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

7.1 Sector overview

In 2006, the LULUCF sector represented the removal of 22,749.3 Gg carbon dioxide equivalent (CO2-e) (29.2 per cent) of total New Zealand greenhouse gas emissions. Net removals have increased by 2,241.6 Gg CO2-e (10.9 per cent) since the 1990 level of 20,507.7 Gg CO2-e (Figure 7.1.1). Figure 7.1.2 shows changes in emissions and removals by land use category from 1990 to 2006.

Carbon dioxide emissions and removals in the LULUCF sector are primarily controlled by uptake from plant photosynthesis and release from respiration, and the decomposition of organic material. Nitrous oxide (N2O) may be emitted from the ecosystem as a by-product of nitrification and denitrification 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-methane volatile organic compounds (NMVOC). All emissions and removals from the LULUCF sector are excluded from national totals.

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 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 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 LULUCF sector net removals from 1990 to 2006 (all figures are Gg CO2-e)

Year

Gg CO2-equivalent

1990

20,507.7

1991

18,648.5

1992

16,646.9

1993

16,957.1

1994

16,479.6

1995

15,924.9

1996

16,647.5

1997

17,719.5

1998

19,675.9

1999

19,557.8

2000

19,974.3

2001

20,092.1

2002

20,673.3

2003

20,619.6

2004

24,230.3

2005

23,681.9

2006

22,749.3

Figure 7.1.2 Change in emissions from the LULUCF sector (net emissions and removals by land use category) from 1990 to 2006 (all figures are Gg CO2-e)

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

Category

1990
(Gg CO2-equivalent)

2006
(Gg CO2-equivalent)

Forestland

-21,239.5

-23,710.8

Cropland

-500.7

-546.5

Grassland

734.1

694.3

Wetlands

Not applicable

Not applicable

Settlements

Not applicable

Not applicable

Other land

26.7

39.8

Other

676.1

373.8

7.1.1 Land use in New Zealand

Before human settlement, natural forests were New Zealand’s predominant land cover, estimated at 75 per cent of total land area. Now, around 23 per cent of New Zealand’s natural forest cover remains. Figure 7.1.3 shows the IPCC land use categories for New Zealand in 2002. Nearly all lowland areas have been cleared of natural forest 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 C (Scott et al, 2001). Historic land-use practices have had serious impacts on New Zealand’s environment, including soil erosion, pollution and increased risk of flooding. Establishment of pastures 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 currently uses a combination of Tier 1 and Tier 2 methodologies 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. However, a Tier 2 modelling approach using New Zealand-specific data has been used to estimate removals and emissions in planted forests (excluding soils).

Land use and land use change

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. For transparency, these factors are tabulated in Tables 7.1.2 and 7.1.3.

Planted forest

Models are used to derive forest carbon from stem volume yield tables and to calculate historic removals and emissions by time-shifting the latest available data backwards. They also allow forecasting of future forest growth and management, including harvesting. Further detail of the modelling for planted forest is given in section 7.2.

Figure 7.1.3 Land use in New Zealand in 2002: IPCC land use categories (mapped from LCDB2)

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 type of land use; (2) a management factor (FMG) that for permanent cropland represents different types of tillage; 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 7.1.1.

New Zealand is using 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, ie, 105 t C ha–1 / 1 / 1.14 / 1.11 = 83 t C ha–1. New Zealand has always applied the default inventory time period of 20 years in calculating the Tier 1 estimates.

Liming

Information on the amount of lime applied is currently aggregated nationally and across all land-use categories. Lime applied to forest land or grassland is not reported separately. In addition, limestone and dolomite are not split, with both reported together under “limestone”. Emissions associated with liming are reported in the ‘other’ category within the CRF reporter (see section 7.8).

Biomass burning

Biomass burning takes place either as a controlled burn or as wildfire on forest land or grassland. Reporting is at a national level based on the total areas of grassland or forest land burned. Burning of crop stubble and prescribed burning of savannah are reported in the agriculture sector. Activity data (eg, areas burned) and other variables related to biomass burning (eg, fuel consumption and initial biomass density) are used in the Tier 1 methodology. Due to climate and vegetation types, fire risk has been relatively low historically and biomass burning is not a significant source of greenhouse gases in New Zealand.

