3.1.2.3 Hot deserts Flashcards
Describe the climate - name 3 general things
- Diurnal temperature → range from very hot in day (e.g. 45°C) to very cold at night (e.g 5°C)
- Very little rainfall → less than 250 mm per year
- When it rains also varies a lot → might only rain once
every 2 or 3 years
What is meant by a diurnal temperature range?
It means it experiences extreme range of temperatures in a single day
Why does the desert have a diurnal temperature range?
Cloudless skies allow high levels of insulation in daytime + rapid heat loss at night
What is the soil like?
- Shallow with coarse, gravelly texture
- Hardly any leaf fall = soil isn’t very fertile
Describe how the plants are like (name 4 things)
- Plant growth is sparse due to lack of rainfall
- Plants have a short life cycle, only appearing when it rains
- Plants usually short (though cacti grow fairly tall) - low shrubs & short woody trees
- e.g. includes cacti & thornbushes
Describe how the animals are like (name 2 things)
- Mammals tend to be small and nocturnal
- Most birds leave desert during harshest conditions
Describe how the people are like (name 2 things)
- Many people living desert grow few crops where there are natural springs or wells to supply water (usually in desert fringes)
- Indigenous people are often nomadic: They travel all the time in search of food and water for their herds (mostly goats and sheep)
What are desert fringes?
Areas at borders of hot deserts where there’s greater
biodiversity and large plants (a.k.a. Semi-desert, semiarid areas, inappropriate agriculture)
Why are hot deserts are fragile, interdependent ecosystems?
Biotic (living) components of deserts + abiotic (non-living) components are closely related → if one of them changes, the others are affected
Give an example how animals and plants are interdependent (nutrients)
- Plants gain their nutrients from soil & provide nutrients and water to animals that eat them
- In turn, animals spread seeds through their dung - helping plants reproduce
Explain how the hot and dry climate affects soil & this affects plants
Soils are salty due to high evaporation and relatively low in nutrients because there’s little decomposition of dead plant material by fungi and bacteria ∴ plants struggle to grow
Explain how the amount of vegetation affects animal populations
Sparse vegetation limits amount of food available → so desert can only support low-density populations of animals
Explain why the water supplies in deserts can be extremely scare
Water supplies in deserts can be extremely scare ← rainfall is very low and coarse desert soil means rain that falls quickly drains away
How does these scare water supplies affect animals and people?
Animals and people find ways of coping e.g. By constantly moving to new places or digging deep wells
What do people ‘have’ to do to grow crops?
People have to irrigate (artificially water) land in order
to be able to grow crops
Why is irrigation bad for animals and plants?
Drawing unsustainable amounts of water from wells lowers level of water underground - reducing amount available to other plants
∴ Plant species and animals that depend on them can struggle to survive as a result
Explain how changes to components of ecosystem (e.g.
cattle overgrazing vegetation) can have knock-on effects
on whole ecosystem
- Without plant roots to stabilise the soil, wind can blow fine sand/soil particles away = soil erosion
- Soil erosion can lead to clouds of dust in atmosphere = can change climate of deserts - reducing rainfall, making it even drier
How are plants’ roots adapted to help them cope with hot, dry conditions?
- Roots are either extremely long to reach very deep water supplies
- OR spread out very wide near surface to catch as much water as possible when it rains
How are succulents adapted to cope with hot, dry conditions?
Have large, fleshy stems for storing water and thick waxy skin to reduce water loss (transpiration)
Name 4 common plant adaptations to cope with hot, dry conditions
- Roots are either extremely long or wide
- Many plants (e.g. cacti) are succulents
- Some plants have small leaves or spines
- Seeds of some plants only germinate when it rains
How does having small leaves or spines help plants to cope with hot, dry conditions?
Gives them a low surface area = reducing transpiration
Why do some plants have sharp spines and toxins?
To stop animals from stealing water from stems
Why do seeds of some plants only germinate when it rains?
