10.3: soils and vegetation Flashcards
(38 cards)
1
Q
biomass productivity
A
-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
2
Q
limited nutrient cycling
A
- 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.
3
Q
decomposition in nutrient cycling
A
- 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.
4
Q
fragility
A
- 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
5
Q
ephermal vegetation
A
- vegetation appears/flowers after rain
- Some desert vegetation has a very
short life cycle, some less than eight weeks - Astragalus
6
Q
vegetation in hot arid areas
A
- shallow-rooted, small in size and with small leaves
7
Q
vegetation adaptations in semi-arid areas and succulents
A
- 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
8
Q
evaders
A
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
9
Q
plant stress evading strategies
A
- 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
10
Q
animal stress evading strategies
A
- 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
11
Q
plant strategies reducing water
expenditure
A
- 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
12
Q
animal strategies reducing water expenditure
A
- 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.
13
Q
plant strategies to prevent death by
overheating
A
- 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
14
Q
animal strategies to prevent death by overheating
A
- 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
15
Q
plant strategies optimising water uptake
A
- 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.
16
Q
animal strategies optimising water uptake
A
- 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
17
Q
plant strategies to control reproduction in
relation to environmental conditions
A
‘Water clocks’ of seed dispersal and germination
Suppression of flowering and sprouting in extreme years
18
Q
animal strategies to control reproduction in
relation to environmental conditions
A
Sexual maturity, mating and birth synchronised with
favourable conditions
Sterility in extreme drought years
- reproduction is suppressed during
periods of drought
19
Q
physical droughts
A
refer to water shortages over an
extended period of time
20
Q
physiological drought
A
occurs when drought conditions are experienced by
plants despite there being sufficient soil moisture
- high rates of evapotranspiration
21
Q
aridisols
A
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.
22
Q
solonchaks
A
- 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
23
Q
solonetz
A
- those with a horizon of Na2CO3 (sodium carbonate)
- black alkali soils
24
Q
surface/sub-surface crusts
A
- 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.
25
salinisation in Pakistan
- 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.
26
desertification
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
27
natural cause of desertification
-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
28
human causes of desertification
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
29
desertification process
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
30
social impacts of desertification
- displacement: loss of culture, home
-overcrowded: health issues
31
environmental impacts of desertification
- dead biodiversity :((
- loss of crops
32
economic impacts of desertification
- not enough food, health etc
- loss of income and property
- increased spending on imports
33
how can we manage desertification
- 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
34
desertification in China
- 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
35
human activities leading to desertification in China
- 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
36
China: effects of desertification
- 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
37
China: solutions for desertification
- 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
38
soil degredation
- 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
