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

7.1 Sector overview

The land use, land-use change and forestry (LULUCF) sector represented the removal of approximately 31.8 per cent of all New Zealand’s greenhouse gas emissions in 2005. Net removals from the sector in 2005 totalled 24,500.81 Gg CO2 equivalent (CO2-e) and are 29.0 per cent above net removals in 1990 (Figure 7.1.1).

Figure 7.1.1 LULUCF sector net removals from 1990 to 2005

 

Year

Gg CO2 equivalent

1990

18,980.59

1991

17,555.74

1992

15,802.61

1993

14,630.11

1994

14,240.60

1995

15,100.36

1996

15,415.59

1997

17,080.88

1998

19,332.89

1999

19,951.28

2000

20,245.11

2001

20,545.44

2002

21,278.62

2003

22,785.99

2004

23,380.87

2005

24,500.81

7.1.1 Methodological issues for LULUCF in New Zealand

Six broad categories of land use are described in GPG-LULUCF. These 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 falls 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.

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.

7.1.1.1 Representation of land areas

To estimate land areas in each LULUCF land category for the current inventory, New Zealand has used 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). 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 UNFCCC reporting, however they are the only national land-cover/land-use spatial databases available that provide current information and can be reasonably mapped to the LULUCF land categories. 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 in the future.

The LCDB1 was completed in 2000 using SPOT satellite imagery acquired over the summer of 1996/97. LCDB2 was released in July 2004 and used Landsat 7 ETM+ satellite imagery acquired over the summer of 2001/02. During processing of LCDB2, the classifications in LCDB1 were checked, corrected and integrated into the LCDB2 database. The inventory uses the corrected LCDB1 data. There are 43 land-cover/land-use classes mapped in LCDB 1 and 2. The classes are mutually exclusive and additive to 100 per cent of the surface area of New Zealand. Additional information on the processing to generate LCDB 1 and 2 is included in Annex 3.3. To complete the UNFCCC inventory, the land-cover classes in the LCDB 1 and 2 were mapped to the applicable LULUCF categories (table A3C.1).

New Zealand does not presently have land-use data for 1990. In the 2005 inventory the 1990 data has been estimated by linear extrapolation of the 1997 data. Until the mapping component of the LUCAS project is completed, which will provide 1990 data, this method provides the best data available for the inventory.

Table 7.1.1 shows a simplified land-use change matrix developed from LCDB1 and LCDB2 for the years 1997 and 2002. More details of the conversions between categories and subdivisions are included in each land-use category in the National Inventory Report. A land-use change matrix for 2002–2005 was generated by extrapolating previous annual trends.

Table 7.1.1 Land-use change matrix between LCDB1 (1997) and LCDB2 (2002)

LCDB2(2002) Land area categories from LCDB1 (1997)(KHA)
Forest land Cropland Grassland Wetlands Settlements Other lands Total
Forest land 10,097.57 0.02 130.88 0.00 0.06 0.06 10,228.59
Cropland 0.22 412.91 4.32 0.00 0.00 0.01 417.44
Grasslands 5.11 0.00 14,360.63 0.00 0.06 0.21 14,336.01
Wetlands 0.00 0.00 0.67 531.24 0.04 0.01 531.96
Settlements 0.56 0.02 5.03 0.00 214.84 0.00 220.46
Other Lands 0.19 0.00 0.06 0.00 0.00 1,056.84 1,057.09
Total 10,103.65 412.95 14,501.58 531.24 215.00 1,057.13 26,821.56
Net 124.94 4.49 -135.57 0.72 5.46 -0.03 0.00

 

7.1.1.2 Inventory carbon pools

Changes in carbon stocks for land-use categories involves estimation from five carbon pools – aboveground biomass, belowground biomass, dead wood, litter, and soil organic matter – as well as emissions of non-CO2 gases from such pools. For UNFCCC inventory reporting purposes, the pools are grouped into living biomass (aboveground biomass and belowground biomass), dead organic matter (dead wood and litter) and soil organic matter.

7.1.1.3 Summary of methodological approaches used in LULUCF

New Zealand has calculated removal and emissions of CO2 by planted forests using a modelling approach and country-specific data. For all other land-use categories a Tier 1 approach is used to estimate emissions and removals. The variables appear in the Tier 1 equations for all land-use categories. For transparency, these factors are tabulated in tables 7.1.3.1, 7.1.3.2 and 7.1.3.3.

