Ecosystems

Ecosystems

1. Rainforests

   • climate factors
     • Latitude - heat concentrated over a larger area at the poles due to the curvature of the earth
     • Distance from the sea - land heats up more quickly during the summer and cools more quickly in the winter than the sea
       • Places towards the centre of continents will have warmer summers and colder winters than those with a coastal location.
     • Prevailing winds - winds are warmed or cooled by the surface they pass over
       • In the winter, coastal areas are milder as the wind picks up heat from the sea.
     • Ocean currents - moves heat from different sides of the world. Moves cold water into hotter water and hotter water into colder water
       • Warm currents raise winter temperatures while cold currents usually lower summer temperatures
     • Altitude - higher you go the colder it gets temperature decreases on average 1°C for 100metres
   • Located along the equator between 23°C north and south (between the tropics)
   • Layers
     • Emergent layer - top layer, more sun and wind
     • Canopy layer - middle layer, warm and wet, no seasonal changes, most dense populated area
     • Understory and forest floor - thin layer of humus on the floor, dark due to many leaves preventing light reaching the floor
   • adaptations
     • plants
       • buttress roots - up to 3m high provide stability for very tall trees in the high winds in the emergent layer
       • small leaves - in the emergent layer reduced surface area limiting water loss through evapotranspiration
       • large leaves - in canopy layer where there is little light increasing the surface area with which to photosynthesise
       • drip tips - leaves have pointed ends so that torrential rainfall channels off their surface quickly so that they don't break under the weight
       • trees grow rapidly - don't waste energy growing side branches which enables them to reach the sunlight quickly
       • pivoting leaves - leaves twist and turn so that they are always facing the sunlight and can then maximise photosynthesis
   • why so important
     • farmland
     • timber
     • pulpwood for paper
     • building material
     • fruits and nuts
     • chemicals
     • soil conservation
     • weaving materials and dyes
     • charcoal
     • new crop varieties
     • medicines
     • fuel wood
     • flood prevention
     • gums and resins
     • watershed protection
     • 28 million of 30 million known species are found in the rainforest
     • 10km² contains 1500 species of flowering plant, 750 species of tree, 400 species of bird, 150 species of butterfly, 100 species of reptiles
     • 1/3 of the oxygen supply comes from the rainforest
   • Deforestation
     • clearing of the rainforest
     • causes
       • farming
         • 'slash and burn'
         • subsistence farming
         • settlement
         • commercial cattle ranching
       • resources
         • timber
         • minerals
         • hydro-electricity
         • transport
   • sustainable management
     • practice of effectively using available resources for economic benefit without reducing the chances of future generations to use the same resources
     • selective cutting
       • harvesting of selected single and groups of trees
       • advantages
         • reduces crowding
         • promotes growth of younger trees
         • allows a more natural regeneration
         • more environmentally friendly
       • disadvantages
         • expensive
         • removal of some trees by machines usually damages others
     • integrated cutting
       • several different species harvested at the same time
       • advantages
         • more economical than selective cutting as trees for different uses are harvested at the same time
       • disadvantages
         • poorer quality trees left
         • quality degenerates over time
     • clearfelling
       • total removal of all trees
       • advantages
         • allows total afforestation
         • higher yields and profits
       • disadvantages
         • leaves ugly scars
         • destroys ecosystem and habitats
         • encourages soil erosion and silting of rivers
     • strip cutting
       • variation of clear felling but often following the contours of land
       • advantages
         • avoids huge scars
         • allows easier regeneration
         • constant income and replacement
       • disadvantages
         • destroys sections of the ecosystem

2. Deserts

   • characteristics
     • low rainfall (less than 250mm per year)
     • unreliable rainfall
     • high daytime temperatures (over 50°C)
     • low night time temperatures (below 20°C)
     • [many have] ground frost or fog in the early morning
   • climate factors
     • relief rainfall - warm moist air rises over a hill, cools and condenses forming clouds which became so heavy relief rainfall occurred
       • air is then dry and cannot produce rainfall
     • descending air - air rises over equator forming rainfall and then descends over the tropics (where the deserts are) and the air is dry
     • land winds - winds which blow over vast areas of land have very little opportunity to pick up moisture and bring dry conditions
       • warm as land heats up more quickly than the sea
     • ocean temperatures - when an ocean current is cold it is difficult for the air above it to gain moisture
       • land next to a cold sea will only have a small amount of morning fog but very little rainfall
   • located along the tropics
   • adaptations
     • plant
       • succulents store water in their stems or leaves
       • plants have small leaves to reduce water loss
       • long roots go deep to absorb as much water
       • waves spread out across the surface to absorb as much water as possible
       • plants have a short life cycle, germinating in response to rain, growing, flowering, and dying within one year evading drought
       • leaves with hair help shade the plant reducing water loss
       • spines discourage animals from eating plants for water
       • waxy coating on stems and leaves help reduce water loss
       • slower growing requires less energy, the plants don't have to make as much food and therefore do not lose as much water
     • animals
       • nocturnal so hide from the heat of the day
       • ectothermic (cold blooded)
       • venemous to warn off predators
       • large surface area to maximise heat loss
   • plants
     • succulents - store water in fleshy leaves and stems and during the rain they absorb more water than they need (e.g. the prickly pear)
     • ephemerals - plants die during periods of drought and they disperse their seeds before dying
       • seeds lie dormant till rain arrives to germinate them and they flower, seed and die in a very short time (e.g. desert verbena)
   • drought - extended period of dry weather causing resevoir and ground water levels to drop
   • desertification
     • physical causes
       • global circulation - air is sinking over the tropics creating high pressure, no rising, cooling or condensing to form clouds
       • continentality - land winds very dry as there is little moisture to evaporate, land heats up quickly as only top few centimetres are heated
       • cold ocean currents - wind blowing over cold ocean currents contain little moisture as the air is not warm enough to evaporate the water
         • not enough water to sustain life
       • rainshadow effect - very dry on inland side as air rises, cools and condenses and precipitates to get over the mountain leaving air dry
     • expansion of deserts, irreversible change and decline is soil productivity so that no plants can grow there, occurs in arid areas
     • human causes
       • agriculture - overcultivation means no nutrients are returned to the soil, overgrazing means that hooves compact the soil so rain cannot infiltrate
       • rapid population growth - high birth rates mean more mouths to feed and greater pressure on farming, more land is cultivated and grazed
       • deforestation - means that nutrients aren't returned to the soil through decomposition of leaf litter, soil is vulnerable to soil erosion
         • sun can evaporate moisture easier
       • water extraction - more drinking water is needed, takes a long time for water levels and wells to return to normal
     • sahel - band from Nigeria to Kenya where there is high desertification
     • recovering desertificated land
       • Magic stones - helps to store water when rain does fall, less soil is eroded by water and there is less bare ground
       • Eden foundation - since 1988 has been carrying out field tests at a field station near Dalli, Niger
         • involves the direct seeding of perennials which can survive with less than 200mm per year
           • perennials - come up every year and don't need to be reseeded, stop soil erosion as roots hold soil in place, leaves intercept water all year round
     • 20millionkm² are degraded every year and it affects 280million people
     • more than 110 countries have dry lands potentially at risk from desertification, with the possibility of affecting 900million people
     • the United Nations claim that $45billion will be needed every year for the next 20 years to reclaim degraded land