Forests: Changes in the Land
Part A: Forests: Wildfires and Deforestation
Why care about forests and the carbon cycle? With your partner, group or class, list as many reasons as you can.
If an average healthy tree absorbs about 13 pounds of carbon per year, imagine how much carbon an entire forest can absorb! But, what happens to the carbon in that forest if many of its trees are cut down to make way for agriculture, farms, cattle ranches, and housing developments? To find out where deforestation is happening in the world, examine the Deforestation Hot Spot Map on the right. Take some time to explore the map and then answer the Checking In questions below.
Checking InCheck your understanding of the map graphic above by using the questions below. Select all the answers that are correct, and then click the Check Answers button at the bottom of the list.
In this next section you will consider forests in Latin America and the Amazon.
Trouble in the Amazon?
Deforestation. Credit: Jamie Dwyer
Because the Amazon forest is so large and so much carbon is stored there, deforestation in this region concerns us all. The larger the forest, the greater its impact on the carbon cycle. What impact will deforestation have on the Amazon Rainforest and its ability to remain a strong carbon sink? To help you answer this question, read a NASA article on deforestation in Rondônia, Brazil. Then, use the interactive timeline at the beginning of the article to view changes in forest cover from 2000 to 2010 taken by NASA's MODIS.
- By 2003, how many square kilometers had been cleared from the Amazonian Forest in Rondônia? How many acres would that be? Use the metric conversion website to help you answer that question. 67,764 sq kilometers = 16,744,849 acres.
- One acre of forests can absorb approximately one ton of carbon dioxide
from the atmosphere each year. If deforestation has cleared 16,744,609
acres in just Rondônia, how many less tons of atmospheric
carbon dioxide will be stored in the trees every year?16,744,609 tons of carbon dioxide
Stop and Think1. Describe how deforestation can impact the the amount of carbon dioxide in the atmosphere.
Up in Smoke: Fire and the Carbon Cycle.
Cutting down trees is only one part of a complex "carbon cycle" story in the Amazon rainforest. When rainforest trees are cut, burned, or left to decompose, what happens to the carbon contained in those trees? What happens to the land left behind? Answers to this last question are dependent on the local economy and the needs of small communities to provide for their families. 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, the nutrients in the soil are used up fairly quickly, the land becomes barren and farmers 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!
The Task: Watch the five Oxfam short videos, or the documentary, linked above. As you watch, take notes that will allow you to compare and contrast the "slash and burn" farming with sustainable "crop alley" farming in terms of:
- Impact on the community
- Pros and cons of each method
- Impact on the carbon cycle
Use your notes to create a diagram, poster or a story that describes how the carbon cycle differs when "slash and burn" methods are used versus sustainable "crop alley" methods. Describe as many changes to the carbon cycle that are part of this story.