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.

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 the Good Practice Guidance for LULUCF (IPCC, 2003) 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.

Table 7.1.3.1 Land-use factors used across land-use categories

Land use

Stock change factors selected from GPG-LULUCF (GPG-LULUCF tables 3.3.4 and 3.4.5)

 

FLU

FMG

FI

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

Table 7.1.3.2 Living biomass carbon stocks in land use before conversion

Land use Value Source/Reference

Natural forest

182 t C ha–1

364 tonnes dm ha–1–1 (Hall et al, 1998); carbon fraction of dm (0.5)

Planted forest

223.2 t C ha–1

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

Annual cropland

0 t C ha–1

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

Perennial cropland

63 t C ha–1

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

High-producing grassland

1.35 t C ha–1

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

63 t C ha–1

1.6 tonnes dm ha–1 (GPG-LULUCF table 3.4.2, warm temperate – wet climate); carbon fraction of dm (0.5)

63 t C ha–1 assumed for grassland woody vegetation

Dm = dry matter

Table 7.1.3.3 Annual growth in living biomass for land converted to another land use

Land use Value Source/Reference

Natural forest

T1 = 0 t C ha–1

T1 = 4.3 t C
ha–1

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 /

T1 = 8.9 t C
ha–1

Tier 2 – included in C-change modelling (Beets et al, 1999, Wakelin, 2007)

Tier 1 – GPG-LULUCF 3A.1.6 and 3A.1.8 (Gw = 14.5 tonnes dm ha–1 (pinus), R = 0.23, Cfrac = 0.5)

Annual cropland

5 t C ha–1

GPG-LULUCF table 3.3.8 (temperate all moisture regimes)

Perennial cropland

2.1 t C ha–1

GPG-LULUCF table 3.3.8 (temperate all moisture regimes)

High-producing grassland

6.75 t C ha–1

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

6.1 tonnes dm ha–1 (GPG-LULUCF table 3.4.9, warm temperate – dry climate), Cfrac = 0.5

Dm = dry matter

7.2 Forest land (CRF 5A)

7.2.1 A history of forestry in New Zealand

Before the first human settlement by Polynesians in about 1250 AD, an estimated 75 per cent of New Zealand’s total land area was natural forest. The forest area had reduced to about 60 per cent by the mid-nineteenth century and was further reduced to the current 23 per cent estimated coverage by subsequent European settlement, the latter due largely to deforestation and clearance for pastoral grazing land. Deforestation (subsequent to human settlement) is estimated to have resulted in vegetation carbon losses of 3,400,000 Gg C (Scott et al, 2001). Establishment of pastures probably slightly increased mineral soil carbon, however some losses of carbon due to erosion are also possible (Tate et al, 2003b).

Government controls on forest clearance (deforestation) were first imposed in the late nineteenth century but the continuing demand for timber and agricultural land resulted in ongoing forest removal. By the 1970s, growing public concern led to stronger conservation measures by Government. 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. Currently, New Zealand has 6.4 million hectares of natural forest. 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 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. Timber harvested from privately-owned natural forests and from forests on exempted Māori lands has continued at a low level since the 1993 controls were imposed. Current proposed legislative changes will continue to exempt the Māori lands although logging has further reduced in these forests.

New Zealand has a substantial estate of planted forests, mainly comprising Pinus radiata, created specifically for timber supply purposes and has well-established data on this estate’s extent and characteristics. These forests have removed and stored more CO2 over the period 1990 to 2005 than has been emitted through forest harvesting of both the combined planted and natural forests. The new planting rate (land reforested or afforested) over the last 30 years has been, on average, 43,000 hectares per year. From 1992 to 1998, new planting rates were high (averaging 69,000 hectares per year). Since 1998 the rate of new planting has declined and in 2005, 6,000 hectares of new forest was established. Between 1990 and 2005 it is estimated that 680,000 hectares of new forest has been established as a result of afforestation and reforestation activities.

Having a large planted forest resource enables New Zealand to sustainably manage its publicly and privately-owned natural forest. Less than 0.1 per cent of New Zealand’s total forest production is now harvested from natural forests.

