Succession is the progression of plant and animal species in an area from smaller simpler organisms to larger more complex organisms, eventually leading to a climax community.

Succession in freshwater lakes

Freshwater lakes usually have at least one stream flowing into them which carries particles of soil and silt. The pioneer population consists of reeds which can grow in the very wet conditions around the outside of the lake. As the reeds grow, the silt particles from the stream get caught around the bottoms of the stems of the reeds and around the rhizomes, and this build up of silt causes the bottom of the lake to rise up. The soil level gradually rises from the outside of the lake towards the middle of the lake, making conditions drier and more suitable for sedges, then trees like alder and eventually oak to become established. The climax community may be dense woodland, with the original stream flowing through it.

Succession on rock surfaces

The pioneer plants on newly bared rocks are usually lichens or mosses because they can survive on the low level of water and nutrients found on rock surfaces. As the lichens and mosses die, they leave behind a small layer of dead organic material which is sufficient to provide more tufted mosses and even some small herbaceous plants with enough water and minerals. As these species flourish, the light to the lichens and mosses is blocked and they are eliminated. As more plants die, the soil gets thicker and is colonised by bacteria which speed up the rate at which nutrients are released into the soil from humus. Small animals may be able to become established in this ground cover, providing a food source for higher carnivores. All the time, larger plants block the light to the smaller ones beneath them. Therefore most of the smaller plants are eliminated as the succession progresses. As the plants get larger, larger animals can find shelter in them and settle there. If abiotic factors allow, bushes and trees can grow and a climax forest appears.

Succession on sand dunes

A sand dune begins to form when sand being blown inland by the wind accumulates round small plants on the beach. These plants, such as marram grass, are well adapted to grow in sand, and they quickly sprout through it, catching more as it blows inland. As more dunes start to appear on the sea-facing side of the first dune, it stops growing and organic material from dead grasses starts to accumulate. A layer of soil is produced containing water and nutrient ions and mosses and eventually herbaceous plants can grow on the dune.

Succession on salt marshes

A succession on a salt marsh is called a halosere. In river deltas, silt accumulates around the roots and stems of plants in the litteral zone, much the same way as it does around the reeds in a freshwater lake. At first, the marsh is invaded by plant species which are adapted to survive long periods of immersion in water. As silt gathers, the level rises and the ground gets drier, supporting a succession of plants.

Secondary succession

A secondary succession differs from a primary succession in that it occurs in an area where a community of plants and animals has recently been wiped out, i.e. the land is already suitable for a wide diversity of species to establish themselves on. A secondary succession can happen on an area of land where a forest fire or parasite wiped out a previous climax community or which has been disturbed in some way by humans e.g. deforestation or arable farming. A secondary succession takes place much more quickly than a primary succession for two main reasons, the most obvious one being that a suitable medium already exists for the new organisms to grow in, and the other being that some seeds or spores from the last plant community can still be present in the soil after the community is destroyed.
A good example of secondary succession can be observed on abandoned farmland in temperate regions. The farmland was at one time probably a forest which was cut down to grow crops or graze animals on. After the land is abandoned, small weeds appear which give way to larger plants, bushes and shrubs, which are then superseded by larger trees and deciduous woodland. This whole succession can take place in just over a hundred years, whilst the succession to woodland in a freshwater lake can take up to ten thousand years.

Conclusion:

All landscapes have resulted from a succession of some sort and complex organisms would not be able to survive without the land first being made habitable by smaller plants with adaptations to survive in hostile conditions. Animal succession relies directly on plant succession to take place, since without the smaller plants as a source of food and shelter, the smaller animals would not be able to become established.