It is not necessary to report CO2 emissions resulting from natural disturbance events if methods are applied that do not capture subsequent re-growth (GPG-LULUCF 3.2.1.4.2). This applies to wildfires in grassland and natural forest in the New Zealand inventory. In the case of wildfire in planted forest land, the CO2 emission 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 with a reduced net stocked area. Only in cases where the damaged stand is grown on to maturity without a reduction in its net stocked area will the inventory under-report CO2 emissions. Given that the total area of wildfires in forests is small this is not regarded as a significant source of error.

Table 7.1.1 Soil stock change factors

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

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

Table 7.1.2 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

223.2 t C ha–1

All living biomass and dead organic matter

1st rotation, 28 years old (Wakelin, 2007).

Annual cropland

0 t C ha–1

All living biomass

Annual crop is harvested. GPG-LULUCF only considers perennial crops (Table 3.4.8).

Perennial cropland

63 t C ha–1

Aboveground biomass only*

GPG-LULUCF Table 3.3.2. Temperate (all moisture regimes).

High-producing grassland

1.35 t C ha–1

Aboveground 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

Aboveground 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 vegetation

T2 = 29 t C ha–1

Aboveground biomass only*

Figure used for Tier 2 clearance of grassland woody vegetation (Wakelin 2007).

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

Table 7.1.3 Annual growth in biomass for land converted to another land use

Land use Value Pools Source/Reference

Natural forest

T1 = 0 t C ha–1

T1 = 4.3 t C
ha–1

All living biomass

New Zealand’s natural forests are assumed to be approximately in steady-state (Tate et al, 2000)

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

IE

All living biomass and dead organic matter

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, and averages 8.0 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

Aboveground biomass only*

GPG-LULUCF Table 3.3.8 (temperate all moisture regimes)

High-producing grassland

6.75 t C ha–1

Aboveground 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

Aboveground 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

Representation of land areas

Land areas are calculated (for the Tier 1 approach) 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 have been reclassified to reflect the IPCC categories. The land cover databases were mapped in 1997 and 2002. Data for all other years is extrapolated from the changes observed between 1997 and 2002.

The LCDB1 and LCDB2 are an example of the wall-to-wall mapping of Approach 3 as described in GPG-LULUCF. The LCDBs were not specifically developed for use in IPCC reporting, however they are the only national land-cover/land-use spatial databases available that provide recent information and can be reasonably mapped to the LULUCF land categories (Table 7.1.4).

To improve transparency and accuracy of reporting in the LULUCF sector, and to meet the additional reporting requirements of the Kyoto Protocol, the Ministry for the Environment is developing the Land Use and Carbon Analysis System (LUCAS). The LUCAS project 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 UNFCCC and the Kyoto Protocol, and will replace LCDB data in the inventory from the 2010 inventory submission onwards.

New Zealand does not presently have land-use data for 1990. In the 2008 inventory submission the 1990 data has been estimated by linear extrapolation of the 1997 data. Until the 1990 mapping component of the LUCAS project is completed, this method provides the best data available for the inventory.

Table 7.1.4 Mapping of LCDB classification to the IPCC land-use categories

IPCC category LCDB class

Cropland

 

CM (perennial)

Orchard and other perennial crops, vineyard

CM (annual)

Short-rotation cropland

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

Grassland  

GM (low prod)

Alpine grass/herbfield, depleted tussock grassland, fernland, gorse and broom, grey scrub, low producing grassland, major shelterbelts, matagouri, mixed exotic shrubland, sub-alpine shrubland, tall tussock grassland, flaxland, herbaceous freshwater vegetation, herbaceous saline vegetation, mangrove

GM (high prod)

High-producing exotic grassland

Other land  

O

Alpine gravel and rock coastal sand and gravel landslide permanent snow and ice river and lakeshore gravel and rock

Settlements  

S

Built-up area, dump, surface mine, transport infrastructure, urban parkland/open space

Wetlands  

W (unmanaged)

Estuarine open water, lake and pond, river

The LCDB1 and LCDB2 include a shrubland vegetation cover category. Such a category does not exist as a LULUCF category. Some shrubland classes were classified as forest land and others were classified as grassland, based on an assessment of whether the species would usually grow to over 5 metres in height in situ. The classification is shown in Table 7.1.4, and will be further refined when the LUCAS project is operational.

Table 7.1.5 shows a simplified land-use change matrix developed from LCDB1 and LCDB2 for the years 1997 and 2002. A land-use change matrix for 2005–2006 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:

  • An increase in planted forest area of almost 140,000 ha (or 7%), mostly from conversion of grassland, a decrease of 135,000 ha (2%).

  • An increase in the area of settlements by 5,500 ha (2.5 %) mostly from conversion of grassland.

