EarthLabs > Climate and the Carbon Cycle: Unit Overview > Lab 4: Forests - Changes in the Land > Lab 4A: Deforestation: Changes in Forest Cover

Forests: Changes in the Land


Part A: Deforestation: Changes in Forest Cover

Examine the image of changes in forest cover on the right. In the past, much of the Earth was once covered by forests. However, the majority of these forests were cleared long ago to make way for a growing human population. This is particularly true in regions with a temperate climate such as Britain and other parts of Europe where agriculture took an early hold. Interestingly, the World Wide Forest Report found that when the Roman Empire was in control of Europe, 90% of the continent was forested. Today, as indicated in the image on the right, Western Europe has now lost over 99% of its primary forest.

Forests and climate:

Forests play an integral role in the Earth's climate. Tropical, temperate and boreal forests each have varying impacts on the climate by both cooling and warming the Earth. The relationship between forests, climate and the carbon cycle is currently an area that scientists are intensively studying.



Deforestation: Causes and stages

If left to themselves, forests impacted by natural events such as wildfires will regenerate over time. Forests can also be restored by reforestation and afforestation Reforestation and afforestation both refer to planting trees on non-treed land. Reforestation refers to reestablishing forest on land that had recent tree cover, whereas afforestation refers to land that has been without forest for much longer. projects. Deforestation is different. When land is deforested, trees are not replaced and the land is converted to a non-forest use. For this reason, deforestation has long term effects on the carbon cycle, climate and the environment. Watch CNN Explains Deforestation to learn about:

Next, click on this link to view the basic Stages of Deforestation. As you view these stages, think about following:

Stop and Think

1. Describe how deforestation can impact the the amount of carbon dioxide in the atmosphere.


Trouble in the Amazon?

When we think about the Amazon Rainforest being cut down, we might immediately think of a tragic loss of biodiversity. However, as indicated in the NASA image on the right, there are massive amounts of carbon stored in the biomass of the Amazon Rainforest.

NASA has used satellites to track changes in tropical forest cover. Click on NASA's time series interactive Forest changes in Rondônia, Brazil to examine satellite images of deforestation from 2000 to 2012. In the times series interactive, you can:

Discussion

In terms of the carbon cycle, explain why deforestation in the Amazon is a global concern and not just a regional concern for the Brazilians.

Mini-Case Study: Using Sustainable Farming to Stop a Vicious Feedback Cycle of Slash and Burn Farming in Honduras.

Cutting down trees is only one part of the complex "carbon cycle" story in areas of deforestation. What happens to the land left behind? Answers to this question are often dependent on the local economy and the needs of small communities to provide for their families.

In many parts of the world, small farmers and ranchers use a very old technique called "slash and burn" to clear and prepare the land for agriculture and cattle. In slash-and-burn agriculture, farmers will typically cut forests months ahead of the dry season. During the dry season, the "slashed" trees dry out and are then burned. The ash from the burned trees fertilizes the soil to support crops such as as rice, corn and soybeans and grass for cattle. Unfortunately, soil nutrients such as nitrogen are used up fairly quickly, the land becomes barren and farmers then move on to slash-and-burn other parts of the rainforest. In this way, fire and soil become part of this complex carbon cycle, the economy of the rainforest and the people who live there. So, what can be done to mitigate the impact of slash and burn farming on the carbon cycle? Read about the work of Mike Hand, a British ecologist, and Inga trees to find out!

Mike Hand, a British ecologist, has lived in and studied the rainforests in Honduras for over twenty years. He observed that slash and burn was creating a vicious feedback cycle that destroyed forests in order to create agricultural land that could be farmed only temporarily. Eventually, the cleared land turned into a nutrient-deficient barren wasteland, farmers grew poorer and poorer and then farmers cut down more rainforest. Mike's ideas and efforts on stopping this vicious feedback cycle of "slash and burn" have recently been portrayed in an award winning documentary Up in Smoke.

Activity:

With a partner or group, watch this PBS Newshour special: Up in Smoke Film Examines Perils of Slash and Burn on YouTube. You can also access this video on the PBS Newshour website As you watch, take notes that will allow you to compare and contrast the "slash and burn" farming method with the sustainable "crop alley" farming method in terms of:

showShow me other ways to watch

  • If available, you can watch the full Up in Smoke documentary.
  • You can watch 5 video clips created by Oxfam and The Guardian from the "Up in Smoke" documentary.

Discussion

In what ways does deforestation impact local people and their economies?

Stop and Think

2. Think about the complex story of deforestation, slash and burn agriculture and the carbon cycle in the Central American and Amazon rainforests. Describe how deforestation, combustion and decomposition all impact the amount of carbon dioxide in the atmosphere.


Extensions (Optional)

Research the latest research! New research on the carbon cycle, climate and the environment is on-going. You can use ScienceDaily and Phys.org to research recent research on deforestation by using combinations of the following tags: deforestation, afforestation, reforestation, carbon, carbon cycle. As you discover and read more recent research, how does this research inform what you have learned so far about the carbon cycle in this module? Here are two examples:

Deforestation is Messing with our Weather and War, Plague no Match for Driving Up CO2

Readings on deforestation, reforestation and afforestation:

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