Deforestation and the Carbon Cycle

Part A: Changes in Forest Cover

Examine the image of changes in forest cover, pictured 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 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

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 CO₂from 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. the combination of the evaporation and transpiration processes in plants, both of which release moisture into the air; water is drawn up by the roots into the plants and some of this water evaporates from the leaves. 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 a measure of the reflectivity of a surface ranging from 0-1; light surfaces reflect more sunlight and do not warm as much as darker surfaces which absorb sunlight. 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 reforestationreestablishing/planting forest on land that had recent tree cover. and afforestation refers to land that has been without forest for a very long time. 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.

1. 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
2. Next, 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).

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.

1. Click on NASA's time series interactive Forest changes in Rondônia, 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.
   • When in the pause mode, click on the "view large" tab on the right. Once the large view comes up, you can click on sections of the image to get a closer look at forest changes.
   • Read the text that accompanies this interactive.
2. Next, listen to scientist Bruce Pengra in the video Amazon Deforestation, describing what the satellite images are revealing.

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" were portrayed in an award-winning documentary Up in Smoke.

Activity:

1. With a partner or group, watch this PBS Newshour special:
   
   Up in Smoke Film Examines Perils of Slash and Burn.
   
   You can also access this video on the PBS Newshour website.
   Show me other ways to watch
   Hide
   • You can watch these 3 video clips created by Oxfam and The Guardian from the "Up in Smoke" documentary. Part 1, Part 2, Part 3
2. 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:
   • Impact on local people and their economies
   • Pros and cons of each method
   • How the carbon cycle responds to each method.

Optional Extensions

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:

• NASA article on Tropical Deforestation
• National Geographic article on Tropical Deforestation
• China's Reforestation Project Program: Big Success or Just an Illusion?