TEACHER: The topic for today's class is land as a resource.
Land, water, trees, oil…these are all resources, and as future environmental scientists,
you need to understand how to manage these resources.
As the world population increases,
managing land resources will become a greater priority.
Land is a limited resource.
Today I'm going to divide the lecture into two parts.
First we'll look at some of the factors contributing to pressures on the land we have,
and then I want to turn to some of the ways
people worldwide are trying to address land problems
and meet the needs of future generations．
Think of it as first the bad news, then the good news.
Let me start by saying there is less good productive land now
than there was even ten years ago. By productive land I mean land that is fertile,
that we can use to grow food and raise animals.
Each year more and more land becomes degraded.
We are losing productive land. Worldwide, new dry areas are developing and expanding.
This is happening on every continent except Antarctica.
I don't mean existing deserts like the Sahara are getting bigger.
I'm talking about new dry areas, areas where land has been declining in quality.
You can see these areas in the map in your book.
Why are these areas forming and expanding?
What do you think? Theresa?
STUDENT 1：it's the climate, isn't it?
the earth is getting, you know, hotter because of global warming.
so water gets evaporated and the land dries out.
TEACHER: OK. Marcel, do you agree?
STUDENT 2: Well, yeah. It has to be the weather. What else could it be?
TEACHER Well, different reasons have been given.
Some people contribute it to global warming or to climate changes.
They say nature simply produces dry regions, like the Sahara Desert,
as well as wet regions, like the Amazon Rainforest….Well,
let's think about this. Is it only the weather?
Let's see if there are other factors contributing to this trend.
Is nature, or the weather, really the problem?
According to a large group of scientists, the weather isn't the main factor.
Instead, they say, people are the main factor.
When they say people are the main problem,
they mean people's actions—how people use and manage land.
Poor land management, overpopulation, poor farming techniques,
too many animals, and so on, can all affect the land.
Look at the chart in your book. As you can see,
researchers have identified several ways human activities contribute to the problem．
The first is overgrazing by farm animals.
They say about 35 percent of the loss of productive land
is due to overgrazing by farm animals.
The second is overcutting of trees, which leads to about30 percent of the loss.
And lastly, 28 percent of the loss of good land is from methods of farming.
Overgrazing, overcutting, and farming methods. Let's look at these one at a time.
The first is overgrazing.
Good topsoil is lost or damaged because of overgrazing by farm animals.
Overgrazing means the animals eat too many of the plants.
There are several bad results of overgrazing.
First, there aren't enough plants left to hold the soil in place.
Then, the topsoil is eroded by wind and rain; they carry it away.
Second, as the animals walk around, the soil is compacted, and gets very hard.
If the soil is too hard, rainwater isn't absorbed into the soil,
and this causes the soil to stay dry and warm.
As the soil gets drier, even fewer plants can grow.
This, in turn, causes the animals to walk around more and more,
in order to find enough food to eat.
And, this causes the ground to get packed down even more,
and get even drier, and so on. So, you can see that overgrazing can create this cycle.
Second, overcutting of trees also contributes to the loss of good land.
The main problem is too many trees are cut and not replanted.
For years we've heard about how this is happening
on a large scale in the Amazon Rain Forest in Brazil.
Trees, like land, are a resource we depend on.
They're vital to the whole environmental balance on earth.
If trees are cut down and not replanted, there is nothing to hold the good soil.
Wind and water carry the good soil away and it erodes quickly,
leaving land that is dry and less productive.
So, overcutting is another reason why land quality is declining.
Third, farming methods are another big factor.
In some places, traditional methods
that have been used for hundreds of years no longer work well.
Why do they no longer work well? Partly because the population is increasing,
and farmers aren't equipped to meet these new demands,
and partly because the soil is getting worn out.
More people need to be fed from less land.
As a result, some farmers may use too much fertilizer on the limited land they have,
or not let the land rest from year to year, causing it to become less fertile.
Irrigation is a huge factor many of us don't think about.
Irrigation water often has salt in it, and when the salt builds up in the soil,
the soil can no longer be used for farming. Currently,
about one third of the irrigated land in the world has too much salt in it.
Irrigation has taken a heavy toll on good land.
So, basically, how people use the land seems to be a bigger factor
in the decrease of productive land than weather.
Of course, weather extremes, like no rain or too much rain,
can add to the problem. However, the weather is not the main reason fox the problem.
Some of the extremes in the weather caused
by global warming can make the situation worse for people who live in these dry areas.
But the weather alone is not the main issue.
The decline of productive land is a worldwide problem. Currently,
about one third of the world's land area is considered unproductive
because it is too dry and damaged.
OK, so that's the bad news. Now let's turn to the good news.
What are countries doing to help preserve land as a resource?
As experts learn more about this worldwide problem,
they have tried to find ways to address it. Right now there are several organizations,
the United Nations for one, that are working to help people.
They try to help countries or communities look at their specific problems
and figure out what possible changes they can make to protect their land.
They talk to people about their farming methods, their animals,
and how they use trees and other resources.
Then they suggest changes that might alleviate some of their problems.
Farmers might try to grow genetically engineered crops
that don't hurt the soil as much; or plant new trees，
or raise fewer animals, or build new irrigation systems that leave less salt in the soil.
They look for local solutions that will work best for that country.
This includes looking at what has been done traditionally
and implementing modern farming methods in ways that respect the local culture.
So, let's review what we covered today. I mentioned
that about one third of the available land worldwide has become dry and less productive.
The main reason for land degradation is people's actions,
including overgrazing by animals,
overcutting of trees, and farming methods. As scientists learn more,
we need to work to help countries make specific changes
and for farmers to become better equipped
so that they can preserve the good land that is left.
Let me just add that if we look at the estimates of
what the world population will be fifty years from now
—about 9 billion people—it helps us see
that protecting the good land that's left needs to be a high priority.
I'll stop there. We'll continue with this next class. That's all for this afternoon.