ghg-inventory-1990-2013

period is 2.2 tonnes C ha –1 yr –1 (Beets et al, 2013). This rate is similar to previously
reported rates of carbon sequestration in regenerating shrubland in New Zealand
(Carswell et al, 2012; Trotter et al, 2005).
Soil organic carbon
Soil carbon stocks in land converted to post-1989 forest are estimated using a Tier 2
method for mineral soils and a Tier 1 method for organic soils, as described in section
6.3. The steady state mineral soil carbon stock in post-1989 forest is estimated to be
91.92 tonnes C ha –1 (table 6.3.2).
In the absence of country- and land-use specific data on the rate of change, the IPCC
default method of a linear change over a 20-year period is used to estimate the change in
SOC stocks between the original land use and planted forest land for any given period.
For example, the soil carbon change associated with a land-use change from low
producing grassland (soil carbon stock 105.98 tonnes C ha –1 ) to post-1989 planted forest
(soil carbon stock 91.92 tonnes C ha –1 ) would be a loss of 14.06 tonnes C ha –1 over the
20-year period.
The IPCC default emission factor for organic soils under planted forest is
0.68 tonnes C ha –1 per annum (table 6.3.3). This is also applied to organic soils on land
converted to post-1989 forest.
Quality assurance and quality control
Quality-assurance and quality-control activities were conducted throughout the post-1989
planted forest data capture and processing steps. These activities were associated with the
following: inventory design (Brack, 2009; Moore and Goulding, 2005); acquisition of raw
LiDAR data and LiDAR processing; checking eligibility of plots; independent audits of
field plot measurements; data processing and modelling; regression analysis and doublesampling
procedures (Woollens, 2009); and investigating LiDAR and ground plot
co-location (Brack and Broadley, 2010). These activities, along with those undertaken
within the post-1989 natural forest, are described in more detail in section 6.4.4.
Non-CO 2 emissions for post-1989 forest
Direct N 2 O emissions from nitrogen fertilisation of forest land and other land
New Zealand activity data on nitrogen fertilisation is not currently disaggregated by land
use and, therefore, all Direct N 2 O emissions from nitrogen fertilisation of forest land
and other land are reported in the Agriculture sector under the subcategory, Direct
soils emissions.
6.4.3 Uncertainties and time-series consistency
Emissions from Forest land are 3.1 per cent of New Zealand’s net emissions uncertainty
in 2013 (annex 2). Forest land introduces 2.6 per cent uncertainty into the trend in the
national total from 1990 to 2013.
Pre-1990 natural forest
The uncertainty in mapping pre-1990 natural forest is 5 per cent (table 6.4.7). Further
details are given in section 6.2.5.
Uncertainty in biomass carbon stock and stock change in New Zealand’s pre-1990 natural
forest is calculated using a published methodology designed specifically for this purpose
(Holdaway et al, 2014c). The pre-1990 natural forest plot network provides biomass
carbon stock estimates that are within 95 per cent confidence intervals of 4.4 per cent of
the mean (257.74 ± 11.33 tonnes C ha –1 ) for tall natural forest and 18.27 per cent of the
250 New Zealand’s Greenhouse Gas Inventory 1990–2013