  • An increase in the area of cropland by 4,500 ha (7%), mostly perennial cropland.

Table 7.1.5 Land-use change matrix between 1997 and 2002

(IPCC land use classes derived from LCDB1 and LCDB2)

1997

Forest land

Cropland

Grassland

Wetlands

Settlements

Other Land

2002 Total

2002

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%

Note: The minimum area shown to represent an actual land-use change is 100ha. Columns and rows may not total due to rounding. * indicates land remaining in each category

7.2 Forest land (CRF 5A)

7.2.1 Description

In 2006, forest land contributed 23,710.8 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. Net removals from forest land have increased by 2,471.3 (11.6 per cent) since the 1990 level of 21,239.5 Gg CO2-e.

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 will be used when forest is mapped by the LUCAS project and reported in future inventories. To complete the 2008 inventory 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).

New Zealand has adopted the definition of managed forest land as provided in the IPCC Guidelines and GPG-LULUCF: “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 is dominant in the LULUCF sector, and is “forest land remaining forest land” is the major key category for the New Zealand inventory. Forests cover almost 40% (around 10,000 ha) of the land area of New Zealand. There has been considerable afforestation since 1990, while deforestation has been small in comparison.

For inventory reporting two sub-categories are used to cover all of New Zealand’s forests – natural forest and planted forest. Natural forests are considered to be approximately in steady-state, that is emissions and removals from these forests are assumed to be equal (Tate et al, 2000).

Natural forest

Natural forest is a term used to distinguish New Zealand’s native or naturally occurring forests from planted production forests. It consists of native forest ecosystems made up of 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. Currently, New Zealand has an estimated 8.2 million hectares of natural forest (including shrublands).

Government controls on natural forest clearance (deforestation) were first imposed in the late nineteenth century, but continuing demand for timber and agricultural land resulted in further forest clearance. By the 1970s, growing 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 mature planted forests.

Further government administrative changes in 1987 resulted in 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 permitted by a 1993 amendment to the Forests Act 1949. The amendment still exempted West Coast publicly-owned forests and forests on specific Māori-owned lands. Further government controls resulted in the cessation of logging of 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. No timber is harvested from New Zealand’s publicly-owned natural 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 indigenous 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. The LUCAS will provide data for similar forests in similar locations to the SILNA 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 will continue to exempt the SILNA forests although logging has further reduced in these forests.

Removals of CO2 in natural forest are calculated by a Tier 1 approach. Preliminary results are 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 to –2.5 Tg C yr–1 (Tate et al, 2000). For this reason removals are set to emissions in the CRF tables. Results from analysis of the Carbon Monitoring System (CMS) data within natural forests as part of the LUCAS project will enable New Zealand to provide improved estimates (refer to Annex 3.2).

Planted Forest

New Zealand has a substantial estate of planted forests, around 90 per cent Pinus radiata (created specifically for timber supply purposes) and has well-established data on the estate’s extent and characteristics. 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 2006 it is estimated that 685,000 hectares of new forest has been established as a result of afforestation and reforestation activities. In 2006, plantation forestry covered an estimated 1.8 million hectares of New Zealand (around 7% of the total land area). Having a large planted forest resource enables New Zealand to sustainably manage it’s publicly and privately-owned natural forest.

The new planting rate (land reforested or afforested) over the last 30 years has been, on average, 43,000 hectares per year (Figure 7.2.1). From 1992 to 1998, new planting rates were high (averaging 69,000 hectares per year). However, since 1998 the rate of new planting has declined and in 2006 only 5,000 hectares of new forest was established (the lowest rate since 1959). Some of the land not being replanted is being converted into pasture.

Figure 7.2.1 Annual forest planting in New Zealand from 1920 to 2006

 

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

7.2.2 Methodological issues

Forest land remaining forest land

Natural forest (Tier 1)

A small amount of harvesting takes place that is exempt from the sustainable management plan requirement. This harvesting is 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 is carried out on a sustainable basis. Estimates of harvesting from exempted natural forests are provided by the MAF. Stem wood volumes are converted to oven-dry weight using a factor of 0.5 (IPCC default value from GPG-LULUCF equation 3.2.4) and then expanded to include non-stem wood biomass using a factor of 2.04 (Wakelin, 2007). These country-specific factors are within the ranges given by GPG-LULUCF (2003 (Tables 3A1.9-1 and 3A1.10)).

