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
