Forests,

Mining Carbon From the Air

Trees grow by taking CO₂ from the air and water and minerals from the soil. They use sunlight for energy to change these raw materials into wood and leaves. The tree’s growth depends on the type of tree, rainfall, soil conditions, latitude, elevation, competition from other trees, etc. Trees also grow slowly. Some trees grow for centuries or even thousands of years. To find how fast trees sequester CO₂, we need to look at different combinations of these factors. We would need hundreds of test plots. Since trees grow slowly, we would need to wait years to see the results.

Fortunately, many scientists have been experimenting with trees. One scientist looked at the effect of rainfall, a second scientist looked at soil conditions, etc. Each scientist makes an equation to predict the effect of his/her factor. If we put these equations together we can predict how different kinds of forests grow. There are many equations. Doing all of the math would take too long and be too confusing. If we put the equations together in a computer program, the computer will do the math for us. We call this kind of program a model.  Doing science using these models is called Computational Science.

You will use a forest model made by Wageningen University and Research Center. The model simulates a hectare plot. A hectare is about the size of 2 football fields. After all of the variables are put in the model you run it. The model reports on the carbon in the forest for the next 300 years. There are 2 sets of data. One set gives the carbon stored in different parts of the forest. One part of the forest is the roots of the trees. These are called the stocks. The second data set gives the carbon that is moving into and out of each part. These are called flows.

The questions we want to investigate are:

1. Where is the carbon stored in the forest?

2. How do these carbon reservoirs change over time?

3. What can we do to increase the carbon stored in the reservoirs?

Ask your teacher if you will be using CO2fix, This is the model made by Wageningen University and Research Center, or the Excel version.

In CO2fix open the model named WUR-ex1. When WUR-ex1 opens you see the carbon stock table. This is the run for the forest plot. Each row corresponds to one year. How many years does this run model the forest? What parts of the tree does the model monitor? What is the total dry mass of the trees when the simulation starts? What is the total mass of the trees at the end of the simulation?

Copy the Biomass dry weight column into an excel spreadsheet. Graph the column to see how the mass changes over time.

What percentage of the Biomass is carbon?

 Find the column that shows the total carbon in the soil. Copy this column to your spreadsheet and graph it.

Which year has the most carbon in the soil? Explain why the soils carbon dips then increases then decreases again.

Explore the data on your own to answer these questions.

Which year has the largest amount of carbon in the forest? How much carbon is in the forest this year?

 Which year is the most carbon being sequestered?

Which year does the forest start producing more CO₂ than it is sequestering?

After the year when the largest amount of carbon is in the forest, what is the relationship between the forest and the atmosphere? Is the forest removing or adding CO₂ to the atmosphere? Since trees are getting bigger and older why doesn’t the forest contain more CO₂?

Which age range of forest would we need to help balance the CO₂ that we are adding to the atmosphere?

If you want the forests to help deal with our CO₂ responsibilities what recommendations would you make for our national forest policy?

What are the product values in the model? (all 0) This forest isn’t harvested. It is managed like a wilderness area is leftt alone. Lumber is removed from most of our forests. This model allows you to simulate harvesting of products from the forest.

The authors of the model suggest you practice thinning your forest by following these directions.

Open ‘WUR-ex2.co2’  you will start to manage the forest and produce wood products

Go to the biomass parameterisation module, and choose the ‘thinning harvest’ tag

Parameterise two thinnings (year 30 and 60) and one final felling at age 100. Fraction removed is resp 0.25, 0.25, and 1.

Allocate of first thinning, .1 to logwood, and .7 to pulp-pap

Allocate of second thinning, .3 to logwood, and .6 to pulp-pap

Allocate of final felling, .7 to logwood, and .2 to pulp-pap. Leave the rest of the cells as they are, i.e. all branches are allocated to slash. 

Now choose ‘Apply’ and ‘OK’

 Go to ‘products parameterisation module’. This has now been parameterised for you. Try to get an idea what has been inserted for products.

  What fraction of products in long term use will be recycled at the end of their life?

What fraction of recycled products in long term use, will go to products with a medium term use?

 Now choose ‘Apply’ and ‘OK’

Under the icon ‘View options’ choose the ‘products’. Analyse what you see.

 Go back to the ‘view carbon stocks table’, and copy the column with the total products carbon stock into an excel sheet.

Graph this column. Explain the curve i.e. why does it spike up and then curve back down over and over again? Is there an overall trend?

On the stocks table copy the column with total atmosphere C. Graph the atmospheric and products C together. What patterns do you see? Both are variable, so how can you find a pattern or trend that they share?

Both have minimum values at 100 year periods. If you graph these minimum values you will see a relationship.

What should we conclude about the forests ability to permanently sequester our carbon?

Suggest ways to change our forest management strategy or product recycling policy. For example, should we harvest on a different schedule, harvest part of the top of the trees into pulp, have a recycling campaign? You need to justify the practicality of your policy changes.