determines to a large extent the types of
plants which can grow there. This in turn influences the types of animals which can survive
there.

6. Tropical Biomes
The zone of the Earth between the Tropic of Cancer (23.50
N) and the Tropic of Capricorn
(23.50
S) is known as the tropics. Within these latitudes is a huge variety of different biomes and
ecosystems. These include
 Equatorial rainforest
 Tropical marine
 Tropical continental
 Hot desert
 Semi-desert
The first two in the list will be looked at in detail
Equatorial rainforest
Latitude/ location: Equatorial rainforest is the most productive ecosystem in the world. Over
40% of the world’s plant and animal species come from the rainforest, yet it only covers just
over 5% of the land surface. The most dense equatorial rainforest is found between 100
N and
100
S of the Equator. Similar ecosystems thrive on either side of this zone and are generally
referred to as tropical rainforest. The main regions are:
 Parts of the Caribbean-southern Cuba, much of Hispaniola, northern Puerto Rico,
Trinidad
 Central America
 The Amazon Basin
 Coastal West Africa (although much has now been cleared for urban development)
 Central Africa- the Congo Basin
 South-east Asia- Malaysia, Indonesia
 Australia- the northern tips of the country.

8. Climate: Constant high temperatures and regular rainfall are typical of the equatorial climate.
The temperatures are high all year round with little to no variation from month to month. In fact
the rainforest has one of0
the lowest annual temperature range out of all the ecosystems that
exists on earth. This is approximately 30
C. A true Equatorial total is 2000mm or more per a year.
Rainforest vegetation
The most obvious characteristic of rainforest vegetation is its layering. Tall trees are common in
rainforest- it is well known for this. Underneath these, however, are several other vegetation
types. From sky to the forest floor these are:
 Emergents- the very tallest trees, which are around 50m in high and grow above all other
vegetation.
 Canopy- The main mass of tall trees, about 40m tall. They formed a closed ‘top’ to the
forest; in other words, if you were flying over it you would see continuous treetops and
no ground at all. Much wildlife lives in this layer, and rarely leaves the relative safety of
the trees: most birds, mammals like sloths and many species of monkey.
 Lower tree layer- this is made up of younger trees which will eventually become part of
the canopy, plus mature trees of smaller species, such as palms (about 15-20m tall).
 Shrub layer- bushes up to 5-10m high. Only 1% of the sunlight received at the canopy
penetrates to this depth, so there is little photosynthesis and plant growth is slow.
 Ground layer- shade- loving plants which are usually less than 1 meter in height. They do
not cover the whole ground surface because few plants can cope with this degree of
shade. Bare ground, with lots of litter, is common the rainforest floor. Wildlife here eats
fruit and seeds from the litter.
Characteristics and adaptations of rainforest plants
The trees and plants of the rainforest have adapted to their environment.
 Trees have slender trunks with thin, smooth bark to help them shed heavy rain. There is
no frost, so no extra protection, such as thick bark is needed.
 Trees are tall and the canopy is wide to reach maximum sunlight for photosynthesis

9.  Their roots are at the based, called buttress roots, are especially wide to help support this
great height. Extra roots, or radicles, grow down from branches to make the trees more
stable.
 Leaves have drip tips, with curved ends, which help them shed excess rain water easily.
They are leathery to protect them from the sun
 Many trees are tall and have relatively straight tree trunks. The branches and leaves are
concentrated near to the very top of the tree to maximize the amount of sunlight they
receive. Having leaves on the lower parts of the trunk will not be very useful as very little
sunlight will reach them.
 Some plants in the lower layers of the rainforest have very large leaves in order to make
efficient use of the little sunlight that reaches them.
 Some plants, known as Lianas, are veins which are rooted in the soil and grow up the
trunks of trees all the way into the canopy where their leaves can get more sunlight.
 Epiphytes are plants that used dead material which has collected in the forks of trees, for
example, as a place in which to root rather than in the soil. They simply use the tree for
support but derive no nourishment from the tree itself.

