10.3: soils and vegetation

Question 1

biomass productivity

Answer 1

-low rates of net primary productivity of 90 g/m2/year
- due to limited organic material and extreme heat and lack of moisture (no producers)
- Productivity can generally be positively correlated with water availability
- limited biodiversity: flora and fauna are relatively species poor

Question 2

limited nutrient cycling

Answer 2

• inputs (rainfall) to the nutrient cycle (dissolved in rain and as a result of chemical weathering) are low
• Most of the nutrients are stored in the soil, limited stores in the biomass and litter: smaller stores of nutrients in the soil, low in biomass due to dry conditions
• nutrient deficiency (especially of nitrogen
  and/or phosphorus) may become critical
• rapid growth following a rain event depletes the store of available nutrients, while decomposition is slow
• in semi-arid areas the amount of nutrients available increases with rainfall and chemical weathering.

Question 3

decomposition in nutrient cycling

Answer 3

• Microbial decomposers are limited
• the fragmentation, erosion and transport of dead organic matter (DOM) by wind and runoff
• consumption of DOM by detritivores such as termites, ants and mites, which are relatively abundant in deserts.

Question 4

fragility

Answer 4

• extreme climatic conditions and the relative lack of biodiversity
• resilient: due to the adaptations of desert organisms to survive water stress
• The hogweed plant in the Sahara takes 8–10 days from seed germination to seed production: before the water runs out: flowers at a time when insect pollinators are abundant

Question 5

ephermal vegetation

Answer 5

• vegetation appears/flowers after rain
• Some desert vegetation has a very
  short life cycle, some less than eight weeks
• Astragalus

Question 6

vegetation in hot arid areas

Answer 6

• shallow-rooted, small in size and with small leaves

Question 7

vegetation adaptations in semi-arid areas and succulents

Answer 7

• succulent (able to store water), and more vegetation is
  located near to water sources
• well-developed storage tissues
• small surface-to-volume ratios and rapid stomatal closure especially during the daytime; deep tap roots
  and very small leaves
  -exert a greater suction pressure
  so they can extract water from fine water-retentive soils

Question 8

evaders

Answer 8

survive periods of stress in an inactive state or by living
Plants permanently or temporarily in cooler and/or moister environments, such as below shrubs or stone, in rock fissures or below ground
- animals: 75 per cent are subterranean, nocturnal or active when the surface is wet. In such ways, plants and animals can control their temperature and water loss

Question 9

plant stress evading strategies

Answer 9

• Inactivity of whole plants
• Cryptobiosis of whole plant: an ametabolic state of life in response to adverse environmental stress; when
  the environment becomes hospitable again, the organism returns to its metabolic state.
• Dormancy of seeds

Question 10

animal stress evading strategies

Answer 10

• Dormancy in time (diurnal and seasonal) and space
  (take refuge in burrows)
• Cryptobiosis of mature animals (aestivation of snails,
  hibernation)
• Cryptobiosis of eggs, shelled embryos, larvae:
  permanent habitation or temporary use of stress-
  protected microhabitats

Question 11

plant strategies reducing water
expenditure

Answer 11

• Small surface : volume ratio
• Regulation of water loss by stomatal movements
• Xeromorphic features
• Postural adjustments
  -Surface growth (spines and hairs)
• diurnal closure of stomata, and xerophytic plants
  have a mix of thick, waxy cuticles, sunken stomata and
  leaf hairs

Question 12

animal strategies reducing water expenditure

Answer 12

• Small surface : volume ratio
• Regulation and restriction of water loss by concentrated urine, dry faeces, reduction of urine flow rate
• Structures reducing water loss
• Postural adjustment
• desert animals have long loops of Henle, allowing greater opportunity to reabsorb water in the medulla in the descending loop of Henle.

