hot deserts and their land scapes : use with notes.

Question 1

what is meant by the term “hot desert”

Answer 1

a part of the workd with very high average temperatures and extremely low temperatures. These areas have less 250mm of rainfall/yr

Question 2

what arethe 3 ways of classifying deserts?

Answer 2

hyper arid, arid and semi arid zones.

Question 3

what is the aridity index of hyper arid zones?

Answer 3

<0.03

Question 4

what are the characteristics of hyper arid zones?

Answer 4

AI of 0.03 Dryland w/o vegetation.

Nomadic pastorlasim os practiced here and annual rainfall is v v low.

Question 5

what is the aridity index of an arid zone?

Answer 5

0.03 - 0.2

Question 6

what is the aridity index od semi arid regions?

Answer 6

0.2 - 0.5

Question 7

what is the aridity index.

Answer 7

The differenence b/w precip and pot evapotransp, It give value of water deficit and thus is used to classify deserts in terms of aridity. the LOWER the number the >er aridity.

Question 8

what is aridity?

Answer 8

the state of being v v dry w/o enough rain for plants.

Question 9

characteristic/ definition of an “arid zone”

Answer 9

the climate of an area that reaches <250mm precipitation/yr.

Question 10

characteristics/definition of a “semi arid” zone?

Answer 10

The climate of an area that recieves b/w 250mm and 5000mm precip/yr.

Question 11

what is potential evapotranspiration?

Answer 11

drying power, ie the amount of water that would evaporate/trapnspire if it was present.

Question 12

EQ: Based on the characteristics of a hot desert in hyper arid, arid what would happen to the water if there was a storm?

Answer 12

HIgh temperatures result in soils being baked hard and as result, water would runoff thus low infiltration and high overland flow.
Hot temperatures also means that the water will evaporate vv quickly.
Cactus have v v long roots and thus will absorb any water v v quickly ( and swell up)

Question 13

Where are hot deserts located Ie the distribution?

Answer 13

Hot deserts cover 1/5th of the surface of the earth adn they run in parralel belts that run along the tropics 30N and south of the equator. They occur in hot arid and semi arid mid and low latitudes. They continetianally tend to sit on the Western side of of continents such as those in SOuth AMerica(the Atacama)
They can also be found behind mountain ranges.

Question 14

what are the major deserts in the N hemisphere?

list by the regions North America, Africa, Asia

Answer 14

North America : Mojave, Sonoran
Africa : Sahara
Asia : Thar streching from the red sea to the middle east to pakistan and India), Arabian desert

Question 15

What are the major deserts in the S hemisphere?

list by continet ie South America, Africa and Australia

Answer 15

S America –> Atacam
Africa : Namib , Kalahri and Karoo
Australia : Great Sandy , Great Victoria and the SImpson desert.

Question 16

which 4 ways can cause aridity?

Answer 16

cold ocean currents
relief (ie rainshadow effect)
continentiality
general pattern of atmispheric circulation.

Question 17

How does the global atmospheric circulation lead to aridity?

Answer 17

At the equator, there is a net gain in energy due to large amounts ofsolar insolation from the overhead sun. Air in contact with the earth will rise and cool forming clouds and leading to precipitation, The rising air is replaced by air rushing in from N and S creating an aea of low pressur e(high rainfall) known as the ITCZ. Rising dry air begins to cool + move polwards + at 20/30 degrees it descends, creating an area of high pressure. As it desends it warms and expands resulting in little cloud formation and thus clear skies which result in high heat and aridity in these areas.
In areas of high pressure, winds also blow outwards so no moisture brought in thus low precip –> v v arid + dry.
High pa also means lack of cloud formation thus >er aridity.

Question 18

how does continentiality result in aridity

Answer 18

Central parts of continents are more arid than coastal areas.
Water heats up the water in coastal areas slowly (and to a lower temp than that of the land) due to high SHC. Evaporation occurs from the water and latent heat is also transferred along water droplets to atoms. Cool and condense ==> rain and thus coastal areas recieve high er amounts of precipitation.
Inland, there are no clouds to block insolation and thus temps vv high durign day but also high diurnal range so land cools rapidly at night. When air moves inland, it has low moisture cotntent (after dropping it all by coasst ) –> high aridity

Question 19

how does relief result in aridity?

