ghg-inventory-1990-2013

with the clearing of vegetation prior to the establishment of exotic planted forest. Belowground
biomass is assumed not to burn. The IPCC default combustion proportion for the
burning of non-eucalypt temperate forest in land clearing fires (0.51) is then applied to
estimate emissions from this activity (Wakelin, 2012).
The survey also provided data on the burning of post-harvest slash prior to restocking.
This activity was found to occur mainly as a training exercise for wildfire control or for
the clearing of slash heaps on skid sites. The data indicated that 0.8 per cent of
restocked area was burnt each year in recent years. This estimate was combined with two
earlier estimates of controlled burning in planted forest (Forest Industry Training and
Education Council, 2005; Robertson, 1998) to provide activity data throughout the time
series. It is assumed that 1.6 per cent of restocked area was burnt from 1990 to 1997.
From 1997, the area burnt declines linearly to 0.8 per cent, which is used from 2005
onwards (Wakelin, 2012).
Activity data is combined with an emission factor derived from the pre-1990 planted
forest carbon-yield table to estimate emissions from the burning of post-harvest slash
(harvest residue) on Forest land. The harvest residue is calculated by subtracting the
amount of above-ground biomass that is taken off site as logs (70 per cent) from the total
above-ground biomass predicted at the age of 28 years (the average harvest age in
New Zealand). Below-ground biomass is assumed not to burn. The IPCC default
combustion proportion for the burning of harvest residue in non-eucalypt temperate forest
(0.62) is applied to estimate emissions from this activity (Wakelin, 2012).
An estimate is provided for burning of post-harvest residues associated with deforestation
in the Inventory. No information is available on the extent of burning associated with
deforestation in New Zealand. Therefore, it is assumed that 30 per cent of conversions
involve burning to clear residues. The IPCC default combustion proportion for the
burning of harvest residue in non-eucalypt temperate forest (0.62) is applied to
subcategory-specific emission factors to estimate emissions from this activity. The
emission factor excludes the proportion of logs taken off site (70 per cent of aboveground
biomass) and is taken from the plot-network-derived yield tables by forest
subclass at the average age of harvest in New Zealand.
Carbon dioxide emissions from controlled burning in planted forests in the Inventory are
captured at the time of conversion or harvest.
Different emission factors derived from the LUCAS plot network are used for wildfire
and controlled burning on grassland with woody biomass in the Inventory.
The differences are due to the vegetation that is typically converted to forest, which is
generally of a lesser stature when compared with other shrubland (Wakelin and
Beets, 2013).
Uncertainties and time-series consistency
Uncertainties arise from relatively coarse activity data for wildfires and controlled
burning activities in New Zealand (table 6.11.3). The biomass burning statistics have gaps
in the time series where data collection did not occur or survey methodologies changed.
Assumptions are made for some activity data, emission factors and burning fractions
where insufficient data exists.
282 New Zealand’s Greenhouse Gas Inventory 1990–2013