Question 13

plant strategies to prevent death by
overheating

Answer 13

• Transpiration cooling
• High heat tolerance
• Mechanisms decreasing and/or dissipating heat load
• Some cacti such as the prickly pear can survive up to 65 °C
  -Surface growth (spines and hairs)
• cooling by transpiration

Question 14

animal strategies to prevent death by overheating

Answer 14

• Evaporative cooling
• High heat tolerance
• Mechanisms decreasing and/or dissipating heat load
• Changing the orientation of the whole body enables the organism to minimise the areas and/or time they are exposed to maximum heat – many gazelle, for example, are long and thin.
• Light colours maximise reflection of solar radiation.
• metabolism and evaporation proportional to surface area to volume ratio

Question 15

plant strategies optimising water uptake

Answer 15

• Direct uptake of dew, condensed fog and water vapour
• Fast formation of water roots after first rain
• Halophytes: uptake of saline water, high salt tolerance, salt-excreting glands
• salt-tolerant plants have a high cell osmotic pressure that allows the efficient uptake of alkaline water.

Question 16

animal strategies optimising water uptake

Answer 16

• Direct and indirect uptake of dew, condensed fog and
  water vapour (e.g. arthropods, water enrichment of
  stored food)
• Fast drinking of large quantities of water (large
  mammals), uptake of water from wet soil (e.g. snails)
• Uptake of highly saline water, high salt tolerance, salt-
  excreting glands

Question 17

plant strategies to control reproduction in
relation to environmental conditions

Answer 17

‘Water clocks’ of seed dispersal and germination
Suppression of flowering and sprouting in extreme years

Question 18

animal strategies to control reproduction in
relation to environmental conditions

Answer 18

Sexual maturity, mating and birth synchronised with
favourable conditions
Sterility in extreme drought years
- reproduction is suppressed during
periods of drought

Question 19

physical droughts

Answer 19

refer to water shortages over an
extended period of time

Question 20

physiological drought

Answer 20

occurs when drought conditions are experienced by
plants despite there being sufficient soil moisture
- high rates of evapotranspiration

Question 21

aridisols

Answer 21

desert soils
-have a low organic content
- only affected by limited amounts of leaching
- Soluble salts tend to accumulate in the soil either near the water table or around the depth of moisture percolation
- As precipitation declines, this horizon occurs nearer to the surface
- limited clay content.
- in semi-arid areas, there is a deeper soil, more chemical weathering and more biomass in the soil, due to the higher rainfall.

Question 22

solonchaks

Answer 22

• Salt concentrations may be toxic to plants: . A high concentration of salt can cause the breakdown of soil structure, increase water stress and affect the health of plants.
• accumulation within 30 cm of surface
• likely in areas where there is a high water table or in the vicinity of salt lakes.
• Soils with a saline horizon of NaCl
• white alkali soils

Question 23

solonetz

Answer 23

• those with a horizon of Na2CO3 (sodium carbonate)
• black alkali soils

Question 24

surface/sub-surface crusts

Answer 24

• high cc of salts
• water content of soil evaporated: ground shrinks: breaks: high risk flash flooding
• different types of hard crust : duricrusts
• Calcrete or caliche: calcium carbonate
  - most common crust in warm desert environments.
  -up to 40 metres, comprising boulders, gravels,
  silt and calcareous materials.
  -It predominates in areas of between 200 and 500
  millimetres.
• Silcrete is a crust cemented by silica.
  
  • It may produce an impermeable hard pan in a soil.
  • found in areas that have more than 50 millimetres
    but less than 200 millimetres of rain, such as
    southern Africa and Australia.

Question 25

salinisation in Pakistan

Answer 25

• irrigation system, many of the drainage canals are in a poor state
• Consequently, there has been a steady rise in the water table, which has caused widespread waterlogging and salinisation.
• Up to 40 000 hectares of irrigated land are lost annually.
  management:
• pumping water from aquifers
  (to reduce the water table)
• vertical and horizontal drainage of saline water
• water tables have been reduced by as much as 7 metres, and up to 45 per cent of saline soils have been reclaimed: use of reclaimed land for agriculture only results in salinisation again.

Question 26

desertification

Answer 26

land degradation in humid and semi-arid areas
- loss of biological and economic productivity
- fertile land becomes arid
- it occurs where climatic variability (especially rainfall) coincides with unsustainable human activities
- lowering the carrying capacity of the area affected
happens where land is gradually turned into a desert, usually on the edges if an existing desert
- estimated one billion people are at risk (mainly next to existing deserts)
- natural process enhanced by human activity
- Australia, UAE

Question 27

natural cause of desertification

Answer 27

-climate change making temperatures hotter and rainfall less reliable and more variable, soil erosion
- areas close to deserts are ecologically fragile: transition between major biomes
- slight changes in temperature and rainfall associated with climate change can have large impacts: even more prone to overgrazing or over-cultivation