Answer 19

Tall mountains force winds upwards and thus the air rises. As the air cools and condenses, its ability to hold water declines and thus water dropped as relief rainfall over the mntns. As prevailing wind continues to carry the air over the mountain inland, the air holds vv little moisture and thus little rainfall occur on the leeward side of the mntns. AIr descenbds on the leeward side of the mntn , and the sinking air warms up slightly resulting in the ar above being v v clear + dry w/ no rainfall (humidity also drops). This is the rainshadow effect.

Question 20

how do cold ocean currents result in aridity?

Answer 20

prevailing winds that pass over cold oceans is cooled, increasing humidity and eventually the moisture condenses to form a fog offshore. As the land heats up quicker than sea, this may generate onshore breezes, which suck fog + mist inland. However the intense heating from the sun directly overhead burns this away resulting in deserts being dry and arid.
When mositure is released as precip its released over the ocenas before hitting land and thus air that does move in has low moisture content and thus low rainfall.

Question 21

what are the main characteristics of hot desert?

Answer 21

The are hot and have large variations in temp
they have little vegetation
the soils are dry and infertile.
spotty rains

Question 22

what kind of temperatures do hot deserts experience?

Answer 22

Diurnal temperatures.

Question 23

What is meant by a diurnal temperature range?

Answer 23

It is the diff b/w the v v high daytime temp(ie >40 deg) where land is heated due to direct insolation from the sun and the v v cool night temps where temp drops rapidly

Question 24

How is the rainfall in hot deserts described as and why?

Answer 24

“Spotty” –> it is sporadic and often unpredictable.

Question 25

Hot desert characterisitc : Hot + large variation in temp

Answer 25

Mean avg temp is around 2- - 30 deg however there is SOME seasonal variation w/ temp risign to 50 de in summer and below 0 in winter.
The temps also vary daily due to the diurnal temp ranges.
in desert margins the annual temps are lower b/w 10 - 20 degs and thus the temp extremes are less extreme.
The large vatriations in temps is due to the high pa dry desert air that has no clouds thus cant block out sunlight during the day OR insulate/trap heat in the night.

Question 26

Hot desert characteristic : little vegetation

Answer 26

Biomass is v v low in hot deserts fue the lack of water which makes it v v hard to grow. Amount of veg varies(ie sand dunes or plenty of cacti and grasses) .
Plants such as cacti are specialised to survive inthe hot and arid conditions.
however in desert marigns, there is more vegetation incl grasses and shrubs. The no of veg increases as u move away from center of desert due to the increaing availability of water.

Question 27

hot desert characteristic: Dry and infertile + unproductive soils

Answer 27

Soils are infertile in some areas due to the high salt content which arises due to the accumulation of salts as a result of capillary action moving water upwards. Soils are unworkable and sandy/rock and dry due to low rainfall and high temps ans thus as a result its v v hard to sew seeds that will root bc soils are tooo dry.

in desert margins however, the soils are much more fertiel than soils in the desert bc there is more vegation to fall and thus create leaf ltter + huma thus org matter which veg needs to grow.
Soil is less sandy than those in deserts duye to greater weathering in desert margins.

Question 28

what percentage of the earths surfaces is desert soils ?

Answer 28

17%

Question 29

how much soils as a % is present in AUstralia ?

Answer 29

44%

Question 30

what is the % of desert soils in Africa?

Answer 30

37%

Question 31

what is the % of desert soils in Eurasia ?

Answer 31

15%

Question 32

why migh soils not develop well in arid climates.

Answer 32

when soils 1st develope in desert soils they start of as thin alkaline and saline soils w/ v v thin profiles.

Question 33

what is the reasoning for the slow rate of soil devlopement.

Answer 33

• little vegetation : due to lack of water from lack of rainfall.
• the little plants that are adapted to the hot desert environment. Plants that are adapted against absicission dont add to hummus layer ie the spines of cacti.
• heat –> high temperature results in water in soils evaporating.

Question 34

what are most desert soils characterised by?

Answer 34

A thick accumulation of basic mineral salts ie Ca2+ and Na+ compounds.

Question 35

why are desert soils saline (ie the crust of aslt)

Answer 35

the high temperatures mean that there are high levels of evaporation>precip resulting in capillary action pulling moisture up from the sand aling w/ dissolved minerals. when the water eveporates, the minerals form a salty crust at the soil surface.

Question 36

apart from creatign a vv dry environment how else does lack of rainfall shape the characteristics of the soils.

Answer 36

the lack of rainfall means that htere is limited weathering of rock, which when it does occur is vv v slow and thus soils are vv thin.

