Why you need to calculate changes in carbon stock
If you have post-1989 forest land registered in the ETS, you need to complete emissions returns at different points in time. For all of these emissions returns, you need to calculate changes in carbon stock for the period that the return covers. This means you must do 2 sets of calculations. You must calculate:
- how much carbon was in the forest at the beginning of the period, and
- how much carbon was present at the end of the period.
You must then work out the difference between these amounts. This will tell you the total change in carbon stock for the period.
There are specific methods you must use for these calculations. These are explained on this page.
Preparing to calculate carbon
To calculate the amount of carbon in your forest land you need to have completed the following 2 steps first.
Step 1: Identify the forest type, region, and age
You need to know certain things about your forest land, such as the species and age of the trees. There are specific rules for how to work these out in the ETS.
Step 2: Group similar areas of forest together into sub-areas
If your forest has trees of more than one forest type or age, or across multiple regions (if it's radiata pine), you also need to do some work to separate your land into sub-areas. You'll do your carbon calculations for each of these sub-areas separately.
Any clearing or planting you do may affect the placement of your sub-areas. This means they may be different for your calculations at the beginning of the period and your calculations at the end of the period.
Using carbon tables
When you do your carbon calculations, you need to refer to "carbon tables". These are tables that tell you how much carbon is in your forest land per hectare.
If your forest is older than the last age on the carbon tables for that forest type, use the value for the last age.
Using standard carbon tables
In the standard carbon tables for post-1989 forest land there are 4 tables. These are used for different situations depending on whether the land was cleared recently.
The first 2 tables show carbon stock per hectare for the forest by forest type (and region for radiata pine).
The other 2 show carbon stock per hectare for residual carbon left from a previous clearing. Residual carbon is the carbon from woody debris left on the land after clearing. It decays over the following 10 years, and continues to produce emissions during that time. These 2 tables are set up in the same way as the first 2. You can ignore these if:
- your forest is on its first rotation, or
- the last clearance was 10 or more years before the start of the period your emissions return covers.
Using participant-specific carbon tables
If you're using carbon tables created specifically for you (known as participant-specific tables), the amount you have depends on the forest types on your land. For each forest type on your land, you'll have a table for forest carbon stock, and one for residual carbon stock.
There are different types of emissions returns that you might need to complete for post-1989 forest land in the ETS. Regardless of what type it is, when you submit one, you must account for the change in carbon stock from the beginning to the end of the period that it covers. This means you need to be able to calculate the amount of carbon in your forest at each date, then work out the difference between the 2 values.
For each carbon accounting area, the carbon stock change is equal to (the carbon stock at the end of the period) minus (the carbon stock at the beginning of the period).
You must round the result to the nearest whole number (0.5 or above rounds up).
If the amount of carbon stored in the carbon accounting area has decreased, the result will usually be a negative value. If it has increased, the result will usually be positive. This number is the one you will use to fill in your emissions return.
Instructions for making the calculations
The instructions in the coloured, expanding boxes tell you how to calculate the carbon in post-1989 forest land at a particular date. There are extra calculations to do if trees on the land have been cleared in the previous 10 years.