Lesson video

Hello, geographers.

My name is Mrs. Griffiths, and today's lesson is about ecosystems that occur at a global scale.

They're called global biomes.

I'm gonna have a bit of a tour all around the world, thinking about the distribution of those biomes, so where are they, and also the characteristics of them.

So shall we make a start? And today's outcome is as follows.

I can describe the distribution and characteristics of global biomes.

So that's what I'd like you to be able to say by the end of the lesson.

I can describe the distribution and characteristics of global biomes.

We've got some keywords for you today.

Those are biome, a large-scale global ecosystem, for example, the tropical rainforest.

Distribution, the spread, which may have a regular pattern of, for example, a type of vegetation.

Climate, the average weather conditions, such as rainfall and temperature, recorded over a period of 30 years.

And latitude, distance from the Equator north or south.

Lines of latitude run east-west on a map, e.

g.

, the Tropic of Cancer.

So those are our keywords that we're gonna be using throughout the lesson.

Now, how does our lesson shape up? Well, we have two parts to it.

So we're gonna be thinking about initially what and where are biomes, and then secondly, what are the characteristics of the major biomes.

So let's start with part one.

What and where are biomes? Now, satellites give us a view of Earth from space.

Ah, so I have a different satellite image here for you, and this is an image where we've actually stripped off the weather.

So we've removed the clouds to see what's going on on the Earth's surface.

I would say to you that you can see Earth's deserts, hot and cold.

They are visible from space.

So we can see Greenland, a cold desert.

We can also see the Sahara, a hot desert.

But what else can you see in that image? Well, as Jacob says here, we can see stripes of brown and green.

So beyond identifying the hot and the cold deserts, we can see what appear to be stripes of brown and green, and this is what we're gonna be thinking about today.

What might those stripes be? And what is the pattern of vegetation across the Earth's surface? So global biomes are large-scale ecosystems defined by their main vegetation type.

We've got a couple of photographs there for you to have a little look at.

Can you identify these two biomes by the type of vegetation shown? So we've got one biome on the right, one on the left.

Have a closer look.

How'd you get on? Well, no doubt, you can tell me that on the left, we've got some lush, tall, and dense forest that is found in the tropical rainforest.

Whereas on the right-hand side of my screen here, we've got evergreen, cone-bearing trees, giving the coniferous forest its name.

It's also known as the taiga, this biome.

Tropical rainforests and coniferous forests are both global biomes, and they're found on multiple continents.

So for example, tropical rainforests are found in the Northern and the Southern Hemispheres.

They're also found on every continent, except Europe and Antarctica.

So tropical rainforest isn't just located in one place.

It's found on a number of continents.

So quick check for you then.

What defines a global biome? We've got three possible answers here.

A, the main type of animal, B, the main vegetation type, and C, the hemisphere.

Pause the video, talk to your partner, and then restart the video when you want to hear the correct answer.

And if you said B, the main vegetation type, you are absolutely right.

Well done.

One more check for you here.

Areas of tropical rainforest are.

Can you finish the sentence? And we've got three options there.

This time, I'd like you to read through the options, and think about which best fits to finish this sentence correctly.

Pause the video.

Talk to a partner.

And I'm sure you said B.

So areas of tropical rainforest are found on every continent, except Europe and Antarctica.

Well done.

Now, we can use maps to show the distribution of global biomes.

Can you see where hot deserts are located on this map? Use the key.

There were lots of possibilities to identify deserts, weren't there? But we can see them in North and South America.

We can see them in the continent of Africa.

We can see them in Asia, and also Oceania.

It's really clear, isn't it, where we've used that yellow in the key for hot deserts.

So it's a complicated pattern here if we're thinking about the global distribution of biomes.

But we've simplified it here to eight different biomes, which are unnamed here, with a ninth labelled other, which is sort of like a catchall, but it includes polar and mountainous landscapes.

But we can see it's quite a complicated pattern.

Though it's complicated, however, the climate is a key factor that influences this global pattern.

So there are some general observations we can make about where those biomes are.

Can you think about what those might be? Can you spot any patterns within this map? One general pattern is that biomes form east-west belts across the globe.

We call this a latitudinal pattern.

So let's have a look at what that looks like.