Question 37

Outline the 4 main fetures of soils in hot desert environments (4m)

Answer 37

• soil is a micture of organic and inorganic material
• deserts have very poorly developed and thin soils due to the lack of organic matter forming humus. Even when the scarce highly adapted vegetation dies, the lack of water stops it decomposing and producing a humus to enrihc a developing soil
• desert soils are v v sandy porous and permeable and thus have a poor moisture retention.
• however, wilst the soils have a poor quality , the lack of rainfall means that leaching is minimal and thus there are some plant nutrients that are avalable and w/ the right irrigation + soil mnagemnent crops an be grown successfully in desert regions ie Almeria , Spain,

Question 38

what is the main soil type in deserts?

Answer 38

Aridisols

Question 39

what are aridisols?

Answer 39

they are a soil characterised by the accumulation of mineral salts near the surface.

Question 40

describe the soil profile for aridisols?

Answer 40

they range from a redding yellow to a grey brown depending on the nature of the parent material.
they are generally v v thin (<100cm).

Question 41

describe some characteristics of aridisols

Answer 41

alkaline,
saline,
infertile
climate drives the vegetation here
low organic content in soils ( due to the lack of decomposition of organic matter as it is v v slow + low)
these soils also have v v sparse vegetation due to the low amounts of rain

Question 42

are deserts just areas of sand?

Answer 42

no, the sand layer has soils beneath them

Question 43

why are desert soils not vv fertile:?

Answer 43

they dont contain much organic matter (due to the lack of vegetation growing here)

Question 44

why are desert soils vv dry

Answer 44

evap>precip
low rainfall
high temperatures.

Question 45

what are the 2 main types of aridisols?

Answer 45

sierozems and raw mineral soils.

Question 46

are siernozems semi arid or arid regions

Answer 46

semi arid

Question 47

are raw mineral soils semi arid or arid regions

Answer 47

arid

Question 48

what kind of texture do raw mineral soils have and why?

Answer 48

coarse textre due to the physical weathering.

chemical weathering also does occur and thius results in capillary action resulting in the accumulation of Ca2+ and Na+

Question 49

why are the soils v v similar b.w the horizons in raw mineral soils

Answer 49

thre is a lack of moisture so there is limited leaching

Question 50

why are the raw mineral soils deemed more unproductive than infertile

Answer 50

they do have some minerals and salts available but the lack or rainfall and the extreme temperatres limit the veg.
the lack of abscission als omeans there is no leaf litter and thus no humus or organic matter.

Question 51

what can form on the surfce of raw mineral soils and why?

Answer 51

hard salt crusts.

Question 52

what are siernozems?

Answer 52

these are grey desert soils

Question 53

where do siernozems occur?

Answer 53

in arid regions where the rainfall recieved is less than 250mm

Question 54

what do siernozems look like? why?

Answer 54

they are darker in colour, due to the presence of some organcic moisture + matter as they often develope beneath desert shrun

Question 55

what are siernozems often used for?

Answer 55

cultivation and with continued irrigation, they form calcium rich horizons

Question 56

what is meant by the term humus?

Answer 56

amouros dark coloured colloidal matter in the soil. Its a complex of of the fractions of organic matter of plant, animal and microbial organisms that are most resistant to decomposition.

Question 57

what ar ethe 3 main factors that make it difficult for vegetation to survive in hot deserts?

Answer 57

lack of rainfall
soil
heat

Question 58

why does the lack of rainfall make it challenging for vegetation to survive inhot deserts?

Answer 58

the rainfall is often spotty and comes in short sharp bursts. The lack of rainfall makes it difficult for plants to grow

Question 59

why does the soil in hot deserts make it hard for vegetation to survive

Answer 59

the soil sare often v v salty and poor quality. they lack nutrients and are victim of slow decomposition

Question 60

why does the heat make it hard for vegetation to survive.

Answer 60

the temperatures are extreme and the effect of diurnal temperatures also makes it v v hard.

Question 61

how do plants in desert survive then?

Answer 61

they have special adaptations.

Question 62

what types or of plants usually grow in deserts?

Answer 62

short woody trees, ground hugging shrubs.

Question 63

why do plants have waxy cuticles?

Answer 63

thick waxy cuticles to reduce water loss but to help reflect suns heat

Question 64

what are the 4 main typees of plant adapted to the desert environment.

Answer 64

xerophytes,
phreotophytes,
ephemrals,
halophytes

Question 65

what are xerophytes and how are they adapted to desert climates?