7.2.2 Description

In New Zealand’s Initial Report under the Kyoto Protocol (MfE, 2006a), national forest definition parameters were specified as required by UNFCCC decision 16/CMP.1. These 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 under the inventories submitted from 2009. To complete the 2005 inventory, the categories of forest land used in the LCDB1 and LCDB2 were applied (an area of 1 hectare and a width of 100 metres).

The LCDB1 and LCDB2 also include a shrubland vegetation cover category, which does not exist as a LULUCF category. Some shrubland classes were classified as forest land and others were classified as grassland, based on whether the species would usually grow to over 5 metres in height insitu. The classification is shown in table A3C, and will be further refined when the LUCAS project is operational.

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 are considered managed forests.

“Natural forest” is a term used to distinguish New Zealand’s indigenous forests from planted production forests. Natural forests are managed for a range of conservation, biodiversity and recreation purposes. New Zealand’s wood needs are almost exclusively met from planted production forests (99.9 per cent). 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 granted to Māori (New Zealand’s indigenous people) under the South Island Landless Natives Act (SILNA) 1906. These forests are currently exempt from the indigenous forestry provisions of the Forests Act that apply to all privately-owned indigenous forests and required a sustainable forest management plan or permit before any harvesting. Approximately 50,000 hectares are in 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.

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 will enable New Zealand to provide a better estimate (refer to Annex 3.2).

Forest land contributed net CO2 removals of 25,461.31 Gg CO2 in the 2005 inventory. This figure includes removals from the growth of planted forests, emissions from the conversion of land to planted forest and emissions from the small amount of harvesting of natural forests.

7.2.3 Methodological issues

Forest land remaining forest land

Planted forest (Tier 2)

Approximately 90 per cent of the forest area is planted in Pinus radiata. These forests are usually composed of stands of trees of a single age class and all forests have relatively standard silviculture regimes applied. Compared to many forest ecosystems, total biomass in New Zealand’s planted forests is relatively straightforward to estimate. The methodology applied for the inventory is:

  • A survey of forest growers is undertaken annually to estimate 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. C_change was previously known as the CARBON/DRYMAT model.

  • The Forestry Oriented Linear Programming Interpreter (FOLPI) (Garcia, 1984; Manley et al, 1991) is used to time-shift the estate forwards to forecast future forest growth and forest management, including harvesting.

  • The FOLPI model also recalculates historic estimates of CO2 removals and emissions by time-shifting the latest available data backwards.

Planted forest survey data

The results of the National Exotic Forest Description (NEFD) survey as at 1 April 2005 are used to calculate removals and emissions provided in the 2005 inventory. This latest information brings in new forest-area data along with data on new planting, restocking and harvesting for the 2005 year (MAF, 2006).

The NEFD survey provides estimates of the forest area and merchantable stem wood volume (via yield tables) by crop-type and age. 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 2005 is based on: (a) the latest area estimates provided by the 2005 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 total estate area for 2004 has been estimated through back-calculations using this latest NEFD area data combined with new planting and harvesting time-series information. The area of new land planting is based on the Ministry of Agriculture and Forestry statistics. These estimates are revised and recalculated annually as provisional estimates are replaced by confirmed actual areas.

Modelling

The C_change model estimates carbon stock per hectare, by vegetation component and annual age-class, from stem wood volume data (Box 7.1).

Box 7.1 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 understorey) 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 p3.25).

For the 2005 inventory, 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 when around 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 should 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 and are reported as three-year averages. 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 2005. 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.

Natural forest (Tier 1)

Removals of CO2 in natural forest are calculated by a Tier 1 approach. Estimates of any harvesting from natural forests are provided by the Ministry of Agriculture and Forestry. Stem wood volumes are converted to oven-dry weight using a factor of 0.5 (accounting for wood moisture) 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)).

Land converted to forest land

Data on the amount of land clearance for new forest planting are sourced from the Ministry of Agriculture and Forestry. 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. Data are available from 1993 to the present and based on these figures it is assumed that the proportion was 20 per cent before 1993. It is estimated that 25 per cent of the vegetation biomass is burnt onsite under controlled burning conditions and that the remainder is left to decay.