Question 28

human causes of desertification

Answer 28

population increasing:
- overgrazing: intensive farming takes nutrients out of the soil and removed natural vegetation: vulnerable to erosion as compaction of the soils reduces infiltration, leading to greater runoff while trampling increases wind erosion
- overcultivation leads to diminishing returns and more land and irrigation: further soil degradation and erosion by lowering soil fertility and promoting salinisation
- demand for wood: deforestation : rainsplash erosion, and the absence of root systems allows easy removal of the soil by wind and water
- in Australia over 40% of the 5 million km2 of desert and semi-arid land has been affected by desertification: pressure of grazing on fragile land affected by drought
- population pressure - over-cultivation - over-grazing

Question 29

desertification process

Answer 29

decreased vegetation - less interception and soil is exposed to sun - sun bakes the soil and it cracks - when it rain water runs over surface rather infiltration - soils is washed away - soil is degraded losing fertility and structure - soil is worn out, poor quality and crops and natural vegetation is more difficult to grow - repeat

Question 30

social impacts of desertification

Answer 30

• displacement: loss of culture, home
  -overcrowded: health issues

Question 31

environmental impacts of desertification

Answer 31

• dead biodiversity :((
• loss of crops

Question 32

economic impacts of desertification

Answer 32

• not enough food, health etc
• loss of income and property
• increased spending on imports

Question 33

how can we manage desertification

Answer 33

• planting Acacia Trees (The Great Green Wall): anchoring soil, preventing soil erosion, prevent dust transportation past
• using stone lines and planting pits: water fallen collects along lines, keeps moisture within soils
  -PAPS rule: people, affordable, place,sustainable

Question 34

desertification in China

Answer 34

• More than 27 per cent, or 2.5 million km2, of the country comprises desert
• 7 per cent of Chinese land feeds about a quarter of the world’s population
• desert areas are still expanding by between 2460 and 10 400 km2 per year
• 400 million people are at risk
• Much of it is happening on the edge of the settled area– which suggests that human activities are largely to blame
• Much of the country is affected by a semi-permanent high-pressure belt, which causes aridity
• continental areas experience intensive thunderstorms: accelerated soil erosion
• sandy desertification caused by wind erosion; land degradation by water erosion; soil salinisation; and other land degradation by engineering construction

Question 35

human activities leading to desertification in China

Answer 35

• human activities such as livestock overgrazing, cultivation of steep slopes, rampant logging and excessive cutting of branches for firewood
• Mongolia Autonomous Region: 133 000 hectares of land degraded by overgrazing: density of animals exceeds the carrying capacity
• Illegal collection of fuelwood and herbal medicines has removed more than one-third of vegetation in the Qaibam basin since the 1980s

Question 36

China: effects of desertification

Answer 36

• annual direct economic losses valued
  at US$6.5 billion
• 180 000 hectares of farmland salinised per year: productivity to fall by 25–75 per cent
• Erosion claims about 5 billion tonnes of China’s topsoil each year, washing away nutrients equivalent to 54 million tonnes of chemical fertiliser – twice the amount China produces in a year
• By the early 1990s, dust storms were an annual problem.
• serious drought turns farmlands into dunes in northern parts of the country, just 100 kilometres away. These dunes are advancing at a rate of 3.5 kilometres a year

Question 37

China: solutions for desertification

Answer 37

• fixing sand by planting: economic, easy, beneficial
• fixing sand by engineering: pebbles, branches clay: fast
• chemical protective top layer on soil in high economic value areas like airports
• water-saving techniques: better irrigation
• plans to build a second green belt of forest around Beijing to achieve a forest coverage of 49.5 per cent by 2020

Question 38

soil degredation

Answer 38

• erosion by wind and water
• biological degradation – for example, the loss of humus and plant/animal life
• physical degradation – loss of structure, changes in permeability
• chemical degradation – acidification, declining fertility, changes in pH
• salinisation
• chemical toxicity
• human activity
  management: afforestation, extensive management farming practices, public awareness, Mechanical methods include building bunds, terracing, contour ploughing and planting shelterbelts, chemical-affected soils can be flushed,leeched, apply chemical and reduced evaporation losses