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Human activity can impose far-reaching effects on an ecosystem. There is a potential conflict of interest between production and conservation

  • Clearing of forests for agriculture or buildings; cleared areas may be mined for mineral ores; timber obtained may be used for paper, charcoal, furniture, building material
  • Reduces transpiration, rainfall, humidity
    • Increases risk of fire
  • Increases velocity of rain reaching the soil
    • Soil erosion / leaching of ions
  • Reduces biodiversity
    • More extreme environment / abiotic factors increase / unstable ecosystem
    • Change in (micro)climate / levels of light / temp / humidity
    • Loss of niches/habitats and complex food webs
    • Animals move away/higher death rate/extinction
  • Lower biomass and productivity per hectare

Effect on Nitrogen Cycle
  • Growth in human population is increasing the demand for agriculture
    • for land for farming
    • for grazing land to provide animal protein
  • Many decomposing fungi live in association with roots of trees
    • Less NH4+ can be absorbed by plants from decomposition
    • The soil itself is often a poor source of mineral ions
    • \ Reduced input in the nitrogen cycle; slower and less recycling of NH4+
  • Nitrogen in soil is lost as smoke but ash is still rich in nutrients for crops
    • Yield falls with subsequent crops
    • Crops are harvested before they die/decompose
    • Nitrogen is not recycled and not returned to the soil
    • Fertilisers (NO3, NH4+) make up that loss
    • Ions from fertiliser readily leach out of the soil by rain into lakes and rivers
    • Increases growth of algae and water plants
  • [EXAM] Ploughing increases the activity of nitrifying bacteria in the soil
    • Oxygen enters the soil
    • Nitrifying bacteria are aerobic
    • Convert ammonia/ammonium ions to nitrite, nitrite to nitrate
    • Nitrate is absorbed/used by plants
    • To make protein/amino acids/DNA/ATP/NAD(P)/chlorophyll
    • Increased yield/growth

Affect on Carbon Cycle
  • Lower CO2 (greenhouse gas) uptake by photosynthesis
  • Burning trees for agriculture and fuels releases CO2
  • Higher conc of CO2 in the atmosphere accelerates greenhouse effect
    • CO2 absorbs outgoing longwave radiation
    • Warms the troposphere (lower atmosphere)
  • Trees can act as carbon sinks [EXAM]
    • Absorb CO2 in photosynthesis
    • Carbon (dioxide) is used in forming permanent plant tissues/biomass/plant structure
    • Carbon is incorporated in organic molecules
  • Reduction in the amount of ploughing lead to more carbon being stored [EXAM]
    • "Less oxygen can enter the soil (from the air)
    • For decomposers/saprobionts/fungi/soil microorganisms/bacteria
    • For use in aerobic respiration
    • Less breakdown of organic matter/humus/dead plants/dead animals
    • Less carbon dioxide released"1

Conservation of Forests is the Sustainable Use of Forests
  • On deforestation
    • Felling one hectare will give space for agriculture for high income
    • But the land loses fertility after a few years
    • Using cleared land for cattle will give a low income per year
  • If the forest is kept
    • Medium income per hectare per year for fruit and rubber production
    • Income from tourists and medicinal plants
    • Gene pools of wild relatives of domesticated organisms - which may be used as a source of genes/alleles in selective breeding or genetic engineering
  • Tropical rainforests should be conserved to avoid [EXAM]
    • "Loss of species / decrease in diversity / loss of niches / disruption of food chains
    • Loss of pharmaceuticals / medicines / timber / wood
    • CO2 build-up in atmosphere / global warming
    • Leaching of ions / minerals / nutrients
    • Soil erosion / mud slides / flooding / desertification"2

References and Further Reading
1) AQA (2002) Mark Scheme June 2002 GCE Biology/Human Biology A Unit BYA5, [PDF]
2) AQA (2004) Mark Scheme January 2004 GCE Biology/Human Biology A Unit BYA5, [PDF]
AQA (2006) GCE Biology/Biology (Human) 2006 specification, [PDF]

BYA5 SECTION: 14.1 14.2 14.3 14.4 14.5 14.6 14.7 14.8 14.9 14.10