Soils, vegetation, desertification, management Flashcards
(95 cards)
Arid
Areas with a permanent rain water defect and less than 250mm rain per annum
Semi arid
Commonly defined as having rainfall of less than 500mm per annum
how do deserts receive runoff
from ephemeral or short lived streams fed by rain and snow from adjacent highlands
what are halophytes and how do they adapt to saline arid soils?
halophytes = a plant that can withstand high levels of salinity arid soils = poor, alkaline soils mean salts are common in soil and water (especially costal deserts e.g. Atacama) they adapt by having a higher than average cell osmotic pressure to counter act the alkaline affect e.g. salt bush some avoid salt by growing in the rainy season when salt concentrations are less date pass can grow in saline groundwater
list of adaptations plants have for avoiding and tolerating heat
Cacti can withstand up to 65 degrees Spine shades keep them cooler than the surrounding air, lowering the temperature of the surface of the cactus Leaves of desert plants tend to be small and narrow - enables leaf temperature to be near air temperature even when stomata are closed Steeper leaf angles - reduce solar interception at midday when the air temp is most severe Colour: blue/grey/green leaves to reduce heat absorption E.g. Low Bluebush, found in the Australia Desert by Roxby Downs
name of plant adapted to tolerate a lack of rainfall
xerophyte
evidence for climate change in hot and semi arid environments
climate change = decades measured through rainfall records/thousands of years ancient and degraded sand dunes in areas that are now rainy e.g. Savannah in Africa now has 1000m of rainfall a year wadis provide evidence of former rivers and drainage systems in areas that are now much drier e.g. Egyptian desert former shorelines and beach features in areas that are now much drier e.g. Lake Chad in the Sahra was once 300,000q km in area dating back to 7000BC anthropological evidence e.g. archeology human life required a water source e.g. Garamantes civilisation in the Ahaggar Mountains, Sahara left behind cave paintings as early at 6000 BC
how does climate change naturally cause desertification
There is periodic/episodic natural climate variability. For example, the Sahel has long experienced a series of historic droughts, dating back to the 17th century. This has occurred periodically in the 1910s, and then the 1940s and then the 1960s-1980s.
how does human induced climate change cause desertification
Global warming arguably increases evapotranspiration, reduces biodiversity and decreases rainfall in drylands. However, carbon dioxide is a major resource of plant productivity, so some dryland species may favourably respond to this increase; this may lead to changes in species composition and abundance. Thus, human induced climate change may increase diversification risk, but the consequences of a loss of diversity are complex and many geologists and scientists have contrasting opinions.
example of an impoverished arid area
Niger, with a HDI of 0.253 and a GDP per capita of $1069; meaning they remain in stage 3 of the DTM with some of the highest population growth rates in the world.
explain how the human activity of deforestation could cause desertification
This occurs as fuel wood is collected by the uprooting of woody species; particularly problematic outside large urban areas where the urban poor can’t afford electricity. The direct removal of vegetation results in a deterioration of the soil - vegetation has a major role in determining the biological composition of the soil, as it has a function in nutrient recycling. The rate of erosion and runoff decrease exponentially with increased vegetation cover; dry soil that is not protected blows away with the wind, or s washed away by flash floods, leaving infertile lower soil layers. This soil then becomes an unproductive hardpan through evaporation.
explain why desertification inducing human activity is most common in LIC areas
These intense population pressures lead to the exploitation of marginal lands for farming. This occurs as areas of unfavourable agro-climatic conditions, an absence of infrastructure and access to markets, poorly adapted production techniques and malnourished and undereducated population, become marginalised. A lack of development and investment by government means that there is increased population pressure on the carrying capacity of the area, giving rise to overgrazing, over-cultivation and deforestation.
describe/explain colour of soils in arid areas vs semi arid areas
SEMI: Increased organic matter (more rainfall provides fertile ground for plant growth) may be enough to colour the top soil to create chestnut-brown soils. Increased rainfall also means increased hydrolysis, which creates reddish brown soils ARID: tend to be grey in colour due to a lack of moisture BOTH: high salt content forming Solonetz of Solonchak soils in the upper horizon Solonetz: sodium chloride; black Solonchak: sodium carbonate; white
solonetz soils
sodium chloride black
solonchak soils
sodium carbonate white
describe/explain how duricrusts are a characteristic of arid and semi arid soils
Duricrust is a hard horizon at the surface or just below the surface, between a few cm and a m in size; deeper in wetter areas, and in dry areas it remains at the surface. They form as material is leeched, duricrust remains and evaporations then leaves salt behind. This is most evident in salt plans, which are essentially salt duricrusts that have accumulated and salinized at the surface. This makes the surface of the soil hard.