The quantity of on-site biomass for both grassland woody vegetation and natural forest, used in the land conversion and biomass burning calculations (see Annex 8.5), is based on the provisional results of research (adapted from Hall et al, 1998). The values reported (136 t dm/ha for grassland with woody vegetation and 364 t dm/ha for mature natural forest) are based on a national area-weighted average for biomass per hectare for a range of species.

Controlled burning

It has been assumed that the biomass fuel consumption rate in fires in both forest biomass and grassland with woody vegetation is 90 per cent. Work is underway to improve biomass burning assumptions in the inventory, however it is now thought that both the fuel consumption rate and the volume of dry matter per hectare for grassland with woody vegetation are overestimated, leading to overestimates of the resulting non-CO2 emissions.

Wildfire burning

Only non-CO2 emissions from wildfires are reported in the inventory (consistent with the IPCC default method). CO2 emissions from wildfires in grasslands are assumed to be zero as they are balanced by subsequent growth. Emissions from wildfires are based on fire reports collected by the National Rural Fire Authority. These reports show the area of forest and grassland with woody vegetation burnt. It is assumed that all forest burning occurs in natural forest. In planted forests, fires occur infrequently and fire-damaged trees are usually salvaged and appear in harvest statistics. Some of the areas reported in the Fire Authority statistics involve land clearing and it is not specified whether this is for agricultural or forestry purposes. This implies that there may be double counting between these figures and those allocated to land clearing for new forest planting. However the most common cause of wildfires is escapes from land clearance burns, and in New Zealand these are mostly in the high country. The Ministry of Agriculture and Forestry assesses the possibility of double counting as relatively minor.

7.2.4 Uncertainties and time-series consistency

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 ± three 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 ± five per cent (MAF, 2006) and the yield tables are assumed to be accurate to within ± five 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 6.2 per cent of New Zealand’s total emissions and removals uncertainty in 2005 (Annex 7). Forest land introduces 2.2 per cent uncertainty into the trend in the national total from 1990 to 2005. This is the third largest impact on the trend after CO2 emissions from the energy sector and CH4 from enteric fermentation.

7.2.5 Source-specific QA/QC and verification

Forest removals and emissions calculated via a Tier 1 approach

The LCDB1 and LCDB2 analysis used to complete the LULUCF inventory allows calculating a coarse Tier 1 estimate for the categories “forest land remaining forest land” and “land converted to forest land”. These estimates are reported in the National Inventory Report to support the modelling approach.

Living biomass

For the category “forest land remaining forest land”, the calculation follows the Tier 1 procedure outlined in GPG-LULUCF equation 3.2.4 using parameters from tables 3A.1.5 for natural forest, 3A.1.6 for plantation forest and root-shoot ratios from table 3A.1.8. The values chosen for the carbon stocks and growth rates (Gw and R) are documented in table 7.1.3.2.

Dead organic matter

In the Tier 1 calculation, the average transfer rate into the dead wood pool equals the transfer rate out of the dead wood pool. The net change is zero (GPG-LULUCF 3.2.1.2).

Soil carbon

In the Tier 1 calculation it is assumed that when forest remains forest, the carbon stock in soil organic matter does not change. For land converted to forest, New Zealand has followed the Tier 1 method outlined in GPG-LULUCF 3.2.2.3. 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. The stock change factors used by New Zealand’s Tier 1 calculation are listed in table 7.1.3.1. New Zealand has used 83 tonnes C ha–1 for reference carbon stock in soils (Tate et al, 2003a).

Decreases in the carbon stock of forest land from harvest were calculated according to GPG-LULUCF equation 3.2.9 – “annual other losses of carbon”. This equation was used in preference to the equation for commercial felling (equation 3.2.7) to keep calculations consistent with the LCDB analysis used for other land categories ie, equation 3.2.7 is based on the extracted roundwood volume rather than the area of forest harvested or disturbed (equation 3.2.9). The annual area of deforestation was calculated from the total area of LCDB1 forest classes that had changed to “harvested forest” in LCDB2, divided by the five years. Carbon stocks in living biomass for planted and natural forest were those documented in table GPG-LULUCF 7.1.3.2. Under the Tier 1 methodology, it is assumed that all aboveground biomass is lost.

