Lesson Plan

Wind Dynamics and Forests

Coniferous treeline
The Alaskan tundra is a windy place -- how is this effected by the presence of forests?
NPS Photo

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Grade Level:
Seventh Grade-Ninth Grade
Subject:
Biology: Plants, Botany, Climate, Climate Change, Conservation, Environment, Landscapes
Duration:
65 minutes
Group Size:
Up to 12 (2-4 breakout groups)
Setting:
classroom
National/State Standards:
Alaska State Standards: SA1, SA2, SA3
Keywords:
climate change, forests, wind

Vocabulary

Climate
Evapotranspiration
Forest density
Canopy\Understory
Boreal forest
Albedo

Overview

Changes in vegetation from human activity have led to significant climatic consequences. How does this happen, and what types of interactions are taking place? Students will set up a model forest to observe changes and their causes.

Objective(s)

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

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.

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

*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.

Procedure

  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 at four different elevations:
  • 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).

 

  1. Turn the fan to a higher level and record the same four positions.
  2. Remove eight bottles, simulating a selectively cut timber operation.
  3. Repeat steps 5 and 6.
  4. Randomly remove eight more bottles and repeat steps 5 and 6.
  5. Remove the remaining eight bottles and again repeat steps 5 and 6.
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Observations and Analysis of Results

  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.

Questions

  1. What does the experiment show?
  2. What might be done to improve the model used?
  3. What other environmental parameters might also show changes as a forest is cut?

Assessment

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.

Ask students how climate change might affect the boreal forests in the eastern part of the Seward Peninsula.

Extensions

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:

  1. Draping paper towels over the bottles
  2. Spraying them lightly with water from a spray bottle
  3. 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

Additional Resources

Lesson plan adapted from: http://www.ucar.edu/learn/1_4_2_19t.htm

Global Climate Change: http://www.ucar.edu/learn/1_4_1.htm