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Identify your forest details for calculating carbon
When you're calculating how much carbon is in your forest land, there are things you need to know about your forest. This is because trees of different species and ages have different amounts of carbon in them. The details you need to know include:
- the forest type in each area
- the age of the trees
- the region in which the forest land is located (if the forest is radiata pine, and you’re using the standard carbon tables from the regulations)
- the type and age of the previous forest when it was harvested (if it's a post-1989 forest on its second or later rotation).
There are specific rules in the ETS for how to identify forest type, age, and region. They might not be what you expect. We explain the rules on this web page.
If you have post-1989 forest land, you may be using the averaging accounting method. If this is the case, the forest type and age you need to use in your calculations may not be the same as what is on the land at the time.
Find out more about how to calculate carbon for post-1989 forest land using averaging accounting
Learn about averaging accounting
Identify forest type
To calculate the amount of carbon in your forest land, you need to know what species the forest is. This is because different species remove carbon from the atmosphere at different rates. Species are grouped into 5 forest types in the ETS.
If you have areas of forest on your land that belong to different forest types, you must calculate the carbon in them separately.
Forest species are grouped as follows. Choose the relevant one for each part of your calculations:
- radiata pine
- Douglas-fir (Pseudotsuga menziesii)
- exotic hardwoods (exotic forest species in the class Magnoliopsida (angiosperms))
- exotic softwoods (exotic forest species in the class Coniferopsida (gymnosperms), other than radiata pine and Douglas-fir)
- indigenous (native forest and eligible regenerating shrub land).
If you have pre-1990 forest land or less than 100 hectares of post-1989 forest land and you have radiata pine forest, you’ll also need to identify which region the forest is in. This is because the carbon tables that you'll use for your calculations take into account the different growth rates of radiata pine in different parts of New Zealand.
Using carbon tables for calculating carbon
Mixed-species forests
If an area of land has trees of different species mixed in together, this may be more complex. You must identify which forest type to use when you do your carbon calculations. If the tree species are unevenly mixed, do this on a hectare-by-hectare basis.
Identify the main tree species in the area (also known as the “predominant” species). If this isn't clear, use the species with the largest total basal area. This is the cross-sectional area of the trunk at 1.4 metres above the ground.
Forests with changing species
The main tree species in a forest may change over time, even without trees being cleared or harvested. This can happen naturally, or when another species is planted throughout the forest (also called "interplanting”).
Different tree species grow at different rates. This means the amount of carbon stored in a single hectare of forest land is different for each tree species. When the main tree species of forest land changes, the amount of carbon stored will also change.
Read more about calculating changes in the amount of carbon for post-1989 forest land
If the main tree species in your forest has changed, this affects how you complete your emissions returns. If the main forest species has changed without you clearing the forest, you will need to manually calculate your emissions return and upload the calculations. The ETS online system, Tupu-ake, is unable to calculate your emissions return for you in these cases.
Read more about how to submit emissions returns
If you are using participant-specific tables, you will need to work out whether your tables still accurately represent the carbon stock in your forest. Find out more below:
Find out what to do if you are using participant-specific tables and the main forest species changes
Work out the age of the forest in years
To calculate the amount of carbon in the forest land, you need to work out the age of the forest in years.
If you have pre-1990 forest land, you need to work out the age of the forest in the year the land was cleared.
If you are submitting an emissions return for post-1989 forest land, it will cover a certain period of time. You must work out the age of the forest at the beginning, and at the end, of this period. If the post-1989 forest was cleared during this period, you need to work out the age in the year it was cleared.
Under ETS rules, there is a specific way to do this.
The rules for identifying age are different for planted forest and regenerating native forest.