Decreases in living biomass carbon stocks associated with land converted to forest was also included in the Tier 1 calculation. For the Tier 1 estimate, it was assumed that the land category “low producing grassland converted to planted forest” was equivalent in area to the clearance of grassland with woody vegetation for forest planting. The value of living biomass carbon stocks in perennial cropland before conversion provided in GPG-LULUCF table 3.3.2 (63 t C ha–1) was used as an approximation of the carbon stock in grassland woody vegetation biomass. This value is similar to the value used in the Tier 2 modelling of 68 t C ha–1 from Hall et al, (1998) (136 t dm ha–1 * 0.5 (carbon fraction of dry matter)).

Table 7.2.5.1 compares the results from the modelled (Tier 2) and Tier 1 approaches for the 2003 inventory. This comparison has not been repeated for the current inventory as results are expected to be similar. The results for the living biomass stock are comparable (11.0 per cent different) but the different approaches mean that the two estimates will always vary. The main reasons for this are the different methodologies used in assessing planted forest estate and planting rates, ie, comparing the annual National Exotic Forest Description survey versus remote sensing and extrapolation of previous interpolated planting trends, the lack of forest age data from the LCDB analysis, mapping of LCDB classes to LULUCF categories and the selection of Good Practice Guidance defaults for annual biomass growth and root-shoot ratios compared to country-specific modelling data.

Table 7.2.5.1 Comparison of the Tier 2 and Tier 1 approaches for forest land in 2003

  Area (KHA) Living biomass stock (Gg C)
Modelled/actual (Tier 2) Tier 1 Difference Modelled/actual (Tier 2) Tier 1 Difference
Forest land remaining forest (planted) 1878 2046 8.9% 6977 7742 11.0%
Land converted to planted forest land 18 26 44% -237 -291 22.8%

Other checks

The information presented in the National Inventory Report and the variables chosen for calculation were reviewed by officials of 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 2005 planted forests removals and emissions have been compared for consistency with the 2004 estimates (Wakelin, 2007).

7.2.6 Source-specific recalculations

New proportions of area by NEFD regime are used to weight the carbon yield in the 2005 inventory. Area data and carbon yields underlying the models in recent reports use 89 crop-type yield tables in the area-weighting procedure, rather than just four. This means that the national yield table better reflects the diversity represented in the NEFD data. Regimes were modelled based on averages from permanent plot data, rather than as notional NEFD regimes. This had the effect of smoothing fluctuations during the period of silvicultural activity and also a minor effect on predicted root/shoot biomass ratios. In addition, dead fine roots were removed from the yield table to avoid double counting with soil carbon estimates from the soil carbon monitoring system (or other sources).

For the planted forest category, no back-casting or recalculation of 1990–2003 values has been included as for previous years. Information on historic areas and/or carbon pools is considered to be less accurate than that used for the current year. Only the 2004 year has been recalculated as it is affected by three-year averaging of available data.

7.2.7 Source-specific planned improvements

Development of the LUCAS will enable New Zealand to revise the time-series in the LULUCF inventory, and reduce uncertainty by using country-specific emission and removal factors and UNFCCC 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, which should provide a more useful breakdown.

Ongoing research is aiming to improve carbon modelling, including partitioning in species other than radiata pine, plantation understorey carbon, biomass decay rates and biomass burning assumptions.

7.3 Cropland (CRF 5B)

7.3.1 Description

Cropland is a key category for New Zealand. In 2005, the net CO2 removals were 639.14 Gg CO2.

Cropland includes all annual and perennial crops as well as temporary fallow land. Annual crops include cereals, oils 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, so there is no long-term storage of carbon in biomass. However, perennial woody vegetation in orchards and vineyards 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 values and activity data from the LCDB analysis described in section 7.1 and Annex 3.3. To align with the methodologies provided in GPG-LULUCF, cropland was partitioned into annual and perennial cropland for the UNFCCC inventory.

Cropland remaining cropland

Living biomass

As per GPG-LULUCF (section 3.3.1.1.1), the change in biomass is only estimated for perennial woody crops. 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 – thus there is no net accumulation of biomass carbon stocks.

