# Biology Fieldwork

A Level

# Discussion

## 3. Discussion

Sophisticated data analysis will help you spot patterns, trends and relationships in your results. Data analysis can be qualitative and/or quantitative, and may include statistical tests. An example of a statistical test is outlined below.

## Calculating the carbon content of a tree

This assumes that you have measured

- the circumference of the tree at chest height
- the height of the tree

*Note that for this method to work, the tree trunk radius must be greater than 25cm (or circumference must be greater than 157cm)*

There are four steps to calculating the carbon content of a tree

- Step 1. Calculate the volume of the tree trunk
- Step 2. Calculate the biomass of the tree trunk
- Step 3. Estimate the biomass of the canopy and the root ball
- Step 4. Calculate carbon content based on the biomass of the whole tree

These steps are based on the analysis used by Forest Research (link to pdf), the research agency of the Forestry Commission.

### Step 1. Calculate the volume of the tree trunk

#### (a) Calculate the radius of the tree trunk at chest height

`"Radius" = "circumference"/(2 xx pi)`

e.g. if you measured the tree circumference to be 3m

`"Radius" = "3/(2 xx 3.14)`

`"Radius" = 0.48 " m"`

#### (b) Calculate the volume of the tree trunk above ground

The approximate volume can be calculated by assuming that the tree trunk is a cone. Use the standard formula for calculating the volume of a cone.

`"Volume of the tree trunk" = pi r^2 xx ("height"/3)`

e.g. if the radius of the tree trunk is 0.48m and the height is 15m

`"Volume of the tree trunk" = 3.14 xx 0.48^2 xx ("15"/3)`

`"Volume of the tree trunk" = 3.62 " m"^3`

### Step 2: Calculate the biomass of the tree trunk

The biomass of the tree trunk can be calculated by

`"Biomass" = "volume" xx "nominal specific gravity"`

If you know what species of tree that you have measured (like oak, ash or larch), you can find precise figures for nominal specific gravity figures on page 46 of Jenkins et al., 2011. Alternatively use the figures below

- For broadleaved trees, nominal specific gravity = 0.53
- For conifers, nominal specific gravity = 0.39

e.g. if the volume of the tree trunk is `3.62 " m"^3`and the tree is an ash tree (a broadleaved tree)

`"Biomass" = 3.62 xx0.53`

`"Biomass" = 1.92 " oven dry tonnes"`

### Step 3. Estimate the biomass of the canopy and the root ball

As well as the tree tunk, a substantial amount of carbon is stored in the tree's canopy (or crown) as well as below ground in the roots.

The biomass of the crown and the roots can be estimated if the radius of the trunk and the species of tree are known. This method is based on the analysis used by Forest Research.

#### (a) Estimate the crown biomass

First take the radius and double it to get the tree's **diameter at breat height (DBH)**. Make sure that this is expressed in centimetres.

There are two ways to calculate the crown biomass, depending on whether the tree is large or small. A large tree has a diameter at breast height of more than 50cm. A small tree has a diameter at breast height of between 7cm and 50cm. Smaller trees cannot be assessed using this method.

If DBH is 7-50cm then `"Crown biomass" = a xx "DBH"^b`

If DBH > 50cm then `"Crown biomass" = c + (d xx "DBH")`

`a`, `b`, `c` and `d` are species-specific constants shown in the table below.

Estimating crown biomass | ||||
---|---|---|---|---|

Species | a | b | c | d |

Larch | 0.000044 | 2.0291 | -0.129047 | 0.005039 |

Corsican pine | 0.000012 | 2.4767 | -0.299529 | 0.009949 |

Lodgepole pine | 0.000018 | 2.4767 | -0.430537 | 0.014300 |

Scots pine | 0.000016 | 2.4767 | -0.394206 | 0.013094 |

Douglas fir | 0.000017 | 2.4767 | -0.411768 | 0.013677 |

Grand Fir | 0.000015 | 2.4767 | -0.353198 | 0.011732 |

Noble Fir & other conifers | 0.000015 | 2.4767 | -0.353198 | 0.011732 |

Hemlock | 0.000015 | 2.4767 | -0.353198 | 0.011732 |

Norwegian Spruce | 0.000015 | 2.4767 | -0.353198 | 0.011732 |

Cedar | 0.000015 | 2.4767 | -0.353198 | 0.011732 |

Sitka Spruce | 0.000015 | 2.4767 | -0.353198 | 0.011732 |

Beech, Sycamore & Maple | 0.000019 | 2.4767 | -0.459519 | 0.015263 |

Oak and all other broadleaved trees | 0.000017 | 2.4767 | -0.411551 | 0.013670 |

e.g. if the DBH is 96cm and the tree is an ash tree (in "all other broadleaved trees")

`"Crown biomass" = -0.411551 + (0.013670 xx 96)`

`"Crown biomass" = 0.932" oven dry tonnes"`

#### (b) Estimate the root biomass

Next you can estimate the biomass of the roots. Again the equation that you use depends on the size of the tree. Remember that the DBH must be expressed in centimetres.

If DBH is 7-50cm then `"Root biomass" = e xx "DBH"^2.5`

If DBH > 50cm then `"Root biomass" = f + (g xx "DBH")`

`e`, `f` and `g` are species-specific constants shown in the table below.

Species | e | f | g |
---|---|---|---|

Larch | 0.000017 | -0.133480 | 0.007296 |

Corsican pine | 0.000011 | -0.082603 | 0.004515 |

Lodgepole pine | 0.000017 | -0.133480 | 0.007296 |

Scots pine | 0.000015 | -0.118673 | 0.006487 |

Douglas fir | 0.000017 | -0.133480 | 0.007296 |

Grand Fir | 0.000015 | -0.118673 | 0.006487 |

Noble Fir | 0.000011 | -0.082603 | 0.004515 |

Hemlock | 0.000015 | -0.118673 | 0.006487 |

Norwegian Spruce & other conifers | 0.000012 | -0.091547 | 0.005004 |

Cedar | 0.000011 | -0.082603 | 0.004515 |

Sitka Spruce | 0.000021 | -0.157579 | 0.008614 |

Beech | 0.000023 | -0.174882 | 0.009559 |

Oak and all other broadleaved trees | 0.000023 | -0.174882 | 0.009559 |

e.g. if the radius is 96cm and the tree is an ash tree (in "all other broadleaved trees")

`"Root biomass" = -0.174882 + (0.00959 xx 96)`

`"Root biomass" = 0.785" oven dry tonnes"`

## Step 4. Calculate carbon content based on the biomass of the whole tree

#### (a) Find the biomass of the whole tree

`"Biomass of whole tree" = "Trunk biomass" + "Crown biomass" + "Root biomass"`

e.g. if the trunk biomass is 1.92 oven dry tonnes, the crown biomass is 0.932 oven dry tonnes, and the root biomass is 0.785 oven dry tonnes

`"Biomass of whole tree" = 1.92 + 0.932 + 0.785`

`"Biomass of whole tree" = 2.64" oven dry tonnes"`

#### (b) Find the carbon content of the tree

The carbon content of the tree is calculated as

`"Carbon content" = "Biomass of whole tree"/2`

e.g. if the biomass of the whole tree is 2.64 oven dry tonnes

`"Carbon content" = 2.64/2`

`"Carbon content" = 1.32" oven dry tonnes" `