10. Tropical marine biome
Latitude
This biome is found between 100
and 20o
North and South of the Equator. These latitudes in the
northern hemisphere coincide with much of the Caribbean. As its name suggests, the sea is the
most important influence on the climate here. The islands on the eastern edge of the Caribbean
region experience this climate: The Bahamas, Antigua, Dominica, St Lucia, Barbados, Grenada
and Tobago.
Climate

11. The trade winds blow all year in these latitudes. These are warm winds that pick up lots of
moisture over the ocean. Two seasons can be identified: a drier season from January to May and
a wetter one between June and December. Figure 8.23 shows climate data for the lowland parts
of Grenada, and this seasonal difference is clear on the rainfall graph. The wetter season is also
slightly warmer. There is no clear division between the seasons. Temperature and rainfall both
rise and fall gradually. Although the drier season is dominated by high pressure systems, some
rain occurs every month. The main difference between equatorial and tropical marine climates is
the rainfall pattern; temperatures are similar.
Ecosystems
There are five main ecosystems within the tropical marine biome, classified according to the
amount of water available: rainforest, mangroves, mesophytic and xerophytic woodland. The
wettest areas can sustain rainforest as described above. Some coastal strips have mangroves, for
example in Grenada.
Semi- evergreen forest is a mesophytic ecosystem, meaning that it needs quite a lot of rain but
can survive a short dry season. There are fewer trees and they are not as tall as in the true

12. rainforest. Some are deciduous, shedding their leaves annually to save moisture. Smaller leaves
also help here. Litter is an important nutrient store in this ecosystem.
Dry woodland is a xerophytic, or drought-resistant ecosystem. It is found in the driest areas,
usually because they are in a rain shadow area. Less moisture means:
 Smaller plants- trees are rarely taller than 25m
 Bark is thicker to help keep moisture in
 Trees are deciduous and/or have small leaves
 Growth is limited- the whole system, both plants and animals, produces less biomass
 The amount of litter limits the growth of ground-cover plants
 Biodiversity is lower than in the other ecosystems- that is, there are fewer species
Much dry woodland has been cleared for farming but this was not always successful. Today
many areas have scrub vegetation which includes cacti and succulents, plants which are truly
xerophytic.

13. Soil and soil profiles
The soil is an important part of any ecosystem. Soil directly affects vegetation and wildlife. In
turn they affect the soil, and so do the bedrock underneath it and the climate above it.
Soil formation
Soil is formed from two different sources:
 The bedrock provides the mineral material
 The vegetation provides the organic material
Climate is also an essential factor in soil formation. Bedrocks breaks down by weathering into
smaller fragments called regolith. This happens particularly in tropical regions of the world such
as the Caribbean because of high temperatures and plentiful rainfall. Chemical reactions that help
to weather rock happen much more quickly in warm wet conditions. Tropical soils are therefore
the deepest in the world, up to 30 meters deep.
As soil develops vegetation takes a hold. When plants die they become part of the litter layer,
where they are broken down by decomposers to form humus. This dark brown/blackish organic
material is mixed into the mineral part of the soil by small animals and insects (soil fauna) such
as earthworms. Organic material and mineral material together forms soil particles, or crumbs,
and between these is air and water, which also make up a very important part of soil. Figure 8.5
shows the approximate proportions of all four parts of soil.

14. Other factors affect the characteristics of soil. Slope is important. Thicker soils form on flat land
or gentle slopes. On steeper land the soil particles move downhill under the force of gravity, so
the steeper the slope, the thinner the soil. Another factor that is easily forgotten is time. Soil
needs time to form, usually thousands of years. The longer they have been developing, the
thicker they are, although each soil type has it maximum depth. The warmer and wetter the
climate, the less time it takes to form a mature soil.
Soil profile
The soil profile is a section down through a soil from the surface to the underlying bedrock. In a
mature soil, the profile usually consists of successive layers, which are called horizons. The O
horizon is mostly organic matter such as decomposing leaves at the surface of the soil. It is also
called the humus layer. The A and the B horizons represent the true soil, while the C horizon is
the subsoil or weathered parent material. The D horizon consists of unweathered bedrock.
Different soil profiles are found under different conditions, and soils are recognized and
classified on the basis of the parts of the profile which are present.

