Ecosystems & Processes (AQA A Level Geography)

This is a stage where human activity has led to the creation of a sub-climax within the ecosystem. Until the human activity ceases the seral stage will remain.

This is a stage whereby no further changes will occur in the succession. The only change that will occur is due to human activity or as a response to environmental change.

This is a stage in the development of the ecosystem as it progresses towards climax. New species which are better adapted to the conditions outcompete a declining species.

This is a stage in the food web. For example, primary consumers feed off the producers. This would be the second seral stage in the development of the food web.

These are stages of a food chain or food web. At each new stage there are species which take energy from those in the previous stage. This process supports life.

This is a stage in succession of plants in an ecosystem. At each new stage a better adapted species will dominate the local environment as it claims a niche in the local conditions.

Trophic levels are a type of species which is responsible for the decay process in the ecosystem. These detritivores consume the dead matter and create conditions for regrowth.

Trophic levels are a measure of the biodiversity within an ecosystem. An ecosystem with high trophic levels is considered to be healthy and free from human interference.

Weathering allows for eroded material to be carried away by aeolian processes. As the eroded material settles in new locations, plant colonisation begins, eg sand dunes.

Weathering releases important minerals which decomposers further break down. Bacteria and fungi break down rock particles for future uptake by plants in the cycle.

The weathered material is a key part of decomposition. Climate directly impacts upon leaf litter to aid the decomposition process. From this nutrients are released.

Weathering processes are essential in the development of healthy soils. Weathered materials are mixed with biotic matter and become available for uptake by plants.

Following a drought, there is almost always significant die-back for most plant species. In these conditions, xerophytic pioneers colonise the area with limited competition.

Pyrophytes are adapted to cope with conditions associated with wildfire. Root systems can cope with loss of vegetation above ground. This vegetation quickly returns after fire.

Plant species which require very few nutrients to survive and will colonise bare rock. These species are the first to colonise following a volcanic eruption and succession follows.

Once human activity has altered the climatic climax vegetation, the species are quick to adapt to the niche which is created. Pioneers readily exploit the available environment.

NPP is the biomass (minus respiration) produced in an ecosystem. It is a measure of the rate at which an ecosystem can capture and store carbon, usually measured in g/m² /yr.

NPP relates to the productivity of land for the purposes of agriculture. The addition of nitrate-based fertilisers or genetically modified crops dramatically increases NPP.

As plants respire they take in oxygen and release carbon dioxide. NPP is a measure of how much oxygen is produced by plants in an ecosystem. This rate is measured as O₂/m³ /yr. 

NPP is the total amount of chemical energy (as biomass) that primary producers create in a given length of time. This is the rate at which decomposition occurs in an ecosystem.