This indicator provides information about the total amount of carbon stored in forest ecosystems. It also describes changes, fluxes or flows in carbon between forests and the atmosphere. A better understanding of these processes will aid the development of appropriate responses to the effects of climate change.
Carbon stocks in New Zealand forests are estimated based on three pools defined in the Intergovernmental Panel on Climate Change (IPCC) Good Practice Guidance for Land Use, Land-use Change and Forestry:
The New Zealand data are being collected through the Land Use and Carbon Analysis System (LUCAS), a comprehensive system for data gathering, management, analysis and reporting. The system reports on land use, land use change and forestry sector under the United Nations Framework Convention on Climate Change (UNFCCC) and its Kyoto Protocol. Data collection has been designed to provide unbiased carbon estimates at the national scale, with methods supported by relevant scientific research.
Analysis of the data will provide nationally applicable values for carbon stock and stock change for the three carbon pools, and the key different forest types: (i) indigenous forest (ii) forests planted for timber purposes, and (iii) forests established prior to 1990 and those established after 1989. It also provides information on non-forest land uses.
The areas under different land uses and land-use change are based on three land use maps derived from satellite imagery at nominal mapping dates of 1 January 1990, 1 January 2008 and 31 December 2012. The forest carbon inventory involves the use of plots located on a systematic grid across New Zealand (8-kilometre grid for pre-1990 forests and 4-kilometre grid for post-1989 forests). Recent and historic plots for soil carbon measurement have been established in different land uses.
New Zealand’s exotic planted forest estate is intensively managed for production forestry, with rapid-growing genotypes selected and enhanced for optimum growth. In 2012, exotic planted forests covered approximately 2.1 million hectares (gross area) – around 7.8 per cent of New Zealand’s total land area. This includes areas not managed for timber supply; for instance, areas planted for erosion control.
In addition to changes in carbon stock that result from the planted forest growing into maturity, and their subsequent harvest, land use change is an important driver of the forest carbon stocks. After 2000, New Zealand experienced deforestation in some of its planted forests (those that were on highly productive agricultural land). This has resulted in a decline in net forest area and a marginal decline in carbon stock when these areas are not replanted. Overall, sequestered carbon remains high and increasing.
From 2013 onwards, harvesting areas will likely continue to increase, and around 2020, planted forest carbon stocks will decline in the short term as the large areas of forests planted (or replanted) in the 1980s and 1990s approach harvestable age.
It is expected that these stocks will recover once the forests are replanted. This cyclical change in forest carbon stock is characteristic of New Zealand’s non- even age class structure across the whole estate.
A negative number for soil carbon in the post-1989 forests shows that the soil carbon pool under forests is less than that under grassland. It takes 20 years after a land-use change for the carbon to stabilise.
From 2014 New Zealand started using the Land Use and Carbon Analysis System (LUCAS) for reporting carbon pools and fluxes in all forests. Forest carbon stocks increased from 3071 million tonnes of carbon in 1990 to 3298 million tonnes in 2012. Of this total, 2844 million tonnes of carbon were in indigenous forests and 454 million tonnes were in the planted production estate.