15. Tropical soils
Tropical soils are very much influenced by their climate and these are called zonal soils. There
are also intrazonal soils, where local factors such as rock type are more important. Tropical red
earths are zonal soils and these cover a large area of the tropics, especially under rainforest.
Latosols/ Tropical red earths
Latosols are found in areas which have a hot, wet climate throughout the year, often where the
natural vegetation is tropical rainforest.
Factors influencing the formation of latosols
Climate
 Latosols form in very hot and wet conditions in the tropics and equatorial regions. High
rainfall and temperature causes rapid chemical weathering. The soil is of great depth due
to rapid weathering of the underlying rock. Latosols are therefore the deepest in the
world, up to 30m deep.
 Precipitation exceeds evaporation in this environment, therefore leaching takes place.
There is so much rain in the tropical rainforest that minerals are quickly dissolved and

16. washed down into the lower soil. If plants do not absorb the nutrients quickly, rainfall
will bring it to lower levels where it is inaccessible to plants and the soil becomes acidic.
Leaching is intense, only iron and aluminum compounds (oxides) remain and this gives
the soil its red colour.
Soil Biota
The soil organisms are greater and more active due to the warm and wet conditions.
Decomposition of organic matter by microorganisms such as bacteria and fungi are very rapid in
this ecosystem.
Vegetation
The tropical rainforest is a very dense and evergreen ecosystem. Vegetation is in abundance and
is very diverse. This suggests that they are rich soils- otherwise how could they support
rainforest? However, this is not really true! Certainly tropical red earths/latosols support
rainforest, but they are quite poor quality soils, because of the very rapid recycling nutrients
within the ecosystem. As soon as plants shed their leaves, they rot down and become humus. Soil
fauna mix this into the soil very quickly, and plants take up the nutrients almost immediately.
The cycling of nutrients in the rainforest system is the fastest in the world.
When rainforest trees are cut down and the land is used for farming, there are few nutrients in the
soil. They are used up very quickly and there is little litter to help replace them. The nutrients
cycle of the ecosystem has therefore been destroyed, because most of the nutrients were held in
the trees, not in the soil. The structure of the soil is damaged and it erodes away easily.

17. Impact of humans on the rainforest
One hectare (10,000m2
) of rainforest is destroyed by people every second- this is the equivalent
of two American football fields- but even more shocking, means that an area larger than New
York City is devastated every day. That equates to the area of a country the size of Poland every
year.
Causes of deforestation
Slash and Burn
Traditional rainforest people grow crops using the system of shifting cultivation or slash and
burn. This involves extended family groups of over 30 individuals clearing undergrowth, cutting
down large trees and burning them, then spreading the ash as fertilizer. Such ground can be
farmed for two to three years with up to three annual crops before the soil is exhausted of
nutrients and needs time to recuperate (fallow periods). Clearings are small enough that heavy
ran does not erode the soil. A single group operates a few clearings at a time and then moves on
to new ones, ideally returning to past lands after 30 years, by this time the soil should be returned
to full fertility. Slash and burn is sustainable as long as it does not become intensive.
 Population increase in West Africa caused plots to be cleared too close to each other,
opening up the forest and allowing rain to cause soil erosion. Fallow periods became
shortened so soil was not able to regain full fertility, making it lose its structure and be
more vulnerable to erosion. Serious forest destruction was the result, leaving people with
no land to form, many were therefore forced to migrate to urban areas to try to earn a
living.
 New transport routes through the rainforest, in particular the Trans-Amazon Highway,
have let new settlers from poverty-stricken Brazil into the rainforest to try to earn a living
through slash and burn. Lack of traditional skills has led to people failing to produce, and
much rainforest destruction.
The Timber industry
Commercial logging is the major cause of deforestation today in Southeast Asia and Africa. In
Amazonia there has been a greater pressure to cut timber sustainably, taking the high value trees

