Soils Soil forms the thin surface layer of the earth’s surface

SoilsSoils

Soil forms the thin surface layer of Soil forms the thin surface layer of the earth’s surface.the earth’s surface.

Soil compositionSoil composition

4 main components of Soil

1. Mineral Matter

2. Organic Matter

3. Air

4. Water

Mineral and Organic matter = 50%

Remaining 50% = Air and Water

Soil CharacteristicsSoil CharacteristicsThe four major components are interlinked and determine the value of soil to agriculture--- they determine

1.Texture

2. Colour

3. Structure

4. Moisture / water retention

5. Humus / Organic matter

6. PH Value

• Mineral Matter > is the largest component > Minerals develop from weathered bedrock or material deposited by rivers.

• Organic Matter > Comes from plants and animals – micro-organisms – earthworms, slugs and mites – after death plants and animals are reduced to dark brown organic matter called “Humus”

• Air and Water proportions vary depending on climate and drainage.

TextureTextureThe Texture of a soil is controlled by the amount sand, silt and clay particles in it.

• Different soils have different amount of pore spaces, which affects soil aeration and drainage

Three main textures:

1. Sandy

2. Silt

3. Clay

Sandy SoilsSandy Soils Positive Sandy Soil Properties

• The coarse particles in these soils, whether wet or dry , are generally loose, making them easy to cultivate.

• Large air spaces between the particles give

good drainage and aeration.

Negative Sandy Soil Properties • Rapid Loss water loss, minerals are leached

and fertilisers need to be added regularly

Silty SoilsSilty Soils

• Finer particles > pore spaces smaller > retaining more moisture

• Lack organic nutrients > which can restrict seedling germination – easily eroded by heavy rainfall

Clay SoilsClay Soils

• Clay particles fit closely together resulting in poor drainage and aeration.

• Prone to water logging and described as heavy.

• They expanded when wet and tend to be sticky and shrink when dry and become hard.

• Clay soils retain their nutrients but it is difficult for plant

roots to penetrate them.

Loam SoilsLoam Soils

• No single size dominates and consists of approx equal measures of sand, silt and clay.

• Good drainage and aeration.

• These soils are preferred by farmers and gardeners and are easily cultivated.

Determining Soil TextureDetermining Soil Texture

• Fill screw top jar two thirds.

• Pour water into jar until almost full.

• Shake jar for a minute.

• Leave to settle for 24 hrs.

• You will then be able to see the different sizes of particles > Heaviest at the bottom

StructureStructure

• Structure refers to the shape of the soil grains called Peds

• Individual particles often gather in Peds due to cementing action of clay water and humus

FourFour types of Pedtypes of Ped

1. Crumb – small rounded particles (breadcrumbs) 1 – 5mm

1. Platy – Thin horizontal particles often overlapping.

2. Blocky – roughly cube shaped close fitting particles.

3. Prismatic – column shaped particles with rounded tops

PH ValuePH Value

• This is a measure of its degree of acidity or alkalinity

PH Value

• This is a measure of its degree of acidity or alkalinity

• Low PH Value – Acidic

• These soils lack calcium, magnesium and potassium

• These soils have been leached heavily by rainfall.

• Increased acidity discourages living organisms – reducing the rate of breakdown leading to Peat formation

• High PH Value = Alkaline• • These soils have a high concentration of

calcium (develop on chalk and limestone landscapes)

• Best PH Value – 6.5…. most suitable for

farming…..favours the growth of bacteria vital for the release of nutrients (sulphur and phosphorous) from organic matter.

Organic Matter / HumusOrganic Matter / Humus

• The dark colour of humus is responsible for making the upper layers of soil dark, rich and fertile

• Black or dark brown jelly like substance.

• Formed from organic matter – decaying plants/animals.

• Worms and insects digest organic matter to create humus (also mix and aerating soil)

Why Humus is important to soil:

• Helps the soil to retain moisture.

• Source of plant nutrients (carbon and nitrogen).

• Improves soil structure > binding soil particles together > reducing risk of erosion.

• It absorbs minerals that would otherwise be washed away.

