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

Forests: Changes in the Land

Have you ever thought about how you would feel if the trees in your neighborhood suddenly disappeared?

Part A: Changes in Forest Cover




Discussion

Take a few minutes to examine the image of changes in Global Tree Cover Loss from 2002-2012.

  • Name five countries or regions that show higher losses in tree cover compared to other countries and regions? Does anything surprise you? Why?
  • Why do you think these countries or regions have higher losses?
  • What questions does this image raise for you? Think of as many as you can.
  • Why should we care about changes in forest cover - especially if these changes occur far away in other places in the world? Think of as many reasons as you can.



Millions of Trees Die in Texas! Severe tree cover loss can happen right in your own backyard. In 2011, Texas experienced its worst and most resilient drought in recorded history. The ongoing drought set the stage for a more active wildfire season as vegetation dried out. According to State Impact Texas over 3 million trees died from drought and related fires. These NASA satellite images show the burn scar from one of these drought-related fires in Bastrop, Texas in 2011. Over 34,000 acres burned. The false-color image (top left) shows a wide-area view of the fire. Vegetation is bright green, and sparsely vegetated or bare land is green-yellow. The burn scar appears in shades of red and orange. Far from uniform, the burned areas are separated by unburned expanses. The area outlined in white in the top image corresponds to the close-up view provided in the natural-color image (top right). Click to enlarge these images and take a minute to study them before moving on.

Discussion

  • What happens to the carbon stored in the 3 million trees that died due to the 2011 Texas drought?? Where will that carbon go?
  • Should Texas implement a reforestation project to replace these trees? Why or why not?

Causes of forest cover loss.

There are both natural causes and man-made causes of forest cover loss. Natural causes include events such as:


Wildfires out west: Climate Central

Wildfires

Not all wildfires are caused by the same environmental conditions. Watch "Wildfires out West" from ClimateCentral. As you watch, make note a note of the different environmental conditions that are involved in creating wildfires in Montana versus wildfires in Nevada.

Not all wildfires are bad for forest ecosystems. As a matter of fact, wildfires have always been a natural and important part of forest ecology. For example, after the 1988 wildfires that burned 1.2 million acres in Yellowstone National Park and surrounding areas, fire ecologists found that fires were important to lodge pole pine trees. Read or listen to the article Yellowstone Fires: Ecological Blessings.

NASA keeps track!

NASA uses satellites, aircraft and ground resources to observe and analyze fires around the world. This research helps scientists understand how fire affects our environment on local, regional and global scales. NASA has created a visualization from ten years of global fire surveillance data taken by the MODIS instruments on NASA's Terra and Aqua's satellites. Take a visual tour of a decade of fires created from these satellite measurements. As you watch, make note of the following:



Checking In

  • 1. Which of the following statements are true? Select all the answers that are true, and then click the Check Answers button at the bottom of the list.
    [INCORRECT]
    [INCORRECT]
    [CORRECT]
    [CORRECT]
    [CORRECT]
    [INCORRECT]
    [CORRECT]
  •   

    How does the carbon cycle respond to wildfires?

    Wildfires in Indonesia provide a clue to this important question. In 1997–98, the growth rate of carbon dioxide in the atmosphere doubled, reaching the highest on record. According to researchers studying the carbon cycle much of this increase in carbon dioxide emissions can be attributed to the forest and peat fires in Indonesia that began in 1997 and lasted into 1998. In addition to releasing higher levels of CO2, these fires spewed carbon-containing smoke particles (black carbon) and spread haze to nearby countries causing air pollution. By the time the 1997-98 forest fires were finally over, more than 8 million hectares of land had burned. According to the researchers, the amount of extra carbon the 1997-98 Indonesian fires pumped into the atmosphere was more than all living things on Earth remove from the atmosphere in one year! That's a lot of carbon!

    Although wildfires around the world differ from each other in a variety of ways, the processes that drive the carbon cycle will respond to wildfires, but at different time scales. They are:


    Activity and Discussion

    • Draw two conceptual model diagrams illustrating how the carbon cycle responds to wildfires at different time scales.