Results from analysis of the Carbon Monitoring System (CMS) data within natural forests, undertaken as part of the LUCAS project will enable New Zealand to provide improved estimates (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 is:

  • A survey of forest growers – the National Exotic Forest Description (NEFD) – is undertaken annually. This provides estimates of the area of forest by age, species, silvicultural regime and location.

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

  • The C_change model (Beets et al, 1999) is 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) is used to recalculate historic estimates of CO2 removals and emissions by time-shifting the latest available data backwards.

  • The FOLPI model also time-shifts the estate forwards to forecast future forest growth and forest management, including harvesting.

Planted forest survey data

The results of the NEFD survey as at 1 April 2006 are used to calculate removals and emissions provided in the 2008 inventory submission. This latest information brings in 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 2006 year (Ministry of Agriculture and Forestry, 2006).

A crop-type is an aggregate of forest stands that are similar species, silviculture and location. Each crop-type has a yield table that provides estimated volumes of stem wood per hectare by age. The total forest area after harvest for the year ending March 2006 is based on: (a) the latest area estimates provided by the 2006 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 area of new land planting is based on the MAF statistics. These estimates are revised and recalculated annually as provisional estimates are replaced by confirmed actual areas.

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 (Box 7.2).

Figure 7.2.2: Planted forest inventory modelling process

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 for litter is 0.37, preliminary NZ data suggests that the litter pool is higher.

For the 2008 inventory 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 may have on the accuracy of calculations of total biomass, but current research will enable the impact to be further assessed. 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.

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 are the LULUCF inventory results for 1990 to 2006. These results include:

  • 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 gives the change in carbon stock between last year’s harvested forests and this year’s unharvested forests. Total carbon yield by stand age and rotation is shown in Figure 7.2.3.

Figure 7.2.3 Total carbon yield by stand age and rotation

Age

Total Carbon

Total Carbon

 

(tC/ha)

(tC/ha)

0

0.0

102.0

1

2.5

89.6

2

3.8

78.2

3

7.6

71.3

4

12.6

67.2

5

18.7

65.6

6

25.5

65.8

7

33.2

67.9

8

41.7

71.7

9

51.4

77.3

10

61.1

83.4

11

71.1

90.6

12

83.7

100.4

13

90.5

105.0

14

95.4

108.0

15

100.5

111.4

16

106.9

116.4

17

115.0

123.3

18

123.2

130.4

19

132.4

138.7

20

142.2

147.6

21

152.1

156.8

22

162.1

166.3

23

172.1

175.8

24

182.7

185.9

25

193.1

195.8

26

203.7

206.1

27

214.1

216.2

28

224.6

226.4

29

234.9

236.5

30

245.0

246.3

31

254.8

256.0

32

264.5

265.5

33

274.0

274.9

34

283.5

284.3

35

292.6

293.2

36

301.7

302.3

37

310.4

310.9

38

319.2

319.7

39

327.6

328.0

40

336.0

336.3

41

334.0

334.3

42

335.2

335.5

43

334.8

335.0

44

335.6

335.7

45

336.3

336.5

46

337.1

337.3

47

337.9

337.9

48

338.8

338.8

49

340.0

340.1

50

341.1

341.2

51

341.7

341.8

52

342.2

342.3

53

342.9

343.0

54

343.5

343.5

55

344.2

344.1

56

344.7

344.8

57

345.4

345.3

58

345.9

345.9

59

346.4

346.4

60

346.9

346.9

61

347.2

347.1

62

347.5

347.5

63

347.9

347.9

64

348.1

348

65

348.5

348.5

66

348.9

348.9

67

349.1

349

68

349.4

349.3

69

349.8

349.8

70

350.2

350.1

71

350.4

350.3

72

350.8

350.7

73

351.2

351.2

74

351.5

351.5

75

351.7

351.7

76

352.0

352.0

77

352.3

352.3

78

352.7

352.7

79

353.0

353.0

80

353.2

353.1

Biomass burning

For “forest land remaining forest land” there is no controlled burning in New Zealand. The inventory reports only emissions resulting from wildfire, where the IPCC default temperate forest fuel consumption rate of 45% of total biomass is 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). Data used in previous years was provided by the NRFA for 1990–2000, but this data is unofficial and has now been discarded from the inventory. For the 2008 inventory submission, the NZFS data was used from June 2001-June 2007, with the average over this period applied back to 1990. Activity data for wildfire is generally poor quality, but it is estimated that 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. Only in cases where the damaged stand is grown on to maturity without a reduction in its net stocked area will the inventory under-report CO2 emissions. Given that the total area of wildfires in forests is small this is not regarded as a significant source of error.

