Lesson video

Hello geographers, my name is Mrs. Griffiths, and today's lesson is all about factors that affect global biomes.

So that is ecosystems of flora and fauna, plants and animals around the world, and we're thinking why it is that they occur where they do.

Now, we can use things like satellite imagery, maps, GIS, and photographs to engage with this question, why is it that ecosystems occur where they do? So should we get started? Our outcome for today's lesson is I can understand how climate and local factors affect biome distribution.

I can understand how climate on the one hand and local factors affect biome distributions.

That's what I want you to be able to say by the end of the lesson.

Okay, so we have some keywords here.

Climate, altitude, and drainage.

Let's look at their definitions.

Climate is the average weather conditions, such as rainfall and temperature, recorded over a 30-year period.

Altitude is the height of land above sea level.

And drainage is the distribution, storage, and movement of water in the environment.

Now we'll be using those keywords throughout the lesson.

So our lesson is structured in this way, we have these two key questions to answer.

How does climate affect biome distribution? And then, how do local factors affect biome distribution? Let's start first of all with climate.

So how does climate affect biome distribution? Climate, as we know, is the average weather conditions, such as rainfall and temperature, recorded over a 30-year period in any given location.

And we can map different climate zones around the world.

Here we have a world map indicating different climate types using colour, and we actually grouped those different climate types under headings like tropical, dry, moderate, continental, and polar.

That's another way of organising those different climate types.

But first, what did I say climate was, can you remember? Pause the video and then press play when you need the answer.

That's right, C is the answer.

Climate is the average weather conditions recorded over a 30-year period, well done.

So when we look at this climate map that I showed you a moment ago, what other map does this map remind you of? Can you think of another world map that we've looked at that it might remind you of? You've maybe looked at with your teacher? What about this one? So this is a map of global biomes.

And when you look at those two maps, just focus on the colours for a moment, we can see there are some similarities in terms of the patterns going on within the continents.

Focus in particular on the Equator.

Have a look at where that equatorial climate is.

And then similarly where the tropical rainforest is on the right-hand side in that dark green colour.

So if we look at the pattern of climate and we look at the pattern of biome, they are both characterised by these latitudinal stripes.

This is because climate is the key factor, so the key factor that influences the distribution of global biomes.

So there's a similarity there for a reason.

So quick check for you then.

Compare these two maps and I want you to this time identify three areas where the climate pattern is similar to the pattern of biomes.

Pause the video, talk to your partner, and then press play when you have an answer.

Okay, so there are lots and lots of examples that we could come up with, but these are the three examples we had.

So if we look at North Africa and compare the arid climate of areas of North Africa to the area where the Sahara Desert occurs, there's a very obvious overlap there, isn't there? Also, take a look at Indonesia there.

Southeast Asia, large areas of Southeast Asia are characterised by tropical rainforest, and of course that's because it has an equatorial tropical climate.

And then thirdly, we have New Zealand as an area with a temperate maritime climate and it's characterised by temperate deciduous woodland.

I'm sure you had something similar or perhaps even better, well done.

Okay, so why is this, why is climate the dominant factor affecting the distribution of biomes? Well, the closer to the Equator an area is, the greater the concentration of the Sun's energy per square kilometre.

So let's have a look at that diagram.

Those solar rays, as they reach areas that are higher latitude, so closer to the North Pole there, are less concentrated when they reach the Earth's surfaces but more concentrated when they reach the Equator.

How does that work or why is that? Well, the curvature of the Earth's surface, remember the Earth is a globe, determines how concentrated or dispersed solar energy is when it reaches the Earth.

So the angle that the Sun hits the Earth means the solar energy is dispersed at higher latitudes.

However, at the Equator, the Sun's energy hits the Earth directly, so this solar energy is concentrated on a much smaller surface area than at that higher latitude.

Quick check for you then, true or false? Have a look at my diagram again.

Solar energy at A and B is equal.

But when this energy reaches the Earth's surface, it is more concentrated at the Equator.

Is that true or false? Pause the video, discuss that with your partner, and then restart it when you've agreed on an answer.

Now you may be telling me that is of course true, but can you explain why? Well, if you told me the curvature of the Earth means solar energy is more dispersed towards the poles and more concentrated at the Equator by comparison, you'd be absolutely right, well done.

Okay, so we've got this map of global biomes and we know that climate is the key factor that influences biome distribution.

What's the impact of climate in particular on plant growth? Okay, so on the distribution of the flora around the world.

So plants need temperatures over 5 degrees centigrade to grow.