So tundra biomes form an east-west belt there in the Northern Hemisphere.

Rainforest biomes form an east-west belt there around the Equator.

So this is a latitudinal pattern.

We can see, as Sofia says, it's a general pattern.

We're generalising here, rather than it being a perfect pattern, 'cause there are lots of local factors that also come into play.

So quick check for you here.

True or false? The pattern of biomes, arranged in east-west belts, is termed a longitudinal pattern.

Is that true or false? Well done if you said it was false.

But can you explain why? That's right.

You've spot it.

It's a bit of a trick question there, isn't it? The pattern of biomes, arranged in east-west belts, is termed a latitudinal pattern.

So it's a latitudinal pattern, not a longitudinal pattern.

We'll have a look at what the difference might mean in that in a second.

Another pattern is the biomes north and south of the Equator roughly mirror one another.

So we've just got a slightly cropped version of the key there for you to have a look at the biomes within the African continent.

If we have a look at that double-sided arrow that runs out from the Equator, north and south across the African continent, what we can see is some level of mirroring north and south of the Equator in terms of the layout of those biomes.

So we're travelling from rainforest to savanna, or tropical grassland, to desert, and then potentially that Mediterranean biome.

Let's have a look at that in a little bit more detail then.

So if we were to travel along the line of longitude 20 degrees east.

Now, you remember that lines of longitude run from pole to pole, whereas the Equator runs around the Earth, often pictured on maps as a horizontal line.

Now, here's our Equator.

Here's our line of longitude.

So we're talking about 20 degrees east of the Greenwich meridian.

If we were to travel on a wonderful journey from the Equator in the heart of the African continent, which would travel north, we would travel through tropical rainforest, tropical grassland, savanna, desert, and into the Mediterranean biome.

So that's going north from the Equator.

But what if we set off south from the Equator to the southern tip of the African continent? What biomes might we travel through then? Well, if we set off from the Equator and travelled south, we would travel through the tropical rainforest, the tropical grassland, the desert, and you guessed it, the Mediterranean biome.

So you can see that mirroring along certain lines of longitude through the African continent.

So these are patterns that we notice as geographers.

So quick check for you.

What can we say about the general pattern of Africa's biomes? Pause the video, and restart it when you have an answer.

Okay, so Jacob has an answer for us here.

He's saying Africa's biomes in the Southern Hemisphere almost mirror the distribution of its biomes in the Northern Hemisphere.

Now, we've got that representation that we clicked through earlier, just showing the arrangements of rainforest around the Equator.

Then, at a further distance, we have that tropical grassland, followed by the hot desert, and then eventually the Mediterranean biome.

Well done if you had that answer.

So if we keep travelling north from the Mediterranean biome, so we're in the Northern Hemisphere, we'd notice that the dominant vegetation changes again and again with climate.

So even if we went as far north as the Arctic Circle and beyond, we'll see that we go through a series of different biomes.

So we're starting from that Mediterranean biome, and then we reach about 45 degrees north of the Equator, and we'd enter the temperate deciduous forest, then the coniferous forest or boreal forest, up to about 70 degrees north.

Beyond that, we'd find the tundra, up to about 80 degrees north of the Equator.

So of course, what that means is as we pass through those biomes, we've got different types of dominant vegetation, and that's all linked to travelling along that same line of longitude that we started from the Equator at.

We're travelling along that line of 20 degrees east.

So you'd notice if we did that walk over perhaps months or years, we would notice the different vegetation in each biome.

Okay, so a check for you here.

Can you choose the correct words to complete this sentence correctly? The pattern of blank is broadly latitudinal, with tropical rainforest near the blank, and tundra near the blank.

And we've got six words to choose from.

So pause the video now, and then click play when you have an answer.

Aha, so the pattern of biomes is broadly latitudinal, with tropical rainforest near the Equator, and tundra nearer the poles.

Congratulations if you've got all three words in the right place.

Okay, so I have a practise task for you now.

Looking at this map again and the photographs, can you state two differences between the tropical rainforest and coniferous forest biomes? I've got a hint here for you.

I'd like you to refer to location and also vegetation.

So pause the video now, and have a go at this task.

See if you can describe two differences in your own words.

Okay, well done for having a go at that task.

We had to come up with two differences between the rainforest and the coniferous biome.