Water Content / RetentionWater Content / Retention• Soil water is essential for plant growth.

• The amount of water a soil can hold depends on the humus content, texture (sandy, silty, clay or loam) and structure (shape of Peds)

• Soils rich in humus can hold more moisture than those which lack humus.

• Sandy soils have low retention properties – water drains between the sand grains quickly.

• Clay soils tend to hold more water due to small grains which have a large surface area which hold more water around them.

• The presence of moisture is important as:

• Enables plants to receive nutrients in solution• Supports micro-organisms• Helps to develop soil horizons• Helps to slow down rate of erosion

Soil HorizonsSoil Horizons• A soil profile is a vertical section taken

from the surface down to the parent material. The letters O, A, B and C are used to identify the horizons.

• O Horizon – mainly organic matter• A Horizon – Called the topsoil (may

have a dark brown colour (Brown Soils). Most biological activity takes place here due to roots etc

• B Horizon – Called subsoil (may be light brown in colour) Many of materials that move down from above accumulate here

• C Horizon – sit directly on the bedrock. It has been little affected by soil forming process.

AirAir• Air fills pore spaces that are not occupied by water.

• This air contains more water vapour and carbon dioxide than atmospheric air (released by plant roots and organisms).

Fertile soil requires adequate supply of air because:

• Essential for seed germination.

• It is needed for the breakdown of organic matter in the soil.

ColourColour

• Soil‘s colour can affect its temperature

• Darker soils (warm soils) absorb heat more than light coloured soils.

• Warm soils will have a rapid breakdown of organic matter – more nutrients.

• Warm soils better for seed germination.

• Warm soils tend to have higher humus content

Factors that affect soil Factors that affect soil formationformation

• Parent Material – source of mineral matter – can be unconsolidated material (e.g. alluvium or glacial drift loess) Consolidated material (solid rock)

• If unconsolidated (is the source) soil formation will progress more rapidly.

• Soils will inherit the parent material’s physical characteristics.

• Climate – Two key climatic influences temperature and precipitation.

• They affect the type and rate of weathering. (Mechanical or Chemical)

• They affect the rate of growth and decay of

organic material.

• They affect the degree of leaching.

Topography

• Soil formation is influenced by gradient, altitude and aspect

• Soils tend to accumulate on flat gently sloping landscapes

• Flat landscapes pose risk of water logging.

• Soils are thinner on steeper slopes – good drainage here.

• The higher the altitude the more precipitation and decrease in temps which impact length of growing season.

• Aspect is important – north and south facing slopes develop different soils.

Living Organisms

• Plants/Roots bind soil & cover soil (protection)/ They take and return nutrients from soil.

• Insects/animals aerate soil.

• Insects fungi and bacterial help in breakdown and decay of organic matter breaking down into humus

Time

• Time allows processes to operate.

• Soils can take a long time to form (can take 400 years per centimetre)

Factors influencing soil Factors influencing soil characteristicscharacteristics

• No two soils have the exact same characteristics.

• This is because a number of physical, chemical and biological processes operate.

• The major processes are

WeatheringWeathering

• Physical breakdown of rock / Chemical weathering breaks down and changes minerals by various processes including oxidation, carbonation, hydration, hydrolysis. Weathering key to release of essential nutrients for plants

The reddish-orange colour of this oxide soil shows is

a result of

oxidation, a chemical

weathering process.

HumificationHumification

• Process where organic matter at the surface is decomposed to form humus

LeachingLeaching

• This occurs when rainwater carries soluble mineral and organic matter from the A horizon downwards through soil profile.

PodzolisationPodzolisation

PodzolisationPodzolisation

• Surface vegetation is moorland or coniferous forest - rain percolating down becomes acidic, dissolving almost all the soil constituents including clay particles. Organic matter and mineral are leached to a lower horizon resulting in a podzol soil that is often infertile.

LaterisationLaterisation

• Leaching process widespread in tropical and equatorial regions. Intense rainfall then leaches down to the lower layers. Rapid decay in vegetation means that there is little acid in the soil. Large concentrations of iron and alluvium remain in the soil close to the surface. The soil becomes reddish and may harden on exposure.