Water is essential, plants grow best when there is year-round availability.

And then thirdly, sunshine hours and the intensity, as we've seen, of solar energy affect the rate of photosynthesis.

So climate in that sense is affecting the growth of plants, those biotic elements of the ecosystem, in three different ways there.

True or false, then.

Average temperature and the number of sunshine hours are the only key factors that influence the distribution of biomes.

Is that true or false? Pause the video.

Remember I'm gonna ask you why in a moment.

Now you might have said, well, that's false actually.

Can you explain why? So our explanation here says, "The availability of the water for plant uptake is the third climatic factor that influences the pattern, so precipitation is important." So we've got average temperature, number of sunshine hours, but they're not the only factors.

The availability of water is also important.

And I do hope that was your answer, I'm sure it was.

Okay, so tropical rainforest is generally found in areas with high annual precipitation and warm temperatures year round.

Take a look at where we find our tropical wet climate on that left-hand side climate map compared to our map of global biomes.

The pattern's very similar, isn't it? In areas with dry and/or cold season, trees are replaced by other types of vegetation such as grasses.

And I've got an example here for you highlighted where we have a semi-arid climate, so thinking about a dry season, also a colder season.

And similarly we get a vegetation which is termed temperate grassland.

So that's the biome that we're seeing in that location, in the interior of Eurasia.

Okay, quick check for you here.

What biome would you expect in a location with a very hot and dry arid climate? Pause the video, talk to your neighbour, and then press play when you think you have the answer.

And of course, if you said desert, you'd be absolutely right.

We have the example here showing the arid climate in the interior of Australia and Oceania there.

And of course we find the desert biome in the interior of that country too.

Well done.

Great answer.

Okay, so I mentioned GIS in the introduction to this lesson and Google Earth is a basic geographical information system.

It allows us to look at geographical data on a digital map.

Now here I've opened the layers tab in Google Earth and you can see that I have clicked on this button here so that we can see the grid lines that indicate latitude and longitude.

And remember we've just been talking about how climate and biomes have similar patterns in terms of what we might term latitudinal belts.

So the same biomes, the same climate being found a certain distance from the Equator.

So we're really interested in lines of latitude when we look at these patterns.

There are other things that you can do with Google Earth and here you can show that I've taken off the grid lines from my view of the Earth and what I've added is a layer of information that allows us to view the clouds, which indicates perhaps where precipitation might have fallen.

It's very clever here because what Google Earth does is it provides you an animation, try it yourself, of the last 24 hours of cloud movement.

With our still here, what do you notice about the location of clouds? Well, to me it's quite clear that there's very little cloud cover around the Sahara, within the African continent.

But where we find the tropical rainforest in Central Africa, we can see the clouds that are needed to provide this year-round heavy rainfall.

Quick check for you.

Using Google Earth to analyse where clouds are located may indicate.

Which do you think is true, A, B, or C? Pause the video and click play when you have an answer.

That's right, precipitation patterns.

So we can use Google Earth to analyse where clouds are located, which may indicate precipitation patterns, and as we've seen how important climate is for the distribution of biomes.

Oh, practise task for you here.

Question one, what would you expect the climate to be like in this location? And I want you to look really carefully at this photograph of this desert biome.

It's a place called Tamanrasset in Algeria.

We've got information about its location so we can see how far north it is from the Equator.

And I would like you to describe the temperature, tell me something about the sunshine and the level of precipitation.

So that's our first task.

But then I've got a second task for you.

So I'd like you to suggest how climate affects plant growth in the tundra biome in Norway, and secondly in the temperate deciduous forest biome in Poland.

And for each of these biomes I picked a single place, so Longyearbyen in Norway and Krakow in Poland.

And we've got those climate graphs.

A quick reminder then, we've got two Y axes for a climate graph and we're using bars to represent precipitation and a line to represent temperature and how it changes across the year.

I notice we've also got a bit extra information there about sunshine hours, so I'd like you to use that information to suggest how climate might affect plant growth based on what we've heard.

So pause the video, write up your answers, and then click play when you want to check them.

Okay, how did you get on? We had two quite different tasks there, didn't we? First resource we wanted you to interpret here was the photograph of Tamanrasset in Algeria.

How would you expect the climate to be in this location? Okay, so we had answers and this might link to your answers, that the temperature appears to be high.

So we can see very little cloud cover.

And given the height of the Sun, it does look like the temperature could be quite high in this location.

We've got that cloudless sky, which suggests the intensity of sunshine is high.

So there's a lot of solar energy reaching ground level.

And the amount of precipitation is low.

