Discuss the relative importance of physical and human factors in accounting for changes to vegetation over time within ecosystems in the British Isles

In terms of human factors accounting for the ecosystems of the British Isles, there can be many impacts upon the ecosystem due to human interference. Successions can be stopped from reaching their climatic climax or defected to another climax by human interferences. This is called the plagioclimax community. Arresting factors in such a situation are activities such as deforestation, animal grazing and fire clearance.  The burning of heather moorland is an example of a plagioclimax community. This is when the herbs/grasses/flowering plants/ferns sere is maintained as the highest succession. Shrubs are burnt to stop succession, leaving heather ferns behind as they are pyrophytic so don't burn.

Secondary successions are ones that develop on land that has previously been vegetated before human interference. These take place when arresting factors such as the management of the area or buildings have been removed. In particular, the colonisation of wastelands throughout the British Isles is seen as a secondary succession which has developed unique ecosystems in highly urban areas. The colonisation of most wastelands is also a  lithosere type of succession. Many wastelands are often temporary and get redeveloped after a couple of years. However if they are allowed to develop after many years the climax community may be reached. This shows that vegetation will adapt to any physical location and continue to grow. In terms of the secondary succession, firstly bare surfaces such as brick, concrete and rubble begin to broken down by many factors such as bacteria, acids and weathering. On any wasteland, there will be substratum variations which are variations in successions due to the differing original purposes of the site. Mosses and Lichens move into the area breaking up concrete to produce a base for soils. In the next stage grasses and flowering plants arrive as cracks in surfaces are the perfect conditions to give shelter for seeds (e.g. windblown) to germinate in. Common invaders are windblown seeds such as Oxford ragwort which has a long flowering seasons and produces millions of seeds. Many of these plants are adapted to tolerate waste ground, rubbish and debris and are known as ruderal species. Such plants demonstrate that vegetation has began to adapt the urban landscape that is spreading through the British Isles. After approximately 3-6 year a thicker more nutrient rich soil has been produced which attracted taller herbs due to the better growing condition. A prime example of this is rosebay willowherb which spreads initially by seeds then by rhizomes which are underground plant stems that produce shoos. These plants gradually shade out smaller plants stopping them photosynthesising. After approximately 8-10, grass increases as soil enrichment continues. Smaller grass species such as meadow grass is replaced by taller species. One invader in particular occurs in this stage which is the Japanese knotwood. Which can grow up to 3 metres in height and shade out most plants beneath them due to a dense canopy. The climax community of this colonisation is scrub woodland such as sycamore and hawthorn. This is due to shrubs being shaded out due to increased competition for enriched soil.

Urban ecology highlights how human factors account for some changes in the vegetation in the ecosystems of the British Isles. There have been many changes in the ecosystems of the British Isles due to increasing urbanisation. Due to the growth of urban areas, many cities have their own urban micro-climate which has an impact on the ecosystems within the areas. Cities are well known for being several degrees Celsius warmer than the surrounding countryside. This is seen to be due to heat energy being released through poorly insulated building and also the absorption of heat by bricks and concrete raising the  temperature of the city. As well as being warmer, urban ecosystems also have more rain. Warmer temperatures lead to the formation of convection currents which can form and strengthen thunderstorms increasing the rainfall in the city. Even though it is clear that the climate is different in urban ecosystems, it is unclear on what effect it has on the vegetation in these areas. However it is suggested that the growing season of some plants has extended.

In terms of urban ecology, distinct ecologies have been found along routeways. They can be distinctive habitats because exotic species and insects can be brought in by traffic. Railway lines enable windblown seeds to be blown along with the trains meaning the plant will follow the railway lines. For example the Oxford ragwort is seen plentifully along this lines as railway lines echo its natural niche. Wildflowers are commonly seen along many road side as nitrogen rich exhaust fumes boost the growth of such flowers.

Overall both physical and human factors are equally important in shaping the ecosystems of the British Isles today. However without the interference of humans on ecosystems, the British Isles will continue in succession as seen in the colonisation of wastelands. We can still not be sure if highly urban areas have an impact on vegetation. It has been noted that the growing season of some plants has been extended but it is unsure if this is a benefit of the urban micro-climate. In the long term this could have impacts on the vegetation diversity and overall survive in urban areas. Also with the growth of cities, it is vital that the deciduous woodland is protected through conservation areas otherwise it may disappear from the British Isles we know today.