Modelling the effect of land-use practices on greenhouse gas emissions and sinks in New Zealand

Abstract

Abstract Data are presented for New Zealand on carbon stocks and flows, for pasture, agroforestry, forestry and land abandonment. The impact on the carbon stock of changing from pasture to other land-uses is investigated at the single-hectare scale and at the national scale. Included are the carbon in vegetation and soil and methane production from livestock. A model is described whereby the user can graph changes in carbon stocks for combinations of soil type, browsing animal, livestock carrying capacity and site productivity. The carbon balance of pasture systems is the least beneficial in terms of atmospheric carbon levels and the trend is downwards due to the continued methane emissions. Since pastoral systems are the predominant land-use in New Zealand this has major implications. The afforestation of marginal pasture will make a significant contribution to meeting the national obligations of the Kyoto Protocol. Carbon uptake by afforestation of pastures in New Zealand since 1990, during the first reporting period defined in the Kyoto Protocol (2008–2012) could be as high as 38 million tonnes of carbon. The change in carbon in the mineral soil may affect this result. There is insufficient data to assess the change in soil carbon over the whole profile, but preliminary data on soil carbon changes in the top 10 cm with afforestation suggests this sequestration value could decrease by 10% due to soil carbon losses over the same period. This loss is almost offset by avoided methane emissions due to the removal of livestock. It should be noted that there is a lack of data available on carbon sinks and sources, associated with land-use, other than radiata pine plantations.