SalinisationSalinisation

• This occurs in regions where precipitation is low and evapotranspiration is high. Ground water drawn upward and evaporated leaving the soluable salts in the upper layers of the soil that form a hard toxic crust

CalcificationCalcification

• Calcium accumulates in soils where rainfall is low and little leaching takes place. It provides a rich environment for plants.

GleyingGleying

• This soil is waterlogged for all or part of a year. Occurs on gentle slopes where water table rises following heavy rain. Theses soils are therefore poorly aerated and the lack of oxygen retards decomposition.

Classifying SoilsClassifying Soils

• Three basic groups under the zonal system (based on climatic zone)

• Zonal Soils

• Intrazonal Soils

• Azonal Soils

Zonal soils Zonal soils

• These develop where the landscape and climate have been stable for a long time.

• They are mature soils with distinctive profiles and clear horizons.

Examples of zonal soils

• Latosols From Tropical/Equatorial climatic zone and Tropical Rainforest Vegetation zone.

• Desert and semi-desert soilsFrom Arid / semi-arid climatic zone and Desert Vegetation zone.

• Brown EarthsFrom Cool temperate maritime and mixed / deciduous forest zone

Intrazonal SoilsIntrazonal Soils

• Within zonal soil belts some local soil forming factors (such as parent material or drainage conditions etc.) exerts a stronger influence than climate and vegetation.

• These can be strong enough to modify the zonal soil to form an Intrazonal soil.

• Examples of Intrazonal soils

• GleyThese have been modified by poor drainage resulting in water logging.

• PeatCold wet climate and extreme water logging

Azonal soilsAzonal soils• These are immature soils that have not had

enough time to develop. They do not have a well-developed profile.

Examples of Azonal soils• Regosols

Recent deposition of material by rivers or wind.

• LithosolsMass movement and erosion are too rapid to allow for soil development

Other topics to investigateOther topics to investigate

• Irish Soils

• Causes of desertification in the Sahel

• Soil Conservation

Exam Brief - Geoecology OptionExam Brief - Geoecology Option

Examine the general characteristics of any one soil type that you have studied (2006 HL)

• It is better to treat of three or four aspects of the theme in some detail, rather than to give a superficial treatment of a large number of points .

• 4 well – developed paragraphs > 6 SRPs in each paragraph

Exam BriefExam Brief Irish Brown earth soils:Development:• Brown earth is a zonal soil. It has developed in response to our cool

maritime climate and the present of deciduous hardwood forest.

• Parent material is mainly boulder clay, deposited in the last ice age.

• Fertile soil due to the presence of humus (composed of autumn leaves and dead animals).

• Moderate amounts of rainfall helps wash nutrients into the soil without out leaching it.

• As there is no leaching there is no distinct horizon.

• It is uniformly brown in colour

Exam BriefExam Brief

Influence of Ph and biological activity:• The PH of brown earth soil in Ireland varies from

slightly alkaline to slightly acidic, PH 5 to 7.

• The ph characteristics of Irish brown results in encouraging bacteria activity.

Exam BriefExam Brief • Fungi and earthworms activity helps to raise the fertility

of the soil by drawing humus into the soil, decomposing it and releasing nutrients.

• The cool temperate climate is warm enough to allow biological activity for more than nine months of the year.

• Brown earth soil has a good crumb texture that provides pore space for air and water, promoting plant growth.

• As a result of its crumb texture, it is well a drained soil.

Exam BriefExam Brief Geographical distribution and characteristics:

• Irish brown soils are highly productive and are use for tillage and pasture.

• In Ireland local conditions have created three variations in brown earth soil.

• Acidic brown earth soil occurs on land 500m above sea level on crystalline rock such as granite, schist or sandstone. Poor in lime content.

Exam BriefExam Brief • Shallow brown earth soil ( rendzina soil)

occur in limestone areas such as the Burren in Co Clare and Co Sligo.

• Although fertile shallow brown earth soil is stony with the parent rock often coming to the surface, thus making cultivation difficult.

