Replant Byron Alliance

What carbon is counted

The IPCC’s (​​6AR) report emphasises the urgency to accelerate CO2 sequestration and ZEB’s objective is to account for the drawdown of local emissions through local tree plantings. 

The Replant Byron Alliance tree tally will not be used for any commercial offsets or rigorously monitored carbon farming. Accurately measuring carbon sequestration for these purposes is a detailed and expensive process undertaken when emission reductions are to be included in commercial or government carbon accounting budgets.   Ideally trees that may have been counted as offsets would be separated out but this only applies to a minority of the plantings in Byron Shire and is proving hard to do on the ground. Natural regenerative processes and camphor laurels continue to draw down a significant proportion of the Shire’s emissions but this is difficult to quantify.  

The Replant Byron Alliance (RBA) tree tally therefore intends to capture all native plantings within Byron Shire between 2015 and 2025. ZEB will quantify our collective drawdown impact by tallying how many trees are planted and estimating how much carbon they are sequestering. CO2 drawdown results will be woven into the compelling stories of our local drawdown champions in motivational messaging to plant more trees!

Carbon Sequestration Methodology

To estimate the carbon sequestered in the above-ground biomass of planted trees, ZEB is using a ‘rule of thumb’ indicative method based on the FullCAM model developed by CSIRO. A test plot was done using the FullCAM model using the following parameters:

• A one hectare plot
• Latitude and Longitude of Bangalow
• Type of planting: environmental planting (rather than eucalyptus carbon planting)
• Planting density: 1200 stems per hectare.

Revegetation in Byron Shire is often planted at a far higher density than 1200 stems per hectare to minimise maintenance.  However, this is the maximum planting density accepted by the FullCAM model because higher density plantings do not result in higher sequestration.  Therefore, carbon sequestration from higher density plantings will be converted to this maximum (see formula below).

Figure 1. FullCAM model for carbon sequestration in 1ha environmental planting at Bangalow

[Carbon loss from fire is very small, only a few percent of sequestration value, and, as destructive bushfire in a mixed mesic environmental planting in Byron Shire is considered to be a low probability, are discarded. Note that fire risk may increase with Climate Change.] 

Calculating carbon sequestration in Byron Shire

Figure 2. Linear approximation of carbon sequestration (yellow line) over 30 years in 1ha environmental planting (1200 or greater stems/ha) at Bangalow.

This graph has an added yellow line indicating linear approximation of sequestration over 30 years. Sequestration for the first four years is overestimated but after about seven years the linear model underestimates sequestration. Over 30 years of growth however the cumulative carbon capture meets the linear approximation. The total sequestration over 30 years is 150 tonnes of total carbon (tC), which is 5 tonnes per hectare per year. This equates to 18.3 tonnes of carbon dioxide (CO2) per hectare per year. [The difference between the weight of carbon and carbon dioxide is the weight of the oxygen. 1 tonne of carbon (tC) = 3.66 tonnes of carbon dioxide (CO2)].

Three data fields required for calculating sequestration;

1. Number of trees (readily provided) 
2. Average tree spacing (readily provided)  
3. Hectares planted (may be difficult for landholders to provide for patch, strip or more widely spaced plantings, or where parts of the terrain are not suitable). 

Higher Density Plantings [>1200 stems/ha i.e. <2.9m spacing]

The FullCAM Methodology indicates that, beyond a planting density threshold of 1200 stems/ha, carbon sequestration plateaus at an approximate value of 18.3tonnes/CO2-e/ha/year. Therefore to generate a carbon sequestration tally for plantings of this density or greater the information required from landholders is the area of trees planted in hectares and confirmation that the density is >1200 stems/ha i.e. stem spacing <2.9m. 

• Example Calculation Carbon Sequestration where planted area (ha) and tree number is provided:

Planted area = 25 ha. Number trees planted = 50,000 

Planting density = 50,000 trees / 25 ha = 2000 stems / ha (which is greater than 1200 stems/ha)

Therefore, total CO2 sequestration = 25 ha * 18.3 tonnes CO2 / ha / year

 = 457.5 tonnes CO2 / year

• Example Calculation Carbon Sequestration where only tree number and spacing is provided:

Where the area of trees planted is not readily available or measured, it can be calculated by multiplying the number of trees by average spacing (m) squared to generate the area planted in m2. Hectares planted can then be calculated by dividing the m2 value by 10,000.

• First calculate area planted (ha) using tree number and average tree spacing (m) : 

(tree number * (tree spacing m)2) / 10,000

Example:

Number trees planted =  3000 with Average tree spacing = 1.8m 

Area of trees planted =   (3000  * (1.8)2) / 10,000

            =   (3000* 3.24) / 10,000

            =    9720 / 10,000 

            =    0.972 ha  

• To convert area planted (ha) to carbon sequestration is:

hectares * 18.3 = X tonnesCO2/ha/year

From above example:  

Hectares planted = 0.972

 0.972* 18.3  = 17.79 tonnes CO2 per year

Lower Density or Individual Tree Plantings [<1200 stems/ha i.e. >2.9m spacing]

In some situations, tree planting densities will be below the maximum carbon sequestration threshold of 1200 stems / ha (>2.9m spacing), i.e. where planted in strips along property boundaries or to facilitate mowing. In these cases the achieved carbon sequestration will depend on the average performance per tree multiplied by total tree number. For our region the FullCAM methodology calculated average carbon sequestration for each big tree (not groundcover, understory shrub or small tree) is at least 15.2kg/CO2/year (0.01525 tonnes C02-e/year). 

Therefore, to generate a carbon sequestration tally for tree plantings of densities lower than 1200 stems/ ha, information required from landholders is the number of trees planted and confirmation that the stem spacing >2.9m. 

• Carbon Sequestration where average stem spacing is known to be >2.9m is: 

tree number x 15.2 kg/CO2/year

Example: Number trees planted =  500 with Average tree spacing = 3m 

Therefore, total CO2 sequestration = 500 * .01525 tonnes CO2 / ha / year

         = 7.625 tonnes CO2 / year

Accommodating diversity 

Landholders requiring more detail or greater accuracy in their carbon accounting are at liberty to adopt the government measurement methodology as required by the Carbon Farming initiative, or another methodology that produces greater accuracy. 

Disclaimer: Zero Emissions Byron estimates carbon drawdown for motivational community campaign purposes rather than for carbon market purposes. The carbon sequestration potential of trees planted within the Shire is an estimate only and does not include trees regenerating naturally or deduct tree mortality, trees planted for external offsets. Efforts are made not to double count trees submitted to the Replant Byron Alliance tree tally.