Class 11 - Tropical deserts Flashcards
Do plants care about rainfall?
Plants don’t care about the rainfall, they care how much water they have access too – being in a valley, dew, soil texture
What are the best soils in deserts?
Stony soils are best in deserts, worst is clay, because the heat makes the water evaporate and rise, not sink, making the plants have access to it
How are the roots?
Plants will have very deep roots or very broad roots at the surface
What are the most common desert plants?
Palms, bushes, legumes, grasses, cacti
What do plants do to survive?
Plants will go dormant when it is dry, bloom and grow when it rains, drop leaves when it gets dry, survive as seeds. Or avoid the drought stress – making leaves very small, no leaves, or thin narrow spiky leaves, water storage organ (succulents, cacti) fat little leaves full of water, long enough roots to reach the ground water. Or tolerate the stress of drought – let the water come and go, looks like it dies, grows when it gets water
Where is the biomass?
Most of the biomass is underground – competing for water not for sunlight
What is an oasis?
Where the groundwater is near the surface
What is a Wadi?
Seasonal river. Dangerous place, because it is dry most of the time but fills with water very very quickly when it rains
Is salination a problem?
Strong tendency for salinization beacuse evaporation exceeds rainfall – high high levels of salt in lakes or water sources – problem for agriculture. Salt in deeper layers will be brought to the surface by the water on irrigated lands
What causes soil erosion?
Soil erosion because of wind – dust storms blowing soil into the ocean or elsewhere – some go all the way across the Atlantic from Sahara to Amazon
What do locals do to capture water for agriculture?
Half-moon shaped fields are built to try and capture rainwater
At which lattitude do deserts occur?
30 degrees north and south
At what sea currents do deserts occur?
Next to cold sea currents
Define fog desert
Almost no rain but seasonally high air humidity
How can a desert occur on a mountain?
In the rain shadow of the mountain
Is desert biodiversity high?
No
How can you escape drought stress by dormancy?
Survive as seed, drop leaves in dry season, underground bulbs or corms
Define desert
Any large, extremely dry area of land with sparse vegetation
What vegetation covers the ground?
Trees are usually absent – shrubs and plants provide incomplete ground cover
Why are deserts often so bare?
Bareness often due to human disturbance from grazing
When did deserts originate?
Deserts are recent in origin – 65.5 million years ago
Example of a plant that is characteristic of deserts?
Welwitschia is a plant with just 2 leaves that are leathery, straplike, grow at the base and erode at the ends
Do deserts have studd in common across the world?
Yes, they are quite similar
Can plants migrate from desert to desert?
Plants have migrated naturally between deserts, some in the last ice age – from north to south in Africa and Americas
What characterises the desert environment?
Shortage of moisture to plants because of an imbalance between precipitation and evapotranspiration – made worse by low rainfall, low humidity, high temperatures and winds
What ia sthe average precipitation?
Average precipitation between 0 and 600 mm, most have rainfall below 400 mm
Define the Hadley cell?
At the equator, there is so much sun that air near the ground heats, rises, expands, then cools. At high levels of moisture, the risen air moves away from the equator to decend in the subtropics when it cools – this air has already lost a lot of moisture so as it decends it becomes compressed and warmer and humidity falls further (this is where deserts lie)
How long can it be between rain?
Time between rain can be vast, like in Chile, where no rain fell for 45 years – usually though, it rains between 15-20 days a year
How are the rainfall patterns?
It often rains in heavy showers over a single month
What is the role of fog and dew?
In some deserts, fog is important as moisture settles on plants and drips to the soil to be absorbed by roots
What is the role of wind?
Winds are not particularly strong in deserts, but their effect is increased at ground levels because of the lack of vegetation – induce erosion and evaporation of moisture
What are the maximuma and minimum temps?
Maximum air temperature is 40 degrees, minimum temps at night are below the freezing point
What is the average temps?
Mean temps are usually between 20-25 degrees
What is the harshest, poorest type of desert?
The harshest and poorest type of habitat is the loose, mobile sand desert
Define the soils
Immature, weakly developed and mostly alkaline – sand, gravelly loams, stony soils, rocky
What type of life does the soil often support?
Even though they are mostly dry, they can support well-developed microbial communities especially around plant roots
What is the most diverse and second most diverse desert plant?
Daisy and bean families
What are common plant families in Africa?
Ice plant and lily
What are common plant families in the Americas?
Cacti, Joshua tree
What is the most common tree found in deserts?
Bean
What grasses grow in most deserts?
Perennial grasses
What animals are common in Australia?
High diversity of reptiles, kangaroos, wallabies, camels, parror birds
What animals are common in Africa and Asia?
Gazelles, ibexes, oryxes, burrowing rodents, reptiles, foxes, hyenas, leopards, lynx
Whata characterises birds?
Birds are nomadic and fly to areas with water and food – finches and pigeons are typical
What do animals do to survive?
During dry periods, many animals burrow underground and only come out at night, reproduction may cease altogether in years of extreme drought
What is desertification?
Deserts are expanding = desertification because of climatic variation and human activities. It is thought that if no human activity had occurred, there would be less deserts
What are the main regions at risk of desertification?
Sahel region south of Sahara, parts of Africa, large areas of Australia, central Asia and North America
Is biological productivity high or low?