• Podzolised (slightly leached) brown earth soils occur on the lowlands and on glacial drift. This soils covers 22% of the country.


Brown earth soil profile:

O horizon • Consist of largely organic matter, plants leaves, twigs.

• The lower portion of the O horizon is made up of decomposed organic matter and microscopic life, bacteria, fungi, algae and insects.

A horizon• Also called the topsoil – has a dark brown colour . It

consist mainly of mineral matter mixed with a mildly acidic humus, called mull.

• Most biological activity takes place in this horizon because plant roots, bacteria, fungi and animals such as earthworms are abundant.


B Horizon

• Also called the sub-soil – light brown colour – Much of the material washed down accumulated here.

• The humus content decreases with depth and is light brown in colour..

C Horizon

• Sits on the bedrock. The soil forming process has little effect in the c horizon, it consist mainly of mineral matter.

Soil Erosion and ConservationSoil Erosion and Conservation

Exam Brief:

• Name and Explain the causes of soil erosion

• Describe in detail how human activities can cause soil erosion.

• Name and explain the primary methods of soil conservation

Human influence on soilsHuman influence on soils

• Human influences can trigger soil erosion due to poor farming methods and deforestation.

• Farming and deforestation > changes soil characteristics and structure.

• Overgrazing – overcropping > leads to desertification , soil erosion and famine.

• Tourism in mountains regions leads to soil loss >Alps , Himalayas

• Soil is not renewable resource . Once eroded it is not put back

Soil erosion / degradationSoil erosion / degradation• US > Annual soil loss = two billion tonnes of top soil.

• China > Soil loss threatens food production.

• Wind and water erosion in Africa contributes to removal of valuable top soil > huge threat to agricultural production.

• Soil erosion is mainly caused by: > wind and by water flowing downhill.

• The amount of erosion that occurs depends on:

1. Quantity of Water• More water more erosion• The amount of rain cannot be controlled but the area over which it collects

can be controlled by constructing barriers on slopes.

Soil erosion / degradationSoil erosion / degradation

2. Speed of water .

• Faster the flow = more erosion • Speed is influenced by the slope gradient and length of the land.

• To reduce the impact of steep slopes terracing is often used , but this takes a long time to construct.

• The length of the slope can also be controlled by barriers at regular intervals.

3. The state of the soil surface and the type of soil:• Few plants, dry, compacted soil = more erosion.

• Soil types cannot be easily changed – can be improved by adding humus –

• State of soil surface can be influenced through cultivation and / or the amount of vegetation cover that is left or put on the land.

• Fertile soils are less likely to be eroded

Desertification in the Sahel region of AfricaDesertification in the Sahel region of Africa• Desertification is the spread of the desert in to new areas >

occurs close to existing deserts – or in well – watered areas asa result of climate change.

• Two main caused of Desertification:

1. Human activity:• Overgrazing – deforestation > Triggered by population growth.

2. Climate change:• Global warming > Increasing drought conditions in certain areas

Desertification in the Sahel region of AfricaDesertification in the Sahel region of Africa

Human Activity:

• Overgrazing> to many animals to graze an area of land

• Overcropping > land is continuously farmed > nutrients are drained from the soil > soil becomes infertile > becomes dry / dusty and easy to erode.

• Deforestation > forest is cut down leaving bare landscape – natural protection is removed – tree and plant roots anchor the soil, preventing soil erosion.

• Overgrazing of cattle major problem in the Sahel > hooves compact the soil destroying its structure > continues grazing removes protective grass cover > Increasing the risk of erosion.


Overcropping in Sahel’s:

• Land is not left to rest – nor fertilised properly > population growth has led land around the edge of crop plantation to be in continuous use. > Soil becomes dry / dusty and blows away

• Economic factors which contribute to overcropping: • Sahelian countries are in depth to developed nations

• Highly Indebted Poor Countries (HIPC)> to qualify for depth relief government’s have to increased the amount of land under cash crops (cashew nuts / cotton) – sold on international markets.

