- A biome is a global-scale ecosystem and is a naturally occurring organic community of plants and animals in the climatic climax stage of succession.
- Tropical rainforests and temperate deciduous woodland are both examples of high energy biomes.
- Low energy biomes are the tundra in the high latitudes and the hot deserts in the low latitudes, the vegetation is scarce and net primary productivity is low.
- Temperate deciduous woodland is a high energy biome which has a relatively high productivity. It is found in mid latitudes on the borders of continents where there is adequate moisture.
Climate:
- Temperature ranges from 5 – 17 in Winter and Summer.
- 500-2,000mm of rain per year, varies seasonally.
- Low pressure systems.
- Westerly winds.
Vegetation:
- Broadleaved deciduous trees are the dominant species, oak is the tallest.
- Trees develop large crowns and broad but thin leaves.
- Shed their leaves in the winter, reduces transpiration when less water is available.
- Net primary production-1,200g dry organic matter per M² per year.
- Most woodlands show some stratification.
- Below the canopy is the shrub layer.
- Just above the forest floor is the herb layer.
- Epiphytes such as lichens and mosses grow on the trunks and branches of trees.
- A thick layer of leaf litter is readily broken down by soil microbes and animals.
Soil:
- Brown Earth soil 1.5m deep.
- Leaf litter makes the soil more fertile in Autumn.
- Well mixed with decomposers so it becomes fertile quickly.
- Leaching occurs when there is snowmelt or intense rain, which is not uncommon.
Arresting Factors
- Plant successions can be stopped from reaching climatic climax or deflected to a different climax, by human interference
- The resulting vegetation is called a plagioclimax, this can be caused by:
- deforestation or afforestation
- animal grazing or trampling
- fire clearance
- A secondary succession is one that develops on land that has previously been vegetated
- The stages of secondary succession may be more rapid than those of primary succession because organic matter is already present in the soil, the pioneer stage may be short or absent- climatic climax is reached in a much shorter time.
Plagioclimax: Heather Moorland
- As the soils deteriorated without the deciduous vegetation, hardy plants such as heather come to dominate the uplands.
- Sheep grazing became the major form of agriculture and the sheep prevented the regeneration of climax woodland by destroying young saplings.
- Many of these uplands have been controlled by managed burning to encourage new heather shoots.
- Burning has eliminated the less fire-resistant species, leading to the dominance of heather.
- One of the aims of burning heather is to ensure as much as possible of the available nutrient is conserved in the ecosystem.
- Burnt on average every 15 years, If the time elapses more then there is too much woody tissue and nutrients are lost in smoke.
Tropical Biomes
- In a tropical rainforest biome due to the constant high temperature and rainfall, vegetation grows more quickly, large amounts of net primary production.
- Biodiversity – the variety of species within an ecosystem.
- Leaching – soluble bases are removed from a soil by downward-percolating water in environments where precipitation exceeds evaporation.
- Net primary production – the amount of energy fixed in photosynthesis minus the energy lost by respiration in plants.