Biological productivity is in general very low but varies in time and place
Is there a trend of global dryland expansion?
There is no evidence of a global trend of dryland expansion (6%), on the contrary, more greening has happened since 1980s (41%), but the trend is declining
Has surface warming been higher or lower in drylands?
Surface warming in drylands has exceeded warming in humid lands due to unsustainable land use, cc
What has happened to biodiversity?
Increased tree mortality og mesic species, losses of bird species
What will happen and why?
Some drylands will expand and others will shrink – increased temps and more irregular rainfall
What extreme weather evvent is expected to be significantly impacted by cc?
Sand and dust storms
What should we do with water management?
We should employ technological options linked to water management which draws on both traditional practice and new innovations
What is the extend of drylands?
Drylands cover 45-47% of global land area and is home to 3 billion people
Are there megacities in drylands?
6% of megacities have been established in arid areas and 2% in hyperarid ones
Where does desertification usually occur in hyper arid areas?
In oases and irrigated land
Main ES
Abundant solar energy, opportunities for tourism, rich plant biodiversity, extensive indigenous knowledge on adapting to warm/dynamic climates
Define the Sahel paradox
In Sahel, there has been an increase of surface and groundwater
Why has there been a greening trend?
Some areas have had greening due to CO2 fertilization and increased rainfall. Increased shrub-cover has been recorded in North American deserts. Farmers have regenerated trees close to villages, which has helped greening
What might happen to soil biocrusts?
Soil biocrusts are sensitive to warming because communities of mosses and lichens might shift in favour of others
What has the drought in the West US done?
In southwesterns USA, a drought since 2000 led by cc, land-use change, invasive plants and wildfire has causes reduction of native plant species and perennial vegetation
How much has the Sahara increased?
10%
What will increase dust and sand storms?
Land degradation, loss of vegetation and drying of water bodies
What countries are carrying out large-scale water transfer projects?
Turkey, Libya, USA and China
In what country has water availability decreased significantly?
Morocco
What are the short-term impacts of sand and dust storms?
Health, food production systems, infrastructure, transport, economic productivity
What are the long term impacts of sand and dust storms?
Loss of ES, loss of biodiversity and habitat, chronic health issues, soil erosion, reduced soil quality, disruption of global climate regulation
What are the health implications of cc?
Risk of water scarcity, food insecurity, malnutrition, respiratory, cardiovascular and infectious disease, displacement, mental health issues, heat stress
Why are droughts very significant?
Drought only represent 4% of hazardous events, but they impact 31% of people
What ahs happened with agriculture in Pakistan?
In Pakistan, less wheat has been yielded due to droughts
How is livestock impacted by cc?
Reduction in plant cover, reduced livestock and increased land degradation and soil nutrient loss
How are women affected differently?
Women is lower-income countries are affected disproportionately since they produce most food, collect wood and water from increasingly distant sources. Women are also excluded from decision making on cc
What caused conflicts in African deserts?
In African deserts, it was found that conflict arose from large-scale resource extraction
What is projected to happen with surface increases of temp?
Surface warming in drylands is projected to reach 6.5 degrees by 2100 – this could trigger desertification in West Africa, Central China and Mongolia and an increase of extremely hot days
Has soil moisture declined globally?
Yes
What is projected to happen with drought stress?
Drought stress is projected to increase by 70% globally
How are populations expected to grow in drylands?
Populations in drylands could increase 700 million people
How much have dust emissions increased
Double
How well do plants and animals adapt to heat?
Plants have long histories of adapting to heat, while many animals are already living at their limits
What happens if grass expands into drylands?
Transforms them significantly
Why are succulents significant?
Succulent species might be particularly vulnerable to increased heat
What is projected to happen with salination?
Salination is projected to increase in drylands due to cc
How to adapt to soil erosion
Rainwater harvesting, soil conservation, agroforestry, new crop varieties, new management strategies
How to adapt to overgrazing?
Modification of systems, changing timing and location of farms, improved breeds and feeding
How to adapt to clearing of natural vegetation?
Carbon sequestration, decreased clearing, better crops, improved land and water management, agroforestry
How to adapt to invasive species and woody encroachment?
Biomass harvesting and selective clearing, fire, browsing, rewilding, chemical removal
How to adapt to droughts?
Promote collective action, optimise livestock policies and subsidies, market intervention, expanding sustainable irrigation, drought resistant crop use, seawater desalination
How to adapt to savanna degradation?
Prescribed fire and tree cutting, invasive plant removal, grazing management, reintroduction of grasses, restoration of soil disturbance
How to adapt to poor livestock productivity?
Promote seasonal herd mobility, complimentary fodder
How to adapt to croplands and soil fertility?
Application of mineral N and P fertilizers, adapting cropping techniques
How to adapt to salination and groundwater depletion?
Indigenous practices, salt tolerant crops, agroforestry
How to adapt to dust and sand storms?
Windbreaks, shelterbelts, protection of loose soil, use of perennial plant species to trap sediments, improve monitoring
General reccomendations
Improve early-warning systems for sand and dust storms, manage and store water using indigenous knowledge, implement restoration and landscape heterogeneity, prevent soil erosion, create drought tolerant food crops through plant breeding, invest in research and development