• Plantation workers use the land on the edge of the plantations to grow their own crops – growing cash crops contributes to desertification

•


Deforestation:

• Increase in population > more felling of trees for fire wood and building material > Soil is easily eroded by wind and flash floods.

• Lack of nutrients and destruction of soil structures renders the soil useless for future farming > land is abandoned > over time the desert takes over.

• Soils become drier due to the increase demand for water for human and animal consumption and for irrigation > more well are sunk > this coupled with climate change has lead to a lowering of the water table.


Climate change:

• Global warming has changed the pattern of rainfall in the Sahel’s.

• A rise in atmospheric temperatures results in more water vapour been stored > result > condensation / precipitation is less likely > seasonal rains are becoming less reliable.

• Rainfalls have decreased by 30% in the last 20 years in the region.

• Droughts have become more frequent and last longer.

• Soil is drying out > exposed to erosion > Desertification continues

Methods of Soil ConservationMethods of Soil Conservation

1. Windbreaks > barriers formed by trees.

2. Contour ploughing > right angles to the slope of the hill > prevents soil been washed away.

3. Stubble planting > (left over stubble from previous crops) > provides anchorage for new seed plants and a source of humus > reduces wind and water erosion.

4. Terraces > reduce slope length and steepness > limits the energy of running water and its ability to carry soil away.

5. Stone walls or bunds > placed on the contour of a hill to stop soil erosion > captures water allowing it to filter into the soil rather then running downhill.

6. Reduce ploughing in dry / windy weather > possibility of soil been carried away in the wind is reduced

BiomesBiomes

Exam BriefExam Brief Describe how plant and animal life adapt to Describe how plant and animal life adapt to

soil and climatic conditions in a biome which soil and climatic conditions in a biome which you have studied (2007 HL)you have studied (2007 HL)

Examine the main characteristics of a biome Examine the main characteristics of a biome that you have studied ( 2006) that you have studied ( 2006)

DefinitionDefinition

An ecosystem is a community of animals An ecosystem is a community of animals and plants treated as a unit with its physical and plants treated as a unit with its physical environment. On a global scale, all environment. On a global scale, all ecosystems of one type are referred to as a ecosystems of one type are referred to as a biome.biome.

Major Biomes includeMajor Biomes includeEcologists recognise nine distinct biomesEcologists recognise nine distinct biomes

1.1.High MountainHigh Mountain2.2.TundraTundra3.3.TaigaTaiga4.4.Temperate ForestTemperate Forest5.5.Temperate grasslandTemperate grassland6.6.MediterraneanMediterranean7.7.DesertDesert8.8.SavannahSavannah9.9.Tropical rainforestTropical rainforest

The Desert BiomeThe Desert Biome

A desert is an arid region, which has little or no A desert is an arid region, which has little or no rainfall and where vegetation is scant or absent. rainfall and where vegetation is scant or absent.

The availability of water is the main factor that The availability of water is the main factor that determines the type of plant life that can survive. determines the type of plant life that can survive.

Desert regions can be specially adapted, Desert regions can be specially adapted, through irrigation, to produce more varied through irrigation, to produce more varied vegetation.vegetation.

• Availability of water determines the type of plant and animal life forms in the desert.

• Deserts have typically low precipitation and high evaporation.

• Precipitation is unpredictable.

• Deserts can be cold or hot.

• Deserts are not regions entirely covered by sand! >Only 10% of deserts are sandy the rest comprise of boulders, gravel and bare rock.

• Of the 9 biomes deserts are the least productive in terms of vegetation and growth.

• Deserts have potentially fertile soils that can be made productive through irrigation.

• All deserts have some form of plan and animal life that have adapted to their environment.

• Some deserts are populated seasonally by nomadic tribes or permanently

Deserts can be divided into three categories Deserts can be divided into three categories

1. Extremely arid > at least 12 months without precipitation.

2. Semi Arid > Annual precipitation between 250 – 500mm

3. Arid – less than 250mm

Distribution of Deserts

• Majority of Deserts lie on the western margins or in the centres of continents between 15 and 30 degrees north and south of equator. > These are referred to as low latitude deserts. > Sahara, Arabian, Kalahari and California’s Sonora Desert

• Deserts found within the continental interiors are found between 30 and 40 degrees north and south of equator. These are referred to as the mid latitude deserts and examples include the Great Basin, the Gobi and Turkestan deserts of central Asia.