Answer 65

succulent plants that contain certain compunds in flesgy leaves/stems that allow them to store ALOT of water.

Question 66

why is it difficult for plants to obtain water after a rainspell in the desert and how are xerophytes adapted to this?

Answer 66

the water doesnt penetrate deep in the soils and the soils dont remain moist for long periods of time. As a result succulents have the ability to rapidly absorb huge amounts of water.

Question 67

what are the adaptaptations that xerophytes have to conserve water?

Answer 67

thicj waxy cuticles
closed stomata –> both of these make the surface water proof
smally spiky or even no leaves to reduce the SA to limit transpration go

Question 68

give an example of a xerophyte and how its adapted to live in the desert

Answer 68

saguaro cactus
- can live for 200yrs and cab abdorb upto 800l of water in arms and stems.
have water in the roots and bulbs on the root systems and they survive on yrs of drought relying on the water recived on a single rain

Question 69

what are phreatophytes?

Answer 69

plants with long root systems that lie just beneath the surface.

Question 70

why are the

roots v v long in phreatophytes?

Answer 70

the water after rainfall doesnt penetrate v v far and thus roots are long to absorb the water near the surface laterally.
,

Question 71

give an example of a phreatophyte and how its adapted to hot deserts?

Answer 71

creosote bush.
has a root system that reaches v v deep ground water as well as being v v radial.
it has a bitter taste + smell to deter animals from eating it.
It also has small leaves and little stomata that close during the day to prevent water loss.
The long roots are also vv tough and hardy and thus anchor them into the sand and allow them to survive in constant;y shifting sand dunes.

Question 72

what are halophytes?

Answer 72

plants that are adapted to the salty poor quality soils in hot deserts.

Question 73

how is the saltbrush adapted to jot deserts

Answer 73

excrete salt from glands when the conditions are too salty

Question 74

how is the pickle weed adapted to the high salinity pf hot desert soils

Answer 74

they have a high water uptake to compensate for the high salt content

Question 75

how else do halophytes adapt to saline conditions

Answer 75

• some develope succulence which dilutes the level of salt in the plant and stores water for use during the dry periods.
  some seeds are kept dormant due to the high salinity but germinate when the rains come and reduce the salinit

Question 76

what are ephemerals?

Answer 76

plants that avoid drought altogether by having v v short life cycles
they blom v v rapidly after a rain , channellign their energy into producing seeds that lay dprmant until future rains.

Question 77

give an example of a ephemeral plant?

Answer 77

desert lily in the Mojave + sonoran
this plant stores energy in the root and bulds which form deep underground. the energy stored in spring allows the plant to survive almost a yr round dormancy.

Question 78

give an example of a perrenial ephemeral plant?

Answer 78

desert paint brush.
thus grows rapidly after the winter rains and flowers + produces seeds. the seed are v v hardy and drought resistant and v v resistant to high temperatures.

Question 79

what are some other ways that plants are adapted to protect themsleves against thirsty desert animals?

Answer 79

spikes + spines
bitter taste or toxicity
living in inaccessible locations
creosote bush gives off toxic chemicals that prevent other plants growing near it and competing for the same local water supply

Question 80

what is allelopathy

Answer 80

Allelopathy is a common biological phenomenon by which one organism produces biochemicals that influence the growth, survival, development, and reproduction of other organisms
it is responsible for plants growing in unifromed spaces in desers.

Question 81

what is a desert hycinth

Answer 81

a parasitic plant that takes nutrients form a halophyte.

It is parasitic bc it cant directly synthesis chlorophyll and thus cant photosynthesise.

Question 82

what are the 3 mechanisms of seed dispersal for desert plants?

Answer 82

wind dispersal (ie tumble weeds) 
water dispersal ( blue palo verde tree) 
animal dipersal (Cholla or the jumiping cactus.

Question 83

how can plants reduce transipration to survive in hot deserts?

Answer 83

• may hav eless seeds, throns and spikes which all have small surface areas and small leaves to reduce moisture loss.
  some lose leaves completely in the summer months BUT still have green stems to allow for photosynthesis .
  Some OPEN stomata duringthe DAY and close them at night to absorb co2 in day for p.synth ad to release h20 via evap. closing stomata during hte day would reduce water loss BUT also limit photosynthesis.
  the stomata w/inthe grooves of the leaf vreate microclimates which are humid + have low water vapour potential gradient and thus reduce water loss via transpiration.