Your answer might include the following points.

So we had the fact that the tropical rainforest biome forms an east-west belt located in the tropics, on or near the Equator, whereas the coniferous biome forms an east-west belt on the Arctic Circle in the Northern Hemisphere.

Quite a lot of detail there, isn't there, and I like the way we got that word, whereas, so we're comparing one with the other, and noticing the differences, but using that linking word.

Secondly, trees in the rainforest are more varied than in the coniferous forest.

Sorry.

So there's huge amounts of biodiversity that's very typical of the tropical rainforest compared to just a few varieties of coniferous trees found in that coniferous forest biome.

Well done if your answer looks like something like that.

Now, second practise task for you.

Using the map and the key, list the biomes you would travel through going south from the Equator across the African continent.

Hint: a line has been added to the map to help you.

So we've got our key there, we've got a map.

If you took that journey along the dashed line, which biomes would you be travelling through? Pause the video now and jot down a list.

Okay, so what did we have for this list of biomes we'd be travelling through going south from the Equator across the African continent? So your answer could include the following.

As you travel south from the Equator across Africa, you might pass through tropical rainforest, savanna, desert, and the Mediterranean biome.

But as Sofia says, this isn't true for all journeys, so it would depend on that line that we took as we travelled across the continent from the Equator travelled south.

So it would depend on where we set off from because those biomes don't form complete latitudinal belts across the continent.

So it's not a perfect pattern.

Thank you for that.

Okay, so we've had a thought about what and where are biomes, but what are the characteristics of the major biomes? So let's focus in on a few of those now.

Ah, so we have four images here of four different major biomes around the world.

Can you spot the odd one out? Have a closer look at those images.

What do you think? Well, I would say that bottom right-hand image doesn't appear to have any trees in it, and that's because this is the tundra biome.

And actually, the word tundra is linked to the Finnish word that means treeless plains.

Okay, so we're gonna find out about the tundra in a minute, but let's go back to the tropical rainforest.

I always think when we're talking about biomes, it's nice to start from the Equator and work out.

So this specific biome, and we've seen this lovely image before, is characterised by an equatorial climate.

So we're talking about high rainfall with little variation in temperature, and this is shown in the climate graph here we have of a location called Mbandaka in the Democratic Republic of Congo.

And if you look at its location, it's pretty much on the Equator, isn't it? 0 degrees north.

So let's have a look at the climate graph.

Just quick recap for you then.

Climate graphs have got two y-axes.

So we've got temperature on the left-hand side, and we've got precipitation on the right-hand side in millimetres.

Along the x-axis, we've got months of the year.

Remember that temperature is illustrated using the line, and the bar graph represents rainfall.

You could almost picture them as cylinders of water sitting on our X-axis.

We can see from that climate graph that we've got relatively constant temperature across the year.

So the temperature's really varying between about 25 degrees and 27 degrees Celsius, not a very big temperature range, and it's moist across the year, bar about two months of June and July.

So this is near-perfect, humid, warm growing conditions, resulting in dense, evergreen rainforest.

So we can see how the climate determines the vegetation.

Can you describe the characteristics of the tropical rainforest in the Democratic Republic of Congo? Have a go.

Pause the video now, and then start it again when you've had a conversation with your partner.

Okay, what did you have? We had this is dense, evergreen rainforest.

We can see that in the image, can't we? The temperature is high all year-round, and large amounts of precipitation is experienced in all but three months here.

Well done if your answer was a bit like that.

Okay, so after the rainforest, we have the tropical grassland biome.

This biome, also called the tropical savanna, has the tropical savanna climate of wet and dry seasons, and still quite a low temperature range.

But notice on our climate graph that the temperature line is a little bit lower.

So the temperature is bobbing around between 20 and 20 degrees, 22 degrees, sorry, Celsius across the Earth.

Still a tiny temperature range, but the temperatures are a little bit lower.

But notice how we've got two peaks in terms of the rainfall.

So the wet season of March, April, May is mirrored by a wet season in November, December, and then a little bit of January.

And this is typical of an area of Africa where seasonal rains sweep across the plains twice in the year, and following those rains are these wildebeests in our image.

There are herds of animals that migrate across these grasslands.

The abundant grazing is available specifically after those seasonal rains, and we have very small scattering of trees.