Deserts are a result ofDeserts are a result of• High-pressure belts (descending dry air)

• Rain shadows (where rain clouds are forced to rise and loose their precipitation on the windward side of coastal mountains leaving the shelter side dry and protected by the rain shadow)

How Deserts Are FormedHow Deserts Are FormedNumber of factors: > high pressure belts, rain shadow,

cold ocean currents and continentality

High Pressure• Most deserts are located in high pressure belts >15

and 30 north and south of the equator.

• Air heated at the equator rises, creating a zone of low pressure. As the air rises it cools and convectional rainfall occurs.

• These equatorial air masses travel away from the equator, cooling further before finally beginning to descend around 30 north and south of the equator.

How Deserts Are FormedHow Deserts Are Formed

• Compression warms the descending air to forms belts of high pressure, known as sub-tropical highs.

• On reaching the surface, the air is returned to the equator as part of the trade winds system.

• These warm air masses are able to hold more water vapour and the atmosphere become very dry.

• Result of dry air > absent of surface water, precipitation,> Clear skies, maximum sunshine and drought.


Rain Shadow Effect:

• Produced by high mountains > coastal mountains create a barrier to the movement of moist, marine air, forcing it to rise > cools as it rises >

• Precipitation occurs on the windward side > the air descending on the leeward side is drier and warmer.

• This creates a rain-shadow effect and, in turn, a rain-shadow desert.


Cold currents:

• Little moisture being evaporated into sky reducing cloud formation and effecting precipitation)

• Several coastal deserts lie along the western margins of continents where ocean water is cold.

• Winds that blow over the ocean currents are cooled, decreasing their capacity to hold moisture.

• On coming in contact with land the hotter land , the air is heated and is able to retain whatever little moisture it holds. > coastal areas remain as desert regions.


Continentality:

• Many deserts are found in continental interiors > winds that reach these areas have already lost their moisture > Low – latitude deserts include centre of the Sahara and Australian Deserts.

• Mid – latitude deserts > Gobi and Turkestan Deserts of Asia – Great basin, USA

North American DesertsNorth American Deserts

Four Desert regions

1. The Chihuahua Desert.

2. The Sonora Desert

3. The Mojave Desert

4. The Great Basin

• These Desert regions are sandwiched between the Rocky Mountains and the Sierra Nevada Mountains.

• They cover an area 12 time the size of Ireland.

• Much of the desert landscape of North America has a Basin and Range Topography. – Mountain ranges interspersed with flat, valley-like basins.

• Three of the deserts regions > Chihuahua, Sonora and Mojave are hot deserts.

• The Great Basin is a cold desert due to its northerly latitude and higher altitude.

Desert Climate• Precipitation is low unpredictable and tends to be concentrated in

short bursts.

• All North American deserts suffer acute water shortages, none are completely dry.

• When rain falls there is a rapid run-off.

• Low levels of infiltration and high rates of evaporation minimises its effectiveness for vegetation growth.

• Precipitation in deserts is mainly seasonal.

• Three hot deserts receive either winter or summer precipitation.

• The cold desert (Great Basin) receives precipitation throughout the year .> Winter precipitation takes the form of snow.

Desert temperatures are characterised by extremes:

• Annual temp range is 20 – 30 degrees Celsius.

• The diurnal range often more than 30 degrees Celsius.

• Daytime temps are high because of sun being high in the sky and lack of cloud and vegetation cover.

• Very little heat is lost by reflection, it is quickly absorbed by bare rock or stone surface.

• In contrast > Night time temps are low and are likely to fall below 0 degrees Celsius > Heat is rapidly lost due to the lack of cloud cover.

Soils of the DesertSoils of the DesertAridisols Soils :

• The characteristics soils of these deserts and semi-deserts are known as aridisols.