Plants grow, flower and release seeds in just a few weeks = ensuring they only grow when there’s enough water to survive
Name 6 animal adaptations to cope with high temperatures and limited supply of water
- Nocturnal
- Able to tolerate high body temperatures
- Can store large amounts of fat
- Get all water they need from what they eat
- Have long limbs or ears
- Minimise water loss from sweat and urine
Name 2 animals that are able to tolerate high body temperatures
Lizards and snakes
Explain how being nocturnal helps to cope with high temperatures
Being nocturnal means animals can stay cool in burrows during day or sit still in shade whist it’s hottest (e.g. Fennec foxes)
Why do animals have long limbs or ears
Gives large surface area to lose heat from
Explain how being able to store large amounts of fat helps to cope with limited supply of water
Some bigger animals store large amounts of fat which they can break down into water when needed (E.g. Camels’ humps)
Give an example of animals that get all water they need from what they eat
Cactus mice get water from cactus fruits and insects
Explain how camels are adapted to cope with sand
Camels keep sand out their eyes and nose during
sandstorms by having triple eyelids, long eyelashes and
being able to close their nostrils. Also have large, flat feet so they don’t sink into the sand.
What is desertification?
The degradation of land so that it becomes more desert-like - it becomes drier and less productive
How much of world’s surface is in risk of desertification?
1/3 of world’s land surface is at risk of desertification (especially margins of deserts)
What is a key part of desertification?
Soil erosion
How soil erosion leads to desertification?
- Soil that is exposed (not covered by plants) is easily removed by wind or water
- Nutrients in soil (e.g. Fallen leaves, dead plants) are lost making soil unproductive
- Eventually ground becomes sandy, dusty, stony or just bare rock
Name the main physical causes of desertification (due to climate change)
- Rainfall - climate change is expected to reduce rainfall in areas that are quite dry
- Temperatures - global temperatures are expected to increase
Explain how reduced rainfall (due to climate change) can lead to desertification
- Less rain means less water available for plant growth so plants die
- Plant roots hold soil together, if plant dies soil easily eroded
Explain how higher temperatures (due to climate change) can lead to desertification
- Higher temperatures mean more water evaporates from land and plants
- Makes soils drier and means plant die (so roots no longer hold soil together)
Name 4 human activities that lead to desertification
- Removal of Fuel Wood
- Overgrazing
- Over-Cultivation
- Population Growth
How does the removal of fuel wood lead to desertification?
- Many people in arid (dry) areas rely on wood for fuel for cooking
- Removal of trees leaves soil exposed so it’s more easily eroded
How does overgrazing lead to desertification?
- Too many cattle or sheep eat plants faster than they can regrow ∴ leads to more soil erosion because plants
no longer hold soil together - Trampling by animals also erodes soil
How does over-cultiavtion lead to desertification?
- If crops are planted in same area continually, all nutrients in soil get used up
- This means plants can no longer be grown in those soils and without plants soil erosion increases
How does population growth lead to desertification?
This puts pressure on land leading to more deforestation (firewood), more overgrazing and more over-cultivation
Name 4 ways how the risk of desertification can be reduced
- Water Management
- Tree Planting
- Soil Management
- Appropriate Technology
Explain how water management can reduce the risk of desertification
- Growing crops don’t need much water (e.g. Olives) can reduce water use
- Using drip irrigation on crops instead of surface irrigation means soil isn’t eroded by lots of water added in one go
Explain 3 ways how planting trees can reduce the risk of desertification
- Growing trees amongst crops protects crops (and soil) by providing shade ∴ reducing temperatures and evaporation rates
- Trees can be planted to act as windbreaks to protect soil from wind erosion
- Trees can stabilise sand to prevent desert from encroaching on farm land
Explain 3 ways how soil management can reduce the risk of desertification
- Leaving areas of land to rest in between grazing or planting lets them recover their nutrients
- Rotating crops that use different nutrients from soil means that same nutrients don’t keep being removed
- Compost can be used to add extra nutrients to soil
What is meant by using appropriate technology?
Means using cheap, sustainable and easily available materials that are easy for local people to maintain
Give an example how technology can be used appropriately to reduce the risk of desertification
Sand fences (barriers to trap windblown sand) or terraces can be constructed to stabilise soil and reduce soil erosion
Give an example how technology can be used appropriately to reduce the rate of deforestation (which leads to desertification)
By using solar cookers which use sun’s energy to heat food → they’re cheap and easy to make and don’t require wood as fuel to work
