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  • Level: GCSE
  • Subject: Science
  • Essay length: 1204 words

Ecological Succession.

Extracts from this essay...

Introduction

Ecological Succession Succession is "A sequence of ecological changes in an area whereby one group of plant or animal species successively gives way to another, culminating in a climax community." This succession occurs in a number of sereal stages. A sere is a stage in a sequence of events by which succession occurs. The complete chain of seres is called a prisere. It begins with a pioneer community and ends with a climax community. This climax community occurs when the ultimate vegetation has become in equilibrium with the local environment. There are four main areas where succession occurs rocky environment called a lithosere, sandy environment called a psammosere, a fresh water environment called a hydrosere and a salt-water environment called a halosere. Two examples of a litosere are Sutsey a newly, formed volcanic island and Krakatoa an island striped of all its vegetation by a series of volcanic eruptions. Sutsey is located to the south east of Iceland and is slowly becoming colonised. The first colonisers of the bare rock on a lithosere environment are blue-green bacteria and single cell photosynthesisers, both of which have no need of a root system.

Middle

This humus is created by the decomposition of marram grass. These grey dunes can support a much wider range of plants due to the increased water level, the reduction in wind and the increased humus level. Some of these plants include red fescue, gorse, bracken and heather. On the land ward side of the dunes about four hundred metres away from the sea are the climax of the succession the ash and oak trees. Hydroseres such as those created around the Talybont reservoir in Wales develop from fresh water lakes and pools. Initially these bodies of water hold little nutrients but sediment carried into the water will enrich the water with nutrients. The pioneer community will use these nutrients, which in this case are algae and mosses. These grow forming vegetation rafts whose surface supports bacteria and insects. Next there will be water loving plants such as lilies which us the nutrients recycled by bacteria from the pioneer community. Marsh plants such as bulrushes, sedges and reeds begin to encroach into the body of water as deposition increases. As marsh plants grow further out into the body of water there is increased deposition of sediment at the expense of the water and small trees may begin to take root forming a marshy thicket.

Conclusion

There is also a difference in the plants ant the different stages of succession the early plants are said to be -r selection. These plants are opportunists with a rapid life cycle. An example of a plant in -r selection is the dandelion, which produces thousands of seeds. In contrast to this the plants later in the process of succession -K selected. Examples of this include the oak and ash trees. They are characterised by long lives and a high amount of investment into their seeds. This high investment therefore means that the seeds are better protected from the environment and therefore less are produced. "Zonation is the distribution of plants or animals into specific zones according to altitude, depth, etc., each characterised by its dominant species." Examples of zonation occur at a beach. The species of plants will vary in zones with an increase in distance from the high water mark. The factors affecting this zonation will be varied but may include things like strength of the tide and the amount of time they are underwater. The also occur on a mountain side where as the climatic conditions change the plants which can best survive in those conditions flourish thus developing clear zones.

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