Wind Dynamics and Forests

In this activity, students will set up a model forest using plastic bottles to observe changes caused by differences in wind speed and differences in forest density. An extension to the activity will allow students to explore the concept of evapotranspiration.

Background

While we often think of climate as a non-biological factor that influences ecosystems, changes in the structure and distribution of living organisms in an ecosystem can, in fact, have profound climate effects both regionally and globally.

Changes in vegetation affect regional atmospheric phenomena, including rainfall and evapotranspiration as well as convection and winds. It is well documented that vegetative changes due to human activity have led to significant climatic consequences. For example, desertification increases the albedo (reflectivity) of the land surface, further reducing local rainfall.

Changes in vegetation reflect and influence the interaction of the land surface and the atmosphere. In this exercise, students explore this powerful but often unexpected interaction by using a simple model of a forest under different wind conditions.

In this activity, students will set up a model forest to observe changes caused by differences in wind speed and differences in forest density. An extension to the activity will allow students to explore the concept of evapotranspiration.

Learning Goals

1. Students will understand that living organisms in an ecosystem can have profound effects upon the local atmosphere.
   
   
2. Students will understand that changes in vegetation can have profound effects upon wind speed.
   
   
3. Students will understand that models are useful to researchers in understanding the shaping of ecosystems.
   
   

Alignment to National Standards

National Science Education Standards

• Unifying Concepts and Processes, Grades K to 12, pg. 117: "Models are tentative schemes or structures that correspond to real objects, events, or classes of events and that have explanatory power."
  
  
• Earth and Space Science, Structure of the Earth System, Grades 5 to 8, pg. 160, Item #11: "Living organisms have played many roles in the earth system, including affecting the composition of the atmosphere, producing some types of rocks, and contributing to the weathering of rocks."

Benchmarks for Science Literacy, Project 2061, AAAS

• Common Themes, Models, Grades 6 to 8, pg. 269, Item #1: "Models are often used to think about processes that happen too slowly, too quickly, or on too small a scale to observe directly, or that are too vast to be changed deliberately, or that are potentially dangerous."
  
  
• The Physical Setting, Processes That Shape the Earth, Grades 6 to 8, pg. 73, Item #7: "Human activities, such as reducing the amount of forest cover, increasing the amount and variety of chemicals released into the atmosphere, and intensive farming, have changed the earth's land, oceans, and atmosphere. Some of these changes have decreased the capacity of the environment to support some life forms."
  
  

Grade Level/Time

• Grade level: 6 to 9
  
  
• Time:
  
  
  • Introduction: 20 minutes
    
    
  • Set-up: 15 minutes
    
    
  • Student activity and discussion: 30 minutes
    
    

Materials

Main Activity

• 24 empty 1- or 2-liter plastic soda bottles
  
  
• 8-foot table (or larger)
  
  
• Sand
  
  
• Fan
  
  
• Wind meter (can be obtained through science supply catalogs)

Extension activity

• Paper towels
  
  
• Spray bottle filled with water
  
  

Procedure

Main activity

1. Pour about 2 inches of sand into each soda bottle.
   
   
2. Arrange the bottles on a table in eight staggered rows, three bottles in each row with each row approximately 12 inches apart. The bottles represent the "forest."
   
   
   
   
3. At one end of the table, place a fan on a stool level with the table.
   
   
4. Place a wind meter level with the table at the opposite end from the fan.
   
   
5. Turn the fan to low and record the wind reading. Record the wind reading at tabletop (ground level), at approximately six inches above the table (mid-canopy level), at the top of the bottles (top of the canopy), and slightly above the bottles (above the canopy).
   
   
6. Turn the fan to a higher level and record.
   
   
7. Remove eight bottles, simulating a selectively cut timber operation.
   
   
8. Repeat steps 5 and 6.
   
   
9. Randomly remove eight more bottles and repeat steps 5 and 6.
   
   
10. Remove the remaining eight bottles and again repeat steps 5 and 6.

To make the 'forest' more realistic, you may use different sized bottles to represent different ages or species, although the activity works just as well representing a 'monoculture' forest.

Observations and Questions

1. Make a table of the results for wind speeds at various levels in the forest when the forest was dense and undisturbed.
   
   
2. Make other tables for each stage of cutting, for example, one third of the trees removed, two-thirds of the trees removed, and all the trees removed.
   
   
3. Graph the results. You might have the students divide into groups with each group graphing a different portion of the data.
   
   
4. Have students compare their graphs and then discuss the significance of the experiment. What does the experiment show?
   
   
5. What might be done to improve the model used?
   
   
6. What other environmental parameters might also show changes as a forest is cut?

Extension

Evapotranspiration from a vegetation canopy is also strongly influenced by wind pattern and direction. Following the wind speed activity, you may wish to simulate a moist forest canopy by:

• Draping paper towels over the bottles
  
  
• Spraying them lightly with water from a spray bottle
  
  
• Observing the pattern of drying that develops as you change wind speed and direction, and/or as you simulate progressively greater levels of tree harvest as described above

This would perhaps best be done as a 'quick and dirty' qualitative analysis of drying levels (which paper towels are completely dry, which remain wet, which are partially dry).

Following the activity, discuss with the students the implications of greater or lesser

• Soil moisture
  
  
• Water supply for the plants
  
  
• Moisture in the air over the forest and downwind

Assessment Ideas

Ask students to imagine a rainforest with frequent rainfall, abundant water, and a low wind speed within the canopy (where most of the plants and animals live). Either by timber harvest or disease, trees begin to disappear. Create three labeled graphs to illustrate how the environment within the original forest might change with the loss of trees.

• Graph A will show wind speed changes
  
  
• Graph B will show changes in evapotranspiration
  
  
• Graph C will show changes in average rainfall over the forest

In a paragraph, explain the significant changes illustrated by each graph.

Modifications for Alternative Learners

• None needed.