Outline The Factors That Are Responsible For

Vegetation Change Over Time Essay, Research Paper

Vegetation develops in many different and varied

environments with each environment having different effects on the vegetation

change over time. This essay will examine these different factors, in different

environments. It will examine different sereal stages in different environment,

the lithosere or rock environment, the psammosere or sand environment, the

halosere or saltwater environment and hydrosere or fresh water environment. A sere is a stage of events by which the vegetation of an

area develops over time. This begins with the pioneer community and end with

the climatic climax vegetation. The first plants to colonise an area are called

the pioneer community. The climatic climax vegetation is when the ultimate

vegetation development has taken place and the environment has reached

equilibrium e.g. when the natural vegetation has reached a stable balance with

the climate and soil of an area. As an environment goes through more sereal

stages the number of species of plants will increase as will their height. The

island of Krakatoa in the Sundra strait between Java and Sumatra is a volcanic

island, which erupted in 1883. Its development was rapid only taking

twenty-five years to develop from the pioneer community to climatic climax

vegetation because of the high humidity and temperatures and the rapid

weathering of the volcanic rock. The diagram below shows the way an environment

such as Krakatoa develops.There are two types of sereal succession primary and

secondary. Primary sereal succession occurs on a new or previously sterile

land. It occurs in four different types of environment lithosere, psammosere,

halosere and hydrosere. A lithosere is a rock environment. These are initially

colonised by blue-green bacteria, which are completely self-sufficient.

Therefore the pioneer community is the mosses and lichens which are capable of

living in areas which lack soil. The lichens and mosses help to weather the

rock along with other types of weathering. This along with the decayed matter

of mosses and lichens helps to form a veneer of soil, which can support more

advanced plant life. Seeds usually of grass then colonise this soil as time

passes the grasses will give way to fast growing shrubs which in turn will be

replaced by fast growing trees. Finally these will face competition from slow

growing trees such as ash and oak. Although each stage of the succession has

been superseded the vegetation from each previous sereal stage still remains

but in smaller amounts. Two examples of areas where the lithosereal development

has taken place are Krakatoa and Sutsey. Sutsey is like Krakatoa in the fact

that it is a newly formed island. The island was created after a volcanic

eruption on 14th November 1963. The island is located off the

south-western coast of Iceland. Unlike Krakatoa it has not developed quickly

because of the local climate which is extremely cold and very windy. These

conditions don.t lead to the quick establishment of life. The diagram below

shows a typical progression for a lithosere ecosystem. Another type of succession is one, which occurs on sand this

is known as a psammosere. The first coloniser of the sand are usually lyme

grass, sea twitch and maram grass these start dune formation known as embryo

dunes. The grasses slowly move back from the high tide mark on to different

dunes. These dunes are very arid and therefore are usually only populated by

maram grass which has adapted to the harsh conditions. Further back from the

main ridge are the older grey dunes, which are shelter from the wind and have

more humus in their soil due to the increased decomposition of the maram grass.

This humus in the soil supports different species and these start to break the

maram grasses dominance on the dunes. Finally around 400m away from the sea the

climatic climax is reached as oak and ash trees develop. One example of a

psammosere is Camber Sands, which has developed over time to have a full

diversity of plants on the different dunes. The diagram below shows the

development of the environment in a psammosere.Freshwater lakes and ponds are known as hydrosere

environments. These also develop through sereal stages. The pioneer coloniser

is usually algae and mosses whose spores have been blown on to the water

surface. These grow to form vegetation rafts, which then support other life

such as bacteria and insects. The next colonisers are the water loving plants,

which may grow on the water surface like lilies or may grow completely

submerged. Bacteria recycle nutrients from these plants encouraging the

encroachment of plants such as bulrushes. The increased sediment created by the

decomposition of these plant leads to increased sediment, which continues to in

fill the lake. Over time the marsh areas at the edge of the lake will be

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