1.4- Amazon rainforest Flashcards
describe the location of the Amazon rainforest
The amazon rainforest covers a large area in the north of South America and lies between the tropics of Cancer and Capricorn, extending approximately 20 degrees north to 20 degrees south of the equator- the majority of the forest lies within Brazil, with the remainder lying mainly in Peru and Colombia
the Amazon rainforest is by far the largest remaining rainforest covering __ million square miles
2.1 million
tropical rainforests cover less than 10% of the Earth’s surface and yet account for __-__% of global photosynthesis
30-50
tropical rainforests absorb huge quantities of carbon dioxide and emit over __% of the world’s oxygen
25
tropical rainforests have an annual rainfall ____+mm and temperatures of 27 degrees Celsius throughout the year which is ideal conditions for plant growth
2000
tropical rainforests have very high biodiversity and are home to about __% of the world’s species of animals and plants
50
explain how inputs into a tropical rainforest’s water cycle are high
precipitation is very high, occurring throughout the year, usually in daily torrential downpour- consequence of low pressure and high humidity in the tropics
in spite of the heavy rain, dense canopy intercepts __% of precipitation
75
some of the intercepted precipitation is evaporated and some reaches the ground via
stemflow or drips from the leaves
half of the availabe rain is used by plants and returned to the atmosphere via evapotranspiration- the other half
infiltrates the soil
explain how the trees of forests are critical to the region’s water supply
through the process of transpiration, trees ensure water enters the atmosphere and in turn produces rain- for example, Amazon Basin produces 1/3 of its own precipitation in the recycling of evapotranspiration (other 2/3 arriving in moisture-laden air from the Atlantic ocean
most rainforest plants have very shallow roots that take rainwater and ________ _______ directly from the decomposing leaf litter
dissolved nutrients
it is estimated that the Amazon rainforest has lost nearly __% of its primary rainforest in the last 50 years largely due to clearance for cattle ranching
20
explain how deforestation has a massive impact on the rainforest water cycle
- reduced evapotranspiration from cleared areas means the air is less moist, resulting in a reduction in cloud cover and thus precipitation
- with fewer trees,most rainfall reaches the ground immediately as there is little interception- the water leaves the area as overland flow and so less is returned to the atmosphere locally. Increased rates of run off also increase the risk of flooding
- more solar radiation is reflected by cleared land (than darker forest canopy) and so temperatures increase
- exposed soil is also at risk of erosion, which limits the chances of regrowth
the impact of deforestation on climate and rainfall has been the subject of
much scientific study
explain why the effects of deforestation on rainfall may vary between regional and global levels
- in some studies, the replacement of forests by pasture land or crops has been shown to lead to reduced atmospheric humidity and suppressing precipitation
- however some previous studies have shown an increase in local rainfall downwind of a deforested area
- nevertheless, a recent study suggests that rainfall levels in the wider region are likely to reduce where there is extensive deforestation- it has been demonstrated that air that has passed over forest in preceding days produced at least twice as much rainfall as air that had passed over little forest
- the study estimated that future deforestation of the Amazon could lead to 20% decline in regional rainfall
explain the impacts of deforestation at a local scale
- some cleared areas have seen an increase in precipitation due to ‘vegetation breezes’
- still, different impacts can be seen in forested areas deliberately burned to clear for agriculture- the burning produces airborne aerosols around which water vapour condenses; as a result smaller droplets of occur in clouds which are too small to precipitate = less rain
what are vegetation breezes?
air over cleared land warms faster, rises more quickly creating localised low pressure, drawing moist air in from forested areas = increased cloud coverage, thunderstorms and rainfall over cleared land
rainfall formed from vegetation breezes is more likely to cause
soil erosion as increased surface flow discharges into local river systems
the warm, humid tropical climate is ideal for plant growth, which explains why tropical rainforests account for __-__% of global photosynthesis
30-50
tropical rainforests absorb huge amounts of carbon from the atmosphere and emit over __% of the world’s oxygen (‘lungs of the Earth’)
25
wood = __% carbon so rainforest vegetation, particularly trees, are a huge carbon store = help mitigate the effects of global warming
50
in a typical year, the Amazon rainforest absorbs . billion tons of carbon dioxide while emitting 1.9 billion tons through decomposition and organism respiration
2.2
some carbon may be stored within the soil then removed by _____ as an output from the rainforest system
streams
rainforests store more carbon (as sugar and starches) than
any other type of ecosystem
rainforests of Amazonia contain between __-__ kilograms of carbon per square metre
14-40
the soils lying under rainforests also contain substantial amounts of carbon, which amounts to about __% of global soil carbon = not all carbon storage occurs within above-ground plant vegetation
25
tropical rainforests are therefore critical elements in the carbon cycle of the planet but their capacity to recycle the world’s increasing carbon dioxide emissions is beginning to
appear in doubt as human activity alters their extent and dominant processes
deforestation is he second largest anthropogenic source of carbon dioxide to the atmosphere after
combustion of fossil fuels
when forests are cleared and burned (whether for farming, mining or settlements) __-__% of carbon is lost to the atmosphere
30-60
burning is cheap and effective but
can burn out-of-control for weeks
the size of the Amazon rainforest has been decreasing at an average rate of_._% per year since 2000
0.3
deforestation also means photosynthesis ceases until new plants colonise the area- plant and animal respiration almost drops to 0. In addition, rain will wash ash into the ground that in the short term
increases the carbon content of the soil- some of this carbon will leave the local system however through increased run off
explain how the Amazon basin no longer represents a continental carbon sink
- although in the past, the Amazon rainforest would typically absorb 2.2 billion tons of carbon dioxide, its capacity to operate as a major carbon sink is declining
- in 2015, it drew down just 1 billion tons of carbon dioxide
- this is less than the total carbon dioxide emitted by Latin American countries each year,so the Amazon basin no longer represents a continental carbon sink
why does the Amazon basin no longer represent a continental carbon sink?
- the reasons for decline are thought to be related to substantial tree death within the Amazon basin
- it has been assumed that increasing atmospheric carbon dioxide levels would stimulate biomass growth (carbon fertilisation) and regulate emission rise
- however, it appears that while rainforest plants do grow faster, they also die sooner
- this has increased metabolic stress compounded by recent drought, unusually high temperatures, continued illegal logging and conversion to agriculture
it appears that the rainforest is under threat from both direc human activity and climate change arising from
indirect action in releasing stored hydrocarbons in such massive quantities
