Lesson video

Hello, Mrs. Harking here.

Today, we're going to be exploring mangrove forests.

These are forests that actually grow in the sea.

I haven't made this up, I promise.

The trees actually grow in the sea water, so it's an interesting lesson with quite a unique type of forest today, and we will be looking at some photographic evidence and some examples to prove that I haven't made the whole thing up.

Today's lesson is Mangroves: forests of the sea.

It's taken from the unit Forest biomes: why are forests so important? Today's outcome is to be able to describe the role of mangrove forests and talk about the impact of forest loss in the Sundarbans, which is our case study for mangroves today.

Here are some keywords that we will be using in today's lesson, so it'll be helpful to know them before we begin.

If there's any that you're not sure about, feel free to pause the video at any point so you can jot them down.

Our first keyword is tide.

This is the regular rise and fall of the sea levels caused by gravity from the Moon and the Sun pulling on Earth's oceans.

Next we've got tropical storms. These are powerful low-pressure weather systems that form in tropical regions.

Then we've got tidal surges.

These are an unusual rise in sea level above the normal level of the high tide, so they can cause flooding.

Urbanisation is the increase in the proportion of people living in towns and cities rather than in countrysides, so we do end up with bigger cities when that happens.

Biodiversity is all the living things in an ecosystem or an area.

Bio is to do with biology, so anything living, and diversity is the range of different things we've got there.

Our lesson outline today breaks the lesson into two parts.

Firstly, we've got What are mangroves and why are they important? And then we're going to have a look at How does deforestation impact the Sundarbans? So first of all, what are mangroves and why are they so important? Here's a photo of a mangrove forest so you can see it is real.

The mangroves are a group of about 80 species of trees and shrubs that grow in tropical and subtropical warm coastal waters.

Time for a check for understanding.

Which image shows mangroves? Is it a, b, or c? Well done.

It's b.

We can tell it's b because you can see that sea water there covering the roots of the trees, whereas the other two examples, both the trees are growing on land.

Mangroves are shown on this map using the green shading.

They grow at the coast in some tropical and subtropical regions as they need warm waters to survive.

So we have no mangroves in high latitudes.

We have most mangroves between the two Tropics, the Tropic of Cancer and the Tropic of Capricorn and we see them in coastal locations, so they obviously won't be in land because they need that sea water there to be growing in, and they won't be in the middle of the ocean because it'll be too deep there for them to grow.

They'd be totally submerged.

Mangroves are found in coastal areas where the water level changes with the tides.

So remember we said the tides are when the sea level rises and falls each day thanks to the Sun and the Moon's gravitational pull on the ocean.

We've got here, "Mangrove roots are covered at high tides" in the photograph, and this happens with all mangroves, so you can't really see the roots there.

The tide has risen, so the seawater covers the roots all the way up to the trunk.

In this photograph here, the tide has fallen, and we can see the tree roots exposed.

So this is what it would look like at low tide.

Time for a quick check for understanding now.

Which location is most likely to have mangroves? Is it a, b or c? Well done, so a is far too far north.

The water would be too cold.

There's not going to be any mangroves there.

b is not on the coast.

There's not going to be any seawater for those mangroves trees to grow in, so that is not an option either.

c is our correct answer.

It's on the coast, and it's just about within the Tropics, so it's a likely location for mangroves.

So mangroves act as a carbon sink, an important habitat, and they prevent soil erosion.

This is just the same as other forests as well, but mangroves do specifically provide coastal flood protection, act as a safe nursery for marine species, and provide resources for coastal communities.

So these are unique to mangroves, these features.

Many coastal areas are very vulnerable to flooding, and this might be from tropical storms or tidal surges, and actually, mangroves can help protect the land behind from these floods.

So they do this because the roots and the branches slow the waves down, and they, therefore, reduce the destructive energy of the waves.

This can be really beneficial to the community living behind and near the mangroves and also for the ecosystem surrounding as well because less damage is done.

Mangroves are also beneficial because they provide a safe nursery for the young of many species of fish and also other animals.