    Drawing 1 assumes regeneration of the forest will occur after the fire through natural regeneration and/or purposeful planting of trees.

    Drawing 2 assumes that no regeneration of the forest will occur after the fire.

    • Share your diagrams with each other and the rest of the class. After 100 years, how will atmospheric concentrations of CO2differ between the two models? Why?


    Deforestation: Permanent loss of forest cover


    If left to themselves, forests will regenerate over time. We can also plant trees to replace trees lost to fire and drought events such as the 2011 drought and wildfires in Texas. Deforestation is different. Trees are not replaced and the land is converted to a non-forest use. Examples of deforestation include cutting down forests and converting that land to cropland, cattle ranches, urban development, roads, and mining operations. Forests can also be cut down to provide wood to burn for cooking and heating. The largest and most direct cause of tropical deforestation is converting forested land to cropland or pasture for cows and other animals.

    Discussion

    Let's examine a well known example of deforestation. Haiti and the Dominican Republic share the same island. The NASA satellite image above shows the border between Haiti on the left and the Dominican Republic on the right. Click on the image to make it larger. Then, take a few minutes to carefully look at and think about the image you are viewing.
    • What difference(s) in forest cover can you observe in this satellite image? What is the evidence for the difference(s) you observe?
    • What do you think might be some contributing causes to the differences in forest cover between these two countries? List all that you can think of.
    • Share your ideas with the rest of the class.


    Basic stages of deforestation




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

    Next, watch the CNN movie Planet in Peril and then answer the Checking In questions below.



    Checking In

    1. What stage(s) of deforestation releases higher than normal amounts of carbon dioxide to the atmosphere? Select all the answers that are correct, and then click the Check Answers button at the bottom of the list.
      [INCORRECT]
      [CORRECT]
      [CORRECT]
      [CORRECT]
    2. Which stage(s) represents a carbon sink - Select all the answers that are correct, and then click the Check Answers button at the bottom of the list.
      [CORRECT]
      [INCORRECT]
      [INCORRECT]
      [INCORRECT]
    3. When deforestation occurs, which carbon cycle process(s) increase the emission of carbon dioxide to the atmosphere.?
      [CORRECT]
      [CORRECT]
      [INCORRECT]
    4. Which of these stages could contribute to soil erosion?
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    Up in Smoke: Fire, farmers and the carbon cycle.

    Slash and Burn Farming.

    Cutting down trees is only one part of the complex "carbon cycle" story in areas of deforestation. 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 often 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, soil nutrients, such as nitrogen 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!

    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 cycle that destroyed forests in order to create agricultural land that could be farmed only temporarily. Eventually, the land turned into a nutrient-deficient barren wasteland, farmers grew poorer and poorer and even more rainforest was cut down. Mike's ideas and efforts on stopping this vicious cycle of "slash and burn" have recently been portrayed in an award winning documentary Up in Smoke. If the full documentary is unavailable to watch, you can watch five video clips created by Oxfam from the documentary here. Then, work with a partner or a group to complete the task below.

    Model and Discussion


    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:

    Use your notes to create a model diagram 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 and the community that are part of this carbon cycle story.


    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.

    Global Forest Watch - Keeping track of forests in real time!



    At the beginning of this lesson, you examined a "Global Forest Watch" map to identify regions of the world that were experiencing forest cover loss from 2000 to 2012. You were also asked to think of some reasons why should we care about changes in forest cover - especially if these changes are occurring far away in other places in the world. Take a few minutes to revisit the list of reasons you made. Would you add any new reasons to your list? Why?

    World Resources Institute and their partners have collaborated to produce "Global Forest Watch" - a mapping application that unites satellite technology, open data, and crowd sourcing to guarantee access to timely and reliable information about forests. Governments, organizations, scientists and citizens all can use this mapping application to both generate questions and data related to those questions. Watch this short Global Forest Watch video to introduce you this powerful new tool. You will use this tool in a research task that is described below.


    Tropical Deforestation from NASA.


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