We can see that because of all that dry dust that's kicking up from the vehicles driving across the plain there.

So if you have something like that, great work.

Secondly, you were asked to suggest how climate affects plant growth in two different locations.

So if we take the example of Norway, Longyearbyen, which is in Svalbard, let's see what your answer might have included.

So we had, "Low temperatures and frozen soil water all limit plant growth, meaning no trees are found in this biome.

Vegetation is low to the ground, such as mosses and lichen." So those of you, some of you might remember that within the tundra biome, this biome is treeless, linked to the finish word for treeless plain meaning tundra.

Okay, so secondly we had, "With limited sunshine hours, plants must complete their entire life cycle in just a few months." So the climate having a huge impact on plant growth there in Svalbard.

And then 2B, you were asked to do the same thing but suggest how climate affects plant growth in Krakow in Poland, so within the temperate deciduous biome.

Your answer might include, well, we've noticed that there's a seven-month long growing season if we think about temperature being five degrees or above, and year-round precipitation, which might allow flowering plants and trees to thrive.

However, if we look at those temperatures again, soil water may freeze for three months of the year.

So think about that limiting plant growth.

Which along with low temperatures would mean that deciduous trees lose their leaves to conserve water and energy in winter.

And of course, the fact that trees effectively shut down for winter does affect the pace and productivity of those trees, of that flora in the deciduous forest biome.

So hopefully you had an answer a little bit like that using the different elements of information we had provided by the climate graph as well the information about sunshine hours.

If you did, brilliant.

Okay, second part of the lesson then.

We've got this second question to answer.

How do local factors affect biome distribution? So the pattern of Earth's major biomes is also shaped by altitude.

We know climate's important, but then altitude is important at a local scale.

What do you notice about areas where some of the world's highest mountains are found? Can you remember where they are? If I add the location of the Himalayas and the Andes there in South America, Izzy's noticed that the Himalayas in Asia and the Andes in South America look like they fall into a different category of biome.

And here it's given the title "other." Bit of a catchall title 'cause it also covers polar areas and areas of ice.

But yeah, it's certainly true that high altitude areas have their own specific biome.

So, altitude is a local factor that, for example, influences the treeline, which is the height above which trees can't grow.

And here in this image we can see trees in the foreground perhaps getting a little bit patchy, so we're close to the treeline, compared to the rocky landscape that's relatively bare in the background.

Altitude, as I said, is the height above sea level, and trees can't grow at high altitude for various reasons.

Firstly, the temperature drops really low and you can imagine the water in the soil there is frozen, so it's not available for trees to take up.

Secondly, the wind speed increases with altitude, so potentially blowing the tree over.

And thirdly, rainfall usually increases.

So the impact of that might be to remove the topsoil and to leave a bare rocky surface that a certainly a tree can't root into.

So, to label our diagram, no trees found at high altitude, but at lower altitude trees are able to survive on this steep slope.

Quick check for you.

Trees are more likely to grow at very high altitudes.

Is that true or false? Pause the video, talk to the person next to you, and then get back to me.

That's right, I can hear you saying that's false, but can you explain why? If you said at high altitude the temperature drops and the wind speed is high, making it really inhospitable for trees, reducing their growth and therefore their survival, you're absolutely right.

Okay, so that photograph we were looking at a moment ago was an area of Nepal in Asia called Annapurna, so we're in the Himalayas here.

And if we look at an image here from Google Earth, so it's an aerial view, it shows us how the pattern of vegetation varies with altitude.

So it's interesting, isn't it, we can really see the network of valleys, we can see how glaciers have shaped this landscape.

But we can also see that at high altitude we have snowy mountains without vegetation.

And we can also see at lower altitude we have valleys that are covered in vegetation, and those will be those conifers that we've seen already.

So that's altitude.

Here's another factor for you.

Local rock type affects soil growth, which in turn affects plant growth.

And we have an image here of orchids growing in a chalk meadow.

The process of weathering bedrock, so we're thinking about chemical, physical, and biological weathering, adds nutrients to the soil.

For example, affecting the pH of the soil.

In the Chilterns National Landscape where this photograph was taken, chalk grassland is a biodiverse habitat, so it's home to some of these rarer species.

And this biodiverse habitat develops on alkaline soils formed by the weathering of chalk bedrock.

So that chalk bedrock is a local factor shaping the type of flora and of course the fauna, the animals, that are found in this place.

How can you tell that this small-scale ecosystem is biodiverse? So we've got another photograph here of the Chilterns National Landscape and this is an example, this location is Prestwood Nature Reserve.