Values for 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) as this is the default regime most applicable to New Zealand. 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

The GPG-LULUCF states there is not sufficient information to provide a basic approach with default parameters to estimate carbon stock changes in dead organic matter pools in cropland remaining cropland. The notation “NE” is used in the CRF tables.

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”. The soil organic carbon stock is calculated from a reference carbon stock multiplied by the three land use and management factors shown in table 7.1.3.1.

Changes in soil carbon stock are caused by changes in the land-use and management factors (FLU, FMG and FI). 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 eg, (83 x 0.82 x 1 x 1.16) – (83 x 0.82 x 1 x 1.16)) x Area)/20 = 0. The values for FLU, FMG and FI are from table 3.3.4 in GPG-LULUCF.

Land converted to cropland

Living biomass

The Tier 1 method is the same approach for all conversions and provided in equation 3.3.8 of GPG-LULUCF. The calculation is based on multiplying the annual area of land converted to cropland by the carbon stock change per area for that type of conversion, including changes in carbon stocks from one year of cropland growth.

At 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 Good Practice Guidance and country-specific values where possible. These are shown in tables 7.1.3.2 and 7.1.3.3.

Dead organic matter

GPG-LULUCF states 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. The notation “NE” is used in the CRF tables.

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 7.1.2.3 in this inventory).

N2O emissions

These 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 global default value of 0.0125 kg N2O – N/kg N is used.

  • C:N ratio: the default ratio of carbon to nitrogen in soil organic matter (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. It is the uncertainty in the IPCC default variables that dominates the overall uncertainty in the estimate provided by New Zealand. The combined effect of uncertainty in cropland is estimated at ± 75 per cent (95 per cent confidence interval).

Table 7.3.3.1 Uncertainty in emissions and removals from cropland

Variable Uncertainty (95% confidence interval)

Uncertainty in cropland remaining cropland

± 75%

LCDB1 (user accuracy 93.9%)

± 6%

LCDB2 (assumed to be equal to LCDB1)

± 6%

Uncertainty in biomass accumulation rates

± 75% (GPG-LULUCF table 3.3.2)

Uncertainty from land converted to cropland

± 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

No specific QA/QC and verification was used for cropland. Sector-level procedures are described in section 7.2.4 forest land.

7.3.5 Category-specific recalculations

There are no recalculations for this category.

7.3.6 Category-specific planned improvements

No specific improvements are planned for cropland. Sector-level improvements resulting from the LUCAS are described in section 7.2.6 forest land.

7.4 Grassland (CRF 5C)

7.4.1 Description

Grasslands in New Zealand can vary greatly in their degree and intensity of management, ranging from the extensively managed rangelands of the South Island high country, to low producing grasslands with woody vegetation cover, to the intensively managed dairy pasture in the Waikato and Taranaki regions. Grasslands generally have vegetation dominated by perennial grasses, with grazing as the predominant land use, and are distinguished from “forest” land by having a woody vegetation cover of less than the threshold used in the forest definition. In 2005, the net emissions from grassland were 748.57 Gg CO2-e. These emissions are from the subcategory “land converted to grassland”.

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 in grassland 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 “NA” in the CRF tables because the activity occurs but there are no removals or emissions associated with it.

Dead organic matter

No estimate is calculated as GPG-LULUCF state that not enough information is available 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 2005 inventory 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.

Liming of grassland

The calculation for CO2 emissions from the liming of grassland soils is included in CRF worksheet 5.5. The calculation is based on the total amount of limestone sold (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.

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 7.1.3.2 and 7.1.3.3. Carbon stocks in biomass immediately after conversion are assumed to be zero.

Dead organic matter

No Tier 1 methodology is provided in GPG-LULUCF.

Soil carbon

Land conversion to grassland can occur from all land uses. In New Zealand the primary change into grassland is from forest land to grassland. 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 7.1.3.1.

7.4.3 Uncertainties and time-series consistency

It is the uncertainty in the IPCC default variables that dominates the overall uncertainty in the estimate provided by New Zealand. The combined effect of uncertainty in grassland is estimated at ± 75 per cent (95 per cent confidence interval).

