Terrestrial Ecosystems (AQA A Level Geography)
Revision Note
Written by: Jacque Cartwright
Reviewed by: Bridgette Barrett
Nature of Terrestrial Ecosystems
Ecosystems vary in size from small (pond) to large (ocean), local (ecosystem) to global (biome)
There are two types of ecosystems:
Terrestrial - land based
Aquatic - water based, either freshwater or marine (salt water)
Terrestrial ecosystems are exclusively land-based system, and distributed around climatic zones:
Forests - consist of multiple flora (particularly trees) fauna and microorganisms, which help in maintaining the temperature of the earth and are a major carbon sink
Grasslands - vegetation is dominated by grasses and herbs. Temperate and tropical or savanna grasslands are examples
Tundra - no trees, limited flora and fauna as found in cold climates or where rainfall is scarce. These are covered with snow for most of the year and in high latitudes and altitudes
Deserts - found throughout the world and classified as either hot or cold and are regions with precipitation rates of less than 250mm per annum - Antarctica is a cold desert, whereas the Sahara is a hot desert
The Earth, taken as whole, is a series of inter-connected ecosystems, often connected as larger biomes, which are loosely organised and based on the species of plants and animals that live in them
Every factor in an ecosystem is co-dependant on other factors, either directly or indirectly
E.g. a change in temperature will affect plant growth
Animals dependant on the plant for food and shelter, either has to adapt to the change, move to another ecosystem, or die
There are various factors that play an important role in determining what can live in that particular ecosystem
Ecosystems are dependent on abiotic factors, or conditions, such as soil, light, temperature, precipitation, geology, altitude, and latitude
Latitude strongly influences an area’s temperature, which produces climates such as polar, tropical, and temperate
These climates determine different natural biomes and have characteristic species of plants and animals
Determining Factors for Terrestrial Ecosystems
Factor | Influence |
|---|---|
Climate | Precipitation - determines levels of vegetation and type. Wetter climates can support more trees Temperature - determines type of plant species that grow - tropical or temperate forest species Latitude - determines amount of light and seasons and therefore, the temperature of the area (or lack of) Nutrient cycling - climate affects the rate of nutrient cycling and the availability of nutrients in the soil |
Topography | Altitude - as altitude increases the temperature drops and growth is slowed. Vegetation tends to be short with fewer species Aspect - determines how much light and warmth vegetation receives for growth Slope angle - the steeper the slope, the less soil available for plant growth, but drainage will be higher and this helps to lower the acidity of the soil Shelter - hills can protect vegetation from prevailing winds and rain. These sheltered areas can form micro-climates on the leeward side and has different growing conditions |
Soil | Affected by climate and the availability of nutrients in the soil. Heavy rain, leaches nutrients away from the soil which affects plant growth Geology affects nutrients available within the soil, along with depth and texture, which in turn dictates type of vegetation growth. Areas that are predominately chalk, have alkaline soils, which are nutrient poor with the main vegetation being grass. Drainage - if poor, leads to waterlogging and limited plant type and growth (heather on moorlands Time - soil takes time to form and colonisation by vegetation is very slow |
Responding to Change in Ecosystems
Due to ecosystem interconnection, any change in one characteristic affects change in other characteristics:
Decreased rates of precipitation, lowers the water table and soil dries
Plants are less adapted to drier conditions and begin to die out
Different herbivores become dominant and this impacts carnivores. Different carnivores hunt different herbivores and this changes the balance of species
Loss of plants exposes soil to erosion with leads to soil degradation and eventually desertification, where the land is no longer bound by plant roots and can the soil can be dispersed by wind
Plants are carbon sinks as they take-in from the atmosphere for photosynthesis. If decreased rainfall kills too many plants, it could lead to further changes in the climate, because of the enhanced greenhouse effect
Decreased precipitation can dry up bodies of water (ponds and rivers), leading to aquatic and other species reliant on these for food will die
There are natural and human changes that ecosystems will respond to:
Main Causes of Ecosystem Change
Factor | Natural Change | Human (anthropogenic) Chane |
|---|---|---|
Climate | Natural climate change is usually slow enough and this allows time for ecosystems to adjust Short-term cycles such as El Nino, tend to be more damaging as they cause sudden floods and droughts | Seasonal and latitudinal shifts have occurred due to recent warming of the planet Extreme weather is linked to global warming caused through human activity (burning fossil fuels) |
Vegetation | Vegetation succession results in changes to food supplies and habitats. Whilst these changes affect wildlife, they do occur at a very slow rate and usually over hundreds of years | The spread of invasive plant species and alien animal species has significant impacts Human management (drainage, rotational burning, deforestation) can be devastating to ecosystem |
Topography | Development of topography is extremely slow, unless, there are high rates of erosion or active mass movement processes | Terracing of slopes or slope stabilisation affects drainage and the soil, which impacts on ecosystems |
Soil | Soil erosion or incidents of pollution can bring an immediate change to an ecosystem
| Indirectly, management of vegetation impacts soil composition. Soils might become compacted or eroded, with cattle, horses etc. Directly with fertilisers and ploughing etc. |
Cascading Positive and Negative Effects of Change
Positive Example | Negative Example |
|---|---|
Tree planting restores local ecosystems affected by deforestation Trees affect water movement, soil development and the range of flora and fauna that can live and thrive in that environment Other conservation measures include the restoration of peatlands and footpaths | Wildfires clear dead wood, which release trace nutrients (e.g. potash, phosphate) Wildfires can trigger seed germination (e.g. the Ponderosa pine tree and grasses However, increasing rates of wildfires are disrupting the natural cycles and native species are beginning to suffer Wildfires increase atmospheric CO2 levels, which strengthen the greenhouse effect and increasing the rate of fires in the future - a positive feedback loop |
Examiner Tips and Tricks
Do not be afraid of using a diagram to support your answer and they will help to gain higher marks. Particularly a well annotated and detailed diagram
Always use topic-specific vocabulary, such as plagioclimax vegetation and seres
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