Non-CO2 emissions are largely based on IPCC default values, and have recently been reviewed (Wakelin, 2006). Previously the wildfire combustion efficiency in forests and grassland with aboveground woody biomass was set at 0.9, which is the IPCC default for the proportion of biomass oxidised as a result of land conversion burns (see GPG-LULUCF 3.4.2.1.1.2). For the 2008 inventory submission, a more appropriate value of 0.45 for temperate forests has been substituted (GPG-LULUCF Table 3A.1.12).

Land converted to forest land

Data on the amount of land clearance for new forest planting are sourced from the annual NEFD survey. The information includes the proportion of new forest planting that occurs on grassland with woody vegetation that falls below and is not expected to exceed, without human intervention, the threshold used to define forest land for New Zealand under the Kyoto Protocol. Data are available from 1993 to the present and based on these figures it is assumed that the proportion of new forest planting on grassland with woody vegetation was 20 per cent before 1993.

A review of the assumptions regarding the volume of biomass on grassland with woody vegetation (Wakelin 2004) concluded that the estimate previously being used was inappropriately high. For the 2008 inventory submission, a lower value of 29 t C/ha (Wakelin, 2007) is used, as it applies only to land identified as carrying “predominantly scrub” prior to planting. This is around half the estimate previously used, and will be revised when the LUCAS plots have been analysed (refer to Annex 3.2).

Biomass Burning

It is estimated that 25 per cent of the land converted to forest land is cleared using controlled burning, with a country-specific fuel consumption rate of 70% of above-ground biomass (Wakelin, 2007). The remainder and all biomass on unburned sites are assumed to decay over ten years (IPCC default value). Current research aims to quantify emissions from the burning of residues that result from the conversion of planted forests to grassland. Emissions of CO2 from controlled burns for afforestation are reported as a stock change in the grassland category. Carbon dioxide emissions resulting from natural disturbance events are not reported, as methods are applied that do not capture subsequent re-growth (GPG-LULUCF 3.2.1.4.2).

7.2.3 Uncertainties and time-series consistency

Adopting a Tier 2 modelling approach has allowed the large body of plantation forestry knowledge in New Zealand to be applied to the greenhouse gas inventory. For example, the wood density of Pinus radiata in New Zealand has been well studied because of its relationship with important end-product values. 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 outerwood 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 were 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 then 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 but it is difficult to quantify the overall error due to the assumptions implicit in the models. Some uncertainties within the C-change (CARBON/ DRYMAT) model are well characterised (Hollinger et al, 1993). These include ± 3 per cent for wood density, ±15 per cent for carbon allocation and ± 5 per cent for carbon content. Combining the uncertainties indicates that the proportional error in the carbon sequestration estimates is likely to be at least ± 16 per cent. The total national planted area is considered to be accurate to within ± 5 per cent (Ministry of Agriculture and Forestry, 2006) and the yield tables are assumed to be accurate to within ± 5 per cent.

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 (CARBON/ DRYMAT) model runs indicate that the precision of the carbon stock estimates could be of the order of ± 25 per cent. As part of the 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 are 6.6 per cent of New Zealand’s total emissions and removals uncertainty in 2006 (Annex 7). Forest land introduces 2.3 per cent uncertainty into the trend in the national total from 1990 to 2006. This is the second largest impact on the trend following CO2 emissions from the energy sector.

7.2.4 Source-specific QA/QC and verification

Carbon-dioxide removals from both “forest land remaining forest land” and “land converted to forest land” are key categories (for both level and trend assessments). In the preparation of this inventory, the data for these emissions underwent Tier 1 quality checks.

The data presented in the 2008 inventory submission were 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 National Exotic Forest Description (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 Land Cover Database estimates and the annual results of Statistics New Zealand’s Agricultural Production Survey. NEFD yield tables have been subject to review (eg, Jaakko Poyry Consulting, 2003; Manley, 2004) and are in the process of being revised.

The 2006 planted forests removals and emissions have been compared for consistency with the 2005 estimates (Wakelin, 2007), with both level and trend closely aligned.

7.2.5 Source-specific recalculations

The main changes in the data for the 2008 inventory submission were due to:

Use of single year values

Three year averages have been used for most activity data in previous inventories. Single year values are now used in calculations for all activity data. The change was made to allow more time for quality control checking prior to submitting the inventory. This change results in greater inter-annual variation, but does not have a major impact on estimates of emissions and removals.

