Human Activity

Deforestation

• 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
  • Thus, 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