Table 7.4.3.1 Uncertainty in emissions and removals from grassland

Variable Uncertainty (95% CI)

Uncertainty in grassland remaining grassland

± 75%

LCDB1 (user accuracy 93.9%)

± 6%

LCDB2 (assumed to be equal to LCDB1)

± 6%

Uncertainty in biomass accumulation rates

± 75% (GPG-LULUCF table 3.4.2)

Uncertainty from land converted to grassland

± 75%

Carbon stocks in previous land use

± 75%

Estimated uncertainty in land management factors

± 12% (GPG-LULUCF table 3.3.4)

7.4.4 Category-specific QA/QC and verification

No specific QA/QC and verification was used for grassland. Sector-level procedures are described in section 7.2.4.

7.4.5 Category-specific recalculations

There are minor recalculations for this category in 2004 due to revised activity data.

7.4.6 Category-specific planned improvements

No specific improvements are planned for grassland. Sector-level improvements resulting from the LUCAS are described in section 7.2.6.

7.5 Wetlands (CRF 5D)

7.5.1 Description

GPG-LULUCF 3.5 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 (Annex 3.3). Other LCDB classes, eg, herbaceous freshwater vegetation, commonly associated as wetlands in New Zealand, have been categorised as grassland following the GPG-LULUCF definitions. In 2005, the net emissions were 0.72 Gg CO2-e. These emissions are from the subcategory “land converted to wetlands”. Wetlands are not a key category for New Zealand.

7.5.2 Methodological issues

Wetlands remaining wetlands

A methodology for this category is not covered in GPG-LULUCF but is addressed in appendix 3a.3 Wetlands Remaining Wetlands: Basis for future methodological development. The appendix covers emissions from flooded land and extraction from peat land. Data is not available for the amount of peat extracted from peat land in New Zealand, but it is considered that any activity would be negligible and emissions are not able to be calculated. Re-cultivation of peat land is included under the agriculture sector. The GPG-LULUCF defines flooded lands 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”.

New Zealand has not reported emissions from flooded land because of a lack of data, i.e., the LCDB does not separate out regulated water bodies where substantial changes in water area occur, and because 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. The CRF tables for LULUCF do not require Parties to prepare estimates for this category (footnote 3, CRF table 5).

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). This 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 7.1.3.2. In Tier 1, it is assumed that the carbon stock after conversion is zero.

GPG-LULUCF does not provide guidance on carbon stock changes from 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.

7.5.4 Category-specific QA/QC and verification

No specific QA/QC and verification was used for wetlands. Sector-level procedures are described in section 7.2.4 forest land.

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 section 7.2.6 forest land.

7.6 Settlements (CRF 5E)

7.6.1 Description

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 different kinds of parks where the parks are associated with urban areas. In 2005, the net emissions from settlements were 97.16 Gg CO2. These emissions are from the subcategory “land converted to settlements”. Settlements is not a key category for New Zealand.

New Zealand has categorised the applicable LCDB land cover classes into the settlements category (Annex 3.3). The LCDB analysis showed that there was 214.84 kha of settlements remaining settlements from 1997 to 2002 with a net gain of 5.46 kha (table 7.1.1). The largest single category change in area was from high-producing grassland converted 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. The CRF tables for LULUCF do not require Parties to prepare estimates for this category (note 3, CRF table 5.)

Land converted to settlements

The fundamental 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 7.1.3.2. 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.

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).

7.6.4 Category-specific QA/QC and verification

No specific QA/QC and verification was used for settlements. Sector-level procedures are described in section 7.2.4 forest land.

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 section 7.2.6 forest land.

7.7 Other land (CRF 5F)

7.7.1 Description

“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. “Other land” is included in New Zealand’s land area for checking overall consistency of land area and tracking conversions to and from other land. In 2005, the net emissions from other land were 38.98 Gg CO2-e. These emissions are from the subcategory “land converted to other land”. Other land is not a key category for New Zealand.

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 fundamental equation (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 7.1.3.2. 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.

Soil carbon

New Zealand uses the IPCC methodology outlined in GPP 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 7.1.3.1) appropriate for the previous land use. New Zealand uses a reference soil carbon stock of 83 t C ha–1 (refer to section 7.1.1.3 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.

7.7.4 Category-specific QA/QC and verification

No specific QA/QC and verification was used for other land. Sector-level procedures are described in section 7.2.4 forest 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 section 7.2.6 forest land.