Revised assumptions for clearance of scrub and biomass burning

For clearance of grassland with aboveground woody biomass, revised emission factors have been applied, while decay of residues has now been spread over 10 years (IPCC default). For biomass burning due to wildfire, revised activity data has been used and country-specific emissions and fuel consumption rates have been applied. These changes improve the accuracy of estimates.

Modelling process and NEFD data

Use of the latest NEFD survey data means that derived historic age class distributions become less robust. Using only the latest data leads to an underestimate of historic removals because of deforestation in recent years. To address this issue the 1990-2004 time series was recalculated from the 2004 planted forest model, while the 2005 and 2006 years were calculated from the 2005 and 2006 planted forest models respectively. Further work is required to assess the appropriate approach to use for future inventories until plot-based LUCAS estimates become available.

7.2.6 Source-specific planned improvements

Development of the LUCAS will enable New Zealand to revise the time-series in the LULUCF sector, and reduce uncertainty by using country-specific emission and removal factors and IPCC category-specific activity data. Details of the research are included in Annex 3.2.

Improvements in NEFD area capture are ongoing. Survey respondents are now being asked to specify whether or not stands are first rotation. This will allow improved analysis of “land converted to forest land” and “forest land remaining forest land”. Estimates of dead organic matter stocks resulting from post-harvest residues will also be improved.

Ongoing research is aiming to improve carbon modelling, including partitioning in species other than Pinus radiata, plantation understory carbon and biomass decay rates.

7.3 Cropland (CRF 5B)

7.3.1 Description

In 2006, cropland accounted for 546.5 Gg CO2-e of net removals. Net removals from cropland have increased 45.8 Gg CO2-e (9.1 per cent) from the 1990 level of 500.7 Gg CO2-e. Cropland is a key category for New Zealand.

Cropland in New Zealand is separated into two sub-categories, annual and perennial. Cropland comprised 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 plantations except where these lands meet the criteria for forest land.

The amount of carbon stored in, and 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 have been calculated using IPCC Tier 1 emission and removal factors and activity data from the LCDB analysis described in section 7.1.2.2.

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 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 GPG-LULUCF Table 3.3.2. New Zealand is using 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.

Dead organic matter

New Zealand does not report estimates of dead organic matter in this category. The notation “NE” is used in the CRF tables. There is not sufficient information to provide a basic approach with default parameters to estimate carbon stock change in dead organic matter pools in cropland remaining cropland (GPF, LULUCF).

Soil carbon

To provide a Tier 1 estimate, New Zealand uses the IPCC default method for mineral soils (equation 3.3.3 of GPG-LULUCF). Mineral soils comprise 99.93 per cent of New Zealand soils (Tate et al, 2004). 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 7.1.1. 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. For example, for perennial cropland remaining perennial cropland the calculation is:

(83 x 0.82 x 1.16 x 0.91) – (83 x 0.82 x 1.16 x 0.91)) x Area)/20 = 0.

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 and country-specific values where possible. These are shown in Tables 7.1.2 and 7.1.3.

Dead organic matter

New Zealand does not report estimates of dead organic matter in this category. The notation “NE” is used in the CRF tables. There is not sufficient information 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

New Zealand has followed 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).

N2O emissions

N2O 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. The IPCC default value of 0.0125 kg N2O – N/kg N is used.

  • 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 analysed as uncertainty in activity data and uncertainty in 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 in the estimate provided by New Zealand. However, uncertainty in activity data used in the inventory will be 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 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)

7.3.4 Category-specific QA/QC and verification

Carbon-dioxide removals from “cropland remaining cropland” are a key category (level assessment). In the preparation of this inventory, the data for these emissions underwent Tier 1 quality checks.

7.3.5 Category-specific recalculations

Recalculations were carried out for this category as emissions or removals from soils were not included in the CRF reporter for the previous submission.

7.3.6 Category-specific planned improvements

The use of historic activity data for cropland is to be investigated. This would allow for improved estimates of land converted to cropland and cropland remaining cropland. A New Zealand specific value for EF1: the emission factor for calculating emissions of N2O from nitrogen in the soil has been applied in the agriculture sector. Use of this factor within the LULUCF sector will be investigated for subsequent inventories. Sector-level improvements resulting from the LUCAS are described in Annex 3.2.

7.4 Grassland (CRF 5C)

7.4.1 Description

In 2006, the net emissions from grassland were 694.3 Gg CO2-e. This is a decrease of 39.8 Gg CO2-e (5.4 per cent) from the 1990 level of 734.1 Gg CO2-e. These emissions are from the subcategory “land converted to grassland”.