18. without destroying everything else around them. Demand from the developed world drives the
market in tropical hardwood timber- without that the business would not be so destructive.
Indonesian rainforest has suffered harshly as the country strived to develop by exporting high
value goods to the more developed world. There is still lack of understanding in North America
and Europe over the environmental consequence of rainforest destruction.
Cattle ranch and Soya Bean production
Ranching has been a huge cause of rainforest deforestation, being responsible for 80% of tree
cutting in all Amazonian countries (Brazil, Peru, and Bolivia) in the early years of the 21st
century. Cattle-ranching is an extensive system of farming, using a whole hectare of cleared
forest for every animal.
Demand from the western world for meet has been important, but today the large rapidly
developing countries like China and India have growing middle class who demand diet that
represents a high standard of living with lots of protein. Carbon emissions from clearance for
ranching caused 3.4% of global output in 2008. Global companies like McDonald have caused
significant rainforest damage and have received public condemnation for this e.g. public pressure
has caused them to change their policy. By 2006 McDonalds claimed to have stopped clearing
rainforest for cattle and no longer bought soya beans grown on cleared forest ground for cattle
feed.
Nevertheless, soya grown on cleared Amazonian rainforest is increasingly used to feed cattle and
chickens. Brazil, the second largest soya producer, exports to the USA, Europe and China, who
produce beef and poultry for other fast-food restaurants and people’s dinner tables. An area the
size of the US state of Vermont has been cleared for soya production in the Brazilian state of
Mato Grosso Alone.
Hydro-electric Power (HEP)
An unlimited supply of water on the Parana River feeds Itaipu, on the Brazil/Paraguay border,
said to be the largest HEP system in the world, ahead of the Three Georges Dam in China. It
supplies electricity for Brazil largest city, Sao Paulo, with its population over 21 million and
expanding industries. In order to create the reservoir behind the dam, 2430km2
of rainforest has
to be flooded, threating several mammal species and whole ecosystems. Brazil is an NIC ( newly

19. industrializing country) whose economy is growing rapidly on the back of such infrastructural
developments.
Soil exhaustion and erosion
Tree roots anchor the soil, preventing erosion, but when trees are gone the soil has little
protection from the heavy rains. Widespread soil erosion has occurred, and is still occurring
throughout the tropics as a result of rainforest clearance. The consequence include:
 Soil loss across tropical regions has been immense, and continues.
Costa Rica loses about 860 million tonnes of valuable top soil every year. Most of this is washed
into rivers and then into the sea. Madagascar loses more soil more than everywhere else- 400
tonnes per hectare per year turning rivers red and staining the sea far out into the Indian Ocean.
Astronauts looking back towards the Earth have said that Madagascar looks as it is bleeding to
death.
 Crop yields decline and people must spend their limited income on expensive imported
chemical fertilizers in order to produce an adequate crop.
 Offshore coral reefs are being suffocated by soil which is washed into the sea. Coastal
fisheries suffer not only from loss of coral reefs but also the silting up of mangrove
swamps.
Sustainable Management
The Forest Stewardship Council (FSC) is an international organization which aims to increase
the proportion of timber and other rainforest resources that are obtained sustainably. It aims to
reduce the demand for rare, valuable tropical hardwoods through educating people of the
consequences of such unsustainable exploitation. Products that have been sourced from
sustainably managed forest have the FSC label.

20. References
Guinness, P., Rocke, J., Nagle, G., Oliphant, K., Rae, A., Ross, S., … Wyllie, A.
(2008). Geography for Csec. Nelson Thornes Ltd.
London, N., & Senior, M. (2004). Principles of Geography for Cxc (2nd ed.). Kingston: Carlong
Publishers Limited.