Desertification: the process by which fertile lands are transformed into deserts through drought and erosion.

Greenhouse effect: the natural phenomenon by which atmospheric gases retain heat in the atmosphere.

Soil erosion: the natural phenomenon by which topsoil is removed; can be caused by rain, waves, currents, ice, river flooding and/or human activity.

Greenhouse gas: any gas molecule made up of more than three atoms. For instance, oxygen (O₂), carbon dioxide (CO₂) and methane (CH₄) are greenhouse gases. Greenhouse gases are one of the leading causes of global warming.

Photosynthesis: the chemical process by which a plant converts sunlight, water and carbon dioxide (CO₂) into energy (glucose) and oxygen (O₂).

*Translations/adaptations of definitions drawn from:
Villeneuve, C., Richard, F. (2007). Vivre les changements climatiques réagir pour l’avenir. Éditions Multimondes, Ste-Foy 450 p.



5.1 Question
How do trees help reduce greenhouse gases and counteract desertification?

Answer
The question aims to have students learn that the roots of trees and bushes hold the soil in place, thus diminishing the effects of wind- and drought-driven soil erosion, which transforms formerly fertile lands into deserts.

Students should also learn that plant leaves extract CO2 from the air through the process known as photosynthesis. In so doing, they absorb quantities of a greenhouse gas that has a significant impact on global warming.


5.2 Applying a scientific approach
Preliminary activities: work methods, taking notes on the computer

Individually or in groups, learn to apply a scientific approach by completing the sheet in Annex 5.2. Students will write the question (5.1), formulate a hypothesis (20 minutes), conduct research online (45 minutes), verify the hypothesis and draw conclusions (20 minutes), and present their findings to the class (30-60 minutes). Review the activity together and link with activities 5.3 and 5.4.

Annex 5.2: Scientific inquiry

The following two sites may be useful:
The role of trees in climate change
The benefits of urban trees


5.3 Photosynthesis
Explain photosynthesis

Annex 5.3: The role of leaves in photosynthesis

5.4 Soil erosion
Questions and answers on soil erosion

Annex 5.4: Soil erosion