Transcript Slide 1

Ecosystems
• Global distribution of ecosystems
• Distribution of tropical rainforest, savanna grasslands and coniferous
forests
• Tropical rainforests- vegetation type, soil and how they adapt
• Coniferous forests- vegetation type, soil and how they adapt
• Savanna grasslands- vegetation type, soil and how they adapt
• The human uses of tropical rainforest
• The social, political and environmental issues involved
• The human uses of savanna grasslands
An ecosystem is a living community of plants and animals within a natural
environment.
The distribution of ecosystems across the world is dependent on the
climate and soil they rely on in order to grow.
Tropical rainforests are found in places with a hot (over 30°C) and wet (over
2000 mm) equatorial climate. Rainforests grow in the tropics, close to the
equator and the plants have a twelve month growing season. As a resultant,
the rainforest is the most luxuriant vegetation system in the world.
Savanna Grasslands are located next to the tropical rainforests. The savanna
climate has a distinct hot, wet season and a hot, dry season. The savanna
changes as you move north or south from a mix of trees and grass to just
grasses. Eventually, it gradually merges into the desert ecosystem.
Coniferous Forests These grow in the northern parts of North America,
Europe and Asia in places a long way north of the equator. It is very cold in
the winter and the growing season is very short. Soils are often thin and
poor.
TROPICAL RAINFORESTS
Vegetation
The tropical rainforest is different from all other ecosystems because of its
biodiversity. Over 50 species of tree may be found in only 1 hectare of soil in the
rainforest. The forests appear to be evergreen but the trees are deciduous and take
it in turns to lose their leaves. The rainforest is organised into five layers. From the
top they are as follows; emergents, canopy, under canopy, shrubs, forest floor.
Soil
The profile of the soil in the rainforest is called a LATOSOL. Latosols are reddish
brown and the red colour comes from the oxides of iron and aluminium in the soil. They
are very deep soils. The heavy rain in the rainforest leads to leaching (minerals washed
out) and this is why the top layer of soil is often light in colour.
Adaptations
As there is great competition for sunlight and water in the rainforest the trees try to
grow very tall. They have a shallow spreading root system to collect as much nutrients
as they can. The wide buttress roots at the base of the tall trees help to prevent
them falling over. Many other plants have to devise methods of competing for light.
Ferns on the forest floor are able to cope in low-light conditions. Lianas are creeping
plants that grow up the tree trunks and use them to get to the sunlight. Parasitic
plants such as orchids grow in cracks in the branches high up in the canopy.
Coniferous Forests
Vegetation
The forests are evergreen. The coniferous trees (fir, pine, spruce) are similar in height,
shape and size. There are often only two or three species of tree in one area. Very few
other types of vegetation grow in the forest.
Soil
The soil profile of a coniferous forest is called a PODSOL. The soil has a humus layer
just below the surface. The A horizon is grey in colour as it has lost its minerals
through leaching (washing out of minerals). The B horizon is a reddish-brown colour as
the minerals lost from the layers above are deposited here. The C horizon consists of
stones and rocks.
Adaptation
The vegetation in the forest make many adaptations due to the harsh, cold climate.
Tree characteristics are as follows;
• Conical shape- they are flexible and bend in strong winds
• Downward sloping branches- snow slides off them more quickly
• Evergreen- so that trees can grow as quick as possible in warm periods
• Needle leaves- to reduce the loss of water
• Thick bark- To protect the tree from severe cold
Savanna Grasslands
Vegetation
There are only two layers of vegetation in the grasslands- the grasses and the trees.
Grasses are tall and form a continuous cover, whereas trees are dotted around and there
can be wide spaces between them. A denser covering of trees shows places where more
water is available.
Soil
During the dry season, minerals in the soil, such as calcium are drawn up to the surface by
the high temperatures and high evaporation rates. Heavy rains in the wet season cause
leaching, which washes the minerals deep into the soil.
Adaptation
The main problem for the vegetation is survival during the dry season. Most plants are
xerophtytic (drought resistant). Grasses turn brown and die back in the dry season.
Trees adapt to the drought by losing their leaves to reduce water loss or the leaves are
small and waxy to reduce transpiration. The roots are usually long to reach underground
supplies of water. Some trees have very thick bark to store water during the dry season
e.g. baobab tree.
The Human Uses of the Tropical Rainforest
Humans use the rainforest in the following ways;
• Logging- chopping down of trees
• Ranching- large areas of trees chopped down for cattle farming
• Mining – valuable minerals such as iron ore, bauxite and even gold.
• Rubber tapping – some trees provide natural rubber from the sap
• Tourism – increasing numbers of tourists want to visit the rainforest
• Farming – farms vary from tiny subsistence farms to huge plantations
growing a single crop such as palm oil
Impact on the rainforest
Social Issues
•
indigenous people e.g. Amerindians are left with out homes and many have been killed, either deliberately or by diseases
introduced by people coming to the rainforest.
• Too many tourists and tourist facilities can damage an area
Environmental Issues
• Chopping down of large areas of woodland can influence global warming
• Animals habitats are destroyed
Political Issues
• Lots of groups do not agree about what should be done with the
rainforest and this leads to great conflict
Human uses of Savannah Grasslands
Local people are often nomadic and keep herds of sheep, cattle or goats. Some
live in permanent villages and grow crops .
One huge problem is desertification which mean the good land is turned in
desert. This has been caused by overgrazing (too many animals) and
overcultivation (growing crops every year and not letting the soil recover its
fertility). Soil is either blown away in the dry season (dust storms) or washed
away in the heavy rains in the wet season.
Many tourists also visit the African savannas on wildlife safaris e.g. in Kenya.
The wildlife is often disturbed and the people and vehicles damage the
landscape.
Summary
• An ecosystem is a living community of plants and animals within a natural
environment.
• The distribution of ecosystems across the world is dependent on the climate
and soil they rely on in order to grow.
• Tropical rainforests are found in places with a hot and wet equatorial climate.
• Savanna Grasslands are found in areas with two different seasons (wet and
dry).
• Coniferous Forests These grow in the northern parts of North America,
Europe and Asia where the climate is very cold and the growing season is very
short.