Deforestation and the Carbon Cycle
Part A: Changes in Forest Cover
Forests influence climate
- 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
- 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
- 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).
Stop and Think
1: Describe how deforestation can impact the the amount of carbon dioxide in the atmosphere.
Trouble in the Amazon?
- 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.
- Next, listen to scientist Bruce Pengra in the video Amazon Deforestation, describing what the satellite images are revealing.
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.
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!
- 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.