In New Zealand, grassland covers a range of land-cover types. Reporting covers two sub-categories; low producing and high producing. Low producing grassland consists of either native tussockland 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 being the main land use. Most New Zealand agriculture is based on extensive pasture systems with animals grazed outdoors year-round. A shift to more intensive pastoral land use has placed greater pressures on the health of some soil and water quality. It has also seen 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 CRF tables because the activity occurs but no estimate of removals or emissions is able to be calculated.

Dead organic matter

New Zealand does not report estimates of dead organic matter in this category. The notation “NE” is used in the CRF tables. GPG-LULUCF states there is not sufficient 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

To provide a Tier 1 estimate, New Zealand uses the IPCC default method for mineral soils (equation 3.4.8 of GPG-LULUCF). As noted in previous sections, mineral soils cover 99.93 per cent of New Zealand (Tate et al, 2004). The LCDB analysis used in the 2008 inventory 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 are considered to be constant and consequently the calculation shows there is no net change in carbon stocks in soils.

Biomass Burning

Non-CO2 emissions from wildfires in low producing grasslands (tussock and grassland with aboveground woody biomass) are reported in the LULUCF sector, while those from controlled (prescribed) burning of savannah are covered in the agriculture sector. CO2 emissions resulting from natural disturbance events are not reported, as methods are applied that do not capture subsequent re-growth (GPG-LULUCF 3.2.1.4.2).

For low producing grassland with aboveground woody biomass the activity data is sourced from the NZ Fire Service 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% would be more appropriate (Wakelin, 2006). In the inventory, this has been applied to the total biomass (rather than above-ground only) using the more general initial grassland with aboveground woody biomass estimate of 136 t dm ha-1 (Hall et al 2001), rather than the specific ‘pre-afforestation’ biomass value used for Grassland (with woody vegetation) converted to forest land.

Wildfire in tussock grassland has not been reported previously in New Zealand’s inventory. Although the area of tussock burned is similar to that of grassland with aboveground woody biomass, emissions are much lower because there is less biomass present. For wildfire in tussock, the assumptions used for controlled burning have been applied to the NZFS wildfire areas.

Land converted to grassland

Living biomass

New Zealand has applied the GPG-LULUCF Tier 1 method where 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 accounting for carbon in biomass that replaces cleared vegetation. Pre-conversion stocks and annual growth figures are shown in Tables 7.1.2 and 7.1.3. Carbon stocks in biomass immediately after conversion are assumed to be zero.

Dead organic matter

Dead organic matter

New Zealand does not report estimates of dead organic matter in this category. The notation “NE” is used in the CRF tables. No Tier 1 methodology exists for calculating emissions or removals from dead organic matter in the category “land converted to grassland”.

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 methodology 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 7.1.1.

7.4.3 Uncertainties and time-series consistency

Uncertainties can be analysed as uncertainty in activity data and uncertainty in 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 in the estimate provided by New Zealand. However, uncertainty in activity data used in the inventory will be 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 mapping is not specific to IPCC categories.

7.4.4 Category-specific QA/QC and verification

Carbon-dioxide emissions from “land converted to grassland” are a key category (level and trend assessment). In the preparation of this inventory, the data for these emissions underwent Tier 1 quality checks.

7.4.5 Category-specific recalculations

Recalculations were carried out for this category as emissions or removals from soils were not included in the CRF reporter for the previous submission as a result of changes to the CRF reporter database.

7.4.6 Category-specific planned improvements

The use of historic activity data for grassland is to be investigated. This would allow for improved estimates of land converted to grassland and grassland remaining grassland. Sector-level improvements resulting from the LUCAS are described in Annex 3.2.

7.5 Wetlands (CRF 5D)

7.5.1 Description

In 2006, the net emissions were 0.7 Gg CO2-e. This estimate is constant over all inventory years. These emissions are from the subcategory “land converted to wetlands”. Wetlands are not a key category for New Zealand.

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 has categorised LCDB land-cover classes for lakes, rivers and estuarine open water in the LCDB into the unmanaged wetlands category (Table 7.1.4). Other LCDB classes, eg, herbaceous freshwater vegetation, commonly thought of as wetlands in New Zealand, have been categorised as grassland following the GPG-LULUCF definitions.

Flooded lands are defined in GPG-LULUCF as “water bodies regulated by human activities for energy production, irrigation, navigation, recreation, etc., and where substantial changes in water area due to water level regulation occur. Regulated lakes and rivers, where the main pre-flooded ecosystem was a natural lake or river, are not considered as flooded lands”.