The tree roots protect the young from predators, waves, and the strong currents.

A great thing to add to your wishlist would be to snorkel and see fish swimming through the roots of these trees, which is a really unusual thing to see and a great experience.

Our third reason why mangroves are important is that many coastal communities benefit from the mangroves.

They might benefit as a source of wood and food.

The fishing industry relies on fish which mature in the mangroves, and tour guides earn a living from mangrove tours as well.

The Sundari tree is a great example of a tree that is used by local communities.

The wood from this tree is very strong.

It's water-resistant and also resists termites, which means that they can use it really well to produce furniture, in construction, and also to build boats.

They also use the bark from these trees to treat certain health conditions, and then also, they use the wood as firewood as well.

So just one tree can do so many different things and have many beneficial properties.

Time for a check for understanding now.

How do mangroves reduce flood risk? Is it a, mangroves slow waves down and, therefore, reduce their destructive energy, b, flooding is more likely in areas where there are mangroves as they are located in coastal regions, or c, no storms hit areas with mangroves as they act as protection? Well done.

It's a.

So mangroves slow waves down, and, therefore, reduce their destructive energy.

Storms do hit areas with mangroves, but the mangroves protects the land behind from those storms by reducing their energy, so c is incorrect.

The Sundarbans in India and Bangladesh are an example of a mangrove forest.

You can see we've identified where this is on the world map here, and we've seen then the circle shows where this forest is.

The Sundarbans are named after the tree the Sundari, which is prevalent in the Sundarbans Forest.

It covers over 10,000 kilometres, and that is the same as more than six times the size of London, so it's vast.

It's the largest mangrove forest in the whole world.

Quick check for understanding now.

The Sundarbans mangrove forest are located in, which two countries is it? Well done.

Did you get them both? India and Bangladesh.

Brilliant work.

For our practise task now, we've got four questions to cover.

Firstly, what are mangroves? Can you write me a sentence to tell me that? Secondly, select the correct answers to complete the sentence.

So mangroves grow, is it inland or at the coast? In some, is it tropical and subtropical, or is it arctic regions? They need warm or cold waters to survive.

You need to pick the correct answer out of each of those options and make sure you've only recorded the correct answer.

Question number 3, where are the Sundarbans? Question number 4, list four reasons why mangroves are important.

You could do that in bullet points.

It would be a good way to approach that question.

Right, pause the video now so that you've got sufficient time to do this really well.

Well done, everyone.

Let's have a look at some answers.

Your answers may look like this.

They might look a little different.

You may want to edit them to make sure that you're improving them as we go.

Firstly, what are mangroves? So mangroves are trees and shrubs that grow in sea water on the coast.

When the tide is high, the roots are covered, and fish can swim between them.

Question 2, mangroves grow at the coast in some tropical and subtropical regions.

They need warm waters to survive.

Question number 3, where are the Sundarbans? So the Sundarbans are located on the coast of parts of India and Bangladesh and are the largest mangroves in the world, covering 10,000 square kilometres.

For question number 4, I asked you to list four reasons why mangroves are important, so your potential answers could be coastal flood protection, important habitats and a safe nursery for many species, provide resources and an income for local communities, act as a carbon sink, and prevent soil erosion.

Excellent work, everyone.

Let's move on to having a look at the second half of our lesson now.

So how does deforestation impact the Sundarbans? This animation is taken from satellite images, and it shows us the change in the Sundarbans from 2014 to 2023.

In this particular part of the Sundarbans, we can see that there's been some forest loss.

Mangroves are among the most threatened habitats in the world.

The risks to mangroves include coastal developments, so for example, urbanisation and tourist resorts can cause deforestation of mangroves.

Many cities are on the coast, so if there is urbanisation which leads to the growth of cities, that can mean that more areas by the coast have to be cleared in order to make space for buildings.

Particularly tourist resorts can be a problem because tourist often would like to see a beautiful sandy beach, and they would like to spend their time on that beach, and that means that many mangrove forests have been cleared in order to make way for some beautiful beaches, such as the one we can see on the image here.

