All A level specification have content based around the carbon cycle, specifically human and physical factors affecting the stores/components and flows/transfers within the carbon cycle. This could include fieldwork considering carbon storage in trees.

Download this page as a PDF

Fieldwork to estimate carbon content in a woodland environment

There are a series of measurements to make in order to get an estimate of carbon content in an individual tree. All the steps given here are based on the analysis used by Jenkins et al. (2011) of Forest Research, the research agency of the Forestry Commission. Jenkins et al (2011)

1. circumference of tree
2. height of tree
3. volume of tree trunk
4. biomass of tree trunk
5. biomass of canopy and root ball
6. carbon content based on the biomass of the whole tree.

Measuring the circumference of a tree:

• Use a tape measure to measure the circumference of the tree at 1.5m height from the base of the tree.

Measuring the height of a tree:

• You need a tape measure and clinometer for this method. You can make your own clinometer if you do not have them. Start next to the tree trunk and walk away until you can see the top of the tree. Use a clinometer to measure the angle of elevation from your eye to the top of the tree.  Record the distance along the ground from the tree trunk to where you took the clinometer reading. Also record your own height. Make sure that all distance measurements are recorded in meters.
• Use the equation below to calculate height:

Tree height = distance from base of tree to feet x Tan (angle of elevation) + height of observer

Volume of tree trunk:

• You will need to know the radius of the tree.

• Now calculate the volume of the trunk with the assumption that a standard tree trunk is a cone shape.

• Use the volume to estimate biomass, using a rough nominal specific gravity figure* of 0.53 for Broadleaf trees and 0.39 for conifers.

*This is a broad estimate for more detailed information see Jenkins et al (2011)

• Estimate the biomass of the canopy of the crown and root ball (this is an extra set of calculations which can be further explained here: https://www.field-studies-council.org/resources/16-18-geography/water-and-carbon/carbon-cycle/data-analysis/
• Calculate carbon content based on the biomass of the whole tree, add together the biomass in the trunk, crown and roots.

Questions:

• How could we scale up the measurements to multiple trees or a larger area?
• How can we make sure our sample is representative of the trees in the area?
• What are the limitations in our methods and/or calculations and what impact do they have on our results and any conclusions we can draw?
• What impact would different management techniques have on the carbon content of an area of woodland?

Data Analysis:

If students can collect carbon content data for two contrasting areas of trees – for example of coniferous trees and deciduous, or mature woodland and coppiced woodlands – they could then use statistics such as Mann Whitney U test to analyse the difference between the two populations Statistics – Field Studies Council

Application:

This fieldwork could form the basis for students’ NEA ideas around comparisons of carbon stores.

The Geographical Association (GA) has worked closely with the Field Studies Council (FSC) to develop these resources.