Vegetation and soil

Ecosystem Distribution

Biomes are ecosystems that extend over large geographical areas and take their name from the dominant vegetation type within (for example, coniferous forest). A biome may cover a large area of a continent or may straddle several (the tropical rainforest is found in three). Each has its own characteristic soil, flora and fauna. Climate determines the distribution pattern of the different biomes. If climate is changing, then it stands to reason that the map of world biomes will also need to be modified.

The global map of biomes shows the British Isles as a zone of Temperate Deciduous Forest. In the absence of local arresting factors to plant succession, this is the normal climatic climax community. Deciduous trees are favoured by the UK's moist maritime (coastal) climate. However, at a local scale the situation is far more complex. Improved or acid grassland, heather moorland, coniferous forest, marshland and alpine (montane) communities are widely distributed in the UK, occurring wherever local edaphic (soil), drainage or relief factors restrict the growth of deciduous forest.

It should also be noted that human activity over thousands of years has cleared almost all of the UK's primary forest growth. Most has been replaced with farmland and where deciduous forest is still present it is often secondary growth.

How might climate change effect ecosystem distribution in the UK?

Deciduous woodlands of southern England may be most susceptible to climate change because of drier summer conditions, which might potentially begin to restrict their range in a high-impact global warming scenario (with temperature rising between 2C and 4C). However, it may also be argued that increased CO₂ and a longer thermal growing season will continue to favour the growth of broad-leaved trees. Trees were not always adversely effected by the hot summers of 1976 and 2006 where water remained available. The impact of higher temperatures on trees varies from place to place according to relief and drainage factors.

Where groundwater remains available, there is no reason why trees will not continue to dominate, even if summer drought becomes a permanent climatic feature .However, in areas of thin soils or poor water retention, trees may die and shrub and grasses could be expected to dominate. The net result might be that forest distribution patterns could become more complex, with much denser forest growth close to rivers and more gaps in the canopy wherever soils, geology and relief offer low potential for water storage.

Some scientists also predict an increase in the acreage of coniferous forest in the UK, as the tree-line will move upwards into areas of high relief (e.g. Scottish Highlands). However, the distribution of montane (alpine) ecosystems would be adversely effected at very high altitude as forest growth extends into areas where the growing season has lengthened. As a result, montane communities will be lost as a result of competition from tree species

Student Practice Question:

Outline the factors influencing the distribution of a named biome.

If deciduous forest is chosen as the named biome, then a good answer might refer to climate change as a factor that may already be modifying the existing distribution pattern in drier parts of the UK (e.g. southern England).