Our second risk is farming.

So shrimp farming requires clearing of mangrove forests, and this can happen on the coast.

Remember, farming doesn't just happen on land.

It happens in the sea as well.

And then our last one is sea level rise, so sea level rise due to climate change can submerge the trees entirely and kill them.

So yes, we can have trees growing in the sea, but they cannot be fully submerged.

If they're fully submerged, they won't survive.

Time for a quick check for understanding.

Can you name one of the risks to mangroves? Well done, so we've got coastal developments, farming, or sea level rise.

Which one did you get? Great work.

The Sundarbans are a UNESCO World Heritage Site, which means they are protected.

However, they're still at risk, leading to many impacts.

Many species will be threatened as habitats, including important nurseries, are destroyed.

This leads to the loss of biodiversity.

A loss of biodiversity means the loss of the number and variety of animals and plants.

A loss of mangrove forest also means more coastal flooding, so some people may lose their homes and be forced to move elsewhere.

Sofia asks, "But why would the coastline flood more?" Lucas answers, "The mangroves prevent flooding by reducing the energy of waves.

If mangroves are cut down, they can't do that anymore." Can you remember that from earlier on in the lesson? Lucas has remembered.

A loss of mangroves means a loss of resources and income.

Jun has asked, "But what resources were people getting from the forest anyway?" Can you remember from the beginning of the lesson? What resources were people getting from the forest? Laura remembered too, said, "They get lots.

People get words and feed.

For example, they would be less fish to catch if there are no mangrove nurseries for the young fish to grow up in." Well done.

Right, time for a check for understanding.

Which best describes the impacts of mangrove loss for the Sundarbans? Is it a, more coastal flooding due to the loss of mangrove trees from the coastline? Is it b, more coastal flooding, a loss of biodiversity, resources, and income, or is it C, more coastal flooding, biodiversity, resources, such as wood, and income? Which one is going to happen if mangroves are cut down, if mangroves are lost? Well done.

Well done.

It's B, more coastal flooding, a loss of biodiversity, resources, and income.

So not a positive outcome.

Task time now.

Can you complete the flow diagram to explain the causes and consequences of changes to mangrove forests? So here on the left-hand side, we've got causes, for example, coastal developments.

Can you name two other causes on the bullet points there, and what does this lead to? So the consequences on the right-hand side, we've got more coastal flooding.

What other consequences were there at those? Question 2, you have to give a tour showing the impacts of mangrove forest loss to a group of tourists visiting the mangroves in the Sundarbans.

What will you tell them on your tour? Pause the video now so you've got sufficient time to complete your task.

Well done, everyone.

Your answer might look like this.

So for your flow diagram, you've got causes on the left, so you might have added farming and sea level rise.

And on the right-hand side we've got consequences, so more coastal flooding, loss of biodiversity, loss of resources and income.

For question 2, your answer might look something like this.

It might look very different, and that's absolutely fine, but feel free to take anything from here to improve your own answer.

Forest loss has a negative impact on the Sundarbans.

There's a greater risk from coastal flooding, from tropical storms and tidal surges, because mangrove roots and branches slow waves down and reduce their energy, so without a forest there that won't happen.

The biodiversity in and around the mangroves will also reduce as mangroves provide a safe nursery from many species.

Young are protected from predators, waves, and strong currents by the tree roots.

Coastal communities and industries may lose important income and resources that they rely on the mangroves for, for example, wood, food, and fish.

Summary time now.

Here are the key takeaways from today's lesson.

Mangroves are shrubs and trees that grow in coastal waters.

Mangroves help protect the land from flooding caused by tropical storms and tidal surges.

The Sundarbans in India and Bangladesh is one example of a mangrove forest.

Mangroves face a variety of threats, including coastal developments, farming, and sea rise.

The impacts of mangrove loss include coastal flooding, loss of biodiversity, resources, and income.

I hope you enjoyed learning about mangroves today.

I certainly did, and I'm looking forward to seeing you next time.

Thank you.