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Chapter 7: Land use, land-use change and forestry (LULUCF)

7.1 Sector overview

In 2007, net removals from the LULUCF sector were 23,836.0 Gg carbon dioxide equivalent (CO2-e). Net removals had increased by 5,697.5 Gg CO2-e (31.4 per cent) over the 1990 removals of 18,138.5 Gg CO2-e (Figure 7.1.1). Figure 7.1.2 shows changes in emissions and removals by land-use category from 1990 to 2007.

Carbon dioxide emissions and removals in the LULUCF sector are primarily controlled by uptake from plant photosynthesis and release from respiration, emissions from harvesting production forests, and the decomposition of organic material. Nitrous oxide (N2O) can be emitted from the ecosystem as a by-product of nitrification and de-nitrification and the burning of organic matter. Other gases released during biomass burning include methane (CH4), carbon monoxide (CO), other oxides of nitrogen (NOx), and non-CH4 volatile organic compounds (NMVOC). All emissions and removals from the LULUCF sector are excluded from national totals unless otherwise specified. This is consistent with Climate Change Convention reporting guidelines.

Six broad categories of land use are described in Good Practice Guidance for Land Use, Land-Use Change and Forestry (IPCC, 2003), hereafter referred to as GPG-LULUCF. The land-use categories are:

  • forest land – all land with woody vegetation consistent with defined national thresholds. It also includes areas of vegetation that currently fall below, but are expected to reach or exceed, the defined national thresholds

  • cropland – arable and tillage land, and agro-forestry systems where vegetation falls below the thresholds used for forest land

  • grassland – rangelands and pasture land that are not considered as cropland. It also includes areas of vegetation that fall below, but are not expected to reach or exceed without human intervention, the national threshold defined in the forest-land category.

  • wetlands – land that is covered or saturated by water for all or part of the year (eg, peat land) and that does not fall into the forest land, cropland, grassland or settlements categories. Natural rivers and lakes are unmanaged subdivisions of wetlands

  • settlements – all developed land, including transportation infrastructure and human settlements unless they are already included under other categories

  • other land – bare soil, rock, ice, and all unmanaged land areas that do not fall into any of the other five categories.

Figure 7.1.1 Annual emissions/removals for the three major land uses from 1990 to 2007

Figure 7.1.1 Annual emissions/removals for the three major land uses from 1990 to 2007 (all values are Gg CO<sub>2</sub>-e)

Year Net removals
Gg CO2-equivalent
Forest land
Gg CO2-equivalent
Cropland
Gg CO2-equivalent
Grassland
Gg CO2-equivalent
1990 -18,138.5 -18,649.2 -477.7 863.9
1991 -17,271.4 -17,806.1 -478.8 888.0
1992 -15,145.9 -15,707.3 -479.7 914.9
1993 -14,907.0 -15,503.3 -480.1 949.3
1994 -15,895.5 -16,531.6 -480.3 988.4
1995 -15,892.6 -16,518.3 -483.5 980.4
1996 -16,652.0 -17,269.7 -486.5 974.7
1997 -18,620.4 -19,282.6 -486.4 1,018.3
1998 -18,859.3 -19,566.1 -486.2 1,061.8
1999 -19,143.3 -19,894.7 -486.0 1,105.4
2000 -19,971.5 -20,761.5 -485.8 1,143.1
2001 -20,358.2 -21,189.7 -485.7 1,183.5
2002 -20,033.3 -20,844.0 -489.8 1,166.2
2003 -21,230.0 -21,989.8 -496.1 1,120.7
2004 -24,853.6 -25,631.6 -497.5 1,139.5
2005 -25,273.7 -26,018.2 -502.0 1,109.7
2006 -23,877.3 -24,577.3 -507.4 1,069.7
2007 -23,836.0 -24,527.9 -510.3 1,063.7

Figure 7.1.2 Change in New Zealand’s emissions/removals from the LULUCF sector (net emissions and removals by land-use category) from 1990 to 2007

Figure 7.1.2 Change in New Zealand's emissions/removals from the LULUCF sector (net emissions and removals by land-use category) from 1990 to 2007 (all values are Gg CO<sub>2</sub>-e)

Note: The per cent change for wetlands and settlements is not applicable (NA) as emissions are assumed constant. These two categories are not key categories.

Category 1990
(Gg CO2-equivalent)
2007
(Gg CO2-equivalent)
Forest land -18,649.2 -24,527.9
Cropland -477.7 -510.3
Grassland 863.9 1,063.7
Wetlands 0.7 0.7
Settlements 97.2 97.2
Other land 26.7 40.6

7.1.1 Land use in New Zealand

Before human settlement, natural forests were New Zealand’s predominant land cover, estimated to have covered around 75 per cent of New Zealand’s total land area. Forestry now covers approximately 38 per cent of New Zealand. This includes natural forest, planted forest and shrubland that meets the threshold for forestry. Figures 7.1.3 and 7.1.4 show the IPCC land-use categories for New Zealand in 2002 (from the Land Cover Database of 2002). Nearly all lowland areas have been cleared of natural forest and are used for agriculture, horticulture, plantation forestry and urban development.

Deforestation following human settlement is estimated to have resulted in vegetation carbon losses of 3,400,000 Gg carbon (Scott et al, 2001). Establishment of pastures has probably slightly increased mineral soil carbon. However, losses of carbon due to erosion are also possible (Tate et al, 2003b). New Zealand soils are naturally acidic with low levels of nitrogen, phosphorus, and sulphur. Consequently, soils used to grow crops and pasture need to be developed and maintained with nitrogen-fixing plants (such as clover), fertilisers and often lime to sustain high-yield plant growth.

7.1.2 Methodological issues for New Zealand

Summary of methodological approaches used

New Zealand uses a combination of Tier 1 and Tier 2 methods for reporting removals and emissions from the LULUCF sector. The Tier 1 approach, based on a simple land-use change matrix, is applied for all six land-use categories, with the exception of the biomass pools for the planted forest category. Key categories identified for the LULUCF sector are forest land remaining forest land (level and trend), conversion to forest land (level), conversion to grassland (trend), conversion to cropland (trend), and cropland remaining cropland (level). Forest land remaining forest land and conversion to forest land are key subcategories. Therefore, a Tier 2 modelling approach using New Zealand-specific data is used to estimate removals and emissions (excluding soils) from these key subcategories.

To improve the transparency and accuracy of reporting in the LULUCF sector, and to meet the supplementary reporting requirements for Article 3.3 of the Kyoto Protocol, New Zealand is developing the Land Use and Carbon Analysis System (LUCAS). The LUCAS programme is described in detail in Annex 3.2. The land categories to be mapped and monitored through LUCAS are designed specifically for reporting under the Climate Change Convention and the Kyoto Protocol, and will be reported in the 2010 inventory submission onwards.

Representation of land areas

Tier 1 approach for all land use – excluding planted forest

Land areas are calculated using an analysis of two existing land-cover maps of New Zealand: the Land-cover Databases 1 and 2 (LCDB1 and LCDB2, respectively) (Thompson et al, 2004). These databases were reclassified to reflect the IPCC land-use categories. The land-cover databases were mapped in 1997 and 2002. Data for all other years was extrapolated from the changes observed between 1997 and 2002.

The LCDB1 and LCDB2 are examples of the wall-to-wall mapping of Approach 3 as described in GPG-LULUCF. Although, the LCDBs were not specifically developed for use in Climate Change Convention reporting, they are the only national land-cover/land-use spatial databases available that provide recent information and that can be mapped to the LULUCF land-use categories (Table 7.1.1). LCDB1 and LCDB2 include national vegetation classes, other than forests, including woody vegetation. These vegetation classes were classified within the forest-land and grassland categories based on an assessment of whether the species would usually grow to over five metres in height in situ and, therefore, meet the forestry definition and the minimum size of the land-cover unit.

At the time of compiling this submission, New Zealand does not have complete land-use data for 1990. Until the 1990 mapping component of the LUCAS project is completed, the extrapolations back from the LCDBs provide the best data available for the inventory. Figure 7.1.4 provides the annual area for each IPCC land-use category for the inventory reporting period (derived from both the Tier 1 and Tier 2 land area data).

Work is underway to improve the estimates of land “converted” and “remaining” within each land-use category. At present, only conversions since 1990 are captured in the Tier 1 method. An assessment of land-use change in the 20 years prior to 1990 will be included in future inventory submissions, making use of historic data from sources such as the Food and Agriculture Organisation of the United Nations Statistics (FAOSTAT database http://faostat.fao.org) and national estimates eg, agricultural census and surveys, and the National Exotic Forest Description (NEFD).

Table 7.1.1 Mapping of LCDB land-cover classification to the IPCC land-use categories

IPCC category LCDB class
Forest land
FM (planted) Afforestation (imaged, post LCDB 1), afforestation (not imaged), deciduous hardwoods, forest harvested, other exotic forest, pine forest – closed canopy, pine forest – open canopy.
FM (natural)

Natural forest, broadleaved natural hardwoods, manuka and/or kanuka.