So it's a particular landscape, and it's defined as the tropical grassland, influenced by the climate here in a part of Tanzania called Mugumu, which is close to the Serengeti National Park.

Then, onto the desert biome.

The desert biome typically has an arid climate, which means a really dry climate.

So we've got high daytime temperatures, but very actually quite low nighttime temperatures.

Worth noticing that.

There's quite a high diurnal range.

And extremely low rainfall.

Look at that climate graph.

What's happened there to our rainfall pattern, comparing that to where we've just been, which was the tropical savanna? This is a part of Algeria called Tamanrasset, and it's very, very dry across the whole year.

Look at the photograph of this place.

We can see the dust kicking up from that image, and imagine just how dry it is.

Plants and animals have to be highly adapted to survive in the desert, given the lack of water and wide range of temperatures within a day.

So you've got all these challenges.

High temperatures, wide range of temperatures within a single day, and super dry.

And now we have a check for you.

Can you describe the characteristics of the desert biome? So we have this image, we have this climate graph.

Pause the video now, and have a think about two or three points that you could make.

How'd you get on? This was our answer.

There is not very much vegetation, and you can see that in the image.

Can't you can see how dusty it is? And look at all those rocky surfaces, which appear to have no vegetation on them, and of course, the sand dunes.

There is very little precipitation all year, and the temperature rises as high as 30 degrees Celsius.

Remember that's on average during the hottest months.

And you might have said, "Well, of course, that's June, July, and August." When we look at that precipitation, it's very low, isn't it, across the whole year.

November doesn't look like there's any precipitation at all.

I don't think there's a single month there that even begins to reach 10 millimetres total rainfall for that month.

So you might have put some data into your answer, and if you have, congratulations.

And onto the coniferous forest biome.

Here, we have the subarctic climate, and a lack of sunshine is a feature of this climate, meaning that the winter is very cold.

Take a look at the climate graph for Umea in Sweden, which is almost 64 degrees north of the Equator.

So we're almost on the Arctic Circle.

And if we look at the winter temperatures, say January and February, we can see the average temperature, remember we're plotting the average on these climate graphs, is dipping down to -7 degrees.

What's the impact on vegetation? Well, if we look at the image, we've got mainly coniferous trees, of course.

So these evergreen trees are adapted to cope with a lack of availability of moisture.

Because with these very low temperatures, water in the soil freezes in winter, or, of course, it's falling as snow rather than rain.

So needle-shaped leaves lose less moisture.

So this helps the trees to cope in winter when there's less moisture available to take in through their roots.

And of course, those needle-shaped leaves are also frostproof.

So this type of tree is very well-adapted to this particular type of climate.

Of course, the seeds will be locked up in cones until the spring as well.

Take another look at that climate graph.

We have really quite a lot of precipitation across the year.

I think most months are, or a lot of months, perhaps 3/4 of the year, are receiving more than 50 millimetres of precipitation on average across the month.

True or false? There is plentiful water for year-round plant growth in the coniferous forest.

Is that true or false? And can you explain why? Now, I'm sure you were telling me that that is false.

We've just heard about how there isn't much water available in winter in the coniferous forest.

So trees have to be adapted, don't they? Did you tell me something about the way trees were adapted because they have needle-shaped leaves? Because the average temperature is below zero for five months of the year, this means that soil water is frozen, and precipitation falls as snow.

So in terms of water in a liquid form that's available for plants to take up, that isn't available to trees in winter.

Well done if you said that.

Now, the tundra biome.

The tundra biome has a polar tundra climate.

And if we look at our climate graph, we can see the temperatures are really plunging to very low temperatures across big chunks of the year.

Okay, so the temperature's only really creeping up above zero degrees for two or three months there, isn't it? Wet all year-round.

But as we know, most of that's gonna be falling as snow.

What impact does that have on vegetation? Well, we've got low-growing grasses here, as opposed to trees.

These are adapted to coping in extremely cold and windy conditions.

And remember, let's have a think about what the soils are like.

The soils are frozen in this environment.

So we've got something called permafrost, which means subsurface layers of the soils are always frozen and we've just got surface layers of melt in the summer, and this is a time when the soil becomes really waterlogged.

