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Geography A Level > B. Desert Ecosystems > Flashcards

B. Desert Ecosystems Flashcards

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1
Q

What is soil?

A

Soil is a natural body of animal, mineral and organic constituents differentiated into horizons of variable depth.

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2
Q

Which 2 influences affect soil?

A
  • Vegetation from above
  • Bedrock from below
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3
Q

What are the 5 layers of soil?

A

Organic layer
Top soil
Subsoil layers
Substratum
Bedrock

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4
Q

What is the organic layer?

A

This is the top layer of soil (1/5) made mostly of dead plant matter

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5
Q

What is the top soil?

A

This is the second layer of soil (2/5).

Like the organic layer, it also contains lots of organic matter, and is usually darkly coloured.

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6
Q

What is the subsoil layer?

A

This is the third layer of soil (3/5).

This layer contains little organic matter.

Sometimes the transition between top soil and subsoil is very sharp and defined, and sometimes they fade into one another.

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7
Q

What is the substratum?

A

This is the fourth layer of soil (4/5).

This layer usually has lots of large rocks mixed in with soil deep underground

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8
Q

What is the bedrock?

A

The final soil horizon (5/5) lying underneath the soil.

In some places, this layer can be quite near the surface, in others it can be very deep.

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9
Q

How do nutrients move up and down through the soil?

A

Nutrients move up through the soil via capillary action
Nutrients move down through the soil via leaching

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10
Q

Which factors affect the formation of soil?

A
  • Parent material (rock type) - permeability, mineral content, texture and nutrients
  • Climate - weathering, precipitation, temperature
  • Organisms (biota) - organic matter, nutrient cycle / recycling, mixing and aeration
  • Relief - altitude, aspect and slope angle
  • Human influences - farming etc.
  • Time - It can take up to 400 years to produce 10cm of soil, 3,000-12,000 years to produce sufficient depths for agriculture
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11
Q

What are the properties of desert soils?

A
  • Dry
  • Very thin (few layers)
  • Sandy
  • Lots of mineral matter (not much organic matter)
  • Can be colourful as lack of rain reduces leaching (capillary action dominates)
  • Can be tough if deflation has occured (desert pavement)
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12
Q

What is an entisol?

A

An entisol is newly created soil e.g. a sand dune - too dry and mobile for any development of soil horizons (layers)

Prevalent in hot arid areas

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13
Q

What is an aridisol?

A

An aridisol is a desert soil that is light in colour, lacks moisutre, has low levels of organic matter and a high pH (alkaline).

Prevalent in semi-arid areas

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14
Q

What does the organic layer (1/5) look like in a desert?

A

Thin / no organic soil horizon due to lack of vegetation

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15
Q

What does the top soil (2/5) look like in a desert?

A

Mainly weathered sand with little to no organic matter, organisms or water

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16
Q

What does the subsoil layer (3/5) look like in a desert?

A

Coloured soil due to buildup of soluble minerals (Gypsum, calcium carbonate, magnesium and silica).

This buildup is due to the lack of leaching and high evaporation

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17
Q

What does the substratum (4/5) look like in a desert?

A

Dominated by weathered parent rock (bedrock)
High pH (alkaline)

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18
Q

Why does salinisation occur?

A

Salinisation occurs when the water in soils evaporates in high temperatures, drawing salts from the soil to the surface via capillary action.

The water evaporated can be natural or due to the irrigation of land - when water is brought to land that is naturally dry, this can cause salinisation on desert margins.

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19
Q

What is an ecosystem?

A

An ecosystem is a community of living organisms and the abiotic elements in their shared environment.

20
Q

What are cryptobiotic crusts?

A

Cryptobiotic soil crusts are soil crusts composed of cyanobacteria, fungi, lichens and microscopic organisms.

21
Q

How do cryptobiotic crusts form?

A

Cyanobacteria, the primary coloniser, releases gelatinous filaments that bind soil particles together in a dense matrix, resulting in a hardened surface layer made from organic and inorganic (rock) matter.

22
Q

Why is cryptobiotic crust important?

A
  • Cryptobiotic crust allows soils to greater resist erosion by wind and water
  • Many cryptobiotic soil crusts are able to absorb water more efficiently than regular soils, reducing runoff and evaporation.
  • Cyanobacteria and some surface lichens are nitrogen fixers, allowing nitrogen to be returned to arid soil, increasing fertility and allowing desert plants to grow
23
Q

Which climatic conditions do plants and animals have to adapt to?

A
  • Low rainfall < 250mm/year
  • Extreme diurnal temperature range
  • Flash floods
  • High rates of evapotranspiration due to heat
  • Little shade
  • High insolation and ground temperatures
  • Dry wind
  • Dust storms
24
Q

Which physical factors do animals and plants have to adapt to?

A
  • Salinisation
  • Limited ground water
  • Lack of vegetation
  • Lack of organic soil matter
  • Shifting sands
25
Q

In which deserts is the creosote bush found?

A

Mojave, Sonoran and Chihuahuan deserts of western North America

26
Q

Which adaptations does the creosote bush have?