describe/explain how high levels of salinity are a characteristic of arid and semi arid soils
IRRIGATION: As water is put on corps and evaporates, salt is left behind; this is famously seen in Pakistan, which have participated in widespread irrigation since 800 BC. CAPILLARY ACTION: salt deposits can be evident as the little soil moisture that exists is drawn upwards by capillary action and may leaving deposits at the surface.
describe/explain how organic content and depth of soil are a characteristic of arid and semi arid soils
low organic content (less than 1%) due to a lack of vegetation (because of a lack of rainfall) Soils are less superficial, occurring at a deeper level than in hot arid environments as there is more rain. They are therefore not subject to the same level of erosion and transportation that hot arid soils are, as semi-arid soils are not as loose and thin.
case study example of Africa’s farmer managed land regeneration as a method for reducing desertification impact
‘Great Green Wall’ stretching from Senegal to Djibouti on the horn of Africa, cutting across the Sahel and the Sahara. Countrywide, 11.4m trees have been planted since 2007 and the scheme has provided gardeners seeds, local staff employment, paid for water bills, bringing in water systems, fertilisers and barbed wire for security. By enabling better farming practices through providing resources, employment and training, the GGW has enabled native sprouting tree growth, increasing soil water retention and decreasing evaporation. E.g. 500 Malian men are trained in a migrant camp in Niger. In this scheme, plants have been used to enrich the soil and restore its fertility. For example, leguminous plants which extract nitrogen from the air and fix it into the soil. The overall restorative effect of this: in Ethiopia, 15m hectares of land have already been restored; in Nigeria, it’s 5m, and in Sudan, 2,000m.
physical adaptations for animals to avoid/tolerate extreme desert temperatures
For example, beetles and scorpions can withstand temperatures of up to 50 degrees. Anatomical: light coloured bodies (reducing heat intake), thin body forms e.g. gazels. desert fox have large ears (with a large number of blood vessels), wet noses in order to increase the heat evaporation rate from their body, cooling them down. ostriches have bare head, throat legs to allow for cooling. long legs keep the body separated from the extreme ground temperatures
behavioural adaptations for animals to avoid/tolerate extreme desert temperatures
BEHAVIOURAL 75% of animals in hot arid environments are nocturnal to avoid high day time temperatures. For example, the white-throated wood rat, create burrows lining them with scavenged debris. This allow them to escape from desert temperatures externally, but it keeps their habitat insulated (for night) by not allowing cool air to escape. The round-tailed ground squirrel, resort to estivation. During the summer months (that can be up to 50 degrees in Death Valley, California), they slow down their metabolism to conserve water and energy. Sand snakes move by side winding meaning only a small part of their body is in contact with sand; lizards assume an erect position when running, keeping their bodies off ground
how can plants adapt behaviourally to a lack of rainfall (physical drought) in arid environments
BEHAVIOURAL: germination The seeds remain dormant and survive in the dry environment; when conditions are favourable the seeds germinate and the plants exploit the wet conditions. For example, Hogweed (found in Sahara), takes 8-10 days for the seed production process – seeds are produced quickly before the water runs out, when insect pollinators are abundant. In the same way, cytobiotic plants respond to a lack of rainfall by reproducing when the environment becomes hospitable: suppressing the flowering and sprouting. For example ironwood and smoke wood have seeds which will only germinate after severe mechanical abrasion during floods.
name of plants adapted to physical drought
Xerophyte
how can plants adapt physically to a lack of rainfall in arid environments?
Anatomical Small leaves of vegetation reduce the rates of water loss and evapotranspiration in plants. (physiological)Plants can diurnally close stomata, giving them a means of conserving water High water storage capacity, with heavily waxed in their stems to reduce circular water loss. Examples include the cotton-top cactus, and the prickly pear that have a swollen or fleshy appearance due to the high amount of water storage in them. Plants can be succulent by having shallow and wide roots that trap rainfall or dew that may collect at the surface, or long and deep in order to reach a more permeant water supply, as with phreatophytes e.g. mesquites.