It's chalk grassland, how can you tell it's biodiverse? Have a look at that image.

Well, as Jun says, "The different coloured seed heads waving above the ground at different heights give us an indication of all the different wild flowers that are found in this location." I also like his point that he makes about the fact that it really contrasts with the landscape in the background, which is of course an arable field.

So we can see the real difference in the biodiverse foreground compared to effectively that monoculture in the background.

So a check for you here.

Which of these are local factors that affect biome distribution? Pause the video and have a think.

And if you said, well, A, local rock type, and B, altitude, are both local factors, you'd be absolutely right.

So two correct answers there.

Global climate zones are not a local factor, so those don't fit as a correct answer for this question.

Drainage is a third factor that affects the distribution of biomes at a local scale.

So drainage is defined as the distribution, storage, and movement of water in the environment.

It's a local factor which affects that pattern of biomes.

Some rock types are more permeable than others.

So I've got an example here for you of limestone pavement, and this is an area called Great Asby Scar in the Yorkshire Dales National Park.

Rock types with high permeability, such as limestone, can lead to sparse vegetation cover locally, as there's less water on the surface available for plants and the soil is very shallow locally.

So we can see the impact of that very shallow soil here with lots of bare rock in the image and just some grasses in between those bare rocks.

If we look at the same area in aerial view, so here we're looking at Google Maps here, an aerial view, we can see Great Asby Scar really clearly in terms of that expanse of rock really breaking up the vegetation cover.

What we notice is that limestone landscapes appear to have very few rivers when we look at them from the air.

However, there are rivers in this landscape, they're just underground, because the water drains underground in this permeable landscape.

This means, however, that there's less water available at the surface for plant growth.

Why do you think this kind of environment is called a limestone pavement? Have another look at that photograph.

It's a funny name, isn't it, limestone pavement.

Well, Sam's got an answer for us here.

She says, "There appears to be small areas of rock defined by deep fissures.

Perhaps this means the bare rock surface looks like it's made of paving slabs." Yeah, I think that's about right.

Okay, check for you here.

How does the limestone pavement affect the vegetation found in this area of the Yorkshire Dales National Park? Have a read of the answers carefully, pause the video, talk to a partner, and then press play when you want to hear the answer.

And if you said C, it allows water to drain away rapidly, limiting plant uptake, you're absolutely right, well done.

Okay, so I have a practise task for you now and it's called odd one out.

I want you to look at the rows of key terms below and I want you to pick out the odd one out thinking about what links the other three key terms. It's something to discuss with your partner or have a think about yourself.

And I'm going to need you to explain your choice of the odd one out in a moment.

So if we take A, for example, I want you to think about biome, drainage, altitude, and rock type.

Which three are linked in some way and which one is the odd one out? Pause the video but think about this task carefully, and then press play when you want to check your answers.

Okay, so if we take row A to start with, biome is the odd one out, but why? The other three terms are all local factors that affect the distribution of major vegetation belts, otherwise known as biomes.

Secondly, so looking at row B, treeline was the odd one out.

But what links the other three? Oh, well, the others are different aspects of the climate, all of which change with altitude and all of which help to define the treeline.

How did you do on that one? Okay, so let's have a look at C.

In this case, wind speed was the odd one out, but why is that? Wind speed isn't a key factor associated with the formation of chalk grassland, but the others are.

So we've got the chalk bedrock weathering to form an alkaline soil, and it's the pH of a soil that influence the plants that grow there.

Well done if you got that one, that was a tricky one.

Then lastly, if we have a look at D, deciduous forest is the odd one out.

And when we think about that limestone pavement, we were talking about drainage in limestone landscapes is predominantly underground.

So we've got that linkage there, meaning that the soil is shallow.

So the deciduous forest isn't the main type of vegetation that grows in this environment.

So the fact that water is underground, draining underground in a limestone pavement environment counts out the sort of deciduous forest isn't found in this landscape.

Well done if you've got all of those right, or perhaps you were able to explain those odd ones out but just in a slightly different way.

Well done to you.

Okay, so what have we covered today? We've covered a couple of key things really, haven't we? Climate largely determines the distribution of different global biomes as plant growth depends on the temperature, availability of water, and solar energy, i.

e.

the sunshine hours, and that intensity of sunshine received at the Earth's surface.

Within each biome there is local variation in the major type of vegetation due to factors such as altitude, rock and soil type, as well as drainage.

So we've covered quite a lot there, haven't we? Well done to you for working hard along with me.

I look forward to seeing you again soon.