Evaluate the relative roles of natural succession and human activities in the creation of ecosystems within the British isles. (40 marks) An ecosystem is a biological community of interacting organisms and their physical environment. Ecosystems can be changed by both human activity and natural succession. Ecological succession is the observed process of change in the species structure of an ecological community over time. The time scale can be decades (for example, after a wildfire), or even millions of years after a mass extinction. This essay aims to identify ways in which vegetation has transformed over time, and to evaluate the importance of both human and physical factors. The British Isles, located in the northern hemisphere is home to a mild climate and varied soils, giving rise to a diverse pattern of vegetation and a climatic climax community of deciduous woodland. A deciduous woodland is an example of succession, which happens in temperate climates and is a naturally occurring organic community of plants and animals in the climatic climax stage of succession.
These varying and regionally different ecological conditions produce distinctive forest plant communities in different regions over time, there have been substantial changes to vegetation as a result of a combination of both natural, physical factors and human interference. The composition of vegetation depends upon the interaction between all of the components that make up the specific environment. Some of the core physical components of a habitat include climate, relief, drainage, geology soils and competition. Plant populations gradually become more complex over time a process that is known as succession. Over time, sometimes even thousands of years, a period of relative stability is reached in which the vegetation has reached its climatic climax – the state in which the species will be in dynamic equilibrium with its environmental conditions. In the British Isles, the climatic climax community at the end of succession is temperate deciduous woodland. As succession develops, it passes through a series of stages called seres, and it is here that the natural processes of invasion, colonisation, competition, domination and decline influence the composition of the vegetation.
The way in which the vegetation naturally changes over time in accordance with these physical processes can be seen in the transformation from pioneer species to the climatic climax community. In primary succession, the plants that first invade the bare ground through dispersal and migration become established. Such plants are known as pioneer species, as they are extremely hardy plants that are adapted to living in harsh conditions. Pioneer species are of great significance, as they can affect the microclimate of the area in terms of wind speed at ground level, shelter, temperature and humidity but most importantly, these plants add organic matter to the developing soil when they die, creating more favourable conditions for the growth of more complex plants. Each stage of colonisation provides better conditions for plant growth than the one before due to the improvements in soil, so an increasing number of species can be found. Next, shrubs invaded and colonised the area.
Shrubs dominate and shade out the sere below them. Small trees such as birch and willow were the following sere which invaded and colonised the area. They produced humus from leaf fall which provided nutrients for the soil through nutrient recycling and encouraged new growth of the sere. The last sere is the larger trees which are oak and ash which dominate the area and shade out smaller trees leading to no further succession happening here. The process of natural succession has been of great importance in accounting for natural changes to vegetation over time, as the British Isles is an example of lithosere succession, in that it began as bare rock from glacial retreat. Secondary succession follows the destruction or modification of an existing plant community. This can occur naturally after a landslide or a forest fire caused by lightning however can also occur through human activity such as deforestation.
In the UK an example of a secondary succession is at the headland project site at the woodland education centre which has been running since 1995. This was due to the woodland being completely cleared in 1993 due to a non-native species being introduced and being dominant .It has now been allowed to regenerate naturally. This is an example of how human factors can affect the creation of ecosystems as they destroyed a habitat due to them introducing a foreign species into the community. Box hill a summit of the North Downs in Surrey, approximately 30 km south west of London and is a plagioclimax community which is a community controlled by humans to not go beyond the climatic climax. This shows humans are important in this because without interference succession would occur and it would become deciduous forest which is the climatic climax.
The chalk grassland at box hill have more biodiversity than a rainforest and contain many endangered species including the small blue butterflies and man orchids. These are specific to the chalk grasslands and there only being 19 sites of chalk grasslands shows just how rare the species are. In the creation of this ecosystem human interference is far more important because if natural succession were allowed to occur then many of the ecosystems would not exist and the biodiversity of the area would suffer. The climax community of the entire area would be deciduous woodland. Sometimes humans produce ecosystems themselves, this occurs in ecological conservation sites.
An example of these is Troopers Hill in Bristol. This was an old industrial area which was cleared to produce this ecosystem. There are other examples in former industrial sites in urban areas where over time vegetation occurs and ecosystems develop but these are usually destroyed by redevelopment. Human activity can also be a destruction of ecosystems. The spraying of pesticides and herbicides on crops creates a monoculture and the cutting down of forest for timber can destroy the ecosystem. Other human activities such as the creation of playing fields and gardens favour just grass.
In conclusion, I think the impact of human activity is much more important in the creation of ecosystems than natural succession. One reason for this is because Box hill has more biodiversity than a rainforest. Therefore the impact of humans through the maintenance of plagioclimax communities are more important than natural succession especially as succession often results in few different ecosystems whereas human activity will often produce a far greater mix of biodiversity.
Courtney from Study Moose
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