Name: The Desert Biome - Biomes #4
Uploaded: 2021-06-02T04:04:27.000Z
Duration: 15 min
Description: 沙漠生態圈Learn the English Usage: desert,biome,vegetation,earth,east,south,bare,western,north,plant,extensive,continent,moisture,andes,salt,sahara,cactus,find,region,rainfall,occur,planet,africa,connected,climate,middle...

This is what the bare earth looks like, the bones of our planet revealed as the skin of

Despite the lack of life, these landscapes nonetheless inspire us with their stark beauty.

A product of endless sunshine and droughts, life yet still finds a way here, for plants

to survive in these regions have gotten smart.

One of the most extreme biomes on our world, from the Sahara to the Sonora, the Gibson

to the Gobi, these are the deserts of planet Earth.

Deserts are  among the most open form of country on earth,

where vegetation is sparse or effectively absent.

The cause of this is simple enough – it's just a lack of water.

Plants, like all forms of life, need that universal solvent, and when it's sparse,

they struggle, and in order to survive, they must get creative.

Deserts exhibit some of the most interesting and strange forms of plant life to be found

The strict definition of deserts in the biome classification system we're using in this

series, known as LONS08, is any biome containing bare earth, either in part between grasses,

This distinguishes the deserts from other desert like biomes, such as scrub, since the

latter will always have a complete covering of grass at ground level between the shrubs.

But while shrubs and grasses, and occasionally even trees, are also often present in deserts,

they are separated by sections of bare earth.

Deserts occur over extensive parts of the continental surface of the earth, present

on every continent, and are in fact the largest biome in terms of land area.

They are basically subdivided into four forms, hot and cold, arid and semi-arid.

Arid deserts have practically no vegetation, while semi-arid regions contain a mix of plants

separated by bare earth as described a moment ago.

Hot deserts occur in the subtropics and are characterised by mild winters and very hot

summers, while cold deserts occur in the temperate latitudes and although they still have relatively

hot summers, experience winters that can be brutally cold.

These elements, hot and cold, arid and semi-arid are mixed up in various ways to produce biomes

that are unique within the greater sphere of deserts.

The correlation between hot and cold deserts and their corresponding Koppen climate zones

Hot desert areas occur in regions defined by the Koppen Hot Arid (BWh) and Hot Semi-Arid

(BSh) zones, while cold deserts are found in the Koppen Cool Arid (BWk) and Cool Semi-Arid

The climate phenomena and causes of these four basic types are discussed at length in

the two episodes of my Secrets of World Climate series that relate to deserts, which you'll

If we consult our Holdridge Lifezones chart, we can find the deserts at the extreme left

of the diagram, where rainfall is at its lowest.

Note that the deserts span every latitude of earth, from the tropics to the poles.

Although parts of Antarctica are the driest on Earth, these regions are classified within

the Ice biome since the perpetually cold temperatures on that continent are considered to be the

defining characteristic over any localised absences of precipitation.

The aridity index – the ratio of evapotranspiration to available water - is at its highest anywhere

on earth in the hot deserts of the subtropics, where searing temperatures combine with a

near-absence of rain to make any plant growing extremely difficult.

The deserts are the only biome where, mostly or completely devoid of vegetation, the bones

Astronomically, earth is regarded as a rocky planet, and beneath any vegetation, or oceans,

its crust is some form of rock, usually oxides of silicon mixed with other minerals.

These other minerals, and the way in which these rocks were formed beneath the earth,

So where you see deserts, these exposed rocks reveal their many colours, from the white

of sodium and calcium salts, to the red of iron, the black of basalt, and the beige of

sandstone, the colour most commonly associated with deserts.

Lacking cloud cover, deserts have high ranges in temperature from night to day.

In a process called weathering, these temperature changes stress the rock where it is exposed,

and eventually break it up, depositing it in heaps of shattered rock below, known as scree.

Additionally, with little root vegetation to hold onto it, desert winds, laden with

sand, further wear at the rocks to create more sand, and in places, this sand gathers

Dunes spread out over a wide area are referred to as ergs, and some of these ergs can stretch

for thousands of square kilometres, such as those found in the Taklamakan desert of Central Asia.

Rivers running into deserts very often end there, due to evaporation from the intense

sun, and as they dry out, they deposit any salt dissolved within.

In geological times past, ancient seas once connected to the oceans were cut off, and,

within the parched desert climate, dried out to form salt lakes.

So very often the soil is salty, and as a consequence many desert plants have adapted

by becoming highly salt tolerant and such plants are called halophytes, after the Greek

Plants that can withstand extensive droughts, on the other hand, are called xerophytes,

after the Greek word “xeros” for dry.

The mechanisms of how such plants deal with drought is numerous, but all centre around

retaining as much moisture as possible from the infrequent rains that might come their way.

Moisture in plants is lost through leaves, and in particular through stomata, the breathing

holes in leaves that exchange CO2 for oxygen.

Since sunlight is readily available in deserts, small leaves are standard for desert plants,

since these leaves provide enough for photosynthesis, but are kept small to reduce moisture loss.

Others keep their stomata closed during droughts, preventing growth, but also greatly reducing

Another adaptation is storing as much water as possible within the plant itself, and this

is the defining characteristic of the class of plants known as Succulents, which have

The most well-known sub-class of the succulents is, of course, the cactus family.

Despite being only found only in the Americas, cacti are regarded as the iconic desert plant,

and could be mistaken for naturally occurring throughout the world, when they are not.

Cacti's excellent ability to store water is well-known – in the case of the Saguaro

cactus, one of the largest, a fully grown specimen can soak up to 200 gallons of water

In these brief interludes between the long droughts, when rain comes to the desert, the

plants therein frantically attempt to reproduce, and so a desert will bloom in a riot of wildflower

colour after a rainstorm, transforming the landscape overnight.

So where in the world do we find the deserts?

Starting in North America, in the Western half of the United States we have the extensive

Great Basin cold desert of Nevada and Utah, while further south, and at lower altitudes,

we have the hot deserts of the Mojave, Sonoran and Chihuahuan deserts extending from Southern

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The Desert Biome - Biomes #4

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