Carbon stocks in forests

  • Image, Estimated forest carbon stocks.

    New Zealand’s indigenous and exotic forests absorb carbon dioxide (CO2) from the atmosphere through photosynthesis and store the carbon as biomass and in the soil. On average, more than twice as much carbon per hectare is stored in New Zealand’s mature indigenous forests than in exotic forests planted for wood production. Regenerating indigenous forests are also an important store of carbon, adding carbon every year as they grow. Total carbon stored in exotic forests will fluctuate over decades as the forests grow from seedlings to mature trees, are harvested, and replanted. Because CO2 is the major driver of climate change, forests provide important mitigation services and help New Zealand meet its climate change commitments.

    We classified Carbon stocks in forests as a national indicator.

    Key findings

     

       Increasing trend in carbon stocks in exotic forest

     

       Increasing trend in carbon stocks in regenerating indigenous forest

     

    New Zealand’s forests removed an average of 8.5 million tonnes of carbon from the atmosphere each year from 1990 to 2015. This amount is almost three times that produced by on-road vehicles in New Zealand, and offsets a portion of New Zealand’s CO2 emissions. Carbon stocks increase as forests grow. However, about 169,000 hectares of forest have been converted for other land uses since 2000, an area almost as large as Stewart Island.

    • In 2015, mature indigenous forests stored the largest amount of carbon, about 1.706 billion tonnes, because they cover the largest area (almost 6.6 million hectares or about 24 percent of New Zealand’s land area) and contain the most carbon per hectare (257.7 tonnes carbon / hectare).
    • From 1990 to 2015, at the 95 percent confidence level, there were increasing trends in carbon stocks in exotic forest and regenerating indigenous forest.
      • The amount of carbon in exotic forest increased 150 million tonnes (114 percent). In 2015, exotic forest covered over 2 million hectares, but many managed forests are nearing maturity and will likely be harvested, which will change this trend. However, these forests could be replanted.

      • The amount of carbon in regenerating indigenous forest increased 41 million tonnes (55 percent) over the same period.

      • From 2000 to 2015 an average of 10,555 hectares of forest a year were converted for other land uses. About 86 percent of the land deforested in this period was exotic forest.

    Figure 1
    Note: Data are sourced from New Zealand’s Greenhouse Gas Inventory 1990–2015.

     

    Figure 2

    Deforestation, 2008–14 – interactive map 

    Map, Gross percent of land deforested by territorial authority area, 2008–2014.

    Data source: MfE/LUCAS

    Definition and methodology

    Forest carbon stocks include the amount of carbon stored in living and dead forest biomass (including trunk, roots, branches, deadwood, and litter) and in soil. Indigenous forests are mainly slow growing, native species originating from the primary forest cover. They also include a smaller area of regenerating forests recovering from previous disturbance (eg logging). Exotic forests are generally fast growing, exotic species (such as pine) actively planted for wood supply or erosion control. Deforestation is the change from forest to an alternative land use. Managed forest land that is harvested does not count as deforestation if it is replanted and used for the same purpose. However, if the managed forest land is harvested and used for another purpose it is counted as deforested area.

    The Ministry for the Environment uses its Land Use Carbon Analysis System (LUCAS) to calculate the amount of carbon stored in each forest, through modelling and from field measurements at a network of forest plots across New Zealand. Land-use maps created from satellite imagery determine the area of each forest type. Data collection of forest carbon stocks started in 1990 because of the need to account for the amount of carbon as set forth in the Kyoto Protocol. For more information on the data collection process, see related links below.

    We calculated CO2 vehicle equivalents using average road transportation emissions for 1990-2015 (10,725.44 kt CO2) as reported in New Zealand’s Greenhouse Gas Inventory 1990–2015 (Ministry for the Environment, 2017). We converted tonnes of CO2 to tonnes of carbon by dividing this by 3.67 to account for the difference in molecular weight between CO2 and carbon.

    Data quality

    We classified Forest carbon stocks as a national indicator.

    Relevance

    relevance-direct   This national indicator is a direct measure of the ‘Land cover and use' topic.

    Accuracy

     accuracy-high  The accuracy of the data source is of high quality.

    See Data quality information for more detail.

    References

    Ministry for the Environment (2017). New Zealand's Greenhouse Gas Inventory 1990-2015. Retrieved from http://www.mfe.govt.nz. 

    Archived pages

    See Estimated forest carbon stocks (archived October 2017). 

     

    Updated 19 October 2017

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