Succession is the progressive change in a community of organisms in an area over time. One community is gradually replaced by another until a stable community is reached.The stages
• Pioneer species are the first organisms to colonise. They are adapted to harsh abiotic conditions, for example they can fix nitrogen, tolerate drought or extreme temperature, or produce many seeds that spread easily.
• Each stage is called a seral stage, and the whole sequence is a sere.
• Each community changes the abiotic conditions. As organisms die and decompose, they add humus to the soil, making it deeper, better at holding water and richer in minerals. This makes the environment more suitable for other species, which then outcompete the earlier ones.
• The final, stable community is the climax community. In the UK this is usually deciduous woodland, such as oak.General trends during succession
• Abiotic conditions become less hostile.
• Soil depth and nutrient content increase.
• Biodiversity (the number of species) increases, although it may drop slightly at the climax as a few dominant species take over.
• Biomass increases, as larger plants such as shrubs and trees establish.
• Food webs become more complex, and the community becomes more stable.
There are two types. Primary succession starts on bare ground with no soil, such as rock or sand. Secondary succession starts where soil is already present but the vegetation has been removed, for example after a fire. These are looked at in the next lessons.
• Pioneer species are the first organisms to colonise. They are adapted to harsh abiotic conditions, for example they can fix nitrogen, tolerate drought or extreme temperature, or produce many seeds that spread easily.
• Each stage is called a seral stage, and the whole sequence is a sere.
• Each community changes the abiotic conditions. As organisms die and decompose, they add humus to the soil, making it deeper, better at holding water and richer in minerals. This makes the environment more suitable for other species, which then outcompete the earlier ones.
• The final, stable community is the climax community. In the UK this is usually deciduous woodland, such as oak.General trends during succession
• Abiotic conditions become less hostile.
• Soil depth and nutrient content increase.
• Biodiversity (the number of species) increases, although it may drop slightly at the climax as a few dominant species take over.
• Biomass increases, as larger plants such as shrubs and trees establish.
• Food webs become more complex, and the community becomes more stable.
There are two types. Primary succession starts on bare ground with no soil, such as rock or sand. Secondary succession starts where soil is already present but the vegetation has been removed, for example after a fire. These are looked at in the next lessons.