The LCDB does not separate out regulated water bodies where substantial changes in water area occur, and the majority of New Zealand’s hydro-electric schemes are based on rivers and lakes where the main pre-flooded ecosystem was 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 methodology 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 “wetlands remaining wetlands”.

Land converted to wetlands

New Zealand has applied the GPG-LULUCF Tier 1 methodology 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 is 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, CRF 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 in the estimate provided by New Zealand. However, uncertainty in activity data used in the inventory will be 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 mapping is not specific to IPCC categories.

7.5.4 Category-specific QA/QC and verification

No specific QA/QC and verification was used for wetlands.

7.5.5 Category-specific recalculations

There are no recalculations for this category.

7.5.6 Category-specific planned improvements

No specific improvements are planned for wetlands. Sector-level improvements resulting from the LUCAS are described in Annex 3.2.

7.6 Settlements (CRF 5E)

7.6.1 Description

In 2006, the net emissions from settlements were 97.2 Gg CO2-e. This estimate is constant over all inventory years. These emissions are from the subcategory “land converted to settlements”. Settlements are not a key category for New Zealand.

This land-use category is described in GPG-LULUCF 3.6 as including “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 has categorised the applicable LCDB land cover classes into the settlements category (Table 7.1.4). This showed that 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. New Zealand does not have this level of activity data available and is unable to estimate emissions for this sub-category. Parties are not required to prepare estimates for this subcategory (note 3, CRF Table 5).

Land converted to settlements

The equation (3.6.1) 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 7.1.2. The default assumptions for a Tier 1 estimate are that all living biomass present before conversion to settlements will be 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 in the estimate provided by New Zealand. However, uncertainty in activity data used in the inventory will be 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 mapping is not specific to IPCC categories.

7.6.4 Category-specific QA/QC and verification

No specific QA/QC and verification was used for settlements.

7.6.5 Category-specific recalculations

There are no recalculations for this category.

7.6.6 Category-specific planned improvements

No specific improvements are planned for settlements. Sector-level improvements resulting from the LUCAS are described in Annex 3.2.

7.7 Other land (CRF 5F)

7.7.1 Description

In 2006, the net emissions from other land were 39.8 Gg CO2-e. Net emissions from other land are 13.1 Gg CO2-e (48.8 per cent) higher than the 1990 level of 26.7 Gg CO2-e. These emissions are from the subcategory “land converted to other land”. Other land is not a key category for New Zealand.

“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 consists of steep, rocky terrain at high elevation, often covered in snow or ice. “Other land” is 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 4 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 7.1.2. The default assumptions for a Tier 1 estimate are that all living biomass present before conversion to other land will be 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 7.1.5).

Soil carbon

New Zealand uses the IPCC methodology 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 in the estimate provided by New Zealand. However, uncertainty in activity data used in the inventory will be 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 mapping is not specific to IPCC categories.

7.7.4 Category-specific QA/QC and verification

No specific QA/QC and verification was used for other land.

7.7.5 Category-specific recalculations

There are no recalculations for this category.

7.7.6 Category-specific planned improvements

No specific improvements are planned for other land. Sector-level improvements resulting from the LUCAS are described in Annex 3.2.

7.8 Other (CRF 5G)

7.8.1 Description

This category includes emissions from the application of lime to forest and grassland. The lime used is agricultural lime, or ground limestone.

In 2006, the net emissions from this category were 676.1 Gg CO2-e. Since the 1990 level of 373.8 Gg CO2-e there has been an increase of other net emissions by 302.3 Gg CO2-e (80.9 per cent).

7.8.2 Methodological issues

The calculation for CO2 emissions from the liming of grassland soils is included in CRF worksheet 5.5. The calculation is based on GPG-LULUCF equation 3.4.11, including the total amount of limestone applied (provided by Statistics New Zealand) and a carbon conversion factor from limestone to carbon. New Zealand uses 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 has been used to represent the data for these years. Since 2002 there has been a noted drop 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.

7.8.3 Uncertainties and time-series consistency

Uncertainties are estimated as ± 40 per cent based on sampling and survey respondent error.

7.8.4 Category-specific QA/QC and verification

Carbon-dioxide emissions from “liming” are a key category (level and trend assessment). In the preparation of this inventory, the data for these emissions underwent Tier 1 quality checks.

7.8.5 Category-specific recalculations

Data for all years are no longer reported as three year averages, but as annual values.

7.8.6 Category-specific planned improvements

No specific improvements are planned for the “other” category.