So any plants that grow here have to be able to cope with that.

Very few sunshine hours also mean a very short growing season across this year.

So you've got such a really small window there in sort of May, June, July, August, September, where actually the seeds can germinate, plants can grow, and complete their life cycles.

They have to be really quite smart and well-adapted.

Okay, so let's have a look at this climate graph.

Quick check for you here.

Which biome would you associate with this climate? Have a look at the climate graph.

Is it A, the tropical rainforest, B, coniferous forest, or C, the tundra? Pause the video now, and have a conversation with the person next to you.

And of course, if you said tundra, you are absolutely right.

Look at the the y-axis of temperature.

We've got into the minus numbers.

We've got temperatures dipping down as low as -15, -16 degrees.

This is not the tropical rainforest.

And the coniferous forest, again, wouldn't be quite so low for such a large chunk of the year.

Okay, practise task for you.

Complete this table about the characteristics of three biomes.

Some information has been completed for you.

So as you can see, if we have a look at the left-hand column there, we've got biome.

Then, you need to complete the climate associated with that biome, and then the vegetation, to do some description there about the vegetation.

So if you want to pause the video now, think carefully about what we've talked through, and what you'd like to include in those four boxes where the information is missing.

Okay, how did you get on? These were our answers.

So tropical rainforest.

We know what its climate is like, but the vegetation is dense, it's evergreen, and it's rainforest.

You might also have a biodiverse environment.

Well done if you had that.

Tropical grassland, the climate is termed the tropical savanna climate.

It has wet and dry seasons, really distinct wet and dry seasons, two wet seasons, and quite a low temperature range.

For the coniferous forest, also known as the taiga, we have a subarctic climate, a lack of sunshine, meaning that the winter is very, very cold, and perhaps in that box about vegetation, you told me something about the way that evergreen trees, coniferous trees, are adapted to cope with the cold winters with needle leaves reducing moisture loss because of that small surface area, and reducing the heat loss because there's frostproof leaves.

Okay, so last bit of the practise task here we have is describe three ways, describe three ways in which climate influences the characteristics of the desert biome.

I've got a hint here for you.

Think about the types of plants and animals found in the desert.

You can picture those.

You might be able to tell me in your own words.

Can you describe three ways in which climate influences the characteristics of the desert biome? So this one involves a bit more thinking.

I'd like you to pause the video, and I'd like you to write up these three ways in full sentences for me, and then restart the video when you want to check your answers.

Okay, how did you get on? That was quite a tricky task, wasn't it? But we have that climate graph from Algeria to give us a few hints and tips, don't we? So the three different ways in which climate influences characteristics of this biome were.

Well, this is what we had.

The low level of precipitation limits plant growth year-round, which, in turn, limits the amount of food available for animals.

So if we think about a biome having characteristics linked to type of vegetation, but also the type of animals that are found there, generally we aren't finding very large populations of plants and animals in this place.

It's not very heavily, it's very sparsely vegetated, isn't it? High temperatures mean evaporation rates are also high.

Water is rapidly lost from the soil, reducing plant growth, so very few plants can survive in this biome.

Very few being adapted, and those that are adapted to grow in this biome no doubt can complete their life cycle in a matter of weeks when it rains.

And then, thirdly, animals must be adapted to cope with a wide temperature range, even an extremely high daytime temperature compared to quite a low nighttime temperature.

So you might have temperatures falling by as much as 40 degrees between the peak in the daytime and into, you know, dropping below zero at nighttime.

How do animals cope with that wide temperature range? So I hope your answer was as detailed as that.

Perhaps you came up with three really different ideas, but clearly, the climate is really shaping the characteristics of this biome.

And that's a lot of what this lesson's been about, hasn't it? The idea that climate is such a key factor in influencing the distribution of biomes.

So let's look at our recap then, the lesson in summary.

Ecosystems at a global scale are called biomes, and occur on multiple continents at the same latitude.

East-west belts of each biome may be found in both the Northern and Southern Hemisphere.

Although, the distribution of global biomes is more limited in the Southern Hemisphere where there is less land.

Climate is an abiotic factor that largely determines the distinctive vegetation type associated with each biome.

Well, we've covered a lot today, haven't we? So well done on taking part in this lesson, and I look forward to seeing you again soon.