ghg-inventory-1990-2013

Living biomass
To calculate carbon change in living biomass on land converted from one subcategory to
another (eg, high producing grassland converted to low producing grassland), it is
assumed the carbon in living biomass immediately after conversion is zero; that is, the
land is cleared of all vegetation. In the same year, carbon stocks in living biomass
increase by the amount given in table 6.1.4 representing the annual growth in biomass for
land converted to another land use. The values given in table 6.1.4 for high producing and
low producing grassland are Tier 1 defaults. The values given for grassland with woody
biomass are country-specific factors based on the LUCAS national plot network (Wakelin
and Beets, 2013).
Dead organic matter
New Zealand does not report estimates of dead organic matter for high producing
grassland or low producing grassland because GPG-AFOLU states there is insufficient
information to develop default coefficients for estimating the dead organic matter pool
(IPCC, 2006a). The notation key NE (not estimated) is used in the CRF tables.
For grassland with woody biomass, an estimate of dead organic matter is derived from the
LUCAS national plot network (Wakelin and Beets, 2013), and estimates of changes in
dead organic matter stocks with conversion to and from this land use are given in the
CRF tables.
Soil carbon
Soil carbon stocks in Grassland remaining grassland are estimated using a Tier 2 method
for mineral soils (table 6.6.4) and a Tier 1 method for organic soils (section 6.3). The
IPCC default emission factors for organic soils under Grassland are 0.25 and
2.5 tonnes C ha –1 per annum for cold temperate and warm temperate regimes,
respectively (IPCC, 2006a).
Table 6.6.4
New Zealand’s soil carbon stock values for the grassland subcategories
Land-use Soil carbon stock density (t C ha –1 )
High producing grassland 105.34
Low producing grassland 105.98
Grassland with woody biomass 98.23
Land converted to grassland
Living biomass
New Zealand uses a Tier 1 method to calculate emissions for Land converted to
grassland. The Tier 1 method multiplies the area of Land converted to grassland annually
by the carbon stock change per area for that type of conversion.
The Tier 1 method assumes carbon in living biomass immediately after conversion is
zero; that is, the land is cleared of all vegetation at conversion. The amount of biomass
cleared when land at steady state is converted is shown in table 6.1.3. The Tier 1 method
also includes changes in carbon stocks from one year of growth in the year conversion
takes place, as outlined in equation 2.9 of GPG-AFOLU (IPCC, 2006a).
Dead organic matter
For land conversion to high and low producing grassland, New Zealand reports only
losses in dead organic matter. The losses are calculated based on the carbon in dead
organic matter at the site prior to conversion to Grassland. It is assumed that,
immediately after conversion, dead organic matter is zero (all carbon in dead organic
New Zealand’s Greenhouse Gas Inventory 1990–2013 265