A
  • Wide and deep root network
  • Water, minerals and nutrients storage capacity
  • Small, wax-coated leaves
  • High efficiency in retrieving nutrients from shedding leaves
  • Longevity
27
Q

How does a wide and deep network of roots help the creosote bush?

A

Tap roots and fibrous roots are able to absorb water boh from brief episodic rainfall as well as from deep underground

  • Taproots can reach depths of 10ft and shallow roots cover an area of 50 square yards
28
Q

How does water, minerals and nutrients storage capacity help the creosote bush?

A

Water, minerals and nutrients are stored in the crown of the creosote bush allowing better water and mineral regulation during droughts.

29
Q

How do small, wax-coated leaves help the creosote bush?

A

Small, wax-coated leaves decrease excess transportation.

These leaves are also in clusters, maximising photosynthesis whilst minimising water loss.

30
Q

How does a high efficiency in retrieving nutrients from shedding leaves help the creosote bush?

A

Creosote bushes are able to retrieve 3/4 of its phosphorous and over 1/2 of its nitrogen from its shed leaves.

31
Q

How does longevity help the creosote bush?

A

Creosote bushes have long lifespans because they can clone themselves, starting from the crown and growing outwards in rings.

A 20ft ring may be 3000 years old!

32
Q

Where is the Joshua Tree found?

A

Found in Joshua Tree National Park, Mojave Desert.

33
Q

What adaptations does the Joshua tree have?

A
  • Thick but narrow waxy leaves - store water but reduce transpiration
  • Shallow and wide-spreading roots
  • Red leave surfaces - minimise transpiration losses
  • Thermoregulation - survive extreme temperature variation
  • Fire resistant bark - protect from wildfires
  • Slow growth - efficient allocation of resources, some live for several hundred years
34
Q

Describe the size of processes in the desert nutrient cycle:

A
  • Small biomass and litter stores as hot dry climate prevents mass plant growth
  • Although desert soil contains minerals, soil store remains small (slightly larger than ↑) due to lack of litter and biomass
  • Small flow of minerals to soil storage due to weathering, little to no leaching, surface runoff or rainfall due to limited rainfall (even if episodic rainfall causes flash floods)
35
Q

What is Net Primary Productivity?

A

Net Primary Productivity is the amount of new growth plants produce per year, measured in grams / square meter / year

36
Q

What are the rates of Net Primary Productivity in different biomes?

A

Desert ≈ 90 g/m2/year - can be as low as 5 g/m2/year

Temperate deciduous forest ≈ 1200

Tropical rainforest ≈ 2,200

37
Q

Why is NPP in deserts so low?

A
  • Low rainfall, harsh conditions
  • Slow rate of plant growth
  • Plant cover is not 100%
  • Plant variety is limited
  • Limited number of plant layers (comparison to jungle)
38
Q

Why are desert ecosystems fragile?

A
  • The ecosystem is easily damaged e.g. cryptobiotic crust, and if damaged, takes a long time to recover because things grow so slowly (low primary productivity)
  • Food chains are short / food webs are simple- there are limited amounts of food for herbivores and carnivores and limited choice, which are vulnerable if these minimal sources decline rapidly
39
Q

What is vegetation like in a hot arid area versus a semi -arid area?

A

☀ Hot Arid Areas

  • Extremely sparse
  • Net primary production may be as low as 3g/m2/year
  • Some dune belts may be completely without vegetation

🌤 Semi-Arid Areas

  • Denser vegetation
  • Net primary production may be as high as 250 g/m2/year
  • Some types of vegetation such as spinifex (porcupine grass) of northern Australia may be very thick
40
Q

What plants appear in hot arid versus semi-arid areas?

A

☀ Hot Arid Areas

  • Plants include tamarisks, clumps of short, spiky grass, dwarf scrub and prostrate plants
  • Some plants from semi-arid areas may appear, but more sparsely and in stunted forms.

🌤 Semi-Arid Areas

  • Main plant is the deciduous acacia. Scrub, thorny succulents and grass can also occur.
41
Q

How do plants grow in hot arid versus semi-arid areas?

A

☀ Hot Arid Areas

  • Most vegetation exists in a dormant state, but rare rainstorms produce short-lived bursts of plant growth

🌤 Semi-Arid Areas

  • Occasional rainstorms produce short-lived bursts of plant growth, when shrubs and herbaceous plants blossom.
42
Q

How much biodiversity is there in hot arid versus semi-arid areas?

A

☀ Hot Arid Areas

  • More limited number of plant species

🌤 Semi-Arid Areas

  • As in the Sonoran desert, there may be over 2000 different plant species
43
Q

Which trophic levels are present in hot arid versus semi-arid areas?

A

☀ Hot Arid Areas

  • Only levels 1-3 may be present (no tertiary consumers)

🌤 Semi-Arid Areas

  • All four trophic levels are present
44
Q

What examples are there of hot arid areas?

A

Central parts of the Sahara, Namib, Atacama and central Australian deserts

45
Q

What examples are there of semi-arid areas?

A

Sonoran desert, most of the Baja desert, Kalahari and Karoo deserts.

Geography A Level (32 decks)

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