Geog CBA2

• Mangrove habitats


  • Inter-tidal zones
  • Salty, brackish water
  • Muddy, water-logged and oxygen-deficient soil
• Three main communities of trees in mangrove habitats

  • Coastal zone (Avicennia and Sonneratia)
  • Middle zone (Rhizophora)
  • Inland zone (Bruguiera)
• Coastal zone trees


  • Colonise mud banks that are usually exposed at low tides
  • Adapted to growing in salt water as this zone is flooded during high tides
• Avicennia


  • Pencil-like roots
• Sonneratia


  • Conical shaped roots
• Rhizophora


  • Prop roots or stilt roots
• Bruguiera


  • Grow best in drier parts of mangrove belts where the soil is stiff clay, flooded only occasionally by high tides
  • Least tolerant of salts, knee-like roots
• Mangrove leaves


  • Broad and green to capture more sunlight
  • Thick and leathery to withstand heat and reduce moisture loss
  • Smooth and waxy to allow rainwater runoff
  • Downward-pointing drip-tips to allow excess water to drip off
  • Salt glands within leaves to secrete and store salt
• Mangrove aerial roots


  • Partially submerged, oxygen-deficient, anaerobic soil
  • Pneumatophores act like snorkels when partially flooded
  • Contain lenticels for gas exchange
  • Contain large air spaces (aerenchyma) to transport air and provide air reservoir
• Avicennia roots


  • Shallow cable roots that spread out from the trunk, with short pencil-like pneumatophores growing up to 30 cm in height
• Sonneratia roots


  • Develop a flat root system with cone-shaped pneumatophores reaching 40-60 cm in height
  • Conical roots can grow in a radius of more than 10 m
• Rhizophora roots


  • Looping branches arise from trunk and lower branches, forming prop roots or stilt roots that arch from the trunk down to the ground
• Bruguiera roots


  • Knee roots emerge from the ground then loop back in, often with a knobbly bump at the highest point
• propagules

  • Viviparous - seeds germinate into propagules while still attached to parent tree
  • Able to photosynthesise while still attached
  • Sharp end of Rhizophora propagules anchor firmly in mud
  • Avicennia fruits are buoyant and take root in coastal areas after floating
• Ecosystem services provided by mangrove forests

  • Provisioning services (food, water, raw materials, medicinal resources)
  • Regulating services (local climate, air quality, carbon sequestration, moderation of extreme events, waste-water treatment, erosion prevention, pollination, biological control)
  • Habitat/supporting services (habitats for species, maintenance of genetic diversity)
  • Cultural services (recreation, tourism, spiritual experience)
• Causes of deforestation


  • Used for urban and construction purposes
  • To grow crops
  • Cattle ranching
  • Logging
  • Soy cultivation
  • Transport infrastructure development
  • Hydroelectric power dam construction
  • Mining and oil and gas development
• Positive effects of deforestation

  • Economic (greater revenue, reducing foreign debt, providing employment)
  • Social (alleviating starvation and hunger, increasing yield and population density)
• Negative effects of deforestation

  • Economic (depletion of forest resources, depletion of non-renewable resources)
  • Socio-cultural (disappearance of tribal-indigenous people, loss of traditional culture and knowledge)
  • Physical/environmental (erosion, increased sedimentation and flooding, water pollution, decline in soil fertility, destruction of flora and fauna, modifications to the atmosphere)
• Avicennia has special salt glands within leaves which secrete excess salt, and as the salt evaporates, crystals form on the surface of their leaves and are blown away by the wind.
• The cone-shaped or pencil-like pneumatophores of the Sonneratia and Avicennia and the knee-like roots of the Bruguiera which grow above the oxygen-poor mud supply the partially submerged root system with oxygen via lenticels on their surfaces.
• The climate change caused by deforestation can lead to extreme weather, wildfires, drought, and food supply disruptions.