Plants are influenced by everything in the environment around them, such as the climate, the soil and human activity. The plants we have in the environment are the species that can exist in the conditions, but the time taken for the ideal plants to exist can be very long. Similar to the way some people believe humans evolved by survival of the fittest, the strong plants live and reproduce while the weaker plants that can’t cope with the environment die off and fail to reproduce. This change in the vegetation over time is known as a succession. Essentially there are two types of succession, Primary and Secondary. Primary succession is basically when vegetation forms on land with no previous vegetation and secondary succession is when vegetation forms with existing plants or when it replaces destructed vegetation.
Since the last ice age a primary succession has took place on the British Isles. The name given to this process is a lithosere.
Britain has followed this general pattern since the last glacial period, initially the bare rock is colonised by bacteria and algae. These types of plants are capable of surviving with very little nutrients, and water. As the bare rock is solid and impermeable the precipitation quickly runs off the surface leaving little water for the plants.
The algae is followed by lichens; these are basically simple plants with no individual division between root, stem and leaves. These too can survive without much water, but they do begin to break down the rock and assist with water retention.
As the water levels begin to increase slightly, on the rock, mosses form and again help improve with the retention of water. Moss also starts the process off which provides soil for more complex plants to live in. Grasses, ferns and flowering plants and herbs follow the moss, as these die they re-release important nutrients and bacteria into the developing soil which helps improve its fertility. Shrubs along with fast growing trees such as willow and birch start to develop, followed by slow growing trees, such as ash and oak.
So what effect has human activity had on the whole process? Without knowing it, we often change the climax of the plants around us. For example deforestation stops or slows down the continuous development of a succession, when a succession is altered it’s called a plagioclimax.
Deforestation leads to the removal of many of the nutrients from the ecosystem and can lead to erosion. Probably the best example found within Britain is the amount of heather moorland we have. Many of these areas were covered by oak forests. Heather would only have featured in small amounts, however due to the forests being removed for various reasons such as the building of roads, it has started to grow in large amounts. The removal of trees caused the soil to lose its fertility causing hardy plants such as heather to dominate the regions, as they could cope with the poor soil. Sheep on the land meant that young plants were destroyed and therefore further development of plants deteriorated. As heather is also resistant to fire, which usually occurs every decade, it has lived when other plants haven’t. Fire can also destroys some of the nutrients in the soil causing it to lose its richness. Although fires aren’t always caused by human activity many are started by people.
Due to the clearing of Forest from the Anglo-Saxon periods much of the UK’s vegetation is plagioclimax. Therefore it’s fair to say that human activity has had a huge impact on many areas of our vegetation, but it would seem especially in areas of environmental conservation that the climax had been reached.
The soil on which plants rely for nutrients also effects which plants live where, and this too can be affected by human activity. When we walk across soil we compress it reducing the amount of air and water within the soils make up, this can reduce the soils ability to provide vital minerals and nutrients for the plants to survive on.
Pollution caused by humans can affect vegetation for example acid rain, which via air currents can travel globally precipitating at any point of the world. Acid rain kills plants and can change the balance of nutrients in the soil destroying or favouring certain types of plants.
Some people would argue that global warming, produced by pollution also kills off some types of plants due to a change in temperature, and therefore this is down to human impact rather than a natural climate change.
Human activity is also responsible for restricting plant growth in certain ways; we use chemicals to stop weeds growing and to control the growth of trees in some forest areas. There is no doubt that this has affected the natural vegetation succession.
In conclusion there are many different things, which effect vegetation change over time. These are both physical factors and human factors and both types can completely change an ecosystem and effect its progression towards its climatic climax vegetation and its establishment as a natural biome. Although we wouldn’t have much of the vegetation around us today if it weren’t down to the climatic changes since the last glacial period, humans have certainly changed the way plants have developed, especially in urban areas. In the future with the increasing use of genetics it would appear that there will be even more division between the vegetation, which suits the climate, and the vegetation which human activity causes to develop.
I wouldn’t say that human activity has had more impact than climatic change but it seems to be an increasing factor in determining what vegetation we have on the British Isles.