• Can range from sandy and fine texture to gravelly and coarse texture >

• Minimum sub-surface horizon development due to the lack of vegetation.

• Many of the basin areas have deep soils as a result of mountain erosion over thousands of years.

• Aridisols are poorly developed as a result of low precipitation and less intense weathering.

• Aridisols are high in mineral content but have little organic matter >

• Lack of organic mater is the result of low plant productivity which restricts the soil-building properties of micro-organisms that convert organic matter in to humus.

• Soils have a light grey colour.

Desert SoilsDesert Soils

• Soils with a low organic mater content are unable to retain all the moisture that falls.

• There is intense evaporation of water from aridisoils, which results in bringing dissolved material – including calcite, sodium and gypsum – close to the surface, producing a strong alkaline soil.

• Calcification > is the dominant process. Nutrients which have been leached down into the soil are drawn back up.

• A solid, calcite – rich layer of hardpan, known as a caliche, builds up in the soil, making it almost impermeable, this impedes the growth of plant roots.

• Salinisation:The high surface content of sodium can lead to extensive saltpan where nothing can grow

Desert VegetationDesert Vegetation

• Deserts are characterised by having sparse vegetation.

• Vegetation that exist has adapted to extremes of both heat, lack of water and humus.

• Soil moisture > supports plant life for a short period of time > fast growing plants (ephemerals) > two / three week cycle.

• Seeds can germinate, mature, flower and produce new seeds within a few weeks.

• Seeds have a waxy coat which protects them until the next rains, which can arrive several years later. (Desert paintbrush)

Desert VegetationDesert Vegetation

• Cactus, Joshua tree > can store water in roots, stem, spine and underground bulbs and fruit .

• A variety of cacti plants have extensive radial root system close to surface – allowing for the quick acquisition of water.

• Other desert plants such as the Mesquite, have taproots allowing them to penetrate deep underground towards water tables (Mesquite roots can be as long as 30m)

• Desert productivity is normally low due to the lack of moisture and humus. Irrigation systems can be used to boost crop productivity, vegetables, fruit and grains can be obtained but these gains are often temporary.

• High evaporation (and capillary action) draws the soluble minerals calcium and sodium to the surface ( calcification & salinisation ) thus impeding growth.

• Overgrazing by sheep and cattle can also cause plant destruction with the loss of many plant species.

• The plating of imported grass from Europe has resulted in the rapid spread of grasslands in desert regions, however high temperatures dries the grass and can cause wildfires which causes further destruction to vegetation .

Desert Animal Life Desert Animal Life

• Relatively few large animal live in the desert as they cannot store sufficient water and withstand heat.

• Like plants, animals of the desert have evolved a variety of strategies for dealing with aridity and high temperatures.

• Many animals, such as elf owl and rattlesnake are nocturnal or are only active in the morning or evening.

• Some animals such as the desert tortoise and kangaroo rat burrow into the ground to avoid the hot sun. They re-emerge to feed when the desert cools.

• Insects move around twigs to stay cool, while jackrabbits follow the cacti’s moving shadow

Desert AnimalsDesert AnimalsMany desert animals have evolved with:

• Pale bodies to ensure they attract less heat and are less conspicuous to predators.

• Developed long appendages to lose some of their body heat.

• Jackrabbit have extremely long ears, kangaroo rat has a tail that is three times longer than its body, which is used a rudder to make sharp turns to avoid predators.

• The squirrel are dormant during the summer. The desert toad has horns on its hind feet which are used as digging tools. It seals itself in a burrow for nine months.

• Reptiles produce uric acid instead of urine, thus wasting little water. Their skin is also waterproof to retain moisture.

• The well known desert bird the road runner spends most of its time on the ground running, using far less energy than if it was flying

Human ActivityHuman Activity Altering a BiomeAltering a Biome

• See handout for Case Study – California

• Assess the impact of human activity on a biome that you have studied. (2006) 80m

• 4 paragraphs > 6 SRPs in each paragraph

Documents

Soils Soil forms the thin surface layer of the earth’s surface