Introduction
The image below shows acres of forest in Mexico being cut down and burned to make way for agricultural land.
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Approximately 50% of a tree’s weight can be traced back to carbon that originated from atmospheric carbon dioxide. What happens to this carbon when forests are cut down to make way for agriculture and cattle farming, or simply to feed a family.
Changes in Forest Cover
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Examine the image of changes in forest cover, pictured above. 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 the needs of 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 land. Today, as indicated in the image on the right, Western Europe has now lost over 99% of its primary forest.
Forests influence climate
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Forests play an integral role in 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.
Forests have a cooling influence on climate by absorbing CO2 from the atmosphere and storing that carbon in their leaves, wood, and roots.
Tropical and temperate forests both have cooling influences on the climate via their strong evaporative cooling rates. Increased evapotranspiration tends to cause clouds to form low in the atmosphere, reflecting the sun’s warming rays back out into space. (G. Ban-Weiss et. al, 2011)
Forests can have a cooling or warming influence on climate based on their albedo effect. For example, the Boreal Forest in the northern latitudes is darker than the surrounding terrain and absorbs the Sun’s energy more easily. This leads to a warming influence on climate in that region.
Causes and stages of deforestation
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 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.
A. Watch CNN explain deforestation in the video below. As you watch, make note of the following:
the causes of deforestation
the impact of deforestation on the carbon cycle and the environment
B. View the basic Stages of Deforestation . As you view these stages, think about following:
Undisturbed forests absorb and store more carbon via photosynthesis than they release via cell respiration.
Trees that have been cut down no longer absorb CO2 from the atmosphere via photosynthesis.
Trees that are burned release CO2 to the atmosphere via combustion.
Trees left behind to decompose emit CO2 via the process of soil microbial respiration.
Agricultural land created from deforested areas emits CO2 to the atmosphere via increased respiration and diffusion from soil that has been turned over (tilled).
Discussion Question:
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 below, there are massive amounts of carbon stored in the biomass of the Amazon Rainforest.
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Click on NASA’s time series interactive Forest changes in Rondnia, Brazil to examine satellite images of changes in tropical forest cover from 2000 to 2012. In the times series interactive, you can:
Click on the arrow to start the time series to look at forest changes over time.
Read the text that accompanies this interactive.
Discussion Question:
2. 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.
3. In what ways does deforestation impact local people and their economies?
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