AQA Ecosystem notes- whole course

Ecosystem notes on A2 AQA geography unit 3 course

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  • Created by: harry h
  • Created on: 10-06-12 14:48
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Ecosystems: Change and Challenge
The Structure of Ecosystems
Ecosystem: a dynamic, stable system characterised by the interaction of plants and animals with each other and with the
non-living components of the environment
The components of an ecosystem are categorised as either biotic and abiotic
Biotic means the living environment, components include:
i). Vegetation (living and decomposing)
ii). Mammals, insects, birds and microorganisms
Biomass-the mass of material in the bodies of animals and plants (total mass of living matter)
Abiotic means the non-living, chemical and physical components of the ecosystem and includes:
i). Climate- in particular the seasonal pattern of temperature and precipitation
ii). Soil characteristics
iii). Underlying parent rock
iv). Relief of the land
v). Drainage characteristics
Ecosystems are open systems because energy and living matter can both enter and leave the system:
Inputs-Energy from the sun, which drives photosynthesis-enabling the plants to grow, water transported into the
ecosystem from precipitation and animals that arrive from elsewhere
Outputs-nutrients are transferred out of the system by: animals can physically move out, water can leave through
evapotranspiration, groundwater flow and throughflow
Flows-nutrients can be transferred from one store to another e.g. capillary uptake
Stores- stores of nutrients: vegetation, plant litter and soils
Energy Flows and nutrient cycling
Energy flows- is the flow of energy through a food chain
Energy flows flow through an ecosystem from one stage to another.
Through photosynthesis plants are able to capture light energy from the sun to make carbohydrates from carbon
dioxide and water to grow and increase their biomass
Within all ecosystems, nutrients are required for plant growth and are recycled from one store to another
e.g. leaves fall from tree-> when they decompose nutrients are returned to the soil
Gersmehl diagram- shows the cycling of nutrients within the main stores of biome
Circles of proportionate size represent the stores of nutrients with the biomass, litter and soil
Nutrient transfers, inputs and outputs are represented by arrows of varying thickness
Inputs- include nutrients(carbon and nitrogen) and minerals(from weathered parent rock)
Outputs-loss of nutrients from the soil by; leaching and surface runoff
Flows-leaf fall from biomass to litter, decomposition of litter, flow of nutrients to soil, uptake of nutrients by plants and trees

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The movement of energy up the trophic levels shows the food chain as each trophic level occupies a different position.
However food chains, in reality, are often more complicated than this. Some species can occupy more than one position in every
food web ­ may be prey to more than one animal etc.
Nutrient cycles in an ecosystem take place between the biotic and abiotic components of the ecosystem. This can be shown
through the Gersmehl diagram.…read more

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There are two basic types of succession:
1. Primary succession-occurs on surfaces that have had no previous vegetation
There are two main types of primary succession:
Xeroseres are formed on dry land, this group can be divided into lithoseres on bare rock and psammoseres on sand
Hydroseres are formed in water, haloseres in salt water and hydroseres in fresh water
2. Secondary succession occurs on land that was formerly vegetated but has undergone a loss of vegetation E.g.…read more

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A hydrosere develops as follows:
i). In a freshwater environment, submerged aquatics are the first plants to develop, they help to trap sediment which
enables other species to move in
ii). The next seral stage is the growth of reed beds and swamp conditions
iii). Colonisation by alder and fern begins, they further modify the environmental conditions, improving drainage and
mineral content of the immature soil, allowing the entry of willow and ash
iv).…read more

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Arresting factors
Plant successions can be stopped from reaching climatic climax or deflected to a different climax, by human interference
The resulting vegetation is called a plagioclimax, this can be caused by:
deforestation or afforestation
animal grazing or trampling
fire clearance
A secondary succession is one that develops on land that has previously been vegetated
The stages of secondary succession may be more rapid than those of primary succession because organic matter is already
present in the soil, the pioneer stage may be…read more

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Humidity is high throughout the year, continuous evapotranspiration adds water vapour to the air
On the forest floor there is little breeze as the trade winds converge here
Underlying soil will have developed naturally over a long period of time and be in balance with its environment, this is known
as zonal soil
The zonal soil associated with the tropical rainforest is a latosolyh
Characteristic features
A latosol can be more than 40m deep
The constant hot wet climate provides perfect conditions…read more

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Climatic climax vegetation has been destroyed, this has resulted in both secondary succession and plagioclimax
The vegetation that replaces the original rainforest tends to be smaller in height and less diverse, with a reduction
in the general biomass
Causes of deforestation
Demand for hardwood, e.g.…read more

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Deep red lateric soils
Influenced by climate
Silica is leached downwards in the wet season
Crust formed in the dry season
Greater towards the equator
Acacia, Baobab, Umbrella Thorn, Elephant Grass
Great animal migrations occur meaning that biodiversity drops at certain times
40% of the land in Tanzania has been designated as a National Park to help conserve biodiversity
African Elephant, Black Rhino, Zebra and Cheetah are endangered
The Savanna grassland biome
The tropical wet and dry climate of Africa…read more

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Northern Ghana characteristics:
lengthy period of moisture deficit
Short period of moisture surplus
Total annual potential evapotranspiration greater than total potential precipitation
Adaptations by vegetation
Vegetation in wetter areas consist of tall coarse grasses, with many deciduous trees- Tree savanna
Shorter tussock grass becomes dominant in desert margins, accompanied by drought-resistant trees e.g.…read more

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Winds blow in from the ocean with very moist air and heavy rainfall during May-October, the rest of the year
the air is drier
Ecological responses
Soil moisture budgets
Precipitation is much higher than potential evapotranspiration during the wet season
High rainfall totals result in saturation of the soil, some of the moisture can be utilised by vegetation
A soil moisture deficits occurs by January, deciduous trees lose their leaves in response to drought
The period of moisture deficit is shorter then…read more


Mr A Gibson

These notes are great. Use them as your notes, build on them from the case studies you use yourself and then use them to create revision cards from. Everything is here - definitions, examples and so on.

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