Cropland
CM (perennial) Orchards, vineyards, and other perennial crops.
CM (annual) Short-rotation cropland.
Grassland
GM (low prod) Alpine grass/herbfield, depleted tussock grassland, fernland, gorse and broom, grey scrub, low-producing grassland, major linear shelterbelts, matagouri, mixed exotic shrubland, sub-alpine shrubland, tall tussock grassland, flaxland, herbaceous freshwater vegetation, herbaceous saline vegetation and mangrove.
GM (high prod) High-producing exotic grassland.
Wetlands
W (unmanaged) Estuarine open water, lakes, ponds and rivers.
Settlements
S Built-up area, dump, surface mine, transport infrastructure, urban parkland/open space.
Other land
O Alpine gravel, rock, coastal sand, gravel landslides, permanent snow, ice, rivers and lakeshore gravel and rock.

Table 7.1.2 shows a simplified land-use change matrix developed from LCDB1 and LCDB2 for the years 1997 and 2002. A land-use change matrix for 2006–2007 was generated by extrapolation. Detail of the conversions between categories and subcategories are included in the sections discussing each land-use category below.

Some prominent land-use changes between 1997 and 2002 include:

  • increased planted forest area of almost 140,000 hectares (a 7 per cent increase), mostly from conversion of grassland, that decreased by 135,000 hectares (2 per cent)

  • increased area of settlements by 5,500 hectares (2.5 per cent) mostly from conversion of grassland

  • increased area of cropland by 4,500 hectares (7 per cent), mostly perennial cropland.

Tier 2 approach for planted forest

The National Exotic Forest Description (NEFD) is an annual survey of forest growers that provides estimates of the area of forest by age, species, silvicultural regime and location. The NEFD data includes the separation of planted forest into “converted” and “remaining” categories, based on forest rotation information provided within the survey.

Figure 7.1.3 New Zealand’s total area for each land use from 1990 to 2007 (all figures kha and based on both Tier 1 and Tier 2 data)

Figure 7.1.3 New Zealand's total area for each land use from 1990 to 2007 (all figures kha and based on both Tier 1 and Tier 2 data)

  Forest Land Cropland Grassland Wetlands Settlements Other Land
1990 9,368.9 407.6 14,664.3 530.4 208.4 1,057.2
1991 9,386.7 408.5 14,637.2 530.5 209.5 1,057.2
1992 9,424.6 409.4 14,610.0 530.7 210.6 1,057.2
1993 9,481.1 410.3 14,582.9 530.8 211.7 1,057.1
1994 9,567.8 411.2 14,555.8 531.0 212.8 1,057.1
1995 9,647.2 412.1 14,528.7 531.1 213.9 1,057.1
1996 9,730.5 413.0 14,501.6 531.2 215.0 1,057.1
1997 9,802.5 413.9 14,474.5 531.4 216.1 1,057.1
1998 9,854.9 414.7 14,447.4 531.5 217.2 1,057.1
1999 9,893.0 415.6 14,420.2 531.7 218.3 1,057.1
2000 9,923.4 416.5 14,393.1 531.8 219.4 1,057.1
2001 9,950.1 417.4 14,366.0 532.0 220.5 1,057.1
2002 9,969.8 418.3 14,338.9 532.1 221.6 1,057.1
2003 9,988.8 419.2 14,311.8 532.2 222.6 1,057.1
2004 10,001.7 420.1 14,284.7 532.4 223.7 1,057.1
2005 10,004.2 421.0 14,257.6 532.5 224.8 1,057.1
2006 9,997.8 421.9 14,230.4 532.7 225.9 1,057.1
2007 9,993.2 422.8 14,203.3 532.8 227.0 1,057.1

Figure 7.1.4 Land use in New Zealand in 2002: IPCC land-use categories (mapped from LCDB2)

Figure 7.1.4 Land use in New Zealand in 2002: IPCC land-use categories (mapped from LCDB2)

Table 7.1.2 New Zealand’s land-use change matrix between 1997 and 2002 (all areas in thousands of hectares) (IPCC land-use classes derived from LCDB1 and LCDB2)

                                         

1997

2002

Forest land Cropland Grassland Wetlands Settlements Other Land 2002 Total
Planted Natural Annual Perennial High Producing Low Producing Unmanaged      
Forest land Planted 1904.5 10.8 91.0 39.6 2046.0
Natural 8182.2 0.3 8182.6
Cropland Annual 333.6   0.1 333.7
Perennial 0.2 1.4 78.0 4.2 83.7
Grassland High Producing 0.1 0.9 8883.8 0.9 8885.8
Low Producing 1.2 2.8 0.1 5475.8 0.2 5480.2
Wetlands Unmanaged 0.6 531.2 532.0
Settlements   0.5 5.0 214.8 220.5
Other Land   0.2 1056.8 1057.1
1997 Total   1906.6 8197.0 335.0 78.0 8985.2 5516.4 531.2 215.0 1057.1 26821.6
Net Change 1997–2002   139.4 –14.4 –1.2 5.7 –99.4 –36.2 0.7 5.5
% Change   7.3% –0.2% –0.4% 7.4% –1.1% –0.7% 0.1% 2.5% 0.0% 0.0%

Notes: Areas are shown here if they are greater than 0.1 kha. Smaller areas are not thought to represent an actual land-use change.

Columns and rows may not total due to rounding. Shaded cells indicate land remaining in each category.

Models and Calculations

Tier 1 approach for all land use excluding planted forest

The variables used in the Tier 1 equations for all land-use categories (excluding planted forests) include the carbon stocks in each land use prior to conversion and annual growth in stocks. These factors are tabulated in Tables 7.1.3 and 7.1.4.

Table 7.1.3 Biomass carbon stocks in land use before conversion

Land use Value Pools Source/Reference
Natural forest 182 t C ha–1 All living biomass 364 tonnes dm ha–1 (Hall et al, 1998); carbon fraction of dm (0.5).
Planted forest 224.8 t C ha–1 All living biomass and dead organic matter 1st rotation, 28 years old (Wakelin, 2008).
Annual cropland 0 t C ha–1 All living biomass Annual crops are harvested. GPG-LULUCF only considers perennial crops (Table 3.4.8).
Perennial cropland 63 t C ha–1 Above-ground biomass only* GPG-LULUCF Table 3.3.2. Temperate (all moisture regimes).
High-producing grassland 1.35 t C ha–1 Above-ground biomass only* 2.7 tonnes dm ha–1 (GPG-LULUCF Table 3.4.2, warm temperate – wet climate); carbon fraction of dm (0.5)
Low-producing grassland 0.8 t C ha–1 Above-ground biomass only* 1.6 tonnes dm ha–1 (GPG-LULUCF Table 3.4.2, warm temperate – wet climate); carbon fraction of dm (0.5)
Low-producing grassland with woody biomass 29 t C ha–1 Above-ground biomass only* Clearance of grassland woody vegetation prior to planting with forest (Wakelin, 2007).

* Some methods only estimate above-ground biomass. dm = dry-matter

Table 7.1.4 Annual growth in biomass for land converted to another land use

Land use Value Pools Source/Reference
Natural forest T1 = 2.2 t C ha–1 All living biomass Tier 1 – GPG-LULUCF 3A.1.5 and 3A.1.8 (Gw=3.5 tonnes dm ha–1 (an average of the conifer (3.0) and broadleaf (4.0) values), R = 0.24, Cfrac = 0.5).
Planted forest T1 = 8.9 t C ha–1 Varies All living biomass and dead organic matter Tier 1 – GPG-LULUCF 3A1.6 and 3A1.8 (Gw=14.5 tonnes dm ha–1 (Pinus), R=0.23, Cfrac= 0.5).Tier 2 – included in C-change modelling (Beets et al, 1999, Wakelin, 2007). Modelled annual growth (net of dead organic matter decay) varies by age from 0.1-12.5 t C ha–1 over a 28-year rotation (net of DOM decay).
Annual cropland 5 t C ha–1 All living biomass GPG-LULUCF Table 3.3.8 (temperate all moisture regimes).
Perennial cropland 2.1 t C ha–1 Above-ground biomass only* GPG-LULUCF Table 3.3.8 (temperate all moisture regimes).
High-producing grassland 6.75 t C ha–1 Above-ground biomass only* 13.5 tonnes dm ha–1 (GPG-LULUCF Table 3.4.9, warm temperate – wet climate), Cfrac = 0.5.
Low-producing grassland 3.05 t C ha–1 Above-ground biomass only* 6.1 tonnes dm ha–1 (GPG-LULUCF Table 3.4.9, warm temperate – dry climate), Cfrac = 0.5.

