Part 4—Model Carbon Data and Compare

Step 1 – Learn About Models and Open the isee Player

  1. If you have not worked with models before, you may want to take a moment to review these modeling concepts.
  2. Learn more about the specifics of the Biomass Accumulation Model.
  3. Launch the isee PLAYER application, select File > Open, and navigate to the file Biomass_Accumulation2.7.STM. When the model opens, the Welcome page appears.
  4. Click the Read About this Model button. This will walk you through an explanation of the model step by step. You can return to the Welcome page by using the little arrow in the upper left, or you can hit the space bar to continue through more background information.
  5. You will need to use your NH_FIA_data2.xls file to run the model. If necessary, launch Excel and open your file that was saved in Part 3.

Step 2 – Run the Biomass Accumulation Model (Biomass Accumulation2.7.STM)

Using the isee Player, you will run the Model for each of the 14 Forest Types (White-red-jack pine, Spruce-fir, etc.) in your NH_FIA_data2.xls file. For each model that you run, you will need to record data for five different time periods. This data will be recorded back into your NH_FIA_data2.xls file.
  1. Click the Model Inputs button on the Welcome page. A new page is displayed, describing the two variables used to run the model. The dials on the left are used to set the Foliar Nitrogen value and the Wood Turnover rate. These values will open to a default of 2.0.
  2. To run the first model, set the Foliar Nitrogen value for the first forest type in the Carbon Scenario Template. (In this case, the input value is 1.0 for the White-red-jack pine). Enter 1.0 into the input box above the Foliar Nitrogen dial.

  3. Click the Go to Model button. This takes you to the Run Model and View Results page.
  4. Click the Change Model Run Time (years) button and set the length of the simulation to 250.
  5. Click the Press to Run Model button. The model will run and display different values graphically and in a table. In the graph, the values for Wood Carbon will appear as line number 5, and be colored brown. You can read the Wood Carbon values for specific years by clicking the graph line with your cursor and then moving along the line until the Years below the x-axis display 50. A gray, vertical dashed line will display and move along with your cursor.

    The Wood Carbon value is displayed at the top of the graph and also to the right in the table. Enter the value for Wood Carbon into the first green cell (STELLA predicted gC/m^2 (year 50) in NH_FIA_data2.xls. Move your cursor until the Years beneath the axis is 80. Enter the new Wood Carbon value into the second green cell. Continue and record the values for years 100, 150, and 250.
  6. Repeat steps 2 - 5 above to make a model run for each of the forest types in the Carbon Scenario Template.
  7. Save the table data from one of your model runs by clicking in the center of the table. Select Save as Text from the right click drop-down menu (or control-click on a Mac). Check Append File Extension and make sure the extension shows as ".TXT." Name the table and specify a place to put it (e.g. Desktop). This table will be used to answer a question in Step 3 below.

Step 3 – Check Your Understanding of the Model Output

Use the model and see what happens when you vary the foliar nitrogen concentration, turnover rate, or harvest. Answer the following questions. Remember you can use the sliders, dials, graphs, table, model diagram or equation tabs to help you. Start by running the model with all default values: Foliar Nitrogen = 2.0, WoodTurnover = 2.0, HarvestYear & HarvestIntensity = 0 . Set the Model Run Time to 500 years.

Pop-up box when equilibrium is reached.


Note: If you get a message indicating that equilibrium has been reached, you need to click Press to Run Model to complete your run. The graphical lines will extend out 500 years, but will remain flat.
end of run after equilibrium pop-up box.


Answer the following questions:
  • In year 100, what is the value of each of the y-axis variables (e.g., woodbiomass, woodlitter)?
  • Using the table, in what year does WoodBiomass reach 20,000.00 g/m2?
  • Using the dotted line function on the graph, identify the y-axis variable that decreases to zero and the year when this first occurs?
  • Using the graph or table, in what year does WoodLitter equal the same number as WoodGrowth? What term do we use to explain this situation?
  • Describe the relationship between 2 variables that follow a similar trend.
    • CHALLENGE: Using the model, write the simple mathematical equation that explains this relationship. Indicate how you came to this conclusion.
  • Using the table you saved in Step 2, number 7, did that model run reach equilibrium?

Step 4 – Compare the FIA data to the Model Output

In the student worksheet, compare total FIA Carbon Storage (orange cell on the bottom left) to Model Carbon Storage (5 runs with totals in the orange cells on the bottom right)

FIAComplete


Does the model computed carbon storage make sense with the approximate forest age and the FIA value for 1997? For New Hampshire, the FIA measurements show total forest carbon to be about 131 MMTC. The model shows NH total forest carbon to be about 100 MMTC after 50 years, 126 MMTC after 80, 137 MMTC after 100 years, 150 MMTC after 150 years, and 157 MMTC after 250 years. This is about right since the height of land in agriculture was 1850, and land has returned to trees since that time.

You can find the completed Excel file in the Teaching Notes.

The model computes carbon storage in grams per meter squared units, but the FIA data reports carbon storage in Million metric tons. This conversion is done for you in the worksheet. But you can look at the conversion if you wish.