* Some methods only estimate above-ground biomass. dm = dry-matter

Tier 2 approach for planted forest

Tier 2 approach for planted forest

Models are used to derive forest carbon from stem volume yield tables and to calculate removals and emissions. Further detail of the modelling for planted forest is given in section 7.2.2.

Soils

The types of land-use and management factors affecting soil carbon stocks are defined in GPG-LULUCF and include: (1) a land-use factor (FLU) that reflects carbon stock changes associated with the type of land use; (2) a management factor (FMG) that for permanent cropland represents different types of tillage used; and (3) an input factor (FI) representing different levels of inputs to soil. The values used for the stock change factors for each land-use category are shown in Table 7.1.5.

Table 7.1.5 Soil stock change factors selected from GPG-LULUCF Tables 3.3.4 and 3.4.5

Land use FLU (Land use) FMG (Management) FI (Input of organic matter)
Planted forest 1 1 1
Natural forest 1 1 1
Annual cropland 0.71 1.0 1.11
Perennial cropland 0.82 1.16 0.91
High-producing grassland 1 1.14 1.11
Low-producing grassland 1 1.14 1
Other land 1 1 1

New Zealand applies the default inventory time period of 20 years in calculating the Tier 1 estimates. New Zealand uses a country-specific reference soil carbon stock value of 83 t C ha–1 for 0–30 cm depth. This value is within the range of the default IPCC values provided in Table 3.2.4 of GPG-LULUCF for warm, temperate, moist climates (a range of 34–88 t C ha–1). The New Zealand value is calculated from the measured soil carbon in New Zealand grassland soils of 105 t C ha–1 (Tate et al, 2003a), divided by the stock change factors for high-producing grassland, that is:

105 t C ha–1 ÷1 ÷ 1.14 ÷ 1.11 = 83 t C ha–1.

For the Tier 2 analysis, it is assumed that where there is no land-use change (for example, forest land remaining forest land), the soil carbon stock does not change.

Liming

Information on the amount of lime applied is aggregated nationally, with limestone and dolomite both reported together under the limestone subcategory. Estimates of lime application by land use are calculated based on information for fertiliser application gathered through the Agricultural Production Survey. The results of these calculations showed that on average around 94 per cent of the lime was applied to grassland, with the remaining 6 per cent to cropland. Emissions associated with liming were reallocated in this inventory submission and are now reported under grassland and cropland categories.

Biomass burning

Biomass burning takes place either as a controlled burn or as wildfire on forest land or grassland. Reporting at a national level is based on the total areas of grassland or forest land burned. Burning of crop stubbles and prescribed burning of savannah are reported in the agriculture sector. Activity data (eg, areas burned, initial biomass density) and other variables related to biomass burning (eg, fuel consumption) are used in the Tier 1 method. Due to climate and vegetation types, the incidence of vegetation wildfires is low in New Zealand compared to many other countries. Biomass burning is not a significant source of emissions in New Zealand.

Emissions resulting from natural disturbance events in natural forests and grasslands are not reported because the subsequent regrowth is not captured in the inventory. In this situation, GPG-LULUCF (3.2.1.4.2.) states that “if methods are applied that do not capture removals by regrowth after natural disturbances, then it is not necessary to report the CO2 emissions associated with natural disturbance events”. In the case of wildfire in planted forest land, the CO2 emissions are captured by the stock change calculation if the fire damaged area was harvested and replanted, or if the stand is allowed to grow on with a reduced net stocked area. Carbon dioxide emissions may be underestimated in the instance where a damaged stand had reached maturity without a reduction in its net stocked area. However, the total area of wildfires in planted forests is small and, therefore, this is not regarded as a significant source of error.

7.2 Forest land (CRF 5A)

7.2.1 Description

In 2007, forest land contributed 24,527.9 Gg CO2-e of net removals. This value includes removals from the growth of planted forests, emissions from the conversion of land to planted forest and emissions from harvesting and deforestation. Net removals from forest land had increased by 5,891.4 (31.5 per cent) over the 1990 level of 18,649.3 Gg CO2-e. In 2007, forest land remaining forest land and conversion to forest land were key categories (trend and level assessment).

In New Zealand’s Initial Report under the Kyoto Protocol (Ministry for the Environment, 2006), national forest definition parameters were specified as required by UNFCCC decision 16/CMP.1. The New Zealand values are a minimum area of 1 hectare, a height of 5 metres and a minimum crown cover of 30 per cent. This definition is used when forest is mapped by the LUCAS project and reported in future inventory submissions. To complete this submission, the categories of forest land as mapped in the LCDB1 and LCDB2 were used (an area of 1 hectare and a width of 100 metres).

The IPCC Guidelines and GPG-LULUCF defines managed forest land as: “Forest management is the process of planning and implementing practices for stewardship and use of the forest aimed at fulfilling relevant ecological, economic and social functions of the forest”. All of New Zealand’s forests, both those planted for timber production and natural forests managed for conservation values, are considered managed forests.

Forest land dominated carbon stock changes in the LULUCF sector. Forestry now covers approximately 38 per cent of New Zealand. This includes natural and planted forest, and shrubland that meets the definition of forestry. In New Zealand, there has been considerable afforestation since 1990, and some deforestation of planted forests has occurred since 2004.

For inventory reporting, two subcategories are used to cover all of New Zealand’s forests: natural forest and planted forest.

Natural forest

Natural forest is a term used to distinguish New Zealand’s native forests from planted production forests. Native forest ecosystems comprise a range of indigenous and some naturalised exotic species. Two principal types of forest exist: beech forests (mainly Nothofagus species) and podocarp/broadleaf forests. In addition, shrublands – made up predominantly of manuka and kanuka – and retired grasslands, have the potential to reach the forest definition in some locations. New Zealand has approximately 8.2 million hectares of natural forest including shrublands (based on LCDB2 estimates).

Government controls on natural forest clearance (deforestation) were first imposed in the late nineteenth century, but demand for timber and agricultural land resulted in further forest clearance. By the 1970s, public concern led to stronger government conservation measures. Large-scale forest clearance for agricultural land ceased and New Zealand’s domestic timber supply came largely from planted forests.

Further government administrative changes in 1987 resulted in the reservation of about five million hectares (18 per cent of New Zealand’s total land area) of publicly owned natural forests. Commercial timber harvest from private natural forest was restricted to that sourced under sustainable forest management plans and permits by a 1993 amendment to the Forests Act of 1949. The amendment exempted West Coast publicly owned forests and forests on specific Māori-owned lands. Further government controls resulted in the cessation of any logging of natural forest on public land including the West Coast publicly owned forests in March 2002.

Less than 0.1 per cent of New Zealand’s total forest production is now harvested from natural forests. New Zealand’s wood needs are now almost exclusively met from planted production forests. The natural forest harvest reported in the inventory refers to harvest of forests on land returned to Māori under the South Island Landless Natives Act (SILNA) 1906. These forests are currently exempt from provisions that apply to all privately-owned natural forests that require a sustainable forest management plan or permit before any harvesting. Approximately 50,000 hectares are covered by the SILNA. There is no specific data to estimate growth in these forests.

Timber harvested from privately-owned natural forests and from SILNA forests has continued at a low level since the 1993 controls were imposed. Current proposed legislative changes to the Forest Amendment Act (2004) of outlined restrictions will continue to exempt the SILNA forests although logging has further reduced in these forests.

Removals of CO2 in natural forest are calculated using an IPCC Tier 1 approach. Preliminary results showed that New Zealand’s natural forests are approximately in steady-state or a possible small sink of carbon ie, changes in vegetation carbon stock lie between 0.3–2.5 Tg C yr–1 (Tate et al, 2000). For this reason, removals were set to emissions in the common reporting format tables. Results from analysis of the Carbon Monitoring System (CMS) data within natural forests as part of the LUCAS programme will enable New Zealand to provide improved estimates (refer to Annex 3.2).

Planted forest

New Zealand has a substantial estate of planted forests, created specifically for timber supply purposes. New Zealand’s planted forests are intensively managed and there is well-established data on the estate’s extent and characteristics. Having a renewable timber resource has allowed New Zealand to protect and sustainably manage its natural forests. Pinus radiata is the dominant species, making up around 90 per cent of the planted forest area. These forests are usually composed of stands of trees of a single-age class and all forests have relatively standard silviculture regimes applied.

Between 1990 and 2007, it is estimated that around 680,000 hectares of new forest was established as a result of afforestation activities. In 2007, plantation forestry covered an estimated 1.8 million hectares of New Zealand (around 7 per cent of the total land area). A large planted forest resource enables New Zealand to sustainably manage its publicly and privately-owned natural forest.

The new planting rate (land reforested or afforested) over the last 30 years was, on average, 40,000 hectares per year (Figure 7.2.1). While new planting rates were high from 1992 to 1998 (averaging 69,000 hectares per year), since 1998 the rate of new planting rapidly declined and is now at very low levels. In 2007, it was estimated that only 2,000 hectares of new forest was established (the lowest level since 1950). Some of the land that was not replanted was converted into grassland. The very low levels of new planting, and conversion of some forest land to grassland, were due to the relative profitability of some forms of pastoral farming (particularly dairy farming) compared to forestry.

Figure 7.2.1 Annual forest planting in New Zealand from 1920 to 2007

Figure 7.2.1 Annual forest planting in New Zealand from 1920 to 2007

 

Hectares of afforestation (000s) Government owned

Hectares of afforestation (000s) Privately owned

1920 1 0
1921 2 2
1922 3 3
1923 4 5
1924 5 6
1925 6 8
1926 9 9
1927 12 11
1928 16 12
1929 19 14
1930 22 15
1931 19 13
1932 15 12
1933 12 10
1934 8 9
1935 5 7
1936 3 4
1937 1 2
1938 1 0
1939 3 0
1940 2 0
1941 2 0
1942 1 0
1943 1 0
1944 1 0
1945 0 0
1946 0 0
1947 1 0
1948 2 0
1949 2 0
1950 2 1
1951 2 1
1952 2 1
1953 2 1
1954 2 2
1955 3 2
1956 3 2
1957 3 2
1958 3 2
1959 3 2
1960 4 2
1961 5 2
1962 6 3
1963 7 4
1964 9 5
1965 8 5
1966 9 6
1967 10 7
1968 13 8
1969 15 8
1970 15 11
1971 13 16
1972 17 16
1973 21 23
1974 21 23
1975 22 23
1976 22 27
1977 20 19
1978 21 22
1979 18 26
1980 17 21
1981 22 23
1982 19 30
1983 20 31
1984 20 36
1985 18 30
1986 15 25
1987 10 20
1988 3 17
1989 0 21
1990 0 16
1991 0 15
1992 0 50
1993 0 62
1994 0 98
1995 0 74
1996 0 84
1997 0 64
1998 0 51
1999 0 40
2000 0 34
2001 0 30
2002 0 22
2003 0 20
2004 0 11
2005 0 6
2006 0 5
2007 0 2

7.2.2 Methodological issues

Forest land remaining forest land

Natural forest (Tier 1)

A small amount of harvesting took place that was exempt from the sustainable management plan requirement (section 7.2.1). This harvesting was assumed to result in an emission of all above-ground biomass carbon, with no compensating forest growth. This is probably a conservative assumption, as it is possible that some harvesting of these forests was carried out on a sustainable basis. Estimates of harvesting from exempted natural forests were provided by the Ministry of Agriculture and Forestry. Stem wood volumes were converted to oven-dry weight using a factor of 0.5 (GPG-LULUCF equation 3.2.4) and then expanded to include non-stem wood biomass using a factor of 2.04 as used by Wakelin, (2008). These New Zealand-specific factors are within the ranges given by GPG-LULUCF (Tables 3A1.9-1 and 3A1.10).

Results from analysis of the natural forest plot collected as part of the LUCAS project will enable New Zealand to provide improved estimates in future submissions (refer to Annex 3.2).

Planted forest (Tier 2)

Compared to many forest ecosystems, total biomass and carbon stocks in New Zealand’s planted forests are relatively straightforward to estimate. The methodology applied for the inventory involved:

  • the annual NEFD surveys

  • stem wood volume yield tables are compiled periodically for combinations of species, silvicultural regime and location

  • the C_change models (Beets et al, 1999) were used to derive forest biomass and carbon from stem volume yield tables

  • the Forestry Oriented Linear Programming Interpreter (FOLPI) (Garcia, 1984; Manley et al, 1991) was used to recalculate historic estimates of CO2 removals and emissions by time shifting the latest available data backwards.

Planted forest survey data

The results of the NEFD survey, as at 1 April 2007, were used to calculate removals and emissions provided in this submission. This latest information provided new forest area data along with data on new planting, restocking and harvesting and merchantable, stem wood volume by crop type and age for the 2007 year (Ministry of Agriculture and Forestry, 2008).

A crop type is an aggregate of forest stands that are similar with respect to species, silviculture and location. Each crop type had a yield table that provided estimated volumes of stem wood per hectare, by age. The total forest area after harvest for the year ending March 2007 was based on: (a) the latest area estimates provided by the 2007 NEFD; (b) an estimate of the area to be planted during the year; and (c) an estimate of the area harvested during the year. The activity data was collected by the Ministry of Agriculture and Forestry. These estimates are revised and recalculated annually as provisional estimates are replaced by confirmed actual statistics.

Modelling

A summary of the modelling steps used in inventory calculations is shown in Figure 7.2.2. The C_change model estimates total dry-matter per hectare, by vegetation component and annual age class from stem wood volume data (see Box 7.2).

Figure 7.2.2: Planted forest inventory modelling process

Figure 7.2.2: Planted forest inventory modelling process

Note: * refers to the national average yield table.

The schematic illustrates an overview of the planted forest inventory modelling process. All of the details in the figure are contained within the text of this chapter (LULUCF).

Box 7.2 Process steps in the C_change model (Beets et al, 1999)

1. Stem wood volume is converted to an oven-dry biomass weight.

2. The dry weight of non-stem wood components (bark, branches, foliage, cones, stumps, roots, floor litter and understory) is calculated from stem wood volume using allometric equations. These allometric equations take account of age, stocking and site fertility.

3. Total forest biomass is converted to carbon weight. The carbon fraction of dry-matter is 0.5 using the IPCC default (GPG-LULUCF p3.25). Note that although the IPCC default carbon fraction for litter is 0.37, initial investigations suggest that the carbon fraction in the litter pool in planted forests in New Zealand is higher. A New Zealand-specific factor of 0.5 is used (Wakelin, 2008).

For this submission, C_change was used to create a corresponding carbon yield table for each wood volume yield table, based on wood density and management assumptions appropriate to the species, regime and region. The allometric equations used were based on data for Pinus radiata. Approximately 10 per cent of the estate is made up of other species such as Douglas fir (Pseudotsuga menziesii) (5 per cent), other exotic softwoods (2 per cent), and exotic hardwoods (3 per cent). It is uncertain what impact these other species have on the accuracy of calculations of total biomass, but current research and data collection will enable the impact to be assessed in future inventory submissions. The output from C_change was a dry-matter yield table with estimates of dry-matter per hectare by age class for each component. These were aggregated into the IPCC non-soil pools and converted to carbon using a carbon fraction of 0.5. To simplify the subsequent modelling, all crop types were then aggregated to form a single, national, area weighted crop type and associated area weighted national yield table. Total carbon yield by stand age and rotation are shown in Figure 7.2.3 below.

The second of the two models, FOLPI, is a linear programming model used to optimise the management of forest estates over time. It simulates actual rates of planting and harvesting where time-series data exists. Carbon stock estimates are calculated for March years, with calendar-year data estimated based on two years of data. The assumption is that the stem wood removed at harvest for both natural and planted forests is oxidised in the year of harvest. The FOLPI model uses the biomass and carbon stocks at one point in time to give total carbon stocks for each modelled year and changes in carbon stocks between those years. Among the outputs of the FOLPI model were the LULUCF results for 1990–2007. These results included:

  • stem wood volume harvested from the planted estate, hence CO2 emitted in that harvest

  • total stock of estate carbon after harvesting in each year (accounting also for the decay of non-stem wood carbon left after harvesting).

The removal of carbon (net of harvest) is calculated from the total stock values. The gross removal of carbon is then calculated by adding the harvested stem wood carbon back into the net carbon removal figures. This provided the change in carbon stock between harvested forests and this year’s unharvested forests.

Figure 7.2.3 Total carbon yield by stand age and rotation

Figure 7.2.3 Total carbon yield by stand age and rotation

Age Total Carbon Total Carbon
  (tC/ha) (tC/ha)
0 0.0 102.1
1 2.5 89.7
2 3.9 78.4
3 7.7 71.6
4 12.7 67.4
5 18.8 65.9
6 25.6 65.9
7 33.3 68.1
8 41.9 71.8
9 51.6 77.5
10 61.2 83.6
11 71.3 90.6
12 83.7 100.5
13 90.7 105.2
14 95.4 108.0
15 100.5 111.5
16 107.1 116.6
17 115.0 123.3
18 123.2 130.4
19 132.4 138.6
20 142.2 147.7
21 152.1 156.9
22 162.2 166.4
23 172.2 175.8
24 182.8 186.0
25 193.2 196.0
26 203.7 206.1
27 214.2 216.2
28 224.8 226.6
29 235.2 236.7
30 245.3 246.6
31 254.9 256.2
32 264.9 266.1
33 274.4 275.4
34 284.0 284.8
35 292.9 293.6
36 302.1 302.7
37 310.9 311.4
38 319.6 320.0
39 328.0 328.3
40 336.6 337.0
41 334.4 334.7
42 335.7 335.9
43 335.4 335.7
44 336.2 336.3
45 336.7 336.8
46 337.5 337.6
47 338.3 338.4
48 339.3 339.4
49 340.4 340.5
50 341.5 341.6
51 342.1 342.1
52 342.6 342.7
53 343.4 343.4
54 344.1 344.1
55 344.6 344.6
56 345.3 345.3
57 345.9 345.9
58 346.6 346.6
59 347.1 347.1
60 347.4 347.4
61 347.8 347.7
62 348.1 348.1
63 348.4 348.4
64 348.7 348.7
65 349.1 349.1
66 349.4 349.4
67 349.8 349.7
68 350.0 349.9
69 350.4 350.3
70 350.7 350.7
71 351.1 351.1
72 351.3 351.3
73 351.7 351.7
74 352.0 352.0
75 352.3 352.2
76 352.6 352.6
77 352.9 352.9
78 353.2 353.2
79 353.5 353.5
80 353.7 353.7

The method in this submission included the use of information on rotation number obtained through the NEFD survey to define the historic afforestation and restocking time series. This allows for a more accurate separation into the forest land remaining forest land, and land converted to forest-land categories, than was previously possible. Existing planted forest areas were allocated to one of two crop types, representing first and second rotation stands respectively. This separation was required so that the carbon stock in residues (resulting from harvesting a previous crop) could be correctly accounted for. In previous inventory submissions, the allocation was made by assuming areas planted before 1970 were first rotation. For areas planted in 1970 or later, the first rotation allocation was based on national afforestation statistics. Any remaining area in planting years 1970–2003 was assumed to be second rotation. For this submission, NEFD rotation information was used in the modelling. As a result, there was a higher proportion of second rotation area present in 1990, with correspondingly lower net carbon uptake due to the presence of decaying harvest residues.

In this submission, estimated deforestation of planted forests was explicitly modelled for the years 2004–2007. This included some deforestation of immature post-1989 stands. Significant deforestation of planted forests is a relatively recent phenomenon. In previous inventory submissions, these deforested areas were not explicitly modelled. Further detail on this improvement is provided in section 7.2.5.

Biomass burning

For the forest land remaining forest-land category there is no controlled burning in New Zealand. The inventory only reports emissions that resulted from wildfire, where the IPCC default temperate forest fuel consumption rate of 45 per cent of total biomass was used (GPG-LULUCF Table 3A.1.12). Wildfire activity data is collected and managed by the New Zealand Fire Service (NZFS) and the National Rural Fire Authority (NRFA). For this submission, the NZFS data was used from June 2001–June 2008, with the average over this period applied back to 1990. Activity data for wildfire is generally of poor quality, but it is estimated there have not been major changes in wildfire occurrence since 1990 (Challands, 2007).

For wildfire in planted forest, CO2 emissions will be captured by the stock change calculation if the fire damaged area is harvested and replanted, or if the stand is allowed to grow on but with a reduced net stocked area. Carbon dioxide emissions may be underestimated in the instance where a damaged stand has reached maturity without a reduction in its net stocked area. However, the total area of wildfires in planted forests is small and, therefore, this is not regarded as a significant source of error.

Land converted to forest land

Previously, New Zealand only reported emissions from the clearance of non-forest vegetation for afforestation purposes in this category. Now carbon stock changes due to afforestation are reported here for one full rotation before the area is transferred into the forest land remaining forest-land category. The modelled rotation length for 1990–2007 varies, with an annual average of 27–29 years. Forest yield and carbon contents are as described for forest land remaining forest land above.

Data on the amount of land clearance for new forest planting were sourced from the annual NEFD survey. The information included the proportion of new forest planted that occurred on grassland. This includes woody vegetation that falls below and was not expected to exceed, without human intervention, the threshold used to define forest land for New Zealand under the Kyoto Protocol.

Data was available from 1993 to 2007. Based on this activity data, it was assumed that the proportion of new forest planting on grassland with woody vegetation was 20 per cent before 1993. This activity data was used to estimate emissions resulting from the clearance of woody vegetation prior to afforestation planting.

Biomass burning

It was estimated that 25 per cent of the land converted to forest land was cleared using controlled burning, with a New Zealand-specific fuel consumption rate of 70 per cent of above-ground biomass (Wakelin, 2007). The remainder of the above-ground biomass and all biomass on cleared but unburned sites were assumed to decay over 10 years (IPCC, 1996). Current research aims to quantify emissions from the burning of residues that resulted from the conversion of planted forests to grassland. Emissions of CO2 from controlled burns for afforestation were reported as a stock change in the grassland category. Carbon dioxide emissions resulting from natural disturbance events were not reported, as subsequent regrowth is not part of the calculation methods (GPG-LULUCF 3.2.1.4.2).

Wildfire emissions are reported under forest land remaining forest land, as the wildfire incidence data does not identify wildfires by rotation number.

7.2.3 Uncertainties and time-series consistency

Pinus radiata had been widely studied in New Zealand because of its significance in the forestry industry. It is known that density varies with temperature, soil fertility, genetic stock and age, and equations have been developed to relate routine field measurements (eg, of outer-wood density from core samples) to whole tree density, and to project this over time. The variation in Pinus radiata outer-wood density at breast height is significant (350 to 600 kg/m3) with the upper limit occurring on warm, low fertility sites (Beets et al, 2001).

In the yield tables that form the national carbon yield table, three broad density regions are recognised, and the effect of age on density is also modelled. As a result, the average density of harvested logs in the model varies with the average clearfell age, and is higher than the average density for the growing stock. The latter is also not constant over time because the age class distribution is variable.

Attempts have been made to quantify the uncertainties in the CO2 removal estimates for planted forests (Table 7.2.3.1) but it is difficult to quantify the overall error due to the assumptions implicit in the models. Some uncertainties within the C-change model are well characterised (Hollinger et al, 1993). Combining the uncertainties indicated that the proportional error in the carbon sequestration estimates is likely to be at least ± 16 per cent.

Table 7.2.3.1 Uncertainty in emissions and removals from planted forest

Variable Uncertainty (95% confidence interval)
Uncertainty in land area  
NEFD Survey ± 5%
Uncertainty in biomass accumulation rates  
C_change model: wood density ± 3%
C_change model: carbon allocation ± 15%
C_change model: carbon content ± 5%
NEFD yield tables ± 5%
Combined uncertainty ± 16%

A sensitivity analysis was conducted using the above accuracy ranges for total planted area and commercial yield, and a proportional uncertainty error of ± 16 per cent. The C_change model runs indicate that the precision of the carbon stock estimates could be of the order of ± 25 per cent. As part of the development of LUCAS, research has been commissioned to better quantify uncertainty. No uncertainty estimates are currently available for emissions from harvesting of natural forests.

Removals from forest land were 6.2 per cent of New Zealand’s total emissions and removals uncertainty in 2007 (Annex 7). Forest land introduced 2.2 per cent uncertainty into the trend in the national total from 1990 to 2007.

7.2.4 Source-specific QA/QC and verification

The forest land remaining forest land (CO2) and land converted to forest land (CO2) were key categories in 2007 (for both the level and trend assessment).

In the preparation of this inventory submission, the data for these categories underwent Tier 1 quality checks.

The data was also reviewed by officials from the Ministry for the Environment and the Ministry of Agriculture and Forestry. Calculated estimates were visually assessed for obvious errors in calculations. Land-use change matrices were used to ensure that the allocation of land between categories produced a consistent national total area of land.

One of the primary input data sets used is the NEFD. The NEFD is New Zealand’s official source of statistics on planted production forests and, as such, is subject to formalised data checking procedures. Each NEFD report is reviewed by a technical NEFD committee before publication. Broad comparisons of forest areas reported in the NEFD reports are made with independent sources of information such as the LCDB estimates and the annual results of Statistics New Zealand’s Agricultural Production Survey. The NEFD tables have been subject to review (eg, Jaakko Poyry Consulting, 2003; Manley, 2004) and are in the process of being revised.

The 2007 planted forests removals and emissions were compared for consistency with the 2006 estimates (Wakelin, 2008), with both level and trend being similar.

7.2.5 Source-specific recalculations

The main changes in the data for the 2009 inventory submission were due to:

NEFD data

The classification of planted forests into first or subsequent rotations in the NEFD data was updated for this submission, as new data for approximately 94 per cent of the total planted forest area was available this year. This information allows for separation into appropriate converted and remaining categories and was used for the first time in calibrating historic activity data. A greater proportion of the total area has been identified as second rotation throughout the time series from 1990. Second rotation stands have a lower net uptake of carbon than first rotation stands of the same age due to the presence of decaying harvest residues. This reduces net uptake compared with previous estimates.

Modelling process

Significant deforestation of areas of planted forest is a recent phenomenon, only occurring since 2004. In previous submissions, deforested areas were not explicitly modelled. Any deforested areas were removed from the NEFD data for the whole time series. Therefore, using NEFD survey data meant that derived historic age class distributions did not include information of the areas deforested. This approach was revised for this submission to explicitly model estimated deforestation of planted forests for the years 2004–2007, including some deforestation of immature post-1989 stands. This was an improvement in the modelling process.

Deforestation is represented as an instantaneous emission but these emissions were not able to be separated from harvested emissions for this submission and are captured in the forest land remaining forest land or grassland converted to forest-land categories. Further work is required to refine the estimates of deforestation activity data and associated emissions and to allow this to be reported against the correct category. The Tier 1 estimates of planted forest deforestation emissions previously reported under forest land converted to grassland have been removed to avoid double counting. Natural forest deforestation and soil emissions are still accounted through the Tier 1 analysis in this submission.

7.2.6 Source-specific planned improvements

This inventory includes a provisional estimate of 10,000 hectares of deforestation in 2007. Updated information in April 2009 indicates the area of deforestation in 2007 was in the range of 15,000-20,000 hectares. The recalculation for the updated area will be included in the 2010 submission.

The revised modelling process to better account for deforestation has provided more accurate estimates of total emissions and removals for forest land. However, emissions due to the conversion of planted forest to grassland will be explicitly separated in the modelling and reported under the grassland land-use category. This will be reported in the 2010 submission.

Development of the LUCAS will enable New Zealand to improve reporting of the LULUCF sector in the 2010 submission. Further details are included in Annex 3.2.

7.3 Cropland (CRF 5B)

7.3.1 Description

In 2007, cropland accounted for 510.3 Gg CO2-e of net removals. Net removals from cropland had increased 32.6 Gg CO2-e (6.8 per cent) from the 1990 level of 477.7 Gg CO2-e. In 2007, the cropland remaining cropland category (CO2) and the conversion to cropland (CO2) categories were key categories (level and trend assessment respectively).

Cropland in New Zealand is separated into two subcategories, annual and perennial. Cropland comprised less than 1.6 per cent (or 417,400 hectares) of New Zealand’s total land area in 2002. This included 333,700 hectares in short rotation/annual cropland and 83,700 hectares in perennial cropland. Annual crops include cereals, grains, oil seeds, vegetables, root crops and forages. Perennial crops include orchards, vineyards and shelter belts.

The amount of carbon stored in, emitted or removed from permanent cropland depends on crop type, management practices, and soil and climate variables. Annual crops are harvested each year, with no long-term storage of carbon in biomass. However, perennial woody vegetation in orchards can store significant carbon in long-lived biomass, the amount depending on species type, density, growth rates, and harvesting and pruning practices.

7.3.2 Methodological issues

Emissions and removals are calculated using IPCC Tier 1 emission and removal factors and activity data from the LCDB analysis described in section 7.1.2.

Cropland remaining cropland

Living biomass

The change in biomass is only estimated for perennial woody crops (GPG-LULUCF (section 3.3.1.1.1.)) For annual crops, increase in biomass stocks in a single year is assumed to be equal to biomass losses from harvest and mortality in that same year and there is no net accumulation of biomass carbon stocks.

The biomass accumulation rate (2.1 t C ha–1 yr–1) in perennial vegetation and biomass carbon loss (63 t C ha–1) are from Table 3.3.2 of the GPG-LULUCF. New Zealand uses the values for a temperate climate (all moisture regimes). The LCDB analysis cannot provide information on areas of perennial vegetation temporarily destocked; therefore, no losses in carbon stock can be calculated. When the results from LUCAS are included in future submissions, it will be assumed that perennial cropland will be reported in the converted land category for the default 20-year period. Beyond the 20-year period it will be assumed that it reaches a “steady state” where growth equals losses with no net change in emissions/removals.

Dead organic matter

New Zealand has not reported estimates of dead organic matter in this category. The notation “NE” is used in the commoning report format tables. Sufficient information is not available to estimate carbon stock change in dead organic matter pools within the cropland remaining cropland subcategory (IPCC, 2003).

Soil carbon

Mineral soils comprise 99.9 per cent of New Zealand soils (Tate et al, 2004). To provide a Tier 1 estimate, New Zealand uses the IPCC default method for mineral soils (equation 3.3.3, GPG-LULUCF). This equation compares the soil organic carbon stock in the inventory year, with the soil organic carbon stock in “T” years before the inventory. New Zealand uses the IPCC default value of 20 years for “T”.

Changes in soil carbon stock are caused by changes in the land-use and management factors. The values for FLU, FMG and FI are from Table 3.3.4 in GPG-LULUCF and are shown for each category in Table 7.1.5. Within the cropland category, the LCDB does not provide sufficient information to determine whether there has been a change in land use and management in the 20 years before the inventory. Therefore, for cropland remaining cropland, the values for FLU, FMG and FI are considered to be constant and there is no net change in carbon stocks in soils.

Liming

Lime used in New Zealand is agricultural lime, or ground limestone. The calculation of CO2 emissions from the liming of cropland soils is based on GPG-LULUCF equation 3.4.11, using the total amount of limestone applied (provided by Statistics New Zealand) and a carbon conversion factor from limestone to carbon. New Zealand used the IPCC (1996) default value of 0.12 for carbon conversion.

The survey data for the amount of lime applied is affected by several gaps in the time series. No survey was carried out in 1991, or for 1997 through to 2001. Linear interpolation was used to represent the data for these years. Since 2002 there was a decrease in the amount of lime applied. It is not clear why this decrease occurred but quantities do vary from year to year depending on a number of factors, including farming returns.

Land converted to cropland

Living biomass

The Tier 1 method multiplies the annual area of land converted to cropland by the carbon stock change per area for that type of conversion. The calculation includes changes in carbon stocks from one year of cropland growth and is provided in equation 3.3.8 of GPG-LULUCF.

For Tier 1, carbon stocks in biomass immediately after conversion are assumed to be zero, (ie, the land is cleared of all vegetation before planting crops). To complete the Tier 1 analysis, New Zealand has selected from default parameter values provided in GPG-LULUCF. These are shown in Tables 7.1.3 and Table 7.1.4.

Dead organic matter

New Zealand does not report estimates of dead organic matter in this category. The notation “NE” is used in the common reporting format tables. Sufficient information is not available to provide a basic approach with default parameters to estimate carbon stock change in dead organic matter pools in land converted to cropland (GPG-LULUCF).

Soil carbon

To calculate soil carbon stocks, New Zealand follows the method outlined in GPG-LULUCF. For Tier 1, the initial soil carbon stock is determined from the same reference soil carbon stocks used for all land uses, together with stock change factors (FLU, FMG, FI) appropriate for the previous land use (refer to section 7.1.2 in this report).

Nitrous oxide emissions

Nitrous oxide emissions are from mineralisation of soil organic matter resulting from conversion of forest land, grassland, settlements or other land to cropland. New Zealand uses the method outlined in GPG-LULUCF equations 3.3.14 and 3.3.15. The input parameters to these equations are:

  • change in carbon stocks in mineral soils in land converted to cropland: this value is calculated from the land converted to cropland soil carbon calculations

  • EF1: the emission factor for calculating emissions of N2O from nitrogen in the soil. A New Zealand-specific value of 0.01 kg N2O-N/kg N is used (Kelliher et al, 2006)

  • C:N ratio: the IPCC default ratio of carbon to nitrogen in soil organic matter (1:15) is used.

7.3.3 Uncertainties and time-series consistency

Uncertainties can be broken down into uncertainty in activity data, and uncertainty in other variables such as emission factors, growth rates, and the effect of land management factors. The combined effect of uncertainty in cropland is estimated at ± 75 per cent (95 per cent confidence interval). As shown in Table 7.3.3.1, while uncertainty in activity data is low, uncertainty in the IPCC default variables dominates the overall uncertainty. However, uncertainty in activity data used in the inventory is greater than assessed for the LCDB alone. Error is introduced from extrapolation as mapping is not repeated annually. Only two years (1997 and 2002) of mapped activity data is used. In addition, the mapping is not specific to IPCC categories.

Table 7.3.3.1 Uncertainty in emissions and removals from cropland (and grassland)

Variable Uncertainty (95% confidence interval)
Uncertainty in land area  
LCDB1 (user accuracy 93.9%) ± 6%
LCDB2 (assumed to be equal to LCDB1) ± 6%
Uncertainty in biomass accumulation rates ± 75% (GPG-LULUCF Tables 3.3.2, 3.4.2)
Carbon accumulation from land use change ± 75%
Carbon stocks in previous land use ± 75%
Estimated uncertainty in land management factors ± 12% (GPG-LULUCF Table 3.3.4)
Uncertainty in liming ± 40%
Combined uncertainty ± 75%

7.3.4 Category-specific QA/QC and verification

In 2007, the cropland remaining cropland category (CO2) and the conversion to cropland (CO2) categories were key categories (level and trend assessment respectively). In the preparation of this inventory submission, the data in this category underwent IPCC Tier 1 quality checks.

7.3.5 Category-specific recalculations

The N2O emissions were updated using the New Zealand-specific N2O emission factor, EF1, to be consistent with emission calculations in the agriculture sector. The time series was recalculated to reflect this change. In addition, recalculations were carried out for the time series due to the inclusion of liming within this land-use category.

7.3.6 Category-specific planned improvements

The use of historic activity data for cropland is being investigated. This will allow for improved estimates of the land converted to cropland and cropland remaining cropland categories to be reported in future inventory submissions. New Zealand will also investigate the potential use of country-specific emission factors for the cropland category.

7.4 Grassland (CRF 5C)

7.4.1 Description

In 2007, the net emissions from grassland were 1,063.7 Gg CO2-e. This was an increase of 199.8 Gg CO2-e (23.1 per cent) from the 1990 level of 863.9 Gg CO2-e. These emissions were from land converted to grassland and grassland remaining grassland categories. Carbon dioxide emissions from conversion to grassland were identified as a key category (trend) for 2007.

In New Zealand, grassland covers a range of land-cover types. Two grassland subcategories are used in this submission, namely low producing and high producing. Low-producing grassland consists of either native tussock land or areas composed of shrubby vegetation (often referred to as “scrub” in New Zealand). Scrub contains woody biomass but does not meet the forest definition (section 7.2.1). High-producing grassland consists of high-intensity pasture land.

In 2002, high-producing pasture covered 33 per cent of the country, while low-producing grassland made up a further 20 per cent. Much of New Zealand’s grassland is grazed, with pastoral agriculture as the main land use. Most New Zealand agriculture is based on extensive pasture systems with animals grazed outdoors year-round. There has been a recent trend for conversion of plantation forest to pasture (deforestation).

7.4.2 Methodological issues

Grassland remaining grassland

Living biomass

In GPG-LULUCF (section 3.4.1.1.1.1), the Tier 1 assumption is no change in living biomass. The rationale is that where management practices are static, biomass carbon stocks will be in an approximate steady-state where carbon accumulation through plant growth is roughly balanced by losses. New Zealand has reported “NE” in the common reporting format tables because the activity occurs but no estimate of removals or emissions was able to be calculated.

Dead organic matter

New Zealand has not reported estimates of dead organic matter in this category. The notation “NE” is used in the common reporting format tables. GPG-LULUCF states there is insufficient information to develop default coefficients for estimating the dead organic matter pool. For Tier 1 and 2 methods, changes in dead organic matter and inorganic carbon stocks should be assumed to be zero.

Soil carbon

Mineral soils cover 99.93 per cent of New Zealand (Tate et al, 2004). To provide a Tier 1 estimate, New Zealand uses the IPCC default method for mineral soils (equation 3.4.8 of GPG-LULUCF). The LCDB analysis used in this submission does not provide sufficient information to determine whether there has been a change in land use and management in grassland for the 20 years before the inventory. Therefore, for areas of grassland remaining grassland, the values for FLU, FMG and FI were considered as constant and, consequently, the calculation shows there was no net change in carbon stocks in soils.

Biomass Burning

Non-carbon dioxide emissions from wildfires in low-producing grasslands (tussock and grassland with above-ground woody biomass) are reported in the LULUCF sector, while those from controlled (prescribed) burning of savannah are covered in the agriculture sector. Carbon dioxide emissions that resulted from natural disturbance events are not reported, as subsequent regrowth is not part of the calculation (GPG-LULUCF 3.2.1.4.2).

For low-producing grassland with above-ground woody biomass, the activity data is sourced from the NZFS and combines their categories for gorse, scrub and wetland. The GPG-LULUCF average default value for the proportion of pre-fire biomass consumed in temperate shrubland is 0.95 (GPG-LULUCF Table 3A.1.12). For New Zealand conditions, it has been suggested that the controlled burn value of 70 per cent would be more appropriate (Wakelin, 2006). This was applied to the total biomass (rather than above ground only) using the more general initial grassland with above-ground woody biomass estimate of 136 t dm hectare–1 (Hall et al, 2001), rather than the specific “pre-afforestation” biomass value used for grassland (with woody vegetation) converted to forest land.

In previous submissions, emissions from wildfire in tussock grassland were not reported. Although the area of tussock burned is similar to that of grassland with above-ground woody biomass, emissions were much lower because there was less biomass present. For wildfire in tussock, the assumptions used for controlled burning were applied to the NZFS wildfire areas.

Liming

Lime used in New Zealand is agricultural lime, or ground limestone. The calculation of CO2 emissions from the liming of grassland soils is based on GPG-LULUCF equation 3.4.11, using the total amount of limestone applied (provided by Statistics New Zealand) and a carbon conversion factor from limestone to carbon. New Zealand used the IPCC (1996) default value of 0.12 for carbon conversion.

The survey data for the amount of lime applied is affected by several gaps in the time series. No survey was carried out in 1991, or for 1997 through 2001. Linear interpolation was used to represent the data for these years. Since 2002, there was a decrease in the amount of lime applied. It was not clear why this decrease occurred but quantities do vary from year to year depending on a number of factors, including farming returns.

Land converted to grassland

Living biomass

To calculate carbon stock changes in living biomass, New Zealand applies the GPG-LULUCF Tier 1 method. The amount of carbon removed is estimated by multiplying the area converted annually, by the difference between average carbon stocks in biomass before and following conversion, and accounts for carbon in biomass that replaces cleared vegetation. Pre-conversion stocks and annual growth figures are shown in Tables 7.1.3 and 7.1.4. Carbon stock changes from planted forest to grassland conversion were not included in the Tier 1 analysis, but were captured in the Tier 2 analysis (forest-land category). Carbon stocks in biomass immediately after conversion were assumed to be zero.

Dead organic matter

New Zealand has not reported estimates of dead organic matter in this category. The notation “NE” is used in the common reporting format tables. No Tier 1 method exists for calculating emissions or removals from dead organic matter in the land converted to grassland category.

Soil carbon

Land conversion to grassland can occur from all land uses. In New Zealand, the primary change into grassland is from planted forest. New Zealand uses the method outlined in GPG-LULUCF (section 3.4.2.2.1.1). For Tier 1, the initial (pre-conversion) soil carbon stock is determined from a reference soil carbon stock, together with stock change factors (FLU, FMG, FI) appropriate for the previous land use as well as for grassland use. The stock change factors used by New Zealand are shown in Table 7.1.5.

7.4.3 Uncertainties and time-series consistency

Uncertainties can be broken down into uncertainty in activity data, and uncertainty in other variables such as emission factors, growth rates, and the effect of land management factors. The combined effect of uncertainty in grassland is estimated at ± 75 per cent (95 per cent confidence interval). As shown in Table 7.3.3.1, while uncertainty in activity data is low, uncertainty in the IPCC default variables dominates the overall uncertainty. However, uncertainty in activity data used in the inventory is greater than assessed for the LCDB alone. Error is introduced from extrapolation as mapping is not repeated annually. Only two years (1997 and 2002) of mapped activity data is used. In addition, the mapping is not specific to IPCC categories.

7.4.4 Category-specific QA/QC and verification

Carbon dioxide emissions from the land converted to grassland (CO2) and grassland remaining grassland (CO2) categories were key categories (level assessment) in 2007. In the preparation of this inventory submission, the data in these categories underwent Tier 1 quality checks.

7.4.5 Category-specific recalculations

The inclusion of liming within this land-use category caused recalculations for the whole time series.

7.4.6 Category-specific planned improvements

The use of historic activity data for grassland is being investigated. This will allow for improved estimates of the land converted to grassland and grassland remaining grassland categories to be reported in future inventory submissions. In addition, the deforestation emissions resulting from the conversion of planted forest to grassland will be reported in this category rather than under the forest-land category as at present. Sector level improvements resulting from the LUCAS are described in Annex 3.2.

7.5 Wetlands (CRF 5D)

7.5.1 Description

In 2007, the net emissions from wetlands were 0.7 Gg CO2-e. This estimate is constant over the time series. These emissions are from the land converted to wetlands category. Wetlands were not a key category in 2007.

New Zealand has 425,000 kilometres of rivers and streams, and almost 4,000 lakes that are larger than 1 hectare. Damming, diverting and extracting water for power generation, irrigation and human consumption modify the nature of these waterways and can deplete flows and reduce groundwater levels.

Demand for accessible land has led to the modification of a large proportion of New Zealand’s wetland areas in order to provide pastoral land cover. Just over 10 per cent of the original wetland environment remains across New Zealand.

Section 3.5 of GPG-LULUCF defines wetlands as: “land that is covered or saturated by water for all or part of the year (eg, peat land) and that does not fall into the forest land, cropland, grassland or settlements categories. It includes reservoirs as a managed subdivision and natural rivers and lakes as unmanaged subdivisions”. New Zealand categorised LCDB land-cover classes for lakes, rivers and estuarine open water into the unmanaged wetlands category (Table 7.1.4). Other LCDB classes (eg, herbaceous freshwater vegetation, commonly thought of as wetlands in New Zealand), were categorised as grassland following the GPG-LULUCF definitions.

New Zealand follows the definition of flooded land provided in the 2006 Guidelines for Agriculture Forestry Other Land Use as “water bodies where human activities have caused changes in the amount of surface area covered by water, typically through water level regulation. Examples of flooded land include reservoirs for the production of hydroelectricity, irrigation and navigation. Regulated lakes and rivers that do not have substantial changes in water area in comparison with the pre-flooded ecosystem are not considered as flooded land”.

The LCDB does not separate out regulated water bodies where substantial changes in water area occur, and the majority of New Zealand’s hydroelectric schemes are based on rivers and lakes where the main pre-flooded ecosystem is a natural lake or river. For this reason, all of New Zealand’s wetlands are categorised as unmanaged.

7.5.2 Methodological issues

Wetlands remaining wetlands

A method for this subcategory is addressed in the appendix (3A.3) to the GPG-LULUCF (“Wetlands Remaining Wetlands: Basis for future methodological development”). The appendix covers emissions from flooded land and extraction from peat land. Re-cultivation of peat land is included under the agriculture sector. For flooded land, the LCDB data does not separate out regulated water bodies where substantial changes in water area occur. For this reason, figures are not reported for flooded land in the wetlands remaining wetlands category.

Land converted to wetlands

New Zealand has applied the GPG-LULUCF Tier 1 method for estimating the carbon stock change due to land conversion to flooded land (GPG-LULUCF equation 3.5.6). A key assumption is that all land converted to wetlands becomes flooded land. The method assumes that the carbon stock of land before conversion is lost in the first year following conversion. The carbon stock of the land before conversion is documented in Table 7.1.2. In Tier 1, it was assumed that the carbon stock after conversion is zero.

GPG-LULUCF does not provide guidance on carbon stock changes for soils due to land conversion to flooded land. Emissions of non-CO2 gases from land converted to flooded land are covered in appendix 3A.3 of GPG-LULUCF but are not reported (note 3, common reporting format table 5).

7.5.3 Uncertainties and time-series consistency

Uncertainties are estimated as ±75 per cent based on the uncertainty for Tier 1 grassland carbon stocks (GPG-LULUCF Table 3.4.2) lost during conversion to wetlands. While uncertainty in activity data is low, uncertainty in the IPCC default variables dominates the overall uncertainty. However, uncertainty in activity data used in the inventory is greater than assessed for the LCDB alone. Error is introduced from extrapolation as mapping is not repeated annually. Only two years (1997 and 2002) of mapped activity data is used. In addition, the mapping is not specific to IPCC categories.

7.5.4 Category-specific QA/QC and verification

No specific QA/QC and verification was performed for the wetlands category.

7.5.5 Category-specific recalculations

There are no recalculations for this category.

7.5.6 Category-specific planned improvements

The use of historic activity data for wetlands is being investigated. This will allow for improved estimates of “land converted to wetlands” and “wetlands remaining wetlands” to be reported in future inventories. Sector-level improvements to result from the LUCAS are described in Annex 3.2.

7.6 Settlements (CRF 5E)

7.6.1 Description

In 2007, the net emissions from settlements were 97.2 Gg CO2-e. This estimate is constant over the time series. These emissions are from the land converted to settlement category. Settlements were not a key category in 2007.

This land-use category described in GPG-LULUCF 3.6 includes “all developed land, including transportation infrastructure and human settlements of any size, unless they are already included under other land-use categories”. Settlements include trees grown along streets, in public and private gardens, and in parks associated with urban areas. New Zealand categorised the applicable LCDB land-cover classes into the settlements category. This showed there was 215 kha of settlements remaining settlements from 1997 to 2002 with a net gain of 5.5 kha (Table 7.1.5). The largest single subcategory change in area was from high-producing grassland to settlements, averaging 1000 hectares per year.

7.6.2 Methodological issues

Settlements remaining settlements

A basic method for estimating CO2 emissions and removals in settlements remaining settlements is provided in appendix 3A.4 of GPG-LULUCF. The methods and available default data for this land use are preliminary and based on an estimation of changes in carbon stocks per tree crown cover area or carbon stocks per number of trees as a removal factor. Due to data availability, New Zealand is not able to provide these estimates. However, reporting is not a requirement to prepare estimates for this subcategory (note 3, common reporting format table 5).

Land converted to settlements

The equation (3.6.1 GPG LULUCF) for estimating change in carbon stocks associated with land-use conversions is the same as applied for other areas of land-use conversion (eg, land converted to cropland and grassland). The carbon stock of the land before conversion is documented in Table 7.1.2. The default assumptions for a Tier 1 estimate are that all living biomass present before conversion to settlements is lost in the same year as the conversion takes place; and that carbon stocks in living biomass following conversion are equal to zero. GPG-LULUCF does not provide guidance on carbon stock changes for soils due to land conversion to settlements.

7.6.3 Uncertainties and time-series consistency

Uncertainties are estimated as ±75 per cent based on the uncertainty for Tier 1 grassland carbon stocks (GPG-LULUCF Table 3.4.2). While uncertainty in activity data is low, uncertainty in the IPCC default variables dominates the overall uncertainty. However, uncertainty in activity data used in the inventory is greater than assessed for the LCDB alone. Error is introduced from extrapolation as mapping is not repeated annually. Only two years (1997 and 2002) of mapped activity data is used. In addition, the mapping is not specific to IPCC categories.

7.6.4 Category-specific QA/QC and verification

No specific QA/QC and verification was performed for the settlements category in 2007.

7.6.5 Category-specific recalculations

There are no recalculations for this category.

7.6.6 Category-specific planned improvements

The use of historic activity data for settlements is being investigated. This will allow for improved estimates of the land converted to settlements and settlements remaining settlements categories to be reported in future inventory submissions. Improvements to result from the LUCAS are described in Annex 3.2.

7.7 Other land (CRF 5F)

7.7.1 Description

In 2007, the net emissions from other land were 40.6 Gg CO2-e. Net emissions from other land were 13.9 Gg CO2-e (51.9 per cent) higher than the 1990 level of 26.7 Gg CO2-e. These emissions are from land converted to other land category. Other land was not a key category in 2007.

Other land is defined in GPG-LULUCF 3.7 as including bare soil, rock, ice, and all unmanaged land areas that do not fall into any of the other five land-use categories. It mostly consisted of steep, rocky terrain at high elevation, often covered in snow or ice. Other land was included in New Zealand’s land area for checking overall consistency of total land area and tracking conversions to and from other land. This category is less than four per cent of total New Zealand land area.

7.7.2 Methodological issues

Other land remaining other land

All of New Zealand’s land area is classified as “managed”. No guidance is provided in GPG-LULUCF for other land that is managed.

Land converted to other land

Living biomass

The equation (GPG-LULUCF 3.7.1) for estimating change in carbon stocks associated with land-use conversions is the same as applied for other areas of land-use conversion (eg, land converted to cropland and grassland). The carbon stock of the land before conversion is documented in Table 7.1.3. The default assumptions for a Tier 1 estimate are that all living biomass present before conversion to other land is lost in the same year as the conversion takes place, and that carbon stocks in living biomass following conversion are equal to zero. The LCDB analysis shows that land converted to other land between 1997 and 2002 was from the category “low-producing grassland” (Table 7.1.2).

Soil carbon

New Zealand uses the IPCC method outlined in GPG-LULUCF (equation 3.7.3). For Tier 1, the initial (pre-conversion) soil carbon stock is determined from reference soil carbon stocks together with stock change factors (Table 7.1.1) appropriate for the previous land use. New Zealand uses a reference soil carbon stock of 83 t C ha–1 (refer to section 7.1.2.1 above). Soil carbon stocks in the inventory year are zero for land converted to other land.

7.7.3 Uncertainties and time-series consistency

Uncertainties are estimated as ±75 per cent based on the uncertainty in carbon stocks lost during the conversion to other land eg, GPG-LULUCF Table 3.4.2. While uncertainty in activity data is low, uncertainty in the IPCC default variables dominates the overall uncertainty. However, uncertainty in activity data used in the inventory is greater than assessed for the LCDB alone. Error is introduced from extrapolation as mapping is not repeated annually. Only two years (1997 and 2002) of mapped activity data is used. In addition, the mapping is not specific to IPCC categories.

7.7.4 Category-specific QA/QC and verification

No specific QA/QC and verification was performed for the other land category.

7.7.5 Category-specific recalculations

There are no recalculations for this category.

7.7.6 Category-specific planned improvements

The use of historic activity data for other land is being investigated. This will allow for improved estimates of the land converted to other land and other land remaining other land categories to be reported in future inventory submissions. Sector level improvements